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3-Phenylpropyl
trans
-2-Chlorocyclopropanecarboxylate (21, Equation 5): To a suspension of CrCl2 (0.98 g, 8.0 mmol) in THF (14 mL) was added a solution of 3-phenylpropyl acrylate (20, 0.19 g, 1.0 mmol) in THF (2 mL) at 0 °C. Carbon tetrachloride (0.19 mL, 2.0 mmol) was added to the suspension at 0 °C over several minutes, and the resulting mixture was stirred at 0 °C for 24 h. The mixture was poured into a saturated NaF solution (10 mL) and stirred at 25 °C for 2.5 h. This mixture was extracted with Et2O (3 × 10 mL), and the organic extracts were dried over anhydrous MgSO4 and concentrated. Purification by column chromatography on silica gel (hexane-EtOAc, 100:1) gave the carboxylate 21 (0.14 g, 0.59 mmol) in 59% yield as a colorless oil: IR(neat): 3064, 3027, 2957, 2926, 2858, 1728, 1454, 1399, 1371, 1268, 1209, 1176, 747, 700, 666 cm-1; 1H NMR (CDCl3): δ 1.32-1.37 (m, 1 H), 1.51-1.59 (m, 1 H), 1.94-2.03 (m, 3 H), 2.70 (t, J = 7.2 Hz, 2 H), 3.35-3.38 (m, 1 H), 4.11 (t, J = 6.4 Hz, 2 H), 7.18-7.33 (m, 5 H); 13C NMR (CDCl3): δ 18.4, 23.7, 30.0, 32.1, 33.3, 64.5, 126.0, 128.4, 128.5, 141.0, 171.5; MS m/z (%): 238 (M+, 0.5), 118(100), 117(56), 91(31), 77(7). HRMS m/z calcd for C13H15ClO2 (M+): 238.0761, found 238.0750.
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16 Because chromium carbenoids shows both electrophilic
[3a]
and nucleophilic characters,
[5a]
the reactivity of the species generated by the reduction of CCl4 with CrCl2 was examined. When the reduction of carbon tetrachloride with chromium(II) (6 equiv) in THF was conducted in the presence of 3-phenylpropanal (4 equiv), (Z)-2-chloroallylic alcohol 24 was obtained in 56% yield based on CCl4, stereoselectively (Equation 6). The product 24 was the 1:2 adduct of CCl4 and the aldehyde, and this new species acts as a chloromethane trianion equivalent.
[18]
Equation 6
17 Quite recently, similar results were reported by Falck and Mioskowski, see: Baati R.
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19 Treatment of the allene 4 with the CCl4-CrCl2 reagent resulted in 91% recovery under the same reaction conditions as in Equation 2.