Contrasting behaviour is
observed when 2- and 4-methoxy-3,5-dinitropyridine
interact with methoxide ion in dimethyl sulphoxide.
The 4-methoxy compound affords both methine and
acetal sigma complexes, the latter being thermodynamically more stable. The interconversion is catalysed by methanol. Labelling
experiments have established that the sigma complex from the 2-methoxypyridine is formed by addition at C6; no conversion
into the acetal could be effected. These observations are rationalized in terms
of differential steric and solvation effects. Demethylation and
rearrangement reactions of 4-methoxy-3,5-dinitropyridine
are reported.
Recent development and applications of semipinacol rearrangement reactions
