Diels‐alder reactivity of vinylsulfoxyallenes

Abstract

Abstract Vinylsulfoxyallenes 3a‐c are prepared from propargylic alcohols in 47‐65% yield. Vinylsulfoxyallenes undergo facile [4 + 2] cycloadditions with methyl triazolidenedione (MTAD) and singlet oxygen to afford phenylsulfinylpyridazines and spirocyclic phenylsulfinyl‐2 H ‐pyran‐3(6 H )‐ones in excellent yields (60‐90%). Spirocyclic phenylsulfinyl‐2 H ‐pyran‐3(6 H )‐ones are oxidized to the corresponding phenylsulfones with peracid or can be epoxidized with basic hydrogen peroxide. Spirocyclic pyranone formation is thought to proceed via the rearrangement of a labile cyclic peroxide intermediate 14.