Abstract
Methyl 1-aryl-2-amino-cyclopropane carboxylates have been readily synthesized in high yields by Rh-catalyzed decomposition of aryldiazoacetates in the presence of N -vinylphthalimide. The reaction is highly trans -selective.
Key words
cyclopropanation - diastereoselective - rhodium - diazoacetates - amino-cyclopropanes
References and Notes
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14 Enantiomeric excess measured by chiral HPLC. Absolute stereochemistry not determined.
15
General Experimental Procedure
To a solution of Rh2 (OAc)4 (0.03 mmol) and N -vinylphthal-imide (3.3 mmol) in CH2 Cl2 (5 mL) at r.t., was added dropwise over 1 h, a solution of aryldiazoacetate (3.0 mmol) in CH2 Cl2 (10 mL). The resulting solution was stirred for an additional 15 min before the solvent was removed in vacuo. Flash chromatography of the crude product [silica gel, eluting with hexane-Et2 O (1:3)] yielded the desired cyclopropane 2 as a white solid. All cyclopropanes 2a -i were characterized by 1 H NMR and 13 C NMR spectroscopy, MS, HRMS and melting points.2a : 1 H NMR (300 MHz, CDCl3 ): δ = 2.14 (dd, 1 H, J = 9.0, 6.3 Hz, CH2 ), 3.15 (t, 1 H, J = 6.1 Hz, CH2 ), 3.69 (s, 3 H, OCH3 ), 3.84 (dd, 1 H, J = 9.0, 5.9 Hz, CH), 7.17 (m, 5 H), 7.61 (m, 4 H). 13 C NMR (75 MHz, CDCl3 ): δ = 16.9 (CH2 ), 34.2 (C), 36.8 (CH), 52.7 (OCH3 ), 123.1 (CH), 127.6 (C), 127.7 (CH), 128.0 (CH), 131.1 (CH), 132.9 (C), 134.0 (CH), 168.3 (C=O), 173.0 (C=O). MS (EI): m/z (%) = 321 (6%) [M+ ], 289 (100), 261 (49), 233 (34), 115 (51). HRMS: m/z calcd for C19 H15 NO4 : 321.1001; found: 321.0989. Mp 145 °C. Crystals of 2a suitable for X-ray crystallography were grown from a solution of pentane and CHCl3 .
