1,2-ASYMMETRIC INDUCTION IN THE RADICAL-ADDITION OF ORGANOTIN HYDRIDES TO (-)-MENTHYL(E)-2,3-DISUBSTITUTED PROPENOATES

The results obtained in the free radical hydrostannation of(-)-menthyl (E)-2,3-diphenylpropenoate (1) with tri-n-butyl- and triphenyltin hydr ide, and of (-)-menthyl(E)-2-phenyl-2-butenoate (7) with trimethyltin hydride are reported. The absolute configuration of the new organotin adducts was determined by combining H-1- and C-13-NMR data with chemic al correlation. The additions took place in all cases following a syn stereochemistry that led to diastereomeric excesses ranging between 73 and 100%. The observed stereochemistry is explained, taking into acco unt both the allylic strain and the hyperconjugation with beta-trialky ltin substituent existing in the intermediate radicals. Full H-1-, C-1 3- and Sn-19-NMR data are given. (C) 1998 Elsevier Science S.A. All ri ghts reserved.