The regioselectivity of the conversion of 1, 3-diketones into β-chloroenones can be changed by the appropriate choice of the reagent: reaction with “Vilsmeier's reagent” prepared from POCl3, and dimethylformamide or treatment of the diketone with the oxalyl chloride in the presence of dimethylformamide.
[Miranda, Pedro O.; Diaz, David D.; Padron, Juan I.; Ramirez, Miguel A.; Martin, Victor S. Journal of Organic Chemistry, 2005 , vol. 70, # 1 p. 57 - 62]