Intramolecular uisgen-type Cyclization of Platinum-Bound Pyrylium Ions with Alkenes and Subsequent Insertion into a Benzylic C- Bond Chang o h,* Ji o Lee, Su Jin Lee, Jae Il Kim, and Chang Seop ong Department of Chemistry, anyang University, Seoul, Korea Angewandte Chemie International Addition, 2008, 47, early view. DI: 10.1002/anie.200802425 C Bn Bn Wipf Group Saturday Morning eting Current Literature Abstracts & Reports Rob Lettan August 30 th, 2008 Rob Lettan @ Wipf Group Page 1 of 11 9/7/2008
xabicyclo[3.2.1]octanes in Natural Products 2 C N platensimycin broad spectrum Gram-positive antibiotic Synthesized by: Nicolaou (2006, racemic) (2007, 2008 asymmetric) Snider (2007, formal, racemic) E. Lee (2008, formal) corianlactone no remarkable inhibition towards K 562 cells cytotoxic, IC 50 > 50 µg/ml R R R R bruguierol C showed moderate activity against Gram-positive and Gram-negative bacteria Synthesized by: Jennings (2007) Ramana (2007, bruguierol A) R R R R Taxane diterpenoids anti-cancer Rob Lettan @ Wipf Group Page 2 of 11 9/7/2008
Strategies for the Construction of 7-mbered Carbocycles: [6C + 1C] Approach C 2 =S() 2 C 2 TFA C 2 92% C 2 NAc (±)-colchicine Evans, D. A., et al. J. Am. Chem. Soc. 1981, 103, 5813-5821. N 2 C 2 Rh II DEIPS C 2 DEIPS DBU 65% C 2 DEIPS harringtonolide Mander, L. N., et al. Aust. J. Chem. 2000, 53, 819-830. Rob Lettan @ Wipf Group Page 3 of 11 9/7/2008
Ac TBS Strategies for the Construction of 7-mbered Carbocycles: Ac DBU CN TBS [5C + 2C] Approach Ac 79% Ac TBS Wender, P. A., et al. J. Am. Chem. Soc. 1997, 119, 7897-7898. phorbol This approach was also used by many others in natural product syntheses: P. Magnus (guanacastepene, taxanes), J. E. Baldwin (cordytropolone: alkyne trap), and Snider (cartorimine: unsat. ester) Review: Wright, D. L., et al. Chem. Eur. J. 2006, 12, 3438-3447. N 2 R Rh 2 (ex) 4 R 85% R tigliane skeleton McMills, M. C., et al. Tet. Lett. 1994, 35, 8311-8314. Dauben, W. G., et al. J. rg. Chem., 1993, 58, 7635-7637. [Rh(C) 2 Cl] 2 Bn RhLn Bn Bn Ln Rh 90% Wender, P. A., Zhang, L. rg. Lett. 2000, 2, 2323-2326. Bn (+)-aphanamol I Rob Lettan @ Wipf Group Page 4 of 11 9/7/2008
Strategies for the Construction of 7-mbered Carbocycles: [4C + 3C] Approach Cl Cl Cl Zn-Cu 70% Cl Wright, D. L., et al. J. rg. Chem. 1999, 1, 1535-1538 erinacine C NBoc TMS TMSTf TMS NBoc 45% NBoc colchicine Cha, J. K., Lee, J. C. Tetrahedron 2000, 56, 10176-10184. 75 C 73% C Boger, D. L., Brotherton, C.E. J. Am. Chem. Soc. 1986, 108, 6713-6719. (±)-colchicine NAc Rob Lettan @ Wipf Group Page 5 of 11 9/7/2008
Strategies for the Construction of 7-mbered Carbocycles: Alternative Approaches N TMS Rh 2 (Ac) 4 TMS N 1. (P 3 ) 3 RhCl, 2 N 2. nbu 4 F 3. C 2, Na(CN)B 3 73% 70%, 3 steps TMS N ferruginine N 2 Davies,. M. L., et al. J. rg. Chem. 1991, 56, 5696-5700. N 2 Rh 2 (S-DSP) 4 140 C 85% 90% ee Davies,. M. L., Doan, B. D. Tet. Lett. 1996, 37, 3967-3970. 2, ClRh(P 3 ) 3 76% tremulenolide PMP h! PMP 1. SmI 2 2. SeBr 3. mcpba PMP Ac C 76% 37%, 3 steps Sorenson, E. J., Shipe, W. D. rg. Lett. 2002, 4, 2063-2066. guanacastepene Rob Lettan @ Wipf Group Page 6 of 11 9/7/2008
Transition-tal Catalyzed Cyclization of Pyrylium Ions with Alkenes/Alkynes 20 mol% W(C) 5 TF TF, rt W(C) 5 Et Et W(C) 5 Et C 2 C 3 C- insertion W(C) 5 TF 76% i-pr Et Iwasawa, N. et al. J. Am. Chem. Soc. 2001, 123, 5814-5815. C 10 mol% AuCl 3 AuCl 3 AuCl 3 Yamamoto, Y., et al. J. Am. Chem. Soc. 2002, 124, 12650-12651. 96% yield >99:1 regioselectivity TsN C [Rh(CD)Cl] 2, dppp 80 C, 8 h TsN Rh Rh [5+2] 2 TsN TsN h, C.., et al. Chem. Commun. 2005, 4429-4431. 87% Rob Lettan @ Wipf Group Page 7 of 11 9/7/2008
Intramolecular Platinum Catalyzed Cyclization of Pyrylium Ions with Alkenes and Subsequent C- Insertion C Bn 5 mol% toluene 120 C, 1h Bn 2a 2 C Catalyst 2a 3a 4a PtCl 2 PtCl 4 25% 35% 20% 40% 3a Pt(P 3 ) 4 20% PtCl 2 (P 3 ) 2 77% 4a PtCl 2 (dppe) 61% 10% Rob Lettan @ Wipf Group Page 8 of 11 9/7/2008
chanistic Proposal C Bn Bn C a b 3a 1. Na 2. PCC Pt a Pt Pt b 4a 2a Rob Lettan @ Wipf Group Page 9 of 11 9/7/2008
Reaction Scope SM Product SM Product C C 80% 74% Bn Bn C C 66% 88% C Bn C C Bn 86% 80% Bn Bn Bn C TBS PDC Bn 76% Rob Lettan @ Wipf Group Page 10 of 11 9/7/2008
Summary thods for the synthesis of 7-membered carbocycles are necessary due to their prevelance in natural products. Several tactics for the formation of 7-membered carbocycles have been developed, including strategies that employ, [6C + 1C], [5C + 2C], [4C + 3C], and other alternatives. h and coworkers have published a platinum-catalyzed cyclization of pyrylium ions with alkenes to give a tetracyclic platinum-carbene complex, which immediately undergoes insertion into a benzylic C- bond to give a highly complex ring system. The power of transition metal-catalyzed pyrylium ion formation and subsequent cyclization has been demonstrated to access various multi-cyclic scaffolds, and lends to possibility of utilization of these methods for the future development of other sophisticated carbon frameworks. Rob Lettan @ Wipf Group Page 11 of 11 9/7/2008