Synthesis of New 2,3-Dihydroindole Derivatives and Evaluation of Their Melatonin Receptor Binding Affinity

2,3-Dihydroindoles are promising agents for the synthesis of new compounds with neuroprotective and antioxidant properties. Usually, these compounds are obtained by direct reduction of the corresponding indoles containing acceptor groups in the indole ring for its activation. In this work, we propose a synthetic strategy to obtain new 2,3-dihydroindole derivatives from the corresponding polyfunctional 2-oxindoles. Three methods were proposed for reduction of functional groups in the 2-oxindole and 2-chloroindole molecules using various boron hydrides. The possibility of chemoselective reduction of the nitrile group in the presence of an amide was shown. The proposed synthetic strategy can be used, for example, for the synthesis of new analogs of the endogenous hormone melatonin and other compounds with neuroprotective properties.

Known to date high-affinity ligands for melatonin receptors are diverse in their structures [15]. Despite the fact that many useful ligands contain bioisosteric replacements of the indole ring by an aromatic or heteroaromatic ring, the scope of melatonin-like modifications of the indole ring is far from being exhausted. We assumed that 2,3-dihydroindoles are a class of compounds that could be easily modulated to provide different receptor subtype selectivity and intrinsic activity profiles. The structural requirements and pharmacophore groups necessary for the binding to the MT 1 /MT 2 and MT 3 melatonin receptors are shown in Figure 1A,B.
Group I, which is either a methoxy group or its homologous (cyclic) analogue, is necessary for the compound to demonstrate agonistic activity toward the MT 1 /MT 2 melatonin receptor subtypes, whereas the presence of this group is not essential for antagonists, for example agomelatin. The presence of amide group II and spacer III, which is exactly equal to two carbon atoms, is also necessary for binding affinity [16]. Structural requirements for low-affinity MT 3 receptor ligands are more tentative. Since the MT 3 receptor is apparently the enzyme quinone reductase 2 with planar FAD cofactor [17], it might be expected that a "good" ligand would contain a planar aromatic ring. It is also known that the presence of carbamoyl group IV substantially improves binding to the MT 3 receptor. exactly equal to two carbon atoms, is also necessary for binding affinity [16]. Structural requirements for low-affinity MT3 receptor ligands are more tentative. Since the MT3 receptor is apparently the enzyme quinone reductase 2 with planar FAD cofactor [17], it might be expected that a "good" ligand would contain a planar aromatic ring. It is also known that the presence of carbamoyl group IV substantially improves binding to the MT3 receptor. Before we present a general and robust approach to synthesize 2-oxoindolylacetonitriles [18][19][20]. Herein, we report a modification of this method that aims to create a sp 3carbon atom in position 3 of the indole ring and introduce an additional substituent R 3 (see Figure 1C). The escape of the acetamide side chain from the plane of the indole moiety can increase activity of the compound toward the MT1/MT2 melatonin receptors [21]. The new compounds with different substituents in positions 2 and 5 of the indole ring were synthesized using this novel approach (see Figure 1C and Scheme 1).

Chemistry
The key step of the proposed approach to the synthesis of various melatonin receptor ligands involves the Knoevenagel condensation of isatins with cyanoacetic acid or its esters (Scheme 1): A series of isatins 1 was synthesized from aniline precursors by the Sandmeyer method and was additionally modified at the indole nitrogen by alkylation according to the described procedure [22] (Scheme 2). The condensation of isatins 1e-k and 1m-n with Before we present a general and robust approach to synthesize 2-oxoindolylacetonitriles [18][19][20]. Herein, we report a modification of this method that aims to create a sp 3 -carbon atom in position 3 of the indole ring and introduce an additional substituent R 3 (see Figure 1C). The escape of the acetamide side chain from the plane of the indole moiety can increase activity of the compound toward the MT 1 /MT 2 melatonin receptors [21]. The new compounds with different substituents in positions 2 and 5 of the indole ring were synthesized using this novel approach (see Figure 1C and Scheme 1).
exactly equal to two carbon atoms, is also necessary for binding affinity [16]. Structural requirements for low-affinity MT3 receptor ligands are more tentative. Since the MT3 receptor is apparently the enzyme quinone reductase 2 with planar FAD cofactor [17], it might be expected that a "good" ligand would contain a planar aromatic ring. It is also known that the presence of carbamoyl group IV substantially improves binding to the MT3 receptor. Before we present a general and robust approach to synthesize 2-oxoindolylacetonitriles [18][19][20]. Herein, we report a modification of this method that aims to create a sp 3carbon atom in position 3 of the indole ring and introduce an additional substituent R 3 (see Figure 1C). The escape of the acetamide side chain from the plane of the indole moiety can increase activity of the compound toward the MT1/MT2 melatonin receptors [21]. The new compounds with different substituents in positions 2 and 5 of the indole ring were synthesized using this novel approach (see Figure 1C and Scheme 1).

