A novel synthetic route to 7-MAC from 7-ACA

An efficient and practical seven-step procedure is described for the synthesis of (6R,7S)-benzhydryl-7-amino-7-methoxy-3-((1-methyl-1H-tetrazol-5-ylthio)methyl)-8-oxo-5-thia-1-aza-bicyclo [4.2.0]oct-2-ene-2-carboxylate (7-MAC, 3) with overall yield of 49 %. This synthesis features a convenient and highly selective method for the introduction of 7α-methoxy group to cephalosporin nucleus in 10 using MeOLi/t-BuOCl in THF.