DIASTEREOSELECTIVE SYNTHESIS OF BETA-TRICHLOROSTANNYL AND BETA-TRIMETHYLSTANNYLKETONES

The addition of chlorostannane (HSnCl3) to alpha,beta-disubstituted-al pha,beta-unsaturated ketones and esters was studied. With the former, the reaction proceeds smoothly and with high diastereoselectivity to g ive good yields. The stereochemical results indicate that the reaction is stereoselective but certainly not stereospecific. The predominance of one diastereomer in the product might be governed by the preferred conformation of the enol intermediate arising from A-strain effects a nd, probably, from electronic interactions between the beta-trichloros tannyl group and the oxygen atom. On the other hand, the addition of c hlorostannane to a,a-unsaturated esters is highly inhibited by the pre sence of just one beta-substituent group. Chemoselective alkylation at the tin atom of the beta-trichlorostannyl compounds with the correspo nding Grignard reagent yielded the beta-trimethylstannyl derivatives i n good yields. The configuration of the new beta-(trimethylstannyl) an d beta-(trichlorostannyl)ketones is assigned based on H-1 and C-13 NMR data. Full H-1, C-13 and Sn-119 NMR data are given.