Chemistry
The key step of the proposed approach to the synthesis of various melatonin receptor ligands involves the Knoevenagel condensation of isatins with cyanoacetic acid or its esters (Scheme 1): A series of isatins 1 was synthesized from aniline precursors by the Sandmeyer method and was additionally modified at the indole nitrogen by alkylation according to the described procedure [22] (Scheme 2). The condensation of isatins 1e-k and 1m-n with Scheme 1. Strategy of the synthesis of new melatonin receptor ligands.

Chemistry
The key step of the proposed approach to the synthesis of various melatonin receptor ligands involves the Knoevenagel condensation of isatins with cyanoacetic acid or its esters (Scheme 1): A series of isatins 1 was synthesized from aniline precursors by the Sandmeyer method and was additionally modified at the indole nitrogen by alkylation according to the described procedure [22] (Scheme 2). The condensation of isatins 1e-k and 1m-n with cyanoacetic acid was performed in the presence of triethylamine according to the procedure described for isatins 1a-c and 1l [23]. cyanoacetic acid was performed in the presence of triethylamine according to the procedure described for isatins 1a-c and 1l [23]. We proposed two synthetic routes to various (2-oxoindolin-3-yl)acetonitriles, which both consist of reduction of the double bond and decarboxylation of Knoevenagel condensation products 2a-j (procedures A and B, see Scheme 3). The approach (A) involves reduction of the double bond followed by decarboxylation of the resulting acid. The palladium-catalyzed hydrogenation of the double bond of unsubstituted (2-oxoindolin-3-yl)cyanoacetic acid was described in the literature [24]; however, partial reduction of the nitrile group occurs as a side process. Hence, we developed and optimized the reduction of the double bond in compounds 2a-2j using the Zn/aq. HCl system. Reduction products were subjected to the decarboxylation without characterization and additional purification. Nitriles 4 were obtained with good yields (Scheme 3, Table 1). The alternative approach B (see stages b-c, Scheme 3) involves decarboxylation of 2 in pyridine to obtain compounds 3 followed by reduction of the double bond. Compounds 4c-4j were synthesized using this procedure, which was described in the literature for the synthesis of compounds 4a-c [18,25]. The overall yields after two steps are given in Table 1. We proposed two synthetic routes to various (2-oxoindolin-3-yl)acetonitriles, which both consist of reduction of the double bond and decarboxylation of Knoevenagel condensation products 2a-j (procedures A and B, see Scheme 3). cyanoacetic acid was performed in the presence of triethylamine according to the procedure described for isatins 1a-c and 1l [23]. We proposed two synthetic routes to various (2-oxoindolin-3-yl)acetonitriles, which both consist of reduction of the double bond and decarboxylation of Knoevenagel condensation products 2a-j (procedures A and B, see Scheme 3). The approach (A) involves reduction of the double bond followed by decarboxylation of the resulting acid. The palladium-catalyzed hydrogenation of the double bond of unsubstituted (2-oxoindolin-3-yl)cyanoacetic acid was described in the literature [24]; however, partial reduction of the nitrile group occurs as a side process. Hence, we developed and optimized the reduction of the double bond in compounds 2a-2j using the Zn/aq. HCl system. Reduction products were subjected to the decarboxylation without characterization and additional purification. Nitriles 4 were obtained with good yields (Scheme 3, Table 1). The alternative approach B (see stages b-c, Scheme 3) involves decarboxylation of 2 in pyridine to obtain compounds 3 followed by reduction of the double bond. Compounds 4c-4j were synthesized using this procedure, which was described in the literature for the synthesis of compounds 4a-c [18,25]. The overall yields after two steps are given in Table 1 The approach (A) involves reduction of the double bond followed by decarboxylation of the resulting acid. The palladium-catalyzed hydrogenation of the double bond of