was already reported by U. Jacquemard Cleavage of carbamates using TBAB et al. tert-butyl in THF has been also described.3 We suppose that bromide attacks the carboxyl group of Boc- to form a tetrahedric intermediate which can give intermediates A or B by two possible pathways as depicted in Scheme IV.67. IV.133 was only isolated in our N-arylformamide case confirming the first pathway of the mechanism. (Scheme IV.67) Scheme IV.67. Proposed Boc- group cleavage during the Corey-Fuchs reaction.120 4.2.1.1.2.2 Corey-Fuchs reaction with pivaloyl- protected formamide IV.131b As Boc- group deprotection occured during the Corey-Fuchs alkynylation, we prepared the more stable pivaloyl protected formamide IV.131b. (Scheme IV.68) Unfortunately, we observed also in this case the cleavage of pivaloyl group leading again to IV.133. N-arylformamide Scheme IV.68. Pivaloyl chloride protection of N-formamide IV.133 and unsuccessful dihalomethylation. 4.2.1.1.2.3 Corey-Fuchs reaction with p-toluensulfonyl protected formamide According to literature,, the selective cleavage of bond in the presence of N-SO2 aromatic-SO2R bond is described. Therefore we decided to use a as p-toluensulfonyl group. Such protecting group was also utilized in protocol.63,64 As Brückner’s depicted in Scheme IV.69, IV.133 was protected with chloride N-formamide p-toluensulfonyl and gave IV.131c in a good yield. (Scheme IV.69) Scheme IV.69. Preparation of N-tosylated formamide IV.131c. Reaction of IV.131c with CCl4 and PPh3 afforded dichloroenamide IV.135c at 60 °C in high yield. (Scheme IV.70) No detosylation reaction was observed in this case. It
was already reported by U. Jacquemard et al. Cleavage of tert-butyl carbamates using TBAB in THF has been also described.3 We suppose that bromide attacks the carboxyl group of Boc- to form a tetrahedric intermediate which can give intermediates A or B by two possible pathways as depicted in Scheme IV.67. N-arylformamide IV.133 was only isolated in our case confirming the first pathway of the mechanism. (Scheme IV.67) Scheme IV.67. Proposed Boc- group cleavage during the Corey-Fuchs reaction.120 4.2.1.1.2.2 Corey-Fuchs reaction with pivaloyl- protected formamide IV.131b As Boc- group deprotection occured during the Corey-Fuchs alkynylation, we prepared the more stable pivaloyl protected formamide IV.131b. (Scheme IV.68) Unfortunately, we observed also in this case the cleavage of pivaloyl group leading again to N-arylformamide IV.133. Scheme IV.68. Pivaloyl chloride protection of N-formamide IV.133 and unsuccessful dihalomethylation. 4.2.1.1.2.3 Corey-Fuchs reaction with p-toluensulfonyl protected formamide According to literature,, the selective cleavage of N-SO2 bond in the presence of aromatic-SO2R bond is described. Therefore we decided to use a p-toluensulfonyl as group. Such protecting group was also utilized in Brückner’s protocol.63,64 As depicted in Scheme IV.69, N-formamide IV.133 was protected with p-toluensulfonyl chloride and gave IV.131c in a good yield. (Scheme IV.69) Scheme IV.69. Preparation of N-tosylated formamide IV.131c. Reaction of IV.131c with CCl4 and PPh3 afforded dichloroenamide IV.135c at 60 °C in high yield. (Scheme IV.70) No detosylation reaction was observed in this case. It
ab-11_mv-part-two_form-8.-bibliography.docx