Spirans. Part 11. A new method for generating o-quinone methides, and its applications to the synthesis of spirochromans. A note on the autoxidation of a naphthol derivative

Abstract

The adducts (5) and (9) formed from quinonyl carbanions and tetramethyl-1,4-benzoquinone are reduced by zinc in acetic acid giving the components phenols. It is considered that o-quinone methides are intermediates, aromatisation of the quinonoid ring being the driving force (Scheme 1). The corresponding ethers (6), (7), and (10) give o-quinone methides that are either readily trapped by acetate ion giving phenolic benzyl acetates (13) and (17) or dimerise giving the bisnaphthol (25)via the spiran (24). The benzylic acetates form excellent substrates for conversion into spirans such as (4) by standard methods; the spiran (24) can be regenerated from the bisnaphthol by oxidative cyclisation.

The naphthol derivative (23) obtained as a by-product is rapidly oxidised by air to give the hydroperoxide (26).