unsubstituted (2-oxoindolin-3-yl)cyanoacetic acid was described in the literature [24]; however, partial reduction of the nitrile group occurs as a side process. Hence, we developed and optimized the reduction of the double bond in compounds 2a-2j using the Zn/aq. HCl system. Reduction products were subjected to the decarboxylation without characterization and additional purification. Nitriles 4 were obtained with good yields (Scheme 3, Table 1). The alternative approach B (see stages b-c, Scheme 3) involves decarboxylation of 2 in pyridine to obtain compounds 3 followed by reduction of the double bond. Compounds 4c-4j were synthesized using this procedure, which was described in the literature for the synthesis of compounds 4a-c [18,25]. The overall yields after two steps are given in Table 1.  In a molecule of 3-alkyl-substituted 2,3-dihydromelatonins acetamide, the side chain is shifted from the plane of the indole moiety and is locked into this conformation. To investigate the influence of these conformational features on affinity to melatonin receptors, we synthesized a few novel 3-substituted nitriles by selective alkylation of nitriles 4a-c using various alkyl halides.
To avoid undesired N-alkylation, the Boc-protecting group was chosen. We found that either N-Boc-acylation products or 1,3-Boc derivatives could be produced depending on the reaction conditions (Scheme 4). Similarly, alkylation of 4b with MeI in the presence of DMAP led to a mixture of mono-and dialkylation products (see Materials and methods).
N-Boc-and N-alkyl-substituted nitriles were alkylated at position 3 with various alkylating agents in the presence of sodium hydride (see Scheme 3, Table 2). In a molecule of 3-alkyl-substituted 2,3-dihydromelatonins acetamide, the side chain is shifted from the plane of the indole moiety and is locked into this conformation. To investigate the influence of these conformational features on affinity to melatonin receptors, we synthesized a few novel 3-substituted nitriles by selective alkylation of nitriles 4a-c using various alkyl halides.
To avoid undesired N-alkylation, the Boc-protecting group was chosen. We found that either N-Boc-acylation products or 1,3-Boc derivatives could be produced depending on the reaction conditions (Scheme 4).  In a molecule of 3-alkyl-substituted 2,3-dihydromelatonins acetamide, the side chain is shifted from the plane of the indole moiety and is locked into this conformation. To investigate the influence of these conformational features on affinity to melatonin receptors, we synthesized a few novel 3-substituted nitriles by selective alkylation of nitriles 4a-c using various alkyl halides.
To avoid undesired N-alkylation, the Boc-protecting group was chosen. We found that either N-Boc-acylation products or 1,3-Boc derivatives could be produced depending on the reaction conditions (Scheme 4). Similarly, alkylation of 4b with MeI in the presence of DMAP led to a mixture of mono-and dialkylation products (see Materials and methods).
N-Boc-and N-alkyl-substituted nitriles were alkylated at position 3 with various alkylating agents in the presence of sodium hydride (see Scheme 3, Table 2).  Similarly, alkylation of 4b with MeI in the presence of DMAP led to a mixture of monoand dialkylation products (see Materials and methods).
N-Boc-and N-alkyl-substituted nitriles were alkylated at position 3 with various alkylating agents in the presence of sodium hydride (see Scheme 3, Table 2).
The obtained (2-oxoindolin-3-ylidene)acetonitriles 3 were also used as precursors of conformationally restricted spiro derivatives. Initially, we intended to use the Corey-Chaykovsky reaction for the synthesis of spirocyclopropane 2-oxindoles. We performed the reaction of esters 2 with trimethylsulfoxonium iodide in the presence of sodium hydride according to standard procedures for cyclopropanation of the double bond bearing two electron-withdrawing substituents. However, the reaction of methyl (2-oxoindolin-3ylidene)cyanate with sulfur ylide produced an inseparable mixture of compounds. Hence, we tested the method based on the [3 + 2]-cycloaddition of diazomethane to compounds 3 in the same way as we previously described for compounds 6a, b [19]. The synthesis was carried out in the presence of a 20-fold excess of diazomethane without any catalyst. The resulting pyrazolines were immediately subjected to thermal decomposition with no additional purification. Spirocyclopropane derivatives 6a, b, e, g, j were synthesized in high yields (see Table 3). The low yield in case of nitriles 6c, d, i can be attributed to side reactions, in particular, to the partial consumption of diazomethane in the methylation of nitrogen in position 1.  