Issue 14, 1997

Homoproline homologation by enolate Claisen rearrangement or direct allylation: syntheses of (-)-trachelanthamidine, (-)-isoretronecanol and (±)-turneforcidine

Abstract

The pyrrolizidine precursors 13 and 14 are obtained both by enolate Claisen rearrangement of the homoproline allyl ester 12 and by direct allylation of N-protected homoproline ethyl ester 15. In both cases, the reactions show poor levels of stereoselectivity. Reduction gives the corresponding alcohols 20a and 21a which are separated and subsequently elaborated to (-)-trachelanthamidine 24 and (-)-isoretronecanol 25 respectively via reductive alkene cleavage, mesylation and spontaneous cyclisation following N-deprotection. The chiral integrity of the original proline-derived asymmetric centre is preserved throughout. A similar enolate allylation gives, with high stereoselectivity, the homologue 34 of the Geissman–Waiss lactone 32, which is similarly transformed into (±)-turneforcidine 31.

Article information

Article type
Paper

J. Chem. Soc., Perkin Trans. 1, 1997, 2089-2098

Homoproline homologation by enolate Claisen rearrangement or direct allylation: syntheses of (-)-trachelanthamidine, (-)-isoretronecanol and (±)-turneforcidine

D. W. Knight, A. C. Share and P. T. Gallagher, J. Chem. Soc., Perkin Trans. 1, 1997, 2089 DOI: 10.1039/A700792B

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