Oxidative formylation and chloromethylation as alternative pathways to chloroformylation in the reaction of O- and Sheterocyclic ketones with dimethylformamide-phosphorus oxychloride

The action of DMFPOCl3 at 20°C on tetrahydro-4H-pyran-4-one, tetrahydro-4H -thiopyran-4-one, chroman-4-one, and thiochroman-4-one affords the corresponding β-chlorovinylaldehydes, whereas with excess DMFPOCl3 at 100°C chroman-4-one affords 3-(chloromethyl)chromone, and thiochromanone gives 3-formylthiochromone.