An efficient Benzannulation protocol for the synthesis of 9,9-Diphenyl-9H-fluorenols using Intramolecular Allene Friedel–Crafts Annulation

Abstract

Herein we report a one-pot cascade benzannulation protocol for the synthesis 9,9-diaryl-9H-fluorenol, a key structure of many important natural products which exhibit the significant biological activities particularly phosphodiesterase-4 (PDE4) inhibitory activity. This approach proceeds through the annulation of tert-propargyl alcohols with 2-methyl acetylacetone through an intramolecular allene Friedel–Crafts reaction using Ca(OTf)2 as the environmentally benign catalyst. Synthetic transformations of these compounds to useful materials are also presented here with the aid of cross-coupling and RCM reactions.