Coupling of cyclobutenediones with Fischer carbene complexes: A one-step synthesis of cyclopentenediones and/or 5-alkylidenefuranones via net insertion of the carbene unit into a C-C bond
M. Zora et al., Coupling of cyclobutenediones with Fischer carbene complexes: A one-step synthesis of cyclopentenediones and/or 5-alkylidenefuranones via net insertion of the carbene unit into a C-C bond, ORGANOMETAL, 18(21), 1999, pp. 4429-4436
The reaction of Fischer carbene-chromium complexes with 3-cyclobutene-1,2-d
iones has been investigated. In most cases, the major product of the reacti
on is the C-C bond insertion product, a 2-alkoxy-4-cyclopentene-1,3-dione,
accompanied by a minor amount of the partial deoxygenation product, a 4-cyc
lopentene-1,3-dione. In some cases, 5-alkylidenefuranones are also formed.
A mechanism involving oxidative. addition of the coordinatively unsaturated
Fischer carbene complex followed by acyl migration and reductive eliminati
on was proposed to account for cyclopentenedione formation. Furanone format
ion was thought to arise via demetalation of the acyl migration product, fo
llowed by O-acylation. An electronic dependence was noted for cyclopentened
ione/alkylidene-furanone ratio, which was evaluated using the Hammett equat
ion.