Synthesis of Phenols with Side-chains containing Si, N or S Atoms

4 Synthesis of Phenols with side-chains containing Si, N or S atoms 

Phenols with side-chains containing Si, N or S atoms (but rarely their combination) are comparatively easily synthesised and either provide valuable terminal products or intermediates for further reactions. This group includes the products of the Mannich reaction, compounds with silicon in place of carbon and a array of sulphur compounds some of which have been discussed in a previous review (ref.40). 

Some of the reactions in this section are summarised in Table 6.4 (refs.41-44) with reference mostly to methylenic side chains. 

A further method of methylthiomethylation is shown in the reaction of methanethiol with 9-methyl-2-phenyl-4H-1,3,2-di-oxaborin[6,5,e]benzofuran- 

8-carboxylate (derived from ethyl 4-hydroxy-5-hydroxymethyl-3-methylbenzofuran-2-carboxylate and phenylboronic acid) in dichloromethane at 0°C in the presence of aluminium chloride (4 equivs.) for 30 mins, followed by 30 mins, at ambient temperature and work-up with hydrochloric acid at 0 C, to furnish, in 56% yield, ethyl 4-hydroxy-3-methyl-5-methylthiomethyl-benzofuran-2-carboxylate (ref.45) by displacement of phenylborinic acid. 

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