PETER YATES and TADAS S. MACAS. Can. J. Chem. 66, 1 (1988).Wessely oxidation of o-(3-alkenyl) phenols (5) with lead tetraacetate gives 6-acetoxy-6-(3-atkeny1)-2,4-cyclohexadien-I-ones (6), which undergo intramolecular Diels-Alder reactions to give isotwistene (hexahydro-1.5-methanoindene) derivatives (7). These, on hydrolysis followed by oxidation with periodic acid, give hexahydro-1-0x0-l H-indene-5-carboxylic acids (41, 46). Compounds 5 were prepared either by Grignard coupling of o-methoxybenzyl chloride with ally1 halides followed by de-0-methylation with sodium thioethoxide or via reduction of dihydrocoumarins (18-20) to 2-chromanols (21-23) with diisobutylaluminum hydride, followed by Wittig reaction of these with ethyl (triphenylphosphoranylidene)acetate. The oxidation of ortho-substituted phenols with lead tetraacetate LTA to give 6-acetoxy-2,4-cyclohexadien-1-ones (oquinol acetates; I ) , which was first reported by Wessely and his co-workers in 1950 (4), is the simplest general method for the synthesis of the latter class of compounds. Wessely early recognized (5) the potential utility of o-quinol acetates in intermolecular Diels-Alder reactions leading to bicyclo[2.2.2]octenones and bicyclo[2.2.2]octadienones (e.g., 2 (R = CH3) 3, (Scheme 1).Work in these laboratories (1, 2) has shown that an intramolecular version of the latter reaction can be effected by Wessely oxidation products that incorporate a dienophilic group in the ester moiety (e.g., 3). This provides a route to tricyclic lactones of type 4, as exemplified in Scheme 2.It occurred to us that a related reaction sequence involving Wessely oxidation of an o-(3-alkenyl) phenol (5) to give a 2,4-cyclohexadienone of type 6, followed by intramolecular cyclic analogues of 4, i.e., isotwistene (hexahydro-l,5-methanoindene) derivatives of type 7 (Scheme 3). Other workers (7) have already demonstrated the practicability of the synthesis of tricyclic systems via intramolecular reactions of alkenyl 1,3-cyclohexadiene derivatives, but none to our knowledge has coupled this reaction with the Wessely oxidation reaction. Can. J. Chem. Downloaded from www.nrcresearchpress.com by 54.213.91.117 on 05/10/18For personal use only.