Formation of xanthen and fluorene derivatives by competitive 1,4- and 1,3-cycloadditions of quinonylmethyl anions to quinones

Abstract

The 3-methyl-1,4-naphthoquinon-2-ylmethyl anion (I) adds to trimethyl-1,4-benzoquinone giving, by 1,4-cycloaddition, the xanthen derivative (III) but not the isomer (VI). Simultaneously, 1,3-dipolar cycloaddition yields the fluorene derivative (VII) but not the isomer (X). These reactions are general for quinonylmethyl anions and 1,4-quinones with one vacant site. Reasons are advanced for supposing that the 1,3-dipolar additions are preferred electronically, but the substituents in the quinone may prevent it while still allowing the 1,4-cycloaddition to occur. In extreme cases neither cycloaddition would be likely and the products of Michael additions then appear.

The structures of all new products are fully established and some of their transformations are studied.