Biscarbene complexes from the reactions of O-ethyl lactim and 1-alkynyl Fischer carbene complexes of chromium and tungsten

Reactions of O-ethyl lactim ∼(CH2)3–Ndouble bond; length as m-dashC(OEt)∼ with 1-alkynyl Fischer carbene complexes (OC)5Mdouble bond; length as m-dashC(OEt)Ctriple bond; length of mdashCPh (M = Cr, W) afforded biscarbene complexes with an azabicyclo[3.2.0]heptene core. Under a nitrogen atmosphere, the resultant chromium biscarbene complex gave a SiO2-promoted rearrangement complex in 86% yield. Thermal annelation of the rearrangement product followed by hydrolysis over SiO2 formed a cyclopentenone derivative. A cyclopentadiene derivative was obtained as a rare example of intermediate Fischer carbene species, suggesting a possible reaction pathway for the thermal annelation of the rearrangement complex. Stepwise oxidation of the chromium biscarbene complexes with an azabicyclo[3.2.0]heptene core with pyridine-N-oxide (PNO) under mild controlled conditions generated partially and completely demetalated carbonyl products, respectively. The key carbene complexes and demetalated compounds were structurally characterized by X-ray crystallographic studies.