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The 2-benzopyran-%ones 7a and 7c undergo intramolecular Diels-Alder addition via preferred endo-addition of the connecting chain, whereas for 7d and 7e (X = S02Ph), exo-addition of the chain is preferred; the main adducts from the latter additions (9d and 9e), give the diterpene-related products 12 (R = H, Y = OMe) and 12 (R = Me, Y = OMe) upon treatment with sodium amalgam.

The 2,3-naphthoquinones 1 (R = Ph, o-tolyl, COPh, CI and Prn) can be generated by desilylationdebromination induced by fluoride ion (4; arrows) and trapped as the adducts 5 with norbornadiene.As deduced from the formation of the appropriate adducts with olefins and dienes, 2,3-naphthoquinone 1 (R = H) and its 1,4diphenyl derivative 1 (R = Ph) are generated by oxidation of the corresponding naphthalene-2,3-diols. 1,2 However the adducts could have been formed by trapping radicals or other intermediates formed during the oxidation of the naphthalenediols rather than from the 2,3-naphthoquinones themselves2 We describe here a non-oxidative generation of 1 (R = Ph) by a process which, unlike the oxidative process, can be applied to several other lP-disubstituted 2,3-naphthoquinones.The route adopted is outlined in Scheme 1 and was first