Methyl 7-(2,2-dimethylpropionylamino)-2H-chromene-8-carboxylate (Intermediate 45, 1.0 g) was dissolved in diglyme (30 mL) and the solution was heated to 160° C. Sodium chlorodifluoroacetate (4.27 g) was added in portions over 15 minutes with the final portion being washed in with diglyme (15 mL). On completion of the addition the mixture was heated at 180° C. for 15 minutes. After cooling, the mixture was poured into water and extracted with ethyl acetate, washed with water, dried (MgSO4) and filtered. The filtrate was evaporated to dryness and the residue was purified by chromatography on silica, eluting with a mixture of ethyl acetate and pentane with a gradient of 2.5-15% to give methyl (1aRS,7bSR)-5-(2,2-dimethylpropionylamino)-1,1-difluoro-1,1a,2,7b-tetrahydro-cyclopropa[c]chromene-4-carboxylate (0.66 g) as a colourless oil.
