7-(1-Acetoxymethylidene)Benzonorbornadiene: A Versatile Reagent for the Synthesis of 7-Formyl and 7-Hydroxymethyl Benzonorbornadienes.

Abstract: 7-(1-Acetoxymethylidene)benzonorbornadiene 3, prepared in one step by theaddition of benzyne to 6-acetoxyfulvene 2, is hydrolysed in acid solution to form a 3:2-epimeric mixture of syn- and anti- 7-formylbenzonorbornadienes 4 and 5, respectively;the corresponding 7-hydroxymethylbenzonorbornadienes 6 and 9 were produced byreduction of the formyl isomers with sodium borohydride. Keywords: Benzyne, cycloaddition, enolacetates, fulvenes, benzonorbornadienes. Introduction 7-Substituted benzonorbornadienes are important reagents, yet simple routes for their synthesisare lacking. In principle, such compounds can be prepared by addition of benzyne to 5-substitutedcyclopenta-1,3-dienes, however these isomers are themselves very unstable, being converted to themore stable 2-substituted and 3-substituted isomers during the course of benzyne addition. Further,the addition of benzyne to cyclopenta-2,4-dienones, which would circumvent the substrateisomerisation problem and provide a carbonyl group in the 7-position for subsequent modification, is