Unique ring expansion of a 6-3 bicyclic ring system forming a functionalized 7-membered ring accelerated by nitrogen functional groups

Abstract

The treatment of (2-hydroxy-5-oxobicyclo [4.1.0] hept-3-en-3-yl) carbamic acid esters and (2-hydroxy-5-oxobicyclo [4.1.0] hept-3-en-3-yl) benzamide with TMSCl gave 7-membered ring compounds in good yields. The structure of the substituent at the C3 position of the cyclohexene ring is crucial for this ring expansion. The reaction mechanism is thought to involve the formation of a norcaradiene (bicyclo [4.1.0] hept-2,4-diene) structure and subsequent electrocyclic reaction.