Benzoisobenzofuran. Formation and Reactions of the Parent and Alkoxy-Substituted Derivatives

Article abstract of DOI:10.1021/jo00170a001

Benzoisobenzofuran (1) is formed by base-induced 1,4-elimination of either acetal 9 or 11 and may be isolated in high yield as a cristalline solid.Cycloaddition reactions of preformed 1 have been carried out with various dienophiles.These reactions may also be accomplished by heating the acetals in the presence of dienophiles and acid catalyst, where 1 is generated as an intermediate.The cycloaddition reaction of 1 and maleic anhydride is found to be reversible at higher temperature (slow at 60 deg C).Unsymmetrical dienophiles react with 1 to give equal amounts of regioisomers, and evidence points to lack of regioselectivity under both kinetically controlled and equilibrating conditions.The acetals 9 and 11 are shown to interconvert with acid catalyst at 140 deg C, where 1 is an intermediate of greater stability than the acetals; the equilibrium K for 9 -> ( <- ) 11 is approximately unity.Various acid-catalyzed cycloaddition reactions of ortho esters 8 and 10, yielding polysubstituted phenanthrene derivatives, are described.