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Zr-Catalyzed Carbometallation

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Zr-Catalyzed Carbometallation Zr-Catalyzed Carbometallation C C C C MLn R C C MLn R ML n MLn R C C MLn C C C C MLn Wipf Group Research Topic Seminar Juan Arredondo November 13, 2004 Juan Arredondo @ Wipf Group 1 11/14/2004 Carbometallation . Term coined for describing chemical processes involving net addition of carbon-metal bonds to carbon-carbon π-bonds. One of the several patterns for C-C bond formation observable with organotransition-metal complexes along with reductive elimination, migratory insertion, etc. C C C C MLn R C C MLn R ML n MLn R C C MLn C C C C MLn C C MLn C MLn ML C C n Juan Arredondo @ Wipf Group 2 11/14/2004 Timeline . In 1959, Natta first reported the polymerization of propylene with TiCl4/AlEt3. Reaction proceeds with relative asymmetric induction with polymer sections of the same absolute configuration (isotactic). Subsequent work was focused on finding a soluble of group IV metallocene catalyst (Ti, Zr, Hf). Controlled Monocarbometallation of Alkenes and Alkynes . Stereo- and regioselective single-state addition of organometallics species can be a valuable synthetic tool. Normant’s carbocupration (1976) was the first example with high selectivity and reasonable generality. Limitations arose from the thermal instability of the alkylcopper reagents and capricious effects of proximal hetereoatoms. R2 H 1 . 2 R Cu MgX2 + R C CH 2 . R Cu MgX2 . Schwartz’s systematic investigation (1974) of hydrozirconation of alkenes and alkynes with Cp2ZrHCl and observations of its addition to alkenes and alkynes by Wales and coworkers. .Kaminsky’s use of Cp2ZrCl2 and methylaluminoxanes as catalyst for alkene polymerization (1976). .Negishi’s catalyzed carboalumination with Ti and Zr (1978). Juan Arredondo @ Wipf Group 3 11/14/2004 Carbometallation: FMO Analysis Dynamic Polarization . Two Lewis acids (or electrophiles) which LUMO HOMO R MLn R MLn make one of them more acidic (or electrophilic), while making the other more basic (or C C C C nucleophilic). HOMO LUMO . Structural requirement for organometallic 1M 1L + 2L 2M reagent is the availability of a low-lying metal empty orbital. Carbometallations that proceed via 1 "ate" 1L dynamic 1 pericyclic reactions can be facile and highly L complexation polarization L 1 δ− 1M 2 M 2M 1M 2 stereoselective. M δ+ M 2 permanent 2 2 L polarization L L . Energy of activation for carbometallation would be higher than that of transmetallation hydrometallation due greater steric requirements of C groups than H. 1M 2L + 1L 2M Negishi E., Kondakov, D, Y., Chem. Soc. Rev. 1996, 26, 417 Juan Arredondo @ Wipf Group 4 11/14/2004 Zirconium-Catalyzed Carboalumination of Alkynes R1 H 1 1 cat. Cp2ZrCl2 H2O R H R C CH + AlR3 CH Cl or 2 2 2 2 R AlR2 R H ClCH2CH2Cl 85-95% Me3Al Cp2ZrCl2 Ph D H2O Ph D PhC CD Me AlMe2 Me H 1. n-BuLi (> 98% Z) 2. D2O Me Al 3 Ph H Ph H Cp2ZrCl2 D2O PhC CH Me AlMe2 Me D (~ 96% E) . If Cp2ZrCl2 is omitted or aluminum- I2 free Cp2ZrMeCl is used, only trace amount of the alkene is obtained. D2O/THF Ph H n-BuLi Ph H Me I Me Li Negishi, E., et al. J. Am. Chem. Soc. 1978, 100, 2252; J. Am. Chem. Soc. 1978, 100, 2254 Juan Arredondo @ Wipf Group 5 11/14/2004 Mechanistic Studies Cl R C C R R C C R δ+ δ− Me3Al + Cp2ZrCl2 Me2Al ZrCp2Me Me ZrCp2 Cl AlMe2Cl Cl R R R R R C C R + Cp2ZrCl2 Me ZrCp Me 1 2 Me AlMe Cp2Zr R Cl Cl 2 XCl AlX2 AlMe2 X = Cl and/or R1 R1 = Me, Et and higher alkyl Cl R C C R δ+ δ− R C C R MenAlCl3-n + Cp2ZrCl2 Me(X)Al ZrCp2Y Me Al Cl ZrCp2Y Cl X Cl R R n = 3 or 2 Cl R R X and Y = Me or Cl + Cp2ZrCl2 Me Al ZrCp2Y Me AlX X Cl R C C R R1 AlX Me AlCl-Cl ZrCp induced carbometallation 2 . 2 2 2 Cp2Zr Cl . Cp2Zr(CD3)Cl deuterium incorporation (< 4%) X = Cl and/or R1 R1 = Me, Et and higher alkyl Negishi, E. et al. J. Am. Chem. Soc. 1978, 100, 2252, J. Am. Chem. Soc. 1981, 103, 4985, J. Am. Chem. Soc. 1985, 107, 6639 Juan Arredondo @ Wipf Group 6 11/14/2004 Synthetic Scope R1 H R R2 H H Pd,Ni R1 H R1 H + 1 2 2 R H R X R AlR3 R1 H 2 R HgCl 2 X R BR'2 MeOBR'2 HgCl2 O R' S R' O R' N O HO 1 R" R H S 2 R O H R R' NH R R" R O 2 1 R AlR3 R R [Cu] O R1 H R' R" R1 H Zn O 2 R Cu R2 Zn R X R R' R" Juan Arredondo @ Wipf Group 7 11/14/2004 Zirconium-Catalyzed Enantioselective Methylalumination of Unactivated Alkenes R H RC CH C C Me AlMe2 Me3Al + Cp2ZrCl2 RC CH2 R CHCH2AlMe2 Me 1. Me3Al 8 mol % (1) R R (R) 2. O2 OH Zr Cl Cl 1 Negishi, E., et al. J. Am. Chem. Soc. 1995, 117, 10771 Pure Appl. Chem. 2002, 74, 151 Juan Arredondo @ Wipf Group 8 11/14/2004 Stoichiometric vs. Catalytic Carbometallation Stoichiometric Process Me MeMLn ML n-Hex n-Hex n H desired product Catalytic Cycle Me Me H Me ML n-Hex MLn n-Hex n n-Hex n-Hex H minor (~ 20%) MeMLn R Me CH2 H ZrL n n-OctML n-Hex n RHC CH2 β−dehydrometallation n-Oct n-Oct n-Hex ML n-Hex n major H Juan Arredondo @ Wipf Group 9 11/14/2004 Competing Reactions H + P Ziegler-Natta Polymerization Cp2Zr R β-H elimination P Cp Zr P H H H 2 Cp Zr 2 R 2 Cp2Zr + P R hydrogen transfer R R'M R transmetalation M R' P Cp2Zr + R . Polymerization and oligomerization . β-Dehydrometallation leading to Zr-catalyzed hydrometallation . Zr-catalyzed cyclic carbometallation of alkenes . Zr-centered carbometallation vs. Al- or other metal-centered carbometallation Juan Arredondo @ Wipf Group 10 11/14/2004 Mechanism R . The use of bulky ligands in (NM)2ZrCl2 or NMI is responsible Me CH2 for suppressing β-H transfer hydroalumination. Polymerization is minimized with the use of one equiv. or less H ZrLn of alkene relative to the alkylalane reagent. RHC CH2 R R* Me3Al Zr R dissociative Me path R *R Zr Cl Cl R* R* R Zr Zr R Cl Me Me3Al Me Al Al Cl associative R *R *R path R* = Negishi, E. In Catalytic Asymmetric Synthesis, Ojima (Ed), 2000, p.165 Juan Arredondo @ Wipf Group 11 11/14/2004 Mechanisms of Carboalumination and related reactions Negishi, E. Pure Appl. Chem. 2001, 73, 239 Juan Arredondo @ Wipf Group 12 11/14/2004 Dzhemilev Ethylmagnesiation of Alkenes (monometallic cyclic) R ZrCp2 R EtMgBr ZrCp2 R MgBr H ZrCp2 R MgBr Et . Reaction failed with methylmagnesium derivatives Dzhemilev, U., M. Russ. Chem. Rev. 2000, 69,121 Juan Arredondo @ Wipf Group 13 11/14/2004 Zr-Catalyzed Enantioselective Ethylalumination n-Oct n-Oct n-Oct 10 % Cp2ZrCl2 AlR2 + AlR2 + CH Cl , 23°C Et H Et 2 2 <5% n-Oct + + n-Oct n-Decyl )2 ZrCl2 n-Oct n-Oct 10% O2 AlR2 OH n-Oct + Et3Al CH2Cl2, 23°C Et Et >85% 10% (Me C ) ZrCl 5 5 2 2 no reaction ( n-Oct recovered >90%) CH2Cl2, 23°C 1. Et3Al Cp2ZrCl2, (CH2Cl)2 n-Oct n-Oct n-Oct D + + D 2. DCl, D O 2 Et Et H Zr n-Oct 37% 20% 20% Cl Cl Et3Al, (1) n-Oct [O] n-Oct Al OH CH CHCl 1 3 2 Et Et 64%, 92% ee Negishi, E., et al. J. Am. Chem. Soc. 1996, 118, 1577 Juan Arredondo @ Wipf Group 14 11/14/2004 Ethyl-alumination of Monosubstituted Alkenes 1. Et3Al Cp2ZrCl2, (CH2Cl)2 n-Oct n-Oct n-Oct D + + D 2. DCl, D2O Et Et H n-Oct 37% 20% 20% Et3Al, (1) n-Oct [O] n-Oct Al OH Zr CH3CHCl2 Et Et Cl Cl 64%, 92% ee 1 . Enantioselectivity (Methyl vs. Ethyl) Negishi, E., et al. J. Am. Chem. Soc. 1996, 118, 1577; Pure Appl. Chem., 2001, 73, 239 Juan Arredondo @ Wipf Group 15 11/14/2004 .Solvent & Temperature Effect Et Al, 1 n-Oct O n-Oct 3 2 OH hexanes AlEt OH 65%, 33%ee n-Oct Et Al, 1 n-Oct O n-Oct 3 Al 2 OH H Et H Et CH3CHCl2 63%, 92%ee Zr Cl Cl 1 Negishi, E., et al. J. Am. Chem. Soc. 1996, 118, 1577 Juan Arredondo @ Wipf Group 16 11/14/2004 Synthetic Applications Hydrometallation/Alkylalumination Tandem Process Negishi, E. et al. Angew. Chem. Int. Ed. 2002, 41, 2141 Juan Arredondo @ Wipf Group 17 11/14/2004 Synthetic Applications O O HO OH NH O Scyphostatin 1. Me3Al 5% (±) [ZrCl2(nmi)2] MAO o CH2Cl2, 0 C ZO ZO OH + ZO OH 2. O2 (2S,4R) (2R,4R) Negishi, E. et al. Angew. Chem. Int. Ed. 2004, 43, 2911 Juan Arredondo @ Wipf Group 18 11/14/2004 Synthetic Applications OH H N OH O OH 6,7-dehydrostipiamide HOOC HO O O HOOC PH Negishi, E. et al. Org. Lett. 2004, 6, 1425 2 O OH OAc O Zaragozic Acid A HO O Vitamin E R1= C