Approaches to the Synthesis. of Tetrahydropyrans. (and closely related heterocycles)
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1 Approaches to the Synthesis of Tetrahydropyrans (and closely related heterocycles) William Morris Literature Presentation July 6, 2004
2 I. Intro A Nomenclature B Prevalence in Nature C Biosynthetic Considerations utline II. Survey (Buffet) of Approaches A Displacement, ing Expansion, Epoxide pening B xymercuration C Polyene cyclization D rganometallic strategies E Lewis Base Approaches III. Prins A Application to phorboxazole B Leucascandrolide A: Mukaiyama Prins Cascade C ole of xonia Cope D Potpourri IV. Tetrahydropyran-4-ones A Jacobson's etero Diels-Alder: Application to F B Clarke's Work / Preview V Summary
3 A Quick Primer: A Few Words on Nomenclature Pyrylium 2-Pyran 4-Pyran Pyran-2-one Tetrahydropyran-4-one 3,4-Dihydro-2-pyran Tetrahydropyran, (TP) (3,4,5,6-tetrahydro-2-pyran)
4 Tetrahydropyran ings in Nature 2 C Ac Ac Ac n-pr C 2 Altohyrtin C Bryostatin 1 3 C 3 C 3 C C 2 C 3 3 C C 3 C 3 C 3 Nanchangmycin Miyakolide
5 E,E,E-premonensin Biosynthetic Considerations: Cane Celmer Westley Model [] Enzymatic polyepoxidation of an acyclic hydroxy polyene followed by a cascade of intramolecular epoxide opening events monensin J. Am. Chem. Soc, 1983, 105, 3594
6 Z,Z,Z-premonensin Biosynthetic Considerations: Townsend's Model Ln M LnM M Ln "metallooxetane" Alkoxy-tethetred, non-heme metal-oxo as monensin Tetrahedron, 1991, 47, 2591 active oxidative cyclization species. Initial [2+2], to give metallooxetane followed by reductive elimination
7 Some Early Approaches Intramolecular Displacement (Towards Antibiotic X-14547A): Bn 1. TsCl, pyr % aq. Ac 3. p-anisyldiphenylmethyl chloride, pyr. 81% Bn Ts 1. Na, Ph 2. 80% aq. Ac 85% over 2 steps Bn Can. J. Chem. 1982, 60, 90 =p-anisyldiphenylmethyl ing Expansion ( Towards Lasalocid A): 1. MsCl, pyr. 2. Ag 2 C 3, aq. acetone J. Am. Chem. Soc. 1978, 100, 2933 Epoxide pening (Towards Antibiotic X-14547A): Bn = TBDPS Z/E = 1:2 1. Amberlite, DME, (C 2 ) 2, 45 C 2. TsCl, pyr 3. Na, 4. TBAF, TF, rt 5. 2, 5% Pd/C, Ac 42% Bn J. rg. Chem. 1985, 50, 1440 cat. CSA, C 2 Cl 2, rt 95% Bn
8 Masamune's Approach to Bryostatins 1. g(ac) 2, TF then KCl Ac 1. NaB 4, 2, DMF, 75% 2. Swern, 85%, 1:1 P 2. AcCl, pyr. C 2 Cl 2 85% P gcl 3. Al 2 3 (3% 2 ), C 2 Cl 2 TBDPS TBDPS TBDPS TBDPS P= MM AC AC P C TBDPS 9:1 TBDPS C 2 Bryostatin 1 C 2 J. rg. Chem. 1989, 54, 2817
9 Evans's Synthesis of Antibiotic X-206 BMBn g(ac) 2, C 2 Cl 2 BMBn Aux rt, then NaCl, 99% Aux gcl n-bu 3 Sn, Ph 25 C to 55 C 94% Aux BMBn Aux = Ph N AuxC g X BM L C 2 X-206 J. rg. Chem. 1988, 110, 2506
10 Polyene Cyclization: Ley's Total Synthesis of Tetronasin 2 C 2 C KMDS, toluene, 0 C 86% 2 C epimer of the natural product C 2 K 2 rings and 4 centers are set in 1 operation! Tet. Lett. 1994, 35, 323
