Isobenzofulvenes. VII. Regio- and site-selective cycloadditions and their potential in anthraquinone synthesis

Abstract

The regiochemistry of the cycloaddition of the 4-methoxyisobenzofulvene (8a) with 5- and 6-chloro- 2-methyl-1,4-benzoquinones has been evaluated. The resulting cycloadducts have been converted into the known 5-methyl ethers of islandicin and digitopurpone. The concept and value of a 'ghost' substituent in controlling the regiochemistry of a cycloaddition is discussed in general and evaluated for a specific case.