Synthetic studies on the Lythraceae alkaloids. 11. Model studies for the synthesis of lythracine V

Stereocontrolled Alkylation of Chiral Pyridinium Salt Toward a Short Enantioselective Access to 2-Alkyl- and 2,6-Dialkyl-1,2,5,6-Tetrahydropyridines

“…Hydrogenolysis of 21c afforded known (ϩ)-solenopsin, [10] while under the same conditions dioxolane 21d gave indolizidine (-)-5. The polysubstituted derivatives can be obtained by epoxidation reactions of tetrahydropyridines [8,12] as illustrated by a three-step synthesis of indolizidine (-)-6 from 21d (Scheme 8). Thus the trifluoroacetic salt of 21d reacts smoothly with pertrifluoroacetic acid to give the rather unstable oxirane 25 as a single diastereoisomer (stereochemistry assigned by comparison with analogous results).…”

“…Thus the trifluoroacetic salt of 21d reacts smoothly with pertrifluoroacetic acid to give the rather unstable oxirane 25 as a single diastereoisomer (stereochemistry assigned by comparison with analogous results). [8,12] The treatment of crude 25 with an excess of Me 2 CuLi gave diol 26 with complete regioselectivity. Finally, hydrogenolysis in acidic medium afforded the indolizidine 6 in 5 steps with 9% overall yield from salt 1c (3 steps, 27% yield from 21d).…”

“…-[α] D ϭ ϩ58.5 (c ϭ 1.38, CHCl 3 ). 8, 26.7, 47.8, 53.6, 61.4, 61.7, 116.0, 124.2, 127.5, 127.9, 128.8, 131.9, 140.4, 140. 5.30 (m,1 H),5.65 (m,1 H),1 H),[5][6][7][8][9][10][11][12][13]CDCl 3 ): δ ϭ 21. 8,31.3,49.7,59.1,62.7,64.4,115.6,122.4,127.6,128.5,128.5,132.2,139.1, When the addition was complete, the solution was stirred for 1 h at 0°C then warmed to room temperature and stirred overnight.…”

An Enantioselective Entry to Substituted 6-Membered Nitrogen Heterocycles from Chiral Pyridinium Salts via Selective Epoxidation of Tetrahydropyridine Intermediates

“…3a After preliminary experiments, pertrifluoroacetic acid was selected as the most convenient epoxidizing agent. 5 Using this procedure, it is necessary to work both on tetrahydropyridine salts as starting materials and to treat the crude reaction mixture with sodium sulfite in order to avoid formation of undesirable N-oxides. We first studied reactions of tetrahydropyridines 6 and 10 under these conditions.…”

Calyciphylline B-Type Alkaloids: Total Syntheses of (−)-Daphlongamine H and (−)-Isodaphlongamine H

“…Subjecting 22 to TFAA and then SOCl 2 smoothly protected the primary and eliminated the tertiary hydroxy groups, respectively. The resulting exocyclic alkene was treated with trifluoroperacetic acid 32 to afford epoxide 23 . 33 Opening of the epoxide at the terminal position was carried out with LiAlH 4 , and the resulting triol was subjected to the established deoxygenation conditions.…”