Ketene from carbonyl ylides

Summary. Intra- and intermolecular carbene or carbenoid reactions resulting from the photochemical and Cu(I)-, Rh(II)-, or Ru(I)-catalyzed decomposition of a-diazo-a-silylacetic esters are described. Among the products reported are (alkoxysilyl)ketenes, silaheterocycles, 1-trialkylsilylcyclopropane-l-carboxylates, and products derived from transient carbonyl ylides. 

The formation of the naphthalene (73) from the bis-ylide (72) and diethyl ketomalonate involves an unusual olefin synthesis on the carbonyl of an ester group. The methylene-pyrans (75) were formed when the diethyl malonates (74) were refluxed with j3-keto-ylides in xylene or decalin. Possible intermediates are the ketens (76) and the allenes (77). Addition of ylide to the allenes gives the betaines (78) which form methylene-pyrans either directly or via acetylenes as shown. 

Looking carefully at the current literature we have learned that the ketene dithioacetal chemistry, widely used for one-carbon homologation of carbonyl compounds, has never been utilized for the construction of ulosonic acids [129]. Besides, ketene dithioacetals, readily available from ketones and aldehydes via the reaction with the ylides generated from substituted dithioacetals in the Peterson, Wittig or Homer-Emmons olefmation, have never been synthesized from lactones. 

Photfrfysis of a-Diazo Carbonyl Compounds - Some recent advances in the matrix photochemistry of diazoketones, including some heterocyclic species, have been reviewed. Flash photolysis of 10-diazo-9(10//)-phenanthrenone (35) in aqueous solution led to the detection of two transient species on the pathway to the final product, fluorene-9-carboxylic acid. These were identified, from solvent isotope effects and the nature of the observed acid-base catalysis, as fluorenylideneketene (36, X = CO) and the enol of fluorene-9-carboxylic acid (36, X = C(0H)2), formed by hydration of the ketene. In related studies, fluorenylideneketene was found to react with amines to give ylides as intermediates on the route to the amide final products. The product distribution from the photochemical reactions of 2-diazo-3-oxo-5,10,15,20-tetraphenylchlorins with alcohols strongly depends on the central metal ion of the irradiated diazoketones. ... 

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