REGIOSELECTIVE FUNCTIONALIZATION IN 2 POS ITION OF 1,3-DISUBSTITUTED BENZENES

Functionalisation in 2 position of benzenes 1,3-disubstituted by para- directing groups has been investigated, involving 2-trimethylsilylated intermediates when the classical methods (particularly these involvin g the anion in 2 position) are ineffective. Thus 2-trimethylsilyl deri vatives of 1,3-dihalo- or 1,3-dimethoxybenzene have been prepared in g ood yields. Their conversion into the corresponding 1,2,3-trisubstitut ed benzenes has been conveniently performed upon acetylation, iodinati on or sulfonation, except in the case of the sulfonation of the 1,3-di methoxylated compound in which the ipso effect of the silyl group is s urpassed by the directing effect of the methoxy substituents. In contr ast, whith the same substrate, cyanation in position 2 was successfull y carried out using chlorosulfonyl isocyanate: to our knowledge this r eaction is the first example of substitution of a trimethylsilyl by a cyano group in the aromatic series.