Table 1. Screening of Solvents Using α,α-Difluoro-β-ketoester 2a.

entry	solvent	temp. (°C)	isolated yield of 4aa (%)	19F NMR yield of 2a (%)	19F NMR yield of 5 (%)
1	DMSO	150	20	0	34
2	DMF	150	13	0	50
3	NMP	150	25	0	40
4	DMA	150	0	0	51
5	toluene	reflux	0	94	0
6	THF	reflux	20	48	7
7	CH3CN	reflux	42	35	0