TANDEM WESSELY OXIDATION AND INTRAMOLECULAR DIELS-ALDER REACTIONS .4.THE SYNTHESIS OF (+ -)-CORONAFACIC ACID/

Ethyl E-5-(4-ethyl-2-hydroxyphenyl)-2-pentenoate (7), prepared in four steps from m-ethylphenol (9), was converted via Wessely oxidation wit h lead tetraacetate followed by intramolecular Diels-Alder reaction in boiling xylene to ethyl dro-8-oxo-1,5-methano-1H-indene-anti-4-carbox ylate (16). Hydrogenation of 16 followed by mild hydrolysis gave ethyl oxy-8-oxo-1,5-methano-1H-indene-anti-4-carboxylate (24), which on oxi dation with periodate gave nyl)-6-ethyloctahydro-1-oxo-1H-indene-5-car boxylic acid (26). Oxidative decarboxylation of this gave a mixture of ethyl ,3a,6,7,7a-hexahydro-1-oxo-1H-indene-4-carboxylate (31) and eth yl ,3a,4,7,7a-hexahydro-1-oxo-1H-indene-4-carboxylate (32); the latter was converted to the former by ethanolic sodium ethoxide. Hydrolysis of 31 with hot hydrochloric acid gave (+/-)-coronafacic acid (4).