Monday, June 22, 2009

A way to make diazo compounds

Michael E. Furrow and Andrew G. Myers*

The bimolecular reaction of carboxylic acids with diazoalkanes
to form esters is among the mildest and most efficient of organic
transformations but is seldom used in synthesis beyond the
important case of methyl esterification.1 This is largely a consequence
of the inaccessibility and poor stability of higher diazoalkanes
as substrates.2 In this work we describe a new method for
the synthesis of diazoalkanes by the oxidation of N-tert-butyldimethylsilylhydrazones
(TBSHs) with (difluoroiodo)benzene,3 a reagent
heretofore unexplored in the context of hydrazone oxidation.
When conducted in the presence of a carboxylic acid substrate,
the oxidation leads to efficient esterification in situ (Scheme 1). In
addition to greatly extending the range of diazoalkanes that are
now available for esterifications, this new protocol offers significant
advantages with regard to safety, for diazo intermediates are neither
isolated nor achieve appreciable concentrations during the reaction.

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