ine-step nantioselective Total Synthesis of (+)-Minfiensine Jones, S. B.; Simmons, B.; MacMillan, D. W. C.* J. Am. Chem. Soc. 2009, ASAP. DI: 10.1021/ja906472m Kara George Wipf Group - Current Literature September 12, 2009 Kara George @ Wipf Group Page 1 of 14 10/3/2009
Strychnos Alkaloids Biological Relevance: folk medicine, antimalarial, cytotoxic, antitumor Synthetic Relevance: xcellent substrates for showcasing methodologies aimed at rapidly assembling polycyclic structures minfiensine strychnine normacusine B C 18-desoxy-Wieland-Gulmich aldehyde C 2 C 2 vincorine echitamine Ramirez, A.; Garcia-Rubio, S. Curr. d. Chem. 2003, 10, 1891. Bonjoch, J.; Solé, D. Chem. Rev. 2000, 100, 3455. Kara George @ Wipf Group Page 2 of 14 10/3/2009
istory of Minfiensine 1989: Isolated from the African plant Strychnos minfiensis by Massiot and coworkers 2005: First total synthesis of (+)-minfiensine reported by verman and coworkers 2008: verman and coworkers publish a full paper including problems encountered in the 1st generation synthesis and a 2nd generation end play for the total synthesis of (+)-minfiensine Qin and coworkers report a total synthesis of (±)-minfiensine Padwa and coworkers report cycloaddition studies directed toward the tetracyclic core of minfiensine 2009: MacMillan and coworkers publish a nine-step total synthesis of (+)- minfiensine Massiot, G.; Thépenier, P.; Jaquier, M.-J.; Le n-livier, L.; Delaude, C. eterocycles 1989, 29, 1435. Dounay, A. B.; verman, L..; Wrobleski, A. D. J. Am. Chem. Soc. 2005, 127, 10186. Dounay, A. B.; umphreys, P. G.; verman, L..; Wrobleski, A. D. J. Am. Chem. Soc. 2008, 130, 5368. Shen, L.; Zhang, M.; Wu, Y.; Qin, Y. Angew. Chem. Int. d. 2008, 47, 3618. Bobeck, D. R.; France, S.; Leverett, C. A.; Sánchez-Cantalejo, F.; Padwa, A. Tet. Lett. 2009, 50, 3145. Kara George @ Wipf Group Page 3 of 14 10/3/2009
verman s Approach to (+)-Minfiensine 1st Generation: Catalytic Assymetric eck eck Cyclization- Carbonylation Sequence Iminium Ion Cyclization Dounay, A. B.; verman, L..; Wrobleski, A. D. J. Am.Chem. Soc. 2005, 127, 10186. 2nd Generation: Catalytic Assymetric eck Pd-catalyzed intramolecular enolate/vinyl iodide coupling Iminium Ion Cyclization Dounay, A. B.; umphreys, P. G.; verman, L..; Wrobleski, A. D. J. Am. Chem. Soc. 2008, 130, 5368. Kara George @ Wipf Group Page 4 of 14 10/3/2009
vermann s Route to the Carbazole Core Boc 2 1. p-ts, Ph 50 C 1. Comins' reagent, amds TF, -78 C TIPS 2. CC 2, LMDS, TF, -78 C TIPS C 2 85% 2. i. 9-BB, 1, 0 C to rt ii. a, rt iii. PdCl 2 (dppf), TF, rt TIPS C 2 58% Comins' reagent CsF, Cs 2 C 3 DMF, rt Boc 20% Pd(Ac) 2, 2, PMP toluene, 100 C, 70 h; or Boc TFA, C 2 Cl 2 Tf C 2 10% Pd(Ac) 2, 2, PMP toluene, microwave 170 C, 30-45 min C 2 2 C Boc 85-95% 75-87%, 99% ee 75%, 2 steps Boc Ph 2 P 1 2 t-bu Features: - Catalytic asymmetric eck-iminium ion cyclization sequence provides access to the carbazole framework in an enantioselective fashion Kara George @ Wipf Group Page 5 of 14 10/3/2009
verman s 1st Generation nd Play 1. m-cpba, C 2 Cl 2, 0 C to rt 2. CF 3 C 2, 0 C to rt 1. (PhSe) 2, ab 4 TF/M, 70 C; 2 2, 0 to 70 C TS 2 C Boc 3. C 2 =CC 2 CCl, K 2 C 3, rt 2 C Alloc 2. TSCl, imidazole C 2 Cl 2, rt 2 C Alloc 78% 75% Pd(PPh 3 ) 4, pyrrolidine, TF, rt; TS Pd(Ac) 2, K 2 C 3, Bu 4 Cl a 2 C, DMF, 80 C TS (Z)-2-iodo-2-butenyl tosylate K 2 C 3, C, 70 C 2 C 96% I 2 C 80% 1. TBAF, TF, rt 2. DMP, C 2 Cl 2, rt C 2 1. ab 4, /TF, 0 C 2. BzTf, pyridine, C 2 Cl 2, 60 C C 2 3. CC 2, LiMDS TF, -78 C 2 C 3. KMDS, TF, -78 C 2 C 70% 50% 1. LiAl 4 2. a (+)-minfiensine 85% Features: - eck cyclization-carbonylation sequence to generate the fifth ring of (+)-minfiensine - 13.4% yield and 16 steps from cat. asymmetric eck - 4.1% overall yield and 22 total steps Kara George @ Wipf Group Page 6 of 14 10/3/2009
