Copper-carbenoid species synthesis

Doyle s use of rhodium(II) to generate a rhodium-carbenoid species from an ot-diazo carbonyl compound is reminiscent of the first successful synthesis of isomunchnones by Hamaguchi and Ibata, which involved copper(ll) to generate a copper-carbenoid species from an a-diazo imide that cyclized to an isomunchnone. 

An alternative approach to aziridine synthesis involves transfer of a carbenoid species to imines. Jacobsen achieved the first asymmetric aziridination of imines by transfer of copper carbenoids derived from copper bis-oxazohne catalysts and ethyl diazoacetate onto imines, but this process only proceeds with moderate yield and selectivity. Better results have been achieved by addition of ethyl diazoacetate to imines in the presence of enantiopure Lewis acids such as the boron-based catalysts prepared from vaulted biaryls such as VAPOL (4.154) and B(OPh)3. A range of aryl and alkyl N-benzylaldimines, for example (4.155) and (4.156), undergo aziridination to give ds-aziridines with high ee using this procedure. 

The fact that carbenes are characterized by their stereospecific transformations has effectively paved the way for numerous innovative developments. The discovery that rhodium acetate can function as a catalyst for carbene generation from diazoacetates [15, 16] with much higher efficiency than copper salts, which had been traditionally used, provided an opening into the vast possibilities offered by transition metal catalysis. The increasing number of novel, stereoselective reactions of carbenoid species have become an indispensable toolbox for the modern practitioner of chemical synthesis [17-22],... 

Yanez et al. reported the synthesis of miconazole and analogs through a carbenoid intermediate. The process involves the intermolecular insertion of carbe-noid species to imidazole from a-diazoketones with copper acetylacetonate as the key reaction of the synthetic route [11]. 

A useful cyclopropane synthesis was developed by H. E. Simmons and R. D. Smith of the DuPont Company. In this synthesis diiodomethane and a zinc-copper couple are stirred together with an alkene. The diiodomethane and zinc react to produce a carbene-like species called a carbenoid ... 

In another route to cyclopropanes, diiodomethane is treated with zinc powder (usually activated with copper) to generate ICH2ZnI, called the Simmons-Smith reagent This species is an example of a carbenoid, or carbene-like substance, because, like carbenes, it also converts alkenes into cyclopropanes stereospecifically. Use of the Simmons-Smith reagent in cyclopropane synthesis avoids the hazards associated with diazomethane preparation. 

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