Nickel-catalyzed ring-opening of α-hydroxycyclobutenones with a remarkable ligand effect

Abstract

A Ni-catalyzed ring-opening of α-hydroxycyclobutenones is reported herein. A remarkable ligand effect was observed during transformations following the ring-opening. The employment of PPh leads to the formation of 2-furanones 2 through a migration of an alkoxyl group, and 2-furanones 3 were generated through a migration of hydrogen in the presence of Xantphos, affording a divergent approach to 2-furanones bearing multiple functional groups.

Trends in the Usage of Bidentate Phosphines as Ligands in Nickel Catalysis

“…Similarly, rac -BINAP gives an 85% yield but is also unselective. Changing the ligand to PPh 3 changes the selectivity to favor product 17a …”

“…Hu and co-workers 574 reported a completely selective electrocyclic ring-expansion of α-hydroxycyclobutenone using Ni-(cod) 2 and Xantphos (1:2) in 80% yield for product 17b (eq 211). DPPE results in an 86% yield but is unselective.…”

Alternative method to Baeyer–Villiger oxidation of cyclobutenones using I2/DMSO catalytic systems

“…Although the mechanism of this protocol is not completely clear yet, a plausible catalytic cycle is outlined in Scheme 4 based on previous reports. 16–18 Initially, substrate 1 undergoes electrophilic halogenation by I 2 , leading to the formation of 4-iodo-2-cyclobutenone I , which was not stable in this catalytic system. Subsequently, the oxygen atom of DMSO performs a nucleophilic attack on I , generating an ion pair intermediate II .…”