11 Alkoxypalladation/Carbonylation 0.1 equiv. PdCl 2, CuCl atm. C,, rt 88% C C equiv. PdCl 2, CuCl atm. C,, rt 84% C 2 No 7-membered rings were isolated ationale: de 97% For E olefin: Pd Pd vs. Pd disfavored Pd For Z-olefin Pd disfavored Pd vs. Pd Pd J. Am. Chem. Soc. 1984, 106, 1496
12 Phosphine-Catalyzed Isomerization/Cyclization Ph C 2 5 mol% Ph 2 P PPh 2 20 mol% Ac, Ph, 90 C, 84% Ph C 2 C 2 Ph 2 P PPh 2 Ph C 2 Ph 2 P PPh 2 C 2 Ph 2 P PPh 2 Ph 2 P PPh 2 + C 2 Ph 2 P Ph 2 P PPh 2 C 2 PPh 2 C 2 J. Am. Chem. Soc. 1994, 116, 10819
13 The Prins Cyclization Base The operation we will cover 'C Lewis Acid ' Nu
14 Application to Phorboxazole Br N N Phorboxazole B Ac Bn TBDPS Cy TBDPS B 0 C, 3d 98% ee Cy TBDPS Bn C 2 DCC, C 2 Cl 2 53%, 3 steps Bn TBDPS 1. DIBAL-, -78 C 2. Ac 2, pyr. DMAP Ac Bn TBDPS 0.1 eq BF 3 2 Ac, hexanes 140 min, 0 C X Bn TBDPS rg. Lett. 2000, 2, X = Ac 52% X = F 5%
15 Mukaiyama Aldol Prins Cascade: Application to Leucascandrolide A Leucascrondrolide A The Basic Concept: + ' LA LA oligomers ' Nu- LA Nu ' ' J. Am. Chem. Soc. 2001, 123,
16 Total Synthesis of Leucascandrolide A Bn + TIPS TMS 1. BF 3 2, 2,6-di-tert-butylpyridine, C 2 Cl 2, -78 C 2. NaB 4, 78%, 5.5:1 dr at C9 Bn 9 TIPS Nu LA 9 + BF 4 -, proton sponge, 4A MS, C 2 Cl 2, 79% Bn TIPS
17 Leucascrandrolide continued s 4, NM 2. NaI 4, 80% (2 steps) 9 TBS Bn TIPS 3. L-selectride, TF, 82% 4. TBAF, TF 92% 5. TBSTf, 2,6-lutidine, C 2 Cl 2, 89% Bn TBS 1. 2, Pd() 2, Ac, 96% 2. Swern, 94% 9 TBS 1. Ac 2, DMAP, pyr. C 2 Cl 2 89% 2. neutral Al 2 3, hexanes, 96% 3. 2 AlCl, 3 SnCCC 2 C() 2, Ph -78 C 80%, 3.5:1 dr 4. ed-al, 2, 60% TBS 3. Swern, 97% 4. NaCl 2, Na 2 P 4, 2-methyl-2-butene, 71% TBS Ac 1. K 2 C 3, 2. Cl 3 C 6 2 CCl, N 3, DMAP, Ph, 56% over 2 steps 3. F pyridine, TF, 96% Leucascrondrolide A
18 ole of xonia Cope earrangements in Prins Cyclizations Br Br Ac SnBr 4 Bn C 2 Cl 2, -78 C Bn Bn 1 58% 2 26% epimerizes! Consider the boat transition state! Bn Br- 1 Bn Bn 2 Bn Br- Br- Bn 1 rg. Lett. 2001, 3, 3815
19 Test for acemization: eduction with Bu 3 Sn Ac Ph Ph 2.0 equiv Bu 3 Sn 1.2 equiv TMSTf C 2 Cl 2-78 C, 30 min Ph Ph Entry [Bu 3 Sn] ee % yield % Ph [3,3] Ph Ph Ph Ph Ph Ph Ph xonia Cope are much faster than typical Prins cyclizations
20 Tuning the eactivity with Aryl Group Substituents C, BF 3 2 Ac, TMSAc 1 Ac Ac 2 3 Ac C 4 5 Entry Cl N There appears to be a trend! rg. Lett. 2002, 4, 577
21 chanistic ationale Ac C [3,3] + C Ac Ac rg. Lett. 2002, 4, 577
22 Sterochemical Considerations C, BF 3 2 Ac, TMSAc (S)-89% ee Ac 14%, 5% ee Cl C, BF 3 2 Cl Ac, TMSAc (S)-94% ee Ac 32%, 78% ee Conclusion: Electron deficient aromatic ring Prins proceeds to give expected 2,4,6-trisubstitued TP ring virtually retaining stereochemistry. Electron rich aromatic rings form the symmetrical TP ring and 2,4,6-trisubstitued TP ring with little stereochemical relay.
