Conjugated and cross-conjugated π-extended cycloproparenes with dithiole and cyclopentadiene functionality

Dithiole and cyclopentadiene rings have been introduced into functionalised cyclopropa[b]naphthalenes to provide highly coloured, conjugated and cross-conjugated pi-extended derivatives that have varying stability. Cyclopentadienylidene-containing cyclopropanaphthalene 18 and its dithiolylidene analogue 25 are prepared from bromophenylcyclopropanaphthalene 12, and the 1,1-biscyclopentadienylidene 20 from dibromide 13. Use of dithiole-containing ketones with 1,1-bis(trimethylsilyl) cyclopropa[b]naphthalene 10 gives the pi-extended cycloproparenes 27 and 29 in Peterson olefinations that are more efficient than Wittig-Horner reactions of cyclopropanthraquinone 31 with dithiolate 24 to give the cross-conjugated cycloproparenes 34 and 35. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).