135905-10-1Relevant articles and documents
Homoproline homologation by enolate Claisen rearrangement or direct allylation: Syntheses of (-)-trachelanthamidine, (-)-isoretronecanol and (±)-turneforcidine
Knight, David W.,Share, Andrew C.,Gallagher, Peter T.
, p. 2089 - 2097 (2007/10/03)
The pyrrolizidine precursors 13 and 14 are obtained both by enolate Clalsen 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 21 a 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.