Similarly, alkylation of 4b with MeI in the presence of DMAP led to a mixture of mono-and dialkylation products (see Materials and methods).
N-Boc-and N-alkyl-substituted nitriles were alkylated at position 3 with various alkylating agents in the presence of sodium hydride (see Scheme 3, Table 2).  The obtained (2-oxoindolin-3-ylidene)acetonitriles 3 were also used as precursors of conformationally restricted spiro derivatives. Initially, we intended to use the Corey-Chaykovsky reaction for the synthesis of spirocyclopropane 2-oxindoles. We performed the reaction of esters 2 with trimethylsulfoxonium iodide in the presence of sodium hydride according to standard procedures for cyclopropanation of the double bond bearing two electron-withdrawing substituents. However, the reaction of methyl (2-oxoindolin-3-ylidene)cyanate with sulfur ylide produced an inseparable mixture of compounds. Hence, we tested the method based on the [3 + 2]-cycloaddition of diazomethane to compounds 3 in the same way as we previously described for compounds 6a, b [19]. The synthesis was carried out in the presence of a 20-fold excess of diazomethane without any catalyst. The resulting pyrazolines were immediately subjected to thermal decomposition with no additional purification. Spirocyclopropane derivatives 6a, b, e, g, j were synthesized in high yields (see Table 3). The low yield in case of nitriles 6c, d, i can be attributed to side reactions, in particular, to the partial consumption of diazomethane in the methylation of nitrogen in position 1. The side chain in position 3 of the indole molecule containing the acetamide group plays a key role in the affinity of the compounds for the MT1 and MT2 melatonin receptors. Hence, an important part of the present study was to develop different methods for reduction of the nitrile group and acetylation of the resulting amines. Previously, we have shown that the reduction of CN group of (2-oxoindolin-3-yl)acetonitrile using hydrogenation with PtO2 as a catalyst in the presence of acetic anhydride is a decent approach to a new melatonin derivatives synthesis [19,20]. A new 2-oxoindole-based melatonin analog 7a was synthesized in the present study using this method (Scheme 5). The side chain in position 3 of the indole molecule containing the acetamide group plays a key role in the affinity of the compounds for the MT 1 and MT 2 melatonin receptors. Hence, an important part of the present study was to develop different methods for reduction of the nitrile group and acetylation of the resulting amines. Previously, we have shown that the reduction of CN group of (2-oxoindolin-3-yl)acetonitrile using hydrogenation with PtO 2 as a catalyst in the presence of acetic anhydride is a decent approach to a new melatonin derivatives synthesis [19,20]. A new 2-oxoindole-based melatonin analog 7a was synthesized in the present study using this method (Scheme 5). Selective nitrile reduction in the presence of cyclic amide was also achieved using NaBH4 in methanol in the presence of catalytic amounts of anhydrous NiCl2. We have previously shown that the addition of acetic anhydride to the reduction mixture could obtain 2-chloromelatonin 7d [26] with good yield (Scheme 6). In this work, we demonstrated that the same reduction followed by one-pot acylation can be used in the case of 2oxindole derivatives and other anhydrides (Scheme 6). The observed lower yields compared to catalytic hydrogenation on PtO2 for 2-oxoderivatives 7a can be explained by loss catalytic activity of nickel boride due to its coordination on amide group.

