Arenes to Substituted Cyclohexadienes: Nucleophile/Electrophile Additions across an Arene Double Bond

Abstract

Alkyl-, vinyl- and aryllithium reagents were reacted with tricarbonylchromium-phenyloxazoline and -phenylmethanimine complexes 1 and 2. The resulting anionic cyclohexadienyl complexes were trapped with primary alkyl, allyl, benzyl, and propargyl bromides to give, after metal removal, 1,3-cyclohexadienes with a 1,5,6-substitution pattern. The results are consistent with exo-nucleophilic addition to the ortho-position of the arene, followed by addition of the electrophile to the metal center. With allyl, benzyl, and propargyl groups, direct reductive elimination then yielded trans-5,6-substituted products. With alkyl halides, reductive elimination was preceeded by CO insertion and acylcyclohexadienes were formed preferentially. In situ deprotonation/alkylation of the acylcyclohexadienes gave products in which three C-substituents had been added across an arene double bond with complete regio-and stereocontrol. The competition between the two pathways is discussed in terms of migratory aptitude to carbonylation and effects of the cyclohexadienyl ligand. Assigned product stereochemistry was confirmed by X-ray structures of two 1,5,6-substituted cyclohexadienes. With complex 2, an intermediate acetyl enamine cyclohexadiene (11a) was isolated and structurally characterized. Its reaction with O 2 gave the corresponding 3,4,5-substituted phenol 12 (X-ray)