Nucleophilicity vs basicity in the reaction of sodium tert-butoxide with beta-stannyl ketones

The reaction of 3-stannyl-1,2,3-triphenyl- and 3-stannyl-1,3-diphenyl-2-met hylpropanones with sodium tert-butoxide in either t-BuOH or dimethyl sulfox ide (DMSO) as solvent Leads to Elimination and/or substitution products. Th e composition of the product mixtures depends essentially on the nature of the ligands attached to the tin atom, on the solvent, and also on the natur e of the substituent on C-2. Thus, beta-(triphenyl), beta-(bromodiphenyl), and beta-(trichlorostannyl) ketones under go an exclusive elimination react ion Leading to an unsaturated Ketone in good to high yields (72%-96% both i n t-BuOH and in DMSO. In the latter the reactions lead to higher yields in shorter times. On the other hand, beta -trimethylstannyl) ketones lead to m ixtures of olefins and substitution products in t-BuOH and exclusively to s ubstitution products in DMSO (96%-98%). Stereochemical results suggest that the elimination reactions proceed through an (E1cB)R mechanism.