1. 1-Chloro-1-(trichloroethenyl)cyclopropane was prepared from tetrachlorocyclopropene as described in Org. Synth., Coll. Vol. VIII 1993, 124.

2. Methanol and methylene chloride were obtained from E. M. Science (Merck & Company, Inc.) and used without further purification.

3. The checkers obtained the same yields for 0.10-mol scale runs. The submitters report yields of 54–58%, however. The submitters report that the yields of 2-chloro-2-cyclopropylidenacetate are consistently better, when a larger excess of sodium methoxide (prepared by dissolving 20.1 g (0.87 mol) of sodium metal in 300 mL of dry methanol) is used. The reaction is monitored by thin layer chromatography; complete consumption of starting material may require up to 48 hr. The workup procedure was also modified. Instead of extracting with ether, the mixture is extracted with three 100-mL portions of methylene chloride. The combined methylene chloride extracts are washed with three 50-mL portions of saturated brine, dried over anhydrous magnesium sulfate, and filtered. The solution is concentrated under slightly reduced pressure in a closed system (rotary evaporator) to a volume of 100 mL. In Step B this solution is treated with 10 g of a strongly acidic ion-exchange resin and the rest of the procedure is followed as described.

4. The submitters report bp 107–109°C (20 mm). The spectral properties of 2-chloro-2-cyclopropylidenorthoacetate are as follows: IR (neat) cm⁻¹: 2840 (OCH₃), 1780 (C=C); ¹H NMR (CDCl₃) δ: 1.27–1.80 (m, 4 H), 3.23 (s, 9 H).

5. The checkers used analytical-grade AG 50W-X8 resin, which is strongly acidic polystyrene-gel-type resin, supplied by Bio-Rad Laboratories. The submitters used the large-pore, strongly acidic ion-exchange resin Lewatit SPC 118, supplied by Bayer AG.

6. The submitters report obtaining 7.0–7.5 g (84–90%) of product, bp 60–63°C (3.7 mm), and note that 4.7–5.0 g of analytically pure material, mp 33–34°C, can be obtained by crystallization at −20°C from 10–15 mL of pentane and the remaining 2.3–2.5 g of product can be recovered from the mother liquor by chromatography on silica gel (60 g) using a 5 : 1 mixture of pentane/diethyl ether as the eluent.

7. The product obtained by the checkers is pure by NMR analysis and shows the following spectral properties: IR (neat) cm⁻¹: 3080 (cyclopropyl CH), 1720 (C=O); ¹H NMR (CDCl₃) δ: 1.42–1.52 (m, 2 H), 1.69–1.78 (m, 2 H), 3.84 (s, 3 H).

8. The submitters report that the product can be obtained in higher yields without isolation of the intermediate orthoester according to the following procedure. To a solution of sodium methoxide, freshly prepared by dissolving 14.0 g (0.61 mol) of sodium metal in 200 mL of dry methanol, at 65°C is added with stirring 30.0 g of 1-chloro-1-(trichloroethenyl)cyclopropane. The stirred mixture is refluxed (oil-bath temperature of 110°C) for 72 hr. After the solution is cooled to room temperature, 200 mL of ice water is added, and the mixture is extracted with three 200-mL portions of ether. The combined ether extracts are washed with three 50-mL portions of saturated brine, dried over anhydrous magnesium sulfate, and filtered. The solvent is removed from the filtrate by distillation at atmospheric pressure. The residue is dissolved in 100 mL of methylene chloride, 10 g of a strongly acidic ion-exchange resin is added (Note 5), and the mixture is stirred at room temperature for 48 hr. The resin is removed by filtration and is washed with three 10-mL portions of methylene chloride. The combined organic solutions are dried over anhydrous magnesium sulfate and filtered, and the solvent is removed from the filtrate by distillation at atmospheric pressure. The residual oil is taken up in 200 mL of pentane and the solution is refrigerated at 5°C. The precipitated crystals are collected by filtration to yield 11–13 g (51–60%) of 2-chloro-2-cyclopropylidenacetate. The checkers obtained a 50% yield of pure product, mp 40–41°C, when this procedure was repeated on about half the scale.