T. Hirao et al., A NOVEL REGIOSELECTIVE RING-OPENING OXIDATION OF CYCLOBUTENONES WITH VO(OET)CI2, Journal of the Chemical Society. Perkin transactions. I, (1), 1994, pp. 3-4
2,2-Dichlorocyclobut-3-enones undergo VO(OEt)Cl-2-induced ring-opening
oxidation in ethanol to give ethyl 2,4,4-trichlorobut-3-enoates regio
selectively.