Exploiting Synergistic Effects in Organozinc Chemistry for Direct Stereoselective C-Glycosylation Reactions at Room Temperature.

Pairing a range of bis(aryl) zinc reagents ZnAr with the stronger Lewis acidic [(ZnAr )] (Ar =C F ), enables highly stereoselective cross-coupling between glycosyl bromides and ZnAr without the use of a transition metal. Reactions occur at room temperature with excellent levels of stereoselectivity, where ZnAr acts as a non-coupling partner although its presence is crucial for the execution of the C(sp )-C(sp ) bond formation process. Mechanistic studies have uncovered a unique synergistic partnership between the two zinc reagents, which circumvents the need for transition-metal catalysis or forcing reaction conditions. Key to the success of the coupling is the avoidance of solvents that act as Lewis bases versus diarylzinc compounds (e.g. THF).