Stereoselective Allyl Amine Synthesis via Enantioselective Addition of
Diethylzinc and Sigmatropic Rearrangement; Synthesis of Lentiginosine

Abstract

A new synthetic method for the preparation of allyl amine derivatives has been developed. The key steps of this method are enantioselective addition of diethylzinc (Soai protocol) and allyl cyanate-to-isocyanate rearrangement. Successful application of this procedure realized the synthesis of lentiginosine (6).

Key words

stereoselective - asymmetric synthesis - amines - rearrangements - natural products

References

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8

The minor isomer produced in the step (8 → 9) was removed at this stage by recrystallisation of 14.

11

Spectroscopic data of our synthetic lentiginosine(6): [α] _d ²⁷ +1.06 (c 0.47, MeOH). ¹H NMR (300MHz, CDCl₃): δ = 1.14-1.34 (2 H, m, H-8), 1.38-1.69 (2 H, m, H-6), 1.74-1.97 (2 H, m, H-7), 1.88-1.97 (1 H, m, H-8a), 2.04 (1 H, td, J = 11, 3 Hz, H-5), 2.61 (1 H, dd, J = 11, 7.5 Hz, H-3α), 2.82 (1 H, dd, J = 11, 2 Hz, H-3β), 2.93 (1 H, br d, J = 11 Hz, H-5), 3.64 (1 H, dd, J = 9, 4 Hz, H-1), 4.06 (1 H, ddd, J = 8, 4, 2 Hz, H-2). ¹³C NMR (75 MHz, CDCl₃): δ = 22.8, 23.8, 27.4, 52.4, 60.1, 68.3, 75.5, 82.8.