1,3-Dioxycyclopentadienes from (1-Alkynyl)carbene Tungsten Complexes - Domino Cyclization/Cycloaddition Reactions

1,3-Dioxytetrahydropentalenes 9 have been generated by base-catalyzed addition of protic oxygen nucleophiles ROH 6a-g (RO = carboxy or phenyloxy) to the [2-(1-cyclopentenyl)ethynyl]carbene tungsten complex 3. Compounds 9 are highly reactive and afford (cyclobutenyl)carbene complexes 12a-g through spontaneous [2+2] cycloaddition to a second molecule of the (1-alkynyl)carbene complex 3. Thermolysis of compounds 12 was found to generate indeno[b]-spiro-tricyclo[5.3.0.0]decadienes 18 through π-cyclization of the 1-tungsta-1,3,5-hexatriene unit involving insertion of carbon monoxide into the WC bond.