Addition of novel benzylmagnesium “ate” complexes of BnR2MgLi type to 2-(thio)pyridones and related compounds

Novel benzylation reagents BnR2MgLi were obtained by mixing benzylmagnesium chloride (BnMgCl) and appropriate organolithium compounds (RLi). As BnR2MgLi complexes are more nucleophilic than the parent Grignard compound they enabled regioselective C6-addition to electrophilic N-substituted 2-(thio)-pyridones and C4-addition to poorly reactive NH 2-(thio)pyridones in high and good yields, respectively. Thus, the application of these new reagents in efficient synthesis of 6-benzyl-3,6-dihydro- and 4-benzyl-3,4-dihydropyridin-2(1H)-ones is described. The prospect of wider application of BnR2MgLi in 1,4-addition to other electrophiles, comprising six-membered α,β-unsaturated systems is also presented.