3 3 pentamethyl 2 3 6 7 tetrahydro 1h indene 4 5 dione is first prepared with 1 1 2 3 3 pentamethyl 1 2 3 5 6 7 hexahydro inden 4 one cashmeran u00ae commercially available at iff via oxidation with 2 2 6 6 tetramethylpiperidin 1 yl oxidanyl tempo prepared as described by barton in tetrahedron letters 1984 25 6 pages 603 606 a 100 ml reaction flask is charged with 1 1 2 3 3 pentamethyl 2 3 6 7 tetrahydro 1h indene 4 5 dione 10 g 0 04 mol and formamide nh 2 cho 50 ml the reaction mixture is heated to 200 u00b0 c and stirred for 24 hours the crude mass is diluted with toluene 50 ml and then washed once with aqueous sodium carbonate 10 100 ml followed by twice with brine 30 ml toluene is recovered by roto evaporation the crude product is further purified with liquid chromatography biotage u00ae system and then crystallized product of a mixture of 6 6 7 8 8 pentamethyl 5 6 7 8 tetrahydro 4h 1 oxa 3 aza as indacene and 6 6 7 8 8 pentamethyl 5 6 7 8 tetrahydro 4h indeno 4 5 d oxazole u02dc 10 g is obtained 1 1 2 3 3 pentamethyl octahydro inden 4 one is first prepared by the hydrogenation of 1 1 2 3 3 pentamethyl 1 2 3 5 6 7 hexahydro inden 4 one cashmeran u00ae commercially available at iff 1 1 2 3 3 pentamethyl hexahydro indene 4 5 dione is subsequently prepared with 1 1 2 3 3 pentamethyl octahydro inden 4 one prepared as described by barton in tetrahedron.