ALTERING THE STEREOCHEMISTRY OF ALLYLATION REACTIONS OF CYCLIC ALPHA-SULFINYL RADICALS - EFFECTS OF SOLVENTS AND LEWIS-ACIDS

Full details of the stereochemical outcome of the allylation of the tetrahydrothiophene-2-yl 1-oxide radical in different solvents and in the presence of Lewis acids are reported. Corrections of the cis/trans ratios initially reported in the original communication are presented and the origin for the systematic overestimation of the ratio was found to be the decomposition of the minor cis diastereoisomer during the GC analysis. However, the originally reported stereoselectivity enhancements in the presence of Lewis acids are still valid, although the effects are of smaller amplitudes. The conclusions about an intermediate oxygen-complexed a-sulfinyl radical stand. We report that the very bulky and oxygenophilic methylaluminum diphenoxides (MAD and MABR), recently intoduced by Yamamoto, are perfectly compatible with radical reactions and provide exceptional levels of stereocontrol (up to 98:2) when used stoichiometrically. A good level of stereoselectivity (90:10) was reached by using a catalytic amount of MABR (10%). The yields and the stereoselectivities of the radical allylations compare favorably with the nucleophilic allylation af the deprotonated tetrahydrothiophene 1-oxide.