Recent ighlights ht from the Danishefsky Laboratory 11-0-Debenzoyltashironin 2 Phalarine Anne-Marie Dechert ovember 7, 2007
11-0-Debenzoyltashironin Background and Structural Features Isolated from the pericaps of Illicium merrillianum Shown to induce neurite outgrowth in fetal rat cortical neurons at low concentrations 7 contiguous stereocenters, 3 all carbon quarternary centers 11-0-Debenzoyltashironin
Synthetic Strategy Ms xidative Dearomatization Ms Ts Ts Transannular Diels-Alder Ms Ts 11-0-Debenzoyltashironin Danishefsy, et al. J. Am. Chem. Soc. 2006, 128, 16440-16441
Synthetic Strategy xidative Ms Dearomatization Ms Ts Ts Transannular Diels-Alder X Ms Ts Believed that the cyclization didn t occur because of the electronic and steric constraints that the mesyl enol ether imposed. 11-0-Debenzoyltashironin Danishefsy, et al. J. Am. Chem. Soc. 2006, 128, 16440-16441
Synthetic Strategy xidative Dearomatization Ts Ts Transannular Diels-Alder Wrong epimer! X Ts 11-0-Debenzoyltashironin Danishefsy, et al. J. Am. Chem. Soc. 2006, 128, 16440-16441
Synthetic Strategy R Ts Ts R TBS Br Bn SnBu 3 Ts
Synthesis of the Aryl Bromide 1. Zn(C) 2,Cl(99%) 2. TsCl (57 %) 3. BnBr, K 2 C 3,TBAI(97%) 1. mcpba 2. TEA 98 % for 2 steps Bn TBS 1. BS (85 %) Br 2. TBSCl, TEA (87%) Bn Ts Ts Danishefsy, et al. J. Am. Chem. Soc. 2006, 128, 16440-16441
Synthesis of the Aryl Bromide 1. Zn(C) 2,Cl(99%) 2. TsCl (57 %) 3. BnBr, K 2 C 3,TBAI(97%) Bn 1. mcpba 2. TEA 98 % for 2 steps Ts Bn TBS 1. BS (85 %) Br 2. TBSCl, TEA (87%) Bn Ts Ts Danishefsy, et al. J. Am. Chem. Soc. 2006, 128, 16440-16441
Synthesis of the xidative Dearomatization Precursor Br TBS Bn SnBu 3 Pd 2 (dba) 3, tbu 3 P 77 % TBS Bn 1. DMP (98 %) 2. 2-propargyloxyTBS, Et 2 Zn, Ti(iPr) 4 (91 %) Ts Ts TBS TBS Bn Ts 1. MsCl, TEA 2. 2 Cu(C)Li 2 (88 %) 3.Bu 4 F, Ac (95 %) R Ts Danishefsy, et al. J. Am. Chem. Soc. 2006, 128, 16440-16441
xidative Dearomitization, Transannular Diels-Alder Bn PIDA Bn Bn Ts Ts Ts μw 65 % Danishefsy, et al. J. Am. Chem. Soc. 2006, 128, 16440-16441
End Game 1. mcpba (71 %) 1. ab 4 (83 %) TMS 2. Wilkinson's Catalyst, Bn 2. TMS-imidazole (99 %) Bn 2 (74 %) Ts Ts TMS Bn Ts TMS LiEt 3 B Bn 32 % 1. DMP (96 %) 2. F- pyr, Bu 4 F (87 %) 3. 2,Pd/C(91%) Danishefsy, et al. J. Am. Chem. Soc. 2006, 128, 16440-16441
Phalarine Isolated from the phalris coerulescens, characterized in 1999 2 Furanobisindole alkaloid Phalarine First synthesis reported by Danishefsky
Synthetic Stratagy 1 2 1' 2' 2 2 Phalarine C 2 C 2 The model system gave the opposite of what was desired! Danishefsky, et al. Angew. Chem. Int. Ed. 2007, 46, 1444-1447.
Retrosynthesis Ts MM 2 Phalarine MM - Li Ts
Azaspiroindolenine synthesis 1. LiAl 4 (99%) 2. BS, 2, Ac (79%) 3. LiMDS, TsCl (89 %) Ts MM Li 96 % Ts 1. TFA (98 %) 2. CSA (72 %) MM Ts Danishefsky, S.; et al. Angew. Chem. Int. Ed. 2007, 46, 1444-1447.
Two chanistic Possibilities Ts - 2 Ts Path A 1, 2 Wagner- erwein Shift Ts Ts Path B Retro-Mannich Pictet-Spengler Ts Ts Ts Ts Ts Danishefsky, S.; et al. Angew. Chem. Int. Ed. 2007, 46, 1444-1447.
Attempted Completion Troc TFA, Troc 95 % Troc Troc Zn dust, Ac 88 % Ts Ts 2 1. a 2,Cl(aq) 2. K (aq), Ts 88 % Et Ts Ts C 2 Et < 5% desired product Danishefsky, S.; et al. Angew. Chem. Int. Ed. 2007, 46, 1448-1450.
Attempted Completion Troc TFA, Troc 95 % Troc Troc Zn dust, Ac 88 % Ts Ts 1. a 2,Cl(aq) 2 2. K (aq), Ts 88 % Et Ts C 2 Et Ts Ts C 2 Et < 5% desired product
End Game a.sc 2 C 2 Et, S 2 Cl 2 b. proton sponge c. Et 3, Ac 2 66 % 1. B 3 2. Rai (90%over2steps) Ts Cl 1. Ac (74 %), 2. a(g), a 2 P 4 (90 %) Ts Phalarine 2 Danishefsky, S.; et al. Angew. Chem. Int. Ed. 2007, 46, 1448-1450.
End Game 2 a.sc 2 C 2 Et, S 2 Cl 2 b. proton sponge c. Et 3, Ac 66 % 1. B 3 2. Rai (90 % over 2 steps) S Ts Ts Cl 1., Ac (74 %) 2. a(g), a 2 P 4 (90 %) Ts Phalarine 2 Danishefsky, S.; et al. Angew. Chem. Int. Ed. 2007, 46, 1448-1450.