| Structure Identification: |
| Angew Chem Int Ed Engl. 2014 Nov 24;53(48):13196-200. | | Organocatalytic asymmetric Mannich cyclization of hydroxylactams with acetals: total syntheses of (-)-epilupinine, (-)-tashiromine, and (-)-trachelanthamidine.[Pubmed: 25264221] |
METHODS AND RESULTS:
An asymmetric, organocatalytic, one-pot Mannich cyclization between a hydroxylactam and acetal is described to provide fused, bicyclic alkaloids bearing a bridgehead N atom. Both aliphatic and aromatic substrates were used in this transformation to furnish chiral pyrrolizidinone, indolizidinone, and quinolizidinone derivatives in up to 89% yield and 97% ee.
CONCLUSIONS:
The total syntheses of (-)-epilupinine, (-)-tashiromine, and (-)-Trachelanthamidine also achieved to demonstrate the generality of the process. | | J Org Chem. 2010 Jun 4;75(11):3578-86. | | Asymmetric synthesis of 2-alkyl-substituted 2,5-dihydropyrroles from optically active aza-Baylis-Hillman adducts. Formal synthesis of (-)-trachelanthamidine.[Pubmed: 20465267] | A series of optically active 2-alkyl-substituted 2,5-dihydropyrroles were prepared via the asymmetric aza-Baylis-Hillman equivalent reaction and subsequent ring-closure metathesis reaction.
METHODS AND RESULTS:
Optically active aza-Baylis-Hillman adducts underwent a smooth two-step conversion to N-allyl-beta-amino-alpha-methylene esters in high yield, which gave chiral 2,5-dihydropyrroles, potential precursors for the aza-heterocyclic synthesis, almost quantitatively through RCM reaction catalyzed by Grubbs catalyst. The conversion was carried out without loss of the optical purity of the starting material. Synthetic application of the method to (-)-Trachelanthamidine was examined. Hydrogenation of 2,5-dihydropyrrole took place smoothly to give the corresponding 2,3-disubstituted pyrrolidine in good yield. The stereoselectivity of the hydrogenation was sensitive to the presence or absence of the protective group in the C2-side chain. The TBS-protected 2,5-dihydropyrrole gave a 1:1 mixture of the cis/trans isomers, while free alcohol afforded the trans-2,3-disubstituted pyrrolidine in a selectivity of 6:1. The formal synthesis of (-)-Trachelanthamidine was achieved in 11 steps from a chiral sulfinimine.
CONCLUSIONS:
This methodology provided a convenient procedure for the preparation of C2-alkyl-substituted 2,5-dihydropyroles with retention of high optical purity. |
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