Metal caibene transformations

Like electrophilic addition to diazo compounds [7] from which diazonium ions and, subsequently, carbocations are generated, transition-metal compounds that can act as Lewis acids are potentially effective catalysts for metal caibene transformations. These compounds possess an open coordination site that allows the formation of a diazo carbon-metal bond with a diazo compound and, after loss of dinilrogen, affords a metal caibene (Scheme 5.2). 

Intramolecular cyclopropanation reactions of alkoiyl diazo carbonyl compounds are among the most useful catalytic metal caibene transformations, and the diversity of their applications for organic S3mtfaeses is substantial [7,10,24,84]. Their catalytic asymmetric reactions, however, have only recently been reported. An early application of the Aratani catalyst 2 (A = PhCH2) to... 

Lewis bases (B ) that can occupy the open coordination site inhibit catalytic activity. The electrophilic nature of the metal caibene is seen in its subsequent reactions with nucleophiles (S ), which occur with the transfer of the carbene entity from the metal to a nucleophile without ever having generated or transformed an actual Tree carbene. 

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