Approach to the core structure of abeo-abietanes and gibberellins via Stork–Danheiser sequence followed by Friedel–Crafts alkylations

A mild and efficient protocol for the synthesis of [6,5,6]-tricyclic framework (4) of abeo-abietanes (1) and gibberellins (2) via Stork–Danheiser sequence on a bicyclic vinylogous ester followed by Lewis acid-catalyzed Friedel–Crafts alkylations of 3-aryl-2-hydroxymethyl-2-cyclohexenones (5) is developed. A variety of 2-cyclohexenone derivatives (5) underwent smooth Friedel–Crafts alkylations to craft the [6,5,6]-tricyclic skeleton (4) in good to excellent yields.