Cycloaddition of nitroso dipolarophiles to thiazolium-4-olates. Part 1. Nitrosobenzene and 1-chloro-1-nitrosocyclohexane

Abstract

Thiazolium-4-olates 1 and nitrosobenzene participated in regiospecific cycloadditions which gave 3-oxa-2,5-diaza-7-thiatrinorbornan-6-ones 5. On storage, compounds 5 rearranged to the azeto-benzothiazine S-oxides 7, fragmented to the benzil diimides 8, and a lost sulfur atom to give the iminoimides 9. The cycloadditions of mesoionic compounds 1 with 1-chloro-1-nitrosocyclohexane exhibited a reversed regiochemistry and formed the trinorbornanes 6, which were subsequently attacked by nucleophiles at the bridgehead to produce the thiazolones 14. The mechanisms of formation of all the products are discussed. Structures 7a and 14d were confirmed by single-crystal X-ray analyses.