Synthesis of Bicyclic Pyrazolinones Using Fischer Carbene Complexes

Significance

A reaction of a 1-alkynyl Fischer carbene complex with substituted pyrazolinones to generate four different types of heterobicycles - syn- and anti-1,5-diazabicyclo[3.3.0]octadiene­diones (9,10-dioxabimanes 7 and 8), pyrazolo[5,1-b][1,3]oxazin-7-ones (9) and pyrazolo[5,1-b][1,3]-oxazin-5-ones (10) - is described. In the first step, a mixture of Fischer carbene complexes 3-6 is generated, which can be separated by column chromatography. The demetalation to the products proceeds with pyridine N-oxide or m-chloroperbenzoic acid in moderate to very good yields. Reaction pathways to the four different products are proposed.