Buchner reaction transition metal-catalyzed

Anciaux, A. J., Demonceau, A., Noeis, A. F., Hubert, A. J., Warin, R., Teyssie, P. Transition-metal-catalyzed reactions of diazo compounds. 2. Addition to aromatic moiecuies cataiysis of Buchner s synthesis of cycioheptatrienes. J. Org. Chem. 1981,46, 873-876. 

The catalytic cycle of the transition-metal-catalyzed Buchner reactions can be generally described as below ... 

Transition metal-catalyzed Buchner reactions of arene substrates proceed via electrophilic carbenoids. In addition to cyclopropanation of the arene double bond, these a-diazoketones possessing an aromatic ring can also participate in C-H insertion reactions. As shown in the decomposition of diazomethyl ketone 53, the benzylic C-H insertion product 56 is obtained as a minor product (vide supra). The rhodium(II) acetate-catalyzed reaction of diazoketone 71 also affords cycloheptatriene derivative 73 along with the benzylic C-H insertion product, y-lactam 72, in a ratio of 1 2. Treatment of 71 with the more electron-rich rhodium(II) caprolactamate [Rh2(Cap)4] favors more C-H insertion, but the cycloaddition pathway is still significant the ratio of 73 to 72 is 1 3.5. 

The thermal or photochemical Buchner reactions produce complex mixtures of cycloheptatrienyl esters, and the daunting complexity of the product mixtures was reduced or even eliminated with the advent of transition-metal catalysts, at first copper-based, then in the early 1980s rhodium(II) catalysts, which were developed by the Belgium group led by Noels and Hubert. The rhodium(II)-catalyzed cyclopropanations of aromatics, especially intramolecular cyclopropanations, have enjoyed a certain popularity due to their high regioselectivity and stereoselectivity. Since the intramolecular Buchner reaction is much more widely used in organic synthesis than the intermolecular version, the former is the focus of this review. 

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