Acyl carbene

The term metalla-/3-diketonate refers to an anionic diacyl complex, such as L M(RCO)(R CO) , in which the two acyl ligands occupy adjacent coordination sites of the metal atom. Resonance stabilization of the negative charge by 7r-delocalization onto the two acyl ligands gives Lewis structures 1 and 2. The two acyl ligands acquire an acyl/carbene... 

For most methoxycarbene complexes a one pot modification of the above method is utilized. This involves direct alkylation of the initially formed lithium acylate carbene complex with trifluoromethanesulfonate or with methyl fluorosulfonate. The method is successfully employed for preparation of chromium140 as well as molybdenum and tungsten monocyclic uation 65), bicyclic (equation 66) and tricyclic carbene complexes... 

Oxazoles of various substitution patterns are well known heterocycles for which a number of methods of synthesis have been reported.129 Acyl carbenes or functionally equivalent species have been found to undergo cyclization with nitriles to give oxazoles in high yield via nitrile ylide intermediates.130,131 This reaction can be induced to occur under thermal, photolytic, or catalytic conditions.129,132,133 Huisgen and coworkers were the first to study this process in some detail.132 Thermolysis (or copper catalysis) of a mixture of ethyl diazoacetate and benzonitrile resulted in the formation of oxazole 254. The isolation of this product is... 

The well-known Arndt-Eistert homologation" of an acyl halide to a carboxylic acid also involves the migration of an R group (with its electron pair) to an electron-deficient acyl carbene (presumably through a hypercarbon species) [Eq. (6.132)]. This rearrangement is also known as the Wolff rearrangement. 

Acyl carbene equivalents The moderately stabilized RCOCH=BPhj ylides are generated from the tetrafluoroborate salts. These ylides react with aldehydes to give a,p-epoxy ketones, in contrast to the stibonium, arsonium, and phosphonium ylides, which afford enones. The weaker Bi-0 bond disfavors decomposition of the adducts into enones and the bismuthine oxides. 

Reports on the insertion of acyl carbenes into benzene for... 

Acid chlorides react readily with carbene anions to give acylated carbene complexes. When the initial acylated product contains an enolizable proton, the corresponding enol ester is isolated (Casey et a/., 1972). 

Photolysis of a-diazoketones produces acyl carbenes, which efficiently rearrange to ke-tenes that are subsequently trapped (Eq. 16.73). This photochemical version of the Wolff re-... 

The simplest acyl carbene, that derived from diazoacetaldehyde, undergoes 16% interconversion of the two carbenes upon photolysis in ether as determined by isotopic labeling.The diphenyl analogs show about 20-30% migration of label. 

A variation of the Wittig reaction between tri phenyl phosphine acyl carbene and bromoacetic ester results in C-alkylation and ylide formation to give structure Treatment of these ylides with aqueous base results in acids pyrolysis of the... 

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