Cascade Reactions of β‐Amino‐Substituted α,β‐Unsaturated Fischer Carbene Complexes with 1,5‐Dien‐3‐ynes as a Convenient Access to Ring‐Annelated Benzene Derivatives

Abstract

AbstractUpon heating pentacarbonyl(3‐dimethylamino‐1‐ethoxypropenylidene)chromium complexes 1 with 1,5‐dien‐3‐ynes 2 in pyridine at 80 °C, benzene‐annelated cyclopentenones 8 and their regioisomers 9, resulting from a sequence of cocyclization, 6π‐electrocyclization and hydrolysis, were isolated in 12–75 % yield (13 examples). The more flexible the alkenyl substituents were in the dienynes 2, the longer were the reaction times needed to achieve good chemical yields. This new cascade reaction of Fischer carbene complexes provides a direct route to trindanone analogues under milder conditions than traditional methods, and is compatible with more functionalities. Compounds 14 and 15 with steroid‐like skeletons were thus prepared in 54–77 % yields (4 examples) from complex 1‐iPr and the bicyclic alkyne 2. Hexacycles 17 and 18 were accessible with high diastereoselectivity in the triquinane moiety by the same method in 45 % yield, (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)