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Synlett 2014; 25(2): 221-224
DOI: 10.1055/s-0033-1340170
DOI: 10.1055/s-0033-1340170
letter
Intramolecular Cyclopropanation of Bromodiazoacetates
Further Information
Publication History
Received: 13 September 2013
Accepted after revision: 08 October 2013
Publication Date:
02 December 2013 (online)
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Abstract
A series of allylic diazoacetates were prepared from the corresponding allylic alcohols and bromoacetyl bromide. When the allylic diazoacetates were treated with 1,8-diazabicyclo[5.4.0]undec-7-ene and N-bromosuccinimide, a rapid full conversion to the corresponding allylic bromodiazoacetates occurred. Exposure of the allylic bromodiazoacetates to rhodium(II) catalysts induced an intramolecular cyclopropanation and gave cyclopropyl bromolactones in yields that were low to good, depending on the substitution pattern.
Supporting Information
- for this article is available online at http://www.thieme-connect.com/ejournals/toc/synlett.
- Supporting Information
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- 12 Cyclopropyl Bromolactones; General Procedure DBU (1.3 equiv) and NBS (1.2 equiv) were added sequentially to a solution of the allylic diazoacetate (1.0 equiv) in CH2Cl2 (5.0 mL/mmol diazo substrate) at 0 °C, and the solution was stirred for 15 min. The solution was then washed with 20% aq Na2S2O3 (6 × 6 mL/mmol diazo substrate), and the aqueous phases were extracted with CH2Cl2 (6.0 ml/mmol diazo substrate) at 0 °C. The organic phases were combined, dried (MgSO4), and filtered through a plug of silica gel, with elution by CH2Cl2 cooled to 0 °C. The filtered soln was diluted with toluene (10 mL/mmol diazo substrate) and the CH2Cl2 was removed in vacuo at 0 °C. To the rapidly stirred toluene solution of the resulting allylic bromodiazoacetate at 0 °C under N2 was added a solution of Rh2(esp)2 (1 mol%) in toluene (2 mL/mmol diazo substrate), and the resulting mixture was stirred for 15–25 min. The solvent was removed in vacuo, and the crude product was purified by flash chromatography (silica gel). 1-Bromo-6-phenyl-3-oxabicyclo[3.1.0]hexane-2-one White solid; 96.6 mg (44% yield); mp 117–118 °C; Rf = 0.33 (20% EtOAc–hexane). 1H NMR (300 MHz, CDCl3): δ = 2.58 (d, J = 5.1 Hz, 1 H), 2.87 (ddd, J = 0.6, 4.7, 5.1 Hz, 1 H), 4.39 (dd, J = 0.6, 9.6 Hz, 1 H), 4.59 (dd, J = 4.7, 9.6 Hz, 1 H), 7.17–7.40 (m, 5 H). 13C NMR (75 MHz, CDCl3): δ = 29.6, 34.2, 35.8, 68.5, 128.1, 128.5, 128.7, 132.9, 172.1. MS (EI): m/z (%) = 254/252 (0.5/0.5) [M+], 174 (25), 173 (100), 145 (34), 128 (30), 115/117 (85/85), 91 (37). HRMS: m/z calcd for C11H9O2Br: 251.9779; found 251.9786 (Δ 2.5 ppm).