Benzoquinones and related compounds. Part 6. Addition of benzenesulfinic acid to substituted 1,4-quinones

Abstract

Benzenesulfinic acid adds to 1,4-quinones in the presence of trifluoroacetic acid affording phenyl-sulfonylhydroquinones. Addition occurs predominantly at the 6-position for methyl-, tert-butyl- and trifluoromethyl-1,4-benzoquinone, but at the 5-position for methoxy-1,4-benzoquinone. Addition to acyl-1,4-benzoquinones occurs exclusively at the 3-position, but under similar conditions phenylsulfonyl-1,4-benzoquinone affords a mixture of 2,3- and 2,6-bisphenylsulfonylhydroquinones, although the former becomes the sole product in the presence of an excess of trifluoroacetic acid. These results are rationalised in terms of selective protonation of the quinone.

Oxidation of the phenylsulfonylhydroquinones yields the corresponding quinones which with 1,3-dienes give the expected Diels–Alder adducts.