Organometallics in organic synthesis. Applications of a new diorganozinc reaction to the synthesis of C-glycosyl compounds with evidence for an oxonium-ion mechanism

The mechanistic and stereochemical features of a new organozinc-based substitution process [heteroatom-C-(R¹,R²)-SPh + R³₂Zn → heteroatom-C-(R¹,R²,R³)], first discovered during a total synthesis of the alkaloid mycotoxin α-cyclopiazonic acid, are described. Phenyl thioglycosides were valuable substrates in studying the nature of this reaction process. Since these sulfur compounds are converted into C-glycosyl compounds with some degree of stereoselectivity, the organozinc chemistry does provide a new entry to these biologically active substances.