Regioselective Synthesis of Indene from 3‐Aryl Propargylic gem‐Dipivalates Catalyzed by N‐Heterocyclic Carbene Gold(I) Complexes.

Abstract: 1‐Aryl‐3,3‐bis(pivaloyloxy)propynes can be converted in good to high yields into either 1,3‐ or 1,2‐bis(pivaloyloxy)indenes, depending on the N‐heterocyclic carbene (NHC) gold(I) hexafluoroantimonate catalyst used. Almost exclusive formation of 1,3‐di(oxycarbonyl)indene derivatives was achieved with cationic gold complexes containing the embracing N,N′‐1,3‐bis(9‐butylfluorenyl)benzimidazolylidene ligand (nBuFNHC). The regioselective issue of the reaction was rationalized by the specific spatial distribution of the steric bulk in the nBuFNHC ligand. In contrast, only modest selectivities in favor of 1,2‐disubstituted indenes were observed with more classical NHC gold complexes, the best selectivity being then obtained with N,N′‐1,3‐bis(2,6‐diisopropylphenyl)‐4,5‐dihydroimidazolylidene gold chloride (SIPrAuCl) as precatalyst. [ABSTRACT FROM AUTHOR]