An Efficient Synthesis of 4-Mono- and 4,4-Di-substituted 3,4-Dihydro-2H-1-benzothiopyran 1,1-Dioxides by LDA-Mediated Cyclization of o-(Methylsulfonyl)styrenes

A new and efficient method for the preparation of 3,4-dihydro-2H-1-benzothiopyran 1,1-dioxide derivatives has been developed. alpha-Substituted o-(methylsulfonyl)styrenes, which can be derived from alpha-substituted o-bromostyrenes by an easily operated two-step sequence, are cyclized on treatment with lithium diisopropylamide (LDA) to give, after aqueous workup, the corresponding 4-monosubstituted 3,4-dihydro-2H-1-benzothiopyran 1,1-dioxides. Addition of electrophiles prior to aqueous workup provides 4,4-disubstituted derivatives.