Asymmetric cycloaddition routes to both enantiomers of trans-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylic acid

Abstract

Fumarates prepared from a series of optically active alcohols were used as dienophiles in Lewis acid catalyzed asymmetric cycloadditions to anthracene. The reactions gave high yields and d.e.'s of the diester cycloaddition products and acid hydrolysis could be performed under conditions yielding only about 10% racemization. The reactions form a valuable synthetic pathway to both enantiomers of the bicyclic dicarboxylic acid, since di-(−)-menthyl fumarate yielded the (−)-( S, S)-enantiomer and di-(+)- iso-menthyl fumarate the (+)-( R, R)-enantiomer of the acid. The other fumarates, obtained from (−)-borneol, (+)-fenchol and (−)-isopulegol, likewise gave the (−)-( S, S)-enantiomer of the acid. The absolute stereochemistry of the products was confirmed via a single crystal X-ray crystallographic structure determination of the brucine salt of the (−)-( S, S)-enantiomer.