Synthesis, Chemical Properties, and Structure of a Sterically Hindered Ketone, 2,2,5,5-Tetramethyl-4,4-diphenyl-3-thiolanone

A sterically hindered ketone, 2,2,5,5-tetramethyl-4,4-diphenyl-3-thiolanone (1), was synthesized in two steps starting from 2,2,4,4-tetramethyl-1,5-diphenyl-3-thiapentane-1,5-dione. The carbonyl group of 1 is unreactive toward a series of nucleophiles which are bulkier than hydride or its equivalents. The observed unreactivity is ascribed to the steric hindrance enhanced by the two methyl groups on C-5 (“buttressing” effect). The result of an X-ray single crystal structure analysis of 1 is also described.