N
2,3-Dihydro derivatives of melatonin were synthesized by reduction of nitriles 4 by in situ generated BH3 using an excess of sodium borohydride in the presence of iodine in dry tetrahydrofuran. However, for 3-monosubstituted oxindoles, the formation of 2,3-dihydromelatonin (8) under these reaction conditions is accompanied by the partial aromatization of the indole ring (9). The reduction of nitriles 3 containing a double bond under these conditions also leads to products 8 and 9 (Scheme 7). Scheme 5. Chemoselective hydrogenation of CN-group in (indolin-3-yl)acetonitriles using Adam's catalyst.
Selective nitrile reduction in the presence of cyclic amide was also achieved using NaBH 4 in methanol in the presence of catalytic amounts of anhydrous NiCl 2 . We have previously shown that the addition of acetic anhydride to the reduction mixture could obtain 2-chloromelatonin 7d [26] with good yield (Scheme 6). In this work, we demonstrated that the same reduction followed by one-pot acylation can be used in the case of 2-oxindole derivatives and other anhydrides (Scheme 6). Selective nitrile reduction in the presence of cyclic amide was also achieved using NaBH4 in methanol in the presence of catalytic amounts of anhydrous NiCl2. We have previously shown that the addition of acetic anhydride to the reduction mixture could obtain 2-chloromelatonin 7d [26] with good yield (Scheme 6). In this work, we demonstrated that the same reduction followed by one-pot acylation can be used in the case of 2oxindole derivatives and other anhydrides (Scheme 6). The observed lower yields compared to catalytic hydrogenation on PtO2 for 2-oxoderivatives 7a can be explained by loss catalytic activity of nickel boride due to its coordination on amide group.
2,3-Dihydro derivatives of melatonin were synthesized by reduction of nitriles 4 by in situ generated BH3 using an excess of sodium borohydride in the presence of iodine in dry tetrahydrofuran. However, for 3-monosubstituted oxindoles, the formation of 2,3-dihydromelatonin (8) under these reaction conditions is accompanied by the partial aromatization of the indole ring (9). The reduction of nitriles 3 containing a double bond under these conditions also leads to products 8 and 9 (Scheme 7). Scheme 6. Selective reduction of CN-group using sodium borohydride/nickel chloride system.
The observed lower yields compared to catalytic hydrogenation on PtO 2 for 2-oxoderivatives 7a can be explained by loss catalytic activity of nickel boride due to its coordination on amide group.
2,3-Dihydro derivatives of melatonin were synthesized by reduction of nitriles 4 by in situ generated BH 3 using an excess of sodium borohydride in the presence of iodine in dry tetrahydrofuran. However, for 3-monosubstituted oxindoles, the formation of 2,3-dihydromelatonin (8) under these reaction conditions is accompanied by the partial aromatization of the indole ring (9). The reduction of nitriles 3 containing a double bond under these conditions also leads to products 8 and 9 (Scheme 7).  The spontaneous aromatization cannot occur in the case of reduction of (indolin-3yl)acetonitriles containing substituents in positions 1 and 3 of the indole ring (Scheme 8). The reduction of nitriles 5 and spironitriles 6 will afford new stable 2,3-dihydroindoles 8,10 (Table 4). The spontaneous aromatization cannot occur in the case of reduction of (indolin-3yl)acetonitriles containing substituents in positions 1 and 3 of the indole ring (Scheme 8). The reduction of nitriles 5 and spironitriles 6 will afford new stable 2,3-dihydroindoles 8,10 (Table 4). The spontaneous aromatization cannot occur in the case of reduction of (indolin-3yl)acetonitriles containing substituents in positions 1 and 3 of the indole ring (Scheme 8). The reduction of nitriles 5 and spironitriles 6 will afford new stable 2,3-dihydroindoles 8,10 (Table 4).   Under these conditions, Boc-containing compounds completely reduce all functional groups, including Boc: the tert-butoxycarbonyl group was reduced to methyl (Scheme 9).
Despite stability in the solid phase, the obtained 2,3-dihydroindoles are sensitive to oxidation in solution. Thus, the oxidation in the NMR tube occurred both in spiro and 3H-containing indolines, but led to different types of products. For compound 8m, aromatization of the indole ring occurred, while 3,3-disubstituted indoline 10a was oxidized to 2-oxindole (Scheme 10). The compounds 8i,l,g were also partially converted to aromatic indoles 9i,l,g during purification by column chromatography. Despite stability in the solid phase, the obtained 2,3-dihydroindoles are sensitive to oxidation in solution. Thus, the oxidation in the NMR tube occurred both in spiro and 3Hcontaining indolines, but led to different types of products. For compound 8m, aromatization of the indole ring occurred, while 3,3-disubstituted indoline 10a was oxidized to 2oxindole (Scheme 10). The compounds 8i,l,g were also partially converted to aromatic indoles 9i,l,g during purification by column chromatography.

