Oxidation of alkoxyphenols. XX. Ring cleavage and lactone formation in the oxidation of a Biphenyl-2,2'-diol by lead tetraacetate

Abstract

Two products in the lead tetraacetate oxidation of 3,3?-di-t-butyl- 5,5?-dimethoxybiphenyl-2,2?-diol have been shown to be (E)-7-t-butyl-5- methoxy-3-[(E)-2?-methoxy-5?,5?-dimethyl-4?-oxohex-2?- enylidenelbenzofuran-2(3H)-one (1) and its (Z,Z) isomer (3). Treatment of these with base causes rearrangement to (E)-8-t-butyl-2-(3?,3?- dimethyl-2?-oxobutylidene)-6-methoxy-2H-1-benzopyran-4-carboxylic acid (13). Further treatment with base produces pinacolone and 8-t-butyl-6- methoxy-2-oxo-2H-1-benzopyran-4-carboxylic acid (14). The latter has been synthesized from 2-t-butyl-4-methoxyphenol via 7-t-butyl-5- methoxy-2,3-dihydrobenzofuran-2,3-dione (15).