verman s 2nd Generation nd Play 1. 9-BB, TF, 100 C; 2 2, a 1. TFA, C 2 Cl 2, rt 2 C Boc 2 C Boc 2. Br I 63% K 2 C 3, C 10 mol % PdCl 2 (dppf) K 2 C 3 (4 equiv) 1. amds, Comins' reagent TF, -78 C 2 C I, 70 C 2 C 2. Pd(Ac) 2, Ph 3 P, t 3 C,, DMF 65% 74% C 2 1. LiAl 4 2 C 77% 2. a (+)-minfiensine 85% Features: - Intramolecular Pd-catalyzed ketone enolate vinyl iodide coupling to construct the final ring of (+)-minfiensine - 19.7% yield and 9 steps from cat. asymmetric eck - 6.5% overall yield and 15 total steps Kara George @ Wipf Group Page 7 of 14 10/3/2009
Macmillanʼs Approach to (+)-Minfiensine rganocatalytic Diels-Alder Cyclization Amine Cyclization Radical Cyclization Jones, S. B.; Simmons, B.; MacMillan, D. W. C.* J. Am. Chem. Soc. 2009, ASAP. DI: 10.1021/ja906472m Kara George @ Wipf Group Page 8 of 14 10/3/2009
Precedence for Cyclization Cascade Sequence Diels-Alder/amine cyclization sequence to access the echitamine ring system tol., sealed tube 160-170 C, 36 h C 2 Bn Bn Bn = C 2 45% 5% Lévy, J.; Sapi, J.; Laronze, J. Y.; Royer, D.; Toupet, L. Synlett 1992, 601. echitamine natioselective organocatalytic construction of pyrroloindolines R R X imidazolidinone catalyst X R R C Ph t-bu imidazolidinone catalyst Austin, J. F.; Kim, S.-G.; Sinz, C. S.; Xiao, W.-J.; MacMillan, D. W. C. Proc. atl. Acad. Sci. U.S.A. 2004, 101, 5482. Kara George @ Wipf Group Page 9 of 14 10/3/2009
natioselective rganocatalytic Construction of Pyrroloindolines: Catalytic Cycle Austin, J. F.; Kim, S.-G.; Sinz, C. S.; Xiao, W.-J.; MacMillan, D. W. C. Proc. atl. Acad. Sci. U.S.A. 2004, 101, 5482. Kara George @ Wipf Group Page 10 of 14 10/3/2009
nantioselective Catalytic Cascade Sequence to Access the Tetracyclic Carbazole Framework of (+)-Minfiensine Boc S Kara George @ Wipf Group Page 11 of 14 10/3/2009
rganocatalytic Diels-Alder Cyclization Cascade Studies Boc X mol% cat. S 3 equiv -40 C, t 2 ; ab 4, CeCl 3 Boc S catalyst 7 catalyst 14 Kara George @ Wipf Group Page 12 of 14 10/3/2009
ine-step Total Synthesis of (+)-Minfiensine Boc 1. a, Cl, DMF, 0 C 2. i. n-buli, TF, -78 C; ii. DMF, -78 C to rt 73% Boc (t) 2 P()C 2 S a, TF, 0 C to rt 87%, 6:1 :Z Boc S 1. TSTf, C, 0 C TS cat. 14 TBA 87%, 96% ee Boc S 2. 4-(tert-Butylthio)but-2-ynal ab(ac) 3, C 2 Cl 2, rt 59%, 2 steps S S t Bu 3 equiv. t-bu 3 Sn 1. Pd/C, 2, TF, -15 C 2. PhS, TFA, rt 90%, >20:1 :Z (+)-minfiensine catalyst 14 Kara George @ Wipf Group Page 13 of 14 10/3/2009
Conclusions and Future Directions MacMillan and coworkers were able to synthesize (+)-minfiensine in only 9 steps and 21% overall yield from commercial materials - 53% yield and 5 steps from the tetracyclic intermediate Access to the tetracyclic carbazole framework was achieved rapidly and enantioselectively by a new organocatalytic Diels-Alder/amine cyclization sequence The final ring system of (+)-minfiensine was accomplished via a 6-exo-dig radical cyclization Application of this methodology could be utilized to access the tetracyclic carbazole moiety of related alkaloids Boc 9 Steps (+)-minfiensine Kara George @ Wipf Group Page 14 of 14 10/3/2009