Esters carbonyl ylide structures

Much of the initial synthetically useful carbonyl ylide work originated from the Ibata group. Exploiting simple disubstituted aromatic diazoketo-esters and structurally diverse dipolarophiles, Ibata and co-workers (64—70) prepared several different cycloadducts 167-169 through an intermolecular ylide cycloaddition (Scheme 4.38). 

N-Metallated azomethine ylides 140 of ester-stabilized types are tautomeric to the metal ester enolates (141) of chelate-stabilized types. The only structural difference is which heteroatom between the imine nitrogen and the ester carbonyl oxygen is connected with the metal (M) by a covalent bond. The difference in chemical properties expected for the ylidic forms 140 and enolate forms 141 is not yet clear. 

Tetrakis(l,T-binaphthyl-2,2 -diyl phosphate) complexes (119) are reported to be much more effective catalysts than the more commonly used carboxylate complexes for enantioselective intramolecular, tandem, carbonyl ylide forma-tion/cycloaddition of a-diazo- -keto esters. The ring-opening reactions of epoxides with diphenyl phosphorazidate (120) have been investigated. A wide range of epoxide substrates have been studied and the products, (121) or (122), depend on the substrate structure. The microbial hydroxylation of novel phos-... 

Padwa subsequently described some intramolecular versions of this reaction. A structurally similar aryl ester, 55, a tethered to a terminal olefin was subjected to rhodium-catalyzed diazo decomposition. Carbonyl ylide formation followed by intramolecular cycloaddition resulted in tricyclic product 56 a, Eq. 39 [66 - 69]. Cycloaddition also occurred with the amide analogue 55 b. 

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