a solution of 4 fluorophenylmagnesium bromide 1 14 m 6 2 ml 7 1 mmol in thf was then added portionwise in 0 9 ml aliquots at 20 min intervals after the addition was complete an aqueous solution of nh 4 oh 1 m was added and the product extracted with diethyl ether the ether extracts were dried k 2 co 3 and concentrated chromatography on elution with cyclohexane diethyl ether 8 1 gave the desired 1 4 dihydropyridine 1 78 g 77 essentially as a single enantiomer de gt 95 a solution of 4 bromofluorobenzene 0 95 ml 8 6 mmol in thf 15 ml was added to magnesium turnings 448 mg 2 25 mmol under nitrogen over 10 minutes the grignard reaction stated immediately after the addition commenced additional 4 bromofluorobenzene 0 40 ml 3 6 mmol was added the grignard solution was stirred at room temperature for 1 h a solution of 3 1 3 dimethyl 4 s 5 s diphenylimidazolidin 2 yl pyridine 2 70 g 8 20 mmol in thf 65 ml was cooled to 73 u00b0 c under nitrogen methyl chloroformate 0 95 ml 12 3 mmol was added over 30 min then copper i bromide dimethylsulphide complex 337 mg 1 64 mmol and lithium bromide 285 mmol 3 28 mmol were added the suspension was allowed to warm to 50 u00b0 c and the brown yellow solution was re cooled to 73 u00b0 c the grignard solution was added over 2 h after the addition was complete the suspension was stirred at.