Organic syntheses via transition metal complexes, CII - 1,3-dioxycyclopentadienes from (1-alkynyl)carbene tungsten complexes - Domino cyclization/cycloaddition reactions

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