23 Pinacol Terminated Prins Cyclizations: 2 More to Consider C acid Prins Pinacol J. Am. Chem. Soc. 1999, 121, 1092 Cyclization of Silylmethyl-Substituted Cyclopropyl Carbinols : Ph TBDPS Acid Ph TBDPS C 2 TBDPS TBDPS Ph Ph J. Am. Chem. Soc. 2004, ASAP
24 Tetrahydro-4-pyranones via etero Diels-Alder TES + 1 C 1. catalyst, 3 mol% 4A MS, rt, h 2. TBAF, Ac, TF 1 N Cr d.r > 20:1 all cis SbF 6 catalyst Yield (%) ee (%) 1 = Ph 1 = C 2 TBS 1 = C 2 Bn 1 = n-c = (C 2 ) 4 C=C 2 1 = C 2 C 2 Ph 1 = C 2 C 2 NBoc 1 = 2-furyl Angew. Chem., Int. Ed. 1999, 38,
25 Jacobson's Synthesis of F Ac N Ac I I N 3 TES TMS TES TMS TES TBS Asymmetric, Catalytic etero Diels-Alder TES TMS TES TBS J. Am. Chem. Soc. 2000, 122, 10482
26 Synthesis of Ac A B Pyran A N TES + TMS catalyst, 5mol% 95% ee TES TMS m-cpba NaC 3 Ph 0 C 70% TMS 1. TsNN 2 2. Na(CN)B 3, p 4 3. NaAc, 4. TBAF 79% t-buk DMS Cp 2 Zr()Cl, then I 2 I 1. ClC 2 S 2 Cl, DMAP, pyr. 2. LiN 3, DMPU N 3 I
27 Synthesis of Ac A B Pyran B N TES + TBS catalyst, 5mol% 98% ee TES TBS 1. m-cpba, NaC 3 C 2 Cl 2, 0 C 2. K 2 C 3 (cat), 63% TBS 1. TIPSTf 2. Ph 3 P=C 2 3. Ac/TF/ 2 4. I 2, PPh 3, imidazole 84% TIPS I 1. TBAF/Ac 2. V(acac) 2, TBP 3. TESTf, N 3 76% TES I
28 Substituted Tetrahydropyran-4-ones BF C, C 2 Cl 2 2 C %, single diastereomer and 1 can be aryl or alphatic rg. Lett. 2002, 4, 4527 Inspired by The Maitland-Japp eaction: + Ph xs-na (aq) >7 days 19% Ph Ph J. Chem. Soc. 1904, 85, 1473 A Catalytic Variant: Sc(Tf) 3, 20 mol% 2 C 1 C, CN 1 Yields 50-90%
29 Catalytic, 1-Pot Process 1. 1 C, CN Sc(Tf) 3, 20 mol% C 2 Ph 2. K(s) Ph 1 Ph 1 More to come on September 28 th!
30 Summary / What You Should Take ome 1. Understand basic nomenclature concepts 2. Be familiar with biosynthesis of these heterocycles 3. Be familiar with general methods for preparing these heterocycles 4. Understand the impact of the xonia-cope on the Prins cyclization 5. thods to construct substituted tetrahydropyran-4-ones
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