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40.1.3.1.4.3 Variation 3: By [2,3]-Sigmatropic Rearrangement

DOI: 10.1055/sos-SD-040-00396

Feng, J. Q.; Li, C.-J.Science of Synthesis, (200940609.

[2,3]-Sigmatropic rearrangements, like their [3,3] counterparts, constitute an exceptionally versatile class of bond reorganizations that have many obvious applications in organic synthesis. For example, the Se-iminations of chiral cinnamyl 2-[1-(dimethylamino)ethyl]ferrocenyl selenides 97 with either N-tosyliminophenyliodinane or chloramine-T afford the corresponding chiral allylic amines 99 via [2,3]-sigmatropic rearrangements of the selenimide intermediates 98. The products can be hydrolyzed to afford the chiral N-tosylated enamine 100, although some of the isomeric sulfonamide 101 is often formed as a byproduct (Scheme 36).[‌118‌] In an illustrative example, treatment of (E)-cinnamyl (S,R)-ferrocenyl selenide (S,R)-97 with N-tosyliminophenyliodinane in dichloromethane at 0°C affords the secondary allylic amine 100 in 42% yield and in 87% enantiomeric excess. In this case none of the isomer 101 is formed and the resulting high stereocontrol supports the view that the initial imination step must proceed with high diastereoselectivity, and that chirality transfer then takes place via a [2,3]-sigmatropic rearrangement with almost no loss of optical purity.

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