NHC-gold(i) catalysed [4 + 2] cycloaddition-acyclic addition of dialkyl substituted propargylic esters with 1,3-diphenylisobenzofuran: Synthesis of novel benzo[c]fluorenols and substituted dienes

Abstract

A gold carbene complex [IPrAuCl/AgSbF6] catalysed novel cycloaddition of propargylic esters with 1,3-diphenylisobenzofuran is reported. A [4 + 2] cycloaddition followed by sequential aromatic allylation leading to pentannulation with the expulsion of benzoic acid, then 1,2-phenyl migration coupled with ring opening and aromatisation leading to a new class of benzofluorenols, is discovered. This process involves facile multiple C-C bond formation. An accompanying second pathway involving the attack of benzoyloxy anion on the central allenic carbon affording substituted dienes is also observed. Key products are characterised by X-ray structure determination. This journal is © the Partner Organisations 2014.