Evolution, Development and Personal Experience in Studies of the Allyl Cyanate-to-Isocyanate Rearrangement

Abstract

Evolution and development of the synthesis and rearrangement of allyl cyanate is described. Allyl cyanate-to-isocyanate rearrangement is a concerted [3.3]-sigmatropic process involving highly selective [1,3]-chirality transfer to the newly formed asymmetric center bearing nitrogen. The usefulness of this rearrangement is manifested by the synthesis of natural products containing nitrogen-substituted quaternary carbon atoms.

1 Background

2 Evolution of the Allyl Cyanate-to-Isocyanate Rearrangement. A Personal History

3 The Stereochemistry and Mechanism of the Allyl Cyanate-to-Isocyanate Rearrangement

4 Synthesis of Natural Products Containing Nitrogen-Substituted Quaternary Carbon Centers

5 Coda

Key words

allyl cyanate - isocyanate - rearrangement - natural product synthesis

References and Notes

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18

To a solution of commercially available nerolidol 41 (a 3:2 mixture of Z- and E-isomers 5.01 g) in hexane cooled to 0 °C was added acetonitrile (14 ml) and TFA (8.0 ml). The resulting biphasic mixture was vigorously stirred at 0 °C for 24 h and then poured into aq NaHCO₃. Usual workup followed by silica gel chromatography (hexane → diethyl ether-hexane, 1:2) gave the recovered starting material (1.23 g) and crude products which were purified by recrystalli-zation (ether and hexane) to furnish aminobisabolenes (a 2:1 mixture of 37 and 38, 195 mg, 4.4% yield based upon the consumed starting materials).