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Aldehydes, diazoacetate homologation

Treatment of benzaldehydes with ethyl diazoacetate and a catalytic quantity of the iron Lewis acid [ -CpFe(CO)2(THF)]+BF4 yields the expected homologated ketone (80). However, the major product in most cases is the aryl-shifted structure (81a), predominantly as its enol tautomer, 3-hydroxy-2-arylacrylic acid (81b). This novel reaction occurs via a 1,2-aryl shift. Although the mechanism has not been fully characterized, there is evidence for loss of THF to give a vacancy for the aldehyde to bind to the iron, followed by diazoacetate attachment. The product balance is then determined by the ratio of 1,2-aryl to -hydride shift, with the former favoured by electron-donating substituents on the aryl ring. An alternative mechanism involving epoxide intermediates was ruled out by a control experiment. [Pg.23]

Methods of chain extensions generally use linear sugars with free aldehydes mostly prepared via dithioacetal formation, protection of the remaining hydroxyl groups and aldehyde recovery. This allows one to use all methods applicable to aldehydes. Among others, the condensation of ethyl diazoacetate has been studied in detail by L6pez-Herrera [207] in a new synthesis of KDO by a two carbon homologation of an open-chain mannose derivative. [Pg.547]


See other pages where Aldehydes, diazoacetate homologation is mentioned: [Pg.112]    [Pg.144]    [Pg.1408]    [Pg.1602]    [Pg.1603]    [Pg.353]    [Pg.24]    [Pg.149]   


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Aldehydes homologation

Diazoacetate

Diazoacetates

Diazoacetic

Homologation Aldehyd

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