2-Hydroxybenzocyclobutenone Ethylene Dithioacetals as Precursors of Highly Substituted 1,4-Dihydronaphthalenes

1,4-Dihydronaphthalenes 2, 9, and 11 with a spiro-connected 1,3-dithiolane ring as well as tetrahydronaphthalenes 15, 17, and 19 have been obtained from o-quinodimethanes 3 and alkynes 4, naphthoquinones 10, or alkenes 14 and 16. Benzocyclobutenol 6 is not an appropriate quinodimethane precursor as it readily rearranges to phthalaldehyde derivative 7. However, silyl ether 8, silyl ether 13, obtained by the hydrosilylation of cyclobutenol 5, or aluminium alkoxide 3d, generated in situ by DIBAL reduction of 5, are useful sources of the corresponding quinodimethanes. The use of 3b,c gives a reversal of regioselectivity compared with 3d in the cycloaddition with propriolate 4a (product 9a vs. 2a). Naphthoquinone 10 reacts in the cycloaddition with 3b,c through its C2=C3 bond or through a C=O unit to give 11 and 12. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)