INTERMEDIATES FOR THE SYNTHESIS OF LINEAR-CHAINS OF 1,2/4,5-FUSED CYCLOHEXA-1,4-DIENE RINGS AND BELTENES BY REPEATED DIELS-ALDER REACTIONS

A synthetic strategy for the preparation of chains of 1,2:4,5-fused cyclohexa-1,4-diene rings, both linear and cyclic (beltenes), based on the repetitive Diels-Alder cycloaddition of p-benzoquinone with a tetramethylene- ethane synthon (3,4-dimethylenetetrahydrothiophene 1,1-dioxide) is described. This route has been developed to yield 5,11-dihydroxy-4,6,7,9,10,12-hexahydro-1H,3H-anthracene-[2,3-c:6,7-c']dithiophene 2,2,8,8-tetraoxide 16, a potential precursor of a tricyclic doubly-exocyclic diene, and 7,10-bis(tert-butyldimethylsilyloxy)-1,4,5,6,11,12-hexahydronaphthacene-1,4-dione 22, a potential precursor for the double dienophile 5,6,11,12-tetrahydronaphthacene-1,4,7,10-diquinone. but the generation of these Diels-Alder components and their combination to form a [9]-beltene derivative has not been accomplished. The synthesis of linear derivatives has proceeded as far as a protected heptacyclic derivative. 7,16-diacetoxy-1,4,10,13-tetrakis(tert-butyldimethylsilyloxy)-5,6,8,9,14,15,17,18-octahydroheptacene 25. The H-1 NMR spectrum of this compound is unexpectedly temperature dependent.