Spirans. Part VIII. 1,2-Naphthoquinone 1-methide and its spiro-dimer in chroman syntheses

Abstract

Fully characterised for the first time, 1-hydroxymethyl-2-naphthol is an unsatisfactory source of 1,2-naphthoquin-one 1-methide (I) because heat rapidly changes it into 1,1′-methyienedi-2-naphthol. 1-Dimethylaminomethyl-2-naphthol, heated with alkenes, gives chroman derivatives mixed with the naphthoquinone spiro-dimer (III). The spirodimer dissociates sufficiently at 160–200° to provide a good source of the naphthoquinone methide with the additional advantages that the absence of bases and protic molecules reduces side reactions and allows the reaction to be prolonged for higher yields.