Formal radical closure onto aromatic rings—a general route to carbocycles

Abstract

A general method is described for indirectly effecting radical carbocyclization of an alkyl chain onto an aromatic ring. Birch reductive-alkylation of aromatic tert-butyl esters with α,ω-dibromides, chromium(VI)-mediated oxidation of the resulting 1,4-dienes and Finkelstein displacement of Br⁻ with NaI gives cross-conjugated ketones that undergo radical cyclization. The products are easily aromatized to phenols by silylation, Saegusa oxidation and treatment with BiCl₃.H₂O. A special feature of the route is that it allows attachment of a substituent to the original aromatic ring in place of the phenolic oxygen of the normal product.