Expeditious synthesis of 3,4-dihydro-2H-1λ6-benzo[e] [1,2]thiazine 1,1-dioxides

Abstract

A novel pathway for the preparation of 3,4-dihydro-2H-1λ6- benzo[e][1,2lthiazine 1,1-dioxides 3 via an orthomethyl lithiation/cyclization reaction of N-acyl-o-toluenesulfonamides 5 is reported. Readily available N-acyl-o-toluenesulfonamides 5 were treated with 2 eq of n-BuLi at -78°C - 0δC to give the corresponding sultams 6 in moderate to good yields. The resulting sultams 6 were converted to saturated sultams 3, which can be considered as one carbon-extended homologues of the Oppolzer suitams 1, in high yields by hydrogenation. Studies on the scope and limitation of this annulation for the preparation of sultams are discussed. Demonstration of the feasibility of using the sultams 3 templates for an electorophilic fluorinating agent is also described.