Triphenylphosphine → 4-Cyclopentyl-6,7-dihydro-6-methyl-1,4-thiazepin-2,5-(3H,4H)-dione

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Reaction Steps

A solution of N-cyclopentyl-N-(3-mercapto-2-methylpropanoyl)glycine (2.0 g., 8.1 mmol) in 125 ml of toluene was freed of air by bubbling nitrogen through it. To this solution was then added 2,2'-dipyridyldisulfide (2.7 g., 12.2 mmol) and triphenylphosphine (3.2 g., 12.2 mmol) and the resulting solution was stirred under nitrogen for 5 hours. This solution was then diluted to 250 ml with toluene and added at a rate of 20-25 ml/hr to 2 l of reluxing toluene under nitrogen. The resulting mixture was stirred at reflux for 48 hours and then cooled to room temperature. The solution was washed successively with 0.1 N hydrochloric acid, saturated sodium bicarbonate, water and brine, dried over anhydrous magnesium sulfate, and then filtered and concentrated under vacuum. The resulting solid material was dissolved in 25% ethyl acetate/hexane, filtered to remove the triphenyl phosphine oxide which crystallized, and purified by medium pressure liquid chromatography, eluting with 25% ethyl acetate/hexane, to give 0.8 g. of a pale yellow solid. This solid was recrystallized from 10% ethyl acetate/hexane to give 0.5 g (27%) of 4-cyclopentyl-6,7-dihydro-6-methyl-1,4-thiazapen-2,5-(3H,4H)-dione as a white crystalline solid, mp. 77°-79°.

Provenance & Evidence