To the residue of (+)-cis/trans-1-chlorocarbonyl-3-(2-chloro-3,3,3-trifluoroprop-1-en-1-yl)-2,2-dimethylcyclopropane (obtained in Example 18) was added a mixture of pyridine (0.12 g) and (+)-α-cyano-3-phenoxybenzyl alcohol (0.33 g) and the mixture thus obtained was stirred for a period of 16 hours at the ambient temperature. Water (20 ml) was added and the mixture extracted with diethyl ether (3×10 ml). The combined extracts were washed with water, saturated sodium bicarbonate solution, and water and dried over anhydrous sodium sulphate. After removal of the ether by evaporation under reduced pressure the residual oil was subjected to preparative thick-layer chromatography, using 2 mm thick silica on glass with chloroform as eluent, to yield (+)-α-cyano-3-phenoxybenzyl (+)-cis-3-(2-chloro-3,3,3-trifluoroprop-1-en-1-yl)-2,2-dimethylcyclopropane carboxylate (Rf 0.52), and the corresponding trans isomers (Rf 0.42), each containing about 90-95% of the Z-isomer. Spectral data: infra red (CHCl3) 1740, 1660, 1590, 1480, 1460 cm-1 ; n.m.r. (CCl4): 6.90-7.50π, 1.60-2.70π, 1.50-1.00τ, and specific peaks at 6.3 τ (benzylic H), 6.85, 6.50, 6.11 and 5.84 π (vinylic H) tentatively assigned to the Z-cis, E-cis, Z-trans and E-trans isomers respectively.
