Substituted Benzocyclobutenes, Indans, and Tetralins via Cobalt-Catalyzed Cooligomerization of αω-Diynes with Substituted Acetylenes. Formation and Synthetic Utility of Trimethylsilylated Benzocycloalkenes

Abstract

A new synthesis of substituted benzocyclobutenes, indans, tetralins and two model anthraquinones is described which utilizes the catalytic ability of η5-cyclopentadienyldicarbonylcobalt to cooligomerize αω)-diynes with substituted monoacetylenes. Yields are best when bis(trimethylsilyl)acetylene (BTMSA) is used as one of the reactants to give the ortho-bistrimeth-ylsilylated derivatives 8a, 14a-16a, and 18a. Reaction of monosubstituted diynes with unsymmetrical monoacetylenes yields the sterically more hindered aromatic products 8d and 8f. Catalytically inert cyclobutadiene cyclopentadienyl cobalt complexes are formed in side reactions when BTMSA is cooligomerized with αω-diynes. These include complexes derived from reaction of one (19) or both (20, 21) ends of the diyne molecule. The synthetic utility of the o-bis(trimethylsilyl)benzene unit in electrophilic substitutions is demonstrated. Selective and stepwise displacement of the trimethylsilyl groups by electrophiles results in a variety of new derivatized benzocycloalkenes. Some mechanistic considerations are presented. © 1977, American Chemical Society. All rights reserved.