[1 + 2] Cycloadditions of Sulfur Monoxide (SO) to Alkenes and Alkynes and [1 + 4] Cycloadditions to Dienes (Polyenes). Generation and Reactions of Singlet SO?

摘要

Recently, we reported that the Diels-Alder reaction of 3,4-di-tert-butylthiophene 1-oxide (1) with dimethyl acetylenedicarboxylate (DMAD) at room temperature affords dimethyl 4,5-di-tert-butylphthalate (3) in high yield probably through extrusion of sulfur monoxide (SO) from the initial adduct 2. The SO, generated here, would be singlet if the SO extrusion from 2 takes places and is concerted. We have thus examined a range of chemical trapping experiments of the SO to characterize its reactivities and to compare them with those of SO generated from other organic sources.