Evidence for the mechanism of formation of N-(1,2-dihydrobenzocyclobut-1-enyl)pyridinium bromides and acetophenones from bisdibromocyclopropane adducts

Abstract

The bis-dibromocarbene adducts (1a–e) when boiled with xylene in the presence of 1,4-diazabicyclo[2.2.2]octane gave the corresponding bicyclo-octadienes (2a–e). These except for (2d, e) invariably gave the pyridinium salts (3) with boiling pyridine. Besides, the 1 :2 adducts (1c, d) also gave the phenacylpyridinium salts (6b; R¹= Me, R²= H) presumably via an alternative route. The bicyclic ketones (7) gave only intractible tars with pyridine, except for (7; R¹= Me, R²= H) from which the phenacylpyridinium salt (6b; R¹= Me, R²= H) was isolated in low yield.