The synthesis of 7,9-dimethoxy-3-propyl-3,4-dihydro-1H-benzo[g]isochromene1,5,10-trione: A potential monomer for the synthesis of the natural product xylindein

Abstract

A novel synthesis of a 3-propyl-substituted-benzo[g]isochromene quinone, a potential monomer of the natural product xylindein, was accomplished in 9 steps (overall yield of 8.2%) from 2,4- dimethoxybenzaldehyde. Key steps included the use of a cross-metathesis reaction in which ethyl-3-allyl-4- (benzyloxy)-1,6,8-trimethoxy-2-naphthoate was converted into ethyl-4-(benzyloxy)-1,6,8-trimethoxy-3-(4- oxopent-2-enyl)-2-naphthoate as a mixture of (E)- and (Z)-isomers. Following an oxa-Michael addition reaction, a racemic mixture of the desired product, 5-(benzyloxy)-7,9,10-trimethoxy-3-(2-oxopropyl)-3,4- dihydro-1H-benzo[g]isochromen-1-one, the basic xylindein lactone skeleton, was obtained.