tert-Butyl-3-methoxy-5,5-dimethyl-6-heptenoate

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Scheme

Preparation of the title compound from the hydroxy ester [1] proved difficult to impossible with almost all protecting groups under a variety of reaction conditions. One pot alkylation with lithio tert-butylacetate in toluene at 0 °C [2] followed by protection of the incipient hydroxy group as the methyl ether provided the b-methoxy ester in 54% unoptimized yield.

To a solution of lithio tert-butyl acetate (1.5g, 12.3 mmol) in dry toluene (20 ml) under Ar at 0 °C, the aldehyde (1.24g, 11.1 mmol) in toluene (5 ml) was added. After 15 minutes, HMPA (5 ml) and methyl iodide (0.8 ml, 12.9 mmol) were added. The solution was warmed to room temperature and stirred overnight. The reaction mixture was diluted with water (25 ml) and extracted with pet ether (3 x 25 ml). The combined organic layers were washed with sat aq NaCl, dried over Na₂SO₄, and concentrated to give, after flash chromatography (20 : 1 pet ether : ether) tert-butyl-3-methoxy-5,5-dimethyl-6-heptenoate as a colorless oil, 1.42g, in 53 percent yield.

¹H NMR (CDCl₃): d: 5.79 (dd, J = 17.2, 10.6Hz, 1H), 4.90 (d, J = 17.2Hz, 1H), 4.89 (d, J = 10.6Hz, 1H), 3.51 (m, 1H), 3.24 (s, 3H), 2.44 (dd, J = 14.6, 5.9Hz, 1H), 2.24 (dd, J = 14.6, 6.9Hz, 1H), 1.56 (dd, J = 14.5, 7.4Hz, 1H), 1.42 (s, 9H), 1.4 - 1.15 (m, 1H), 1.02 (s, 3H), 1.00 (s, 3H).

IR (CDCl₃): 2970, 2940, 1720, 1460, 1370, 1295, 1160.

MS (m/e): 186, 154 (100), 127, 117, 116, 103, 95, 94, 69, 57.

1. Smith, D. tert-Butyl-3-hydroxy-5,5-dimethyl-6-heptenoate, Molecules 1997, 2, M29.
2. Rathke, M. W.; Sullivan, D. F., J. Am. Chem. Soc. 1973, 95, 3050.

Sample Availability: No sample available.

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