Rhodium carbene reactions methyl

The use of ylides as carbene precursors constitutes a novel original approach to control or extend carbenic reactions. The thiophenium ylide XXVIII prepared by catalytic decomposition of methyl diazomalonate in the presence of dichloro-2,5-thiophene has been successfully applied as a carbene equivalent or precursor to the cyclopropanation of olefins, the OH insertion and the C-H insertion reaction in activated arenes [112, 113] the catalyst being rhodium(II) acetate or copper(II) acetylaceto-nate. 

Rhodium(II)-MEPY and rhodium(II)-MACIM (methyl 1-acetylimidazolidin-2-one-4-carboxylate) complexes are efficient chiral catalysts for intramolecular carbon-hydrogen insertion reactions of diazoacetates (224) and metal carbene transformations (225). Dirhodium(II) carboxylates of similar structure (eg, piperidinonate complexes of the Rh2(ligand)4 type) have been found efficient catalysts for asymmetric cyclopropanation of olefins (226). 

Substituted bicyclo[ . 1.0]alkanes may also be obtained by condensation of secondary amines with 2-haloketones. A variety of nucleophilic reactions can be carried out on the intermediate cyclopropaniminium salt 116251 (Scheme 108). Competing alkene scission and cyclopropanation occurs on reaction of enamines with pentacarbonyl-chromium carbene complexes252 (Scheme 109). N-Silylated allylamines and their derived N-silylated enamines undergo rhodium or copper catalysed cyclopropanation by methyl diazoacetate253 (Scheme 110). 

Mechanistic studies of rhodium porphyrins as cyclopropanation catalysts have resulted in the spectroscopic identification of several potential intermediates in the reaction of ethyl diazoacetate with olefins, including a diazoniumfethoxy-carbonyl)methyl-rhodium complex formed by electrophilic addition of the rhodium center to the a-C atom of ethyl diazoacetate [29]. It is not known if analogous intermediates are also formed in analogous reactions of copper catalysts. However, the initial part of the catalytic cycle leading to the metal carbene intermediate is not of primary concern for the enantioselective reactions described herein. It is the second part, the reaction of the metal-carbene complex with the substrate, that is the enantioselective step. 

Reaction of Cp Rh(H)2(SiMe3)2 with 2 equiv. of butyllithium, followed by addition of Af-methyl-2-chloro-pyridinium tetrafluoroborate, gave the bis(carbene) complex Cp Rh[=C(NMe)CH=CH]2. Other dimetallic alkoxycarbene Cp complexes of Rh and Ir were also reported. The chemistry of the di-/it-methylene-bis(penta-methylcyclopentadienyl-rhodium) complexes was reviewed. ... 

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