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Treatment of 1,1-diethoxyphthalan with 1,4-benzoquinone gave the homoquinone, ethyl 2-[(1′R*,6′S*,7′S*)-2′,5′-dioxo-3′-norcaren-7′-yl]benzoate, 3, instead of an anthracene derivative expected of a normal cycloaddition reaction. The structure of the homoquinone was deduced from an examination of its spectroscopic properties (ir, 1H nmr, and 13C nmr) and verified by an X-ray crystallographic study. The homoquinone, 3, is triclinic, P1, with a = 10.601(2), b = 10.434(3), c = 6.491(3) Å, α = 105.53(3), β = 95.21(2), γ = 100.66(2)° and has two formula units per unit cell. The crystal structure was determined by direct methods and refined to R1 = 0.059, R2 = 0.048, based on 2378 independent reflections. The data set was obtained using a Syntex P21 diffractometer and MoKα radiation. Bond angles and distances within the molecule are normal. Homoquinones were also isolated as major products of reaction of 1,1-diethoxyphthalan and 5,6-dimethoxy-1,1-diethoxyphthalan with 1,4-benzoquinone and 1,4-naphthoquinone. A mechanism for the formation of homoquinones is offered that involves the same type of transient intermediates proposed for the reactions of 1,1-diethoxyphthalans with activated acetylenes and ethylenes.

The 15-thia-15-deoxy analogue of prostaglandin E1 methyl ester has been prepared by the zirconocene chloride mediated conjugate addition of an n-pentyl ethynyl sulfide derived anion to an appropriately substituted cyclopentenone. Similar methodology has also been used to prepare other 3-(3′-thia-1′-octenyl)-cyclopentanones.

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. Can. J. Chem. 58,2580Chem. 58, (1980. The reactions of I,]-diethoxyphthalan with diethyl maleate and with maleic anhydride have been studied. The reaction with diethyl maleate in a sealed tube gave a mixture of diethyl 1-hydroxynaphthalene-2.3-dicarboxylate and its 0-ethyl derivative. The same reactants at atmospheric pressure gave the ethoxy ester above along with a mixture of isomeric diethyl 1,2-dihydro-1-hydroxy-4-ethoxynaphthalene-2,3-dicarboxylates. The reaction with maleic anhydride gave only diethyl-l-ethoxynaphthalene-2,3-dicarboxylic acid anhydride. These reactions provide further insight into the mechanism of the reaction of phthalans with dienophiles.