A Practical and Controllable Enantioselective Synthesis of 2-Phenyl-1-cyclopropanecarboxylates via a Camphor-Derived Sulfonium Ylide

Abstract

We have developed a practical and controllable enantio­selective synthesis of 2-phenyl-1-cyclopropane-carboxylates via camphor-derived sulfonium ylide. The procedure has many advantages such as cheap starting materials, facile synthetic procedures, good yields, excellent diastereoselectivities and high enantioselectivities.

Key words

enantioselective synthesis - practical method - cyclopropanecarboxylate - sulfonium ylide - diastereoselectivity

References

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4: Mp 103-105 °C. ¹H NMR: δ = 5.77 (s, 1 H), 5.57 (d, J = 16.6 Hz, 1 H), 5.39 (d, J = 16.6 Hz, 1 H), 5.22 (d, J = 7.1 Hz, 1 H), 4.33 (q, J = 7.0 Hz, 2 H), 4.25 (m, 1 H), 3.19 (s, 3 H), 2.04 (d, J = 4.5 Hz, 1 H), 2.03-1.87 (m, 2 H), 1.56-1.50 (m, 2 H), 1.35 (t, J = 7.1 Hz, 3 H), 1.23 (s, 3 H), 1.01 (s, 3 H), 0.87 (s, 3 H). MS (ESI): m/z = 287.1 (M - Br). 5: 4.16-4.14 (m, 1 H), 4.15-3.90 (m, 3 H), 3.85 (d, J = 7.2 Hz, 1 H), 2.96 (s, 1 H), 2.82 (s, 3 H), 1.85-1.81 (m, 3 H), 1.56-1.48 (m, 2 H), 1.26 (t, J = 7.0 Hz, 3 H), 1.21 (s, 3 H), 0.97 (s, 3 H), 0.84 (s, 3 H). 8: Mp 107-109 °C. ¹H NMR: δ = 7.60 -7.27 (m, 5 H), 6.21 (d, J = 7.4 Hz, 1 H), 5.71 (d, J = 12.0 Hz, 1 H), 5.51 (d, J = 12.0 Hz, 1 H), 4.54 (d, J = 7.4 Hz, 1 H), 4.11 (t, J = 7.4 Hz, 1 H), 2.86 (s, 3 H), 1.97 (d, J = 4.5 Hz, 1 H), 1.84-1.80 (m, 1 H), 1.66 (s, 1 H), 1.46-1.29 (m, 2 H), 1.15 (s, 3 H), 0.95 (s, 3 H), 0.81 (s, 3 H). MS (ESI): m/z = 291.1 (M - Br).

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General procedure for the controllable enantioselective synthesis of 2-phenyl-1-cyclopropanecarboxylates 7c-f via camphor-derived sulfonium ylide 9: To a stirred suspension of sulfonium salt 8 (445 mg, 1.2 mmol) and α,β-unsaturated ester (1.0 mmol) in THF (6 mL) was added t-BuOK (336 mg, 3.0 mmol) or NaH (72 mg, 3.0 mmol) in one portion at the desired temperature (Table [1] ). After stirring for the time indicated (Table [1] ), the reaction mixture was passed through a short silica gel column, which was eluted with ethyl acetate. After concentration of the eluent, the residue was purified by flash column chromatography or preparative TLC, giving 2-phenyl-1-cyclopropanecarboxylate 7c-f.