Sowden homologation

The Sowden homologation [21], based on the nitroaldol condensation (Henry reaction) [22] between the aldehydo sugar and nitromethane in basic medium, followed by the Nef decomposition [23] of the resultant nitronate in strongly acidic conditions, has been employed in a more limited number of cases than the cyanohydrin synthesis. A recent example in this area is shown by the stepwise homologation of (V-acetyl-D-mannosamine (11) into /V-acetylneuraminic acid (12) [24] (Scheme 4). Also, this procedure has found... 

In the classical Sowden-Fischer procedure for the extension of sugars by a one-carbon unit, [ C]nitromethane is added to the aldehyde function of the next lower homolog, thereby producing a mixture of two C2-epimeric nitro alcohols 274 and 275... 

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