Melatonin Receptor Binding Activity
The newly synthesized indole derivatives were evaluated for their binding affinity and intrinsic activity at human MT1 and MT2 receptors stably transfected in Chinese hamster ovary (CHO) cells using 2-[ 125 I]iodomelatonin as a radioligand, and the results are shown in Tables 5 and 6. Under these conditions, Boc-containing compounds completely reduce all functional groups, including Boc: the tert-butoxycarbonyl group was reduced to methyl (Scheme 9).  Despite stability in the solid phase, the obtained 2,3-dihydroindoles are sensitive to oxidation in solution. Thus, the oxidation in the NMR tube occurred both in spiro and 3Hcontaining indolines, but led to different types of products. For compound 8m, aromatization of the indole ring occurred, while 3,3-disubstituted indoline 10a was oxidized to 2oxindole (Scheme 10). The compounds 8i,l,g were also partially converted to aromatic indoles 9i,l,g during purification by column chromatography.

Melatonin Receptor Binding Activity
The newly synthesized indole derivatives were evaluated for their binding affinity and intrinsic activity at human MT1 and MT2 receptors stably transfected in Chinese hamster ovary (CHO) cells using 2-[ 125 I]iodomelatonin as a radioligand, and the results are shown in Tables 5 and 6.

Melatonin Receptor Binding Activity
The newly synthesized indole derivatives were evaluated for their binding affinity and intrinsic activity at human MT 1 and MT 2 receptors stably transfected in Chinese hamster ovary (CHO) cells using 2-[ 125 I]iodomelatonin as a radioligand, and the results are shown in Tables 5 and 6. First, compounds 7a, 7d containing heteroatoms in position 2 were evaluated for MT binding assay using melatonin and selective MT2 receptor antagonist 4-P-PDOT as reference (Table 5 and Supplementary Material). The presence of 2-oxindole ring dramatically decreased MT1/MT2 receptor binding affinity for melatonin derivatives while 2-chloromelatonin 7d was more active than melatonin with respect to both types of MT receptors.  First, compounds 7a, 7d containing heteroatoms in position 2 were evaluated for MT binding assay using melatonin and selective MT2 receptor antagonist 4-P-PDOT as reference (Table 5 and Supplementary Material). The presence of 2-oxindole ring dramatically decreased MT1/MT2 receptor binding affinity for melatonin derivatives while 2-chloromelatonin 7d was more active than melatonin with respect to both types of MT receptors. The same tendency was observed in the case of 2,3-dihydroindoles: their binding affinity to both types of MT receptors was sufficiently lower than the activity of melatonin (Table 6).  6.95 ± 0.11 0.63 ± 0.14 7.33 ± 0.015 0.61 ± 0.03 8h 8.28 ± 0.14 1.04 ± 0.14 8.64 ± 0.011 0.85 ± 0.08 8l 6.60 ± 0.05 0.61 ± 0.15 6.78 ± 0.06 0.83 ± 0.05 9l 6.11 ± 0.15 0.38 ± 0.14 6.68 ± 0.04 0.52 ± 0.05 1 see acknowledgements. For detailed biological experiment, see [27].
First, compounds 7a, 7d containing heteroatoms in position 2 were evaluated for MT binding assay using melatonin and selective MT 2 receptor antagonist 4-P-PDOT as reference (Table 5 and Supplementary Material). The presence of 2-oxindole ring dramatically decreased MT 1 /MT 2 receptor binding affinity for melatonin derivatives while 2-chloromelatonin 7d was more active than melatonin with respect to both types of MT receptors.
The same tendency was observed in the case of 2,3-dihydroindoles: their binding affinity to both types of MT receptors was sufficiently lower than the activity of melatonin (Table 6).

General Procedure of Alkylation of N-Boc/alkyl-(2-oxoindolin-3-yl)acetonitriles
A mixture N-Boc/alkyl-(2-oxoindolin-3yl)acetonitrile, sodium hydride (60% suspension in oil) and dry THF was stirred under argon atmosphere for 30 min. Reaction mixture was cooled with ice bath (0 • C), and excess of alkyl halide was added. After stirring at room temperature for 48 h, the solvent was evaporated and the resulting oil was washed with ice water, dichloromethane (for N-Boc, Bn) or chloroform (for N-Me) and dried with MgSO 4 .
Compound 5e was obtained as orange solid (yield 0.124 g, 17%). The spectral data of this compound are the same as for compound obtained from 4g.

General Procedure for Selective Reduction of Nitrile Group
Method A: The acetonitrile 4 was dissolved in glacial acetic acid and hydrogenated at room temperature and atmospheric pressure in the presence of acetic anhydride. The platinum catalyst was filtered off, and the reaction mixture was evaporated to dry residue. The solid was washed with NaHCO 3 and extracted with dichloromethane.
Method B: The acetonitrile 4 was dissolved in methanol, and then, acetic anhydride and anhydrous NiCl 2 were added. The reaction mixture was cooled, NaBH 4 was added slowly portionwise. Reaction mixture was vigorously stirred for 4 days, the solvent was evaporated, dry residue washed with saturated solution of K 2 CO 3 and extracted with dichloromethane.