A 2,3,5,6-tetramethylenebicyclo[2.2.0]hexane derivative: a novel bisdiene molecule that produces a Dewar benzene skeleton upon two successive Diels–Alder reactions with dienophiles

Abstract

A new bisdiene molecule 1, the 1,4-acetal-bridged derivative of the hitherto unknown 2,3,5,6-tetramethylenebicyclo[2.2.0]hexane, is synthesized in four steps from dimethyl acetylenedicarboxylate and (E)-1,4-dichlorobut-2-ene. Reaction of 1 with dimethyl acetylenedicarboxylate or benzyne leads to the formation of the Dewar benzene derivatives 6 and 7, respectively, through two successive Diels–Alder additions of the dienophiles to 1. Dehydrogenation of the adducts 6 and 7 affords the corresponding 9,10-Dewar anthracene derivative 10 and 6,13-Dewar pentacene derivative 11, respectively. Compound 11 is characterized crystallographically. Reactions of 1,4-benzoquinone and N-phenylmaleimide with 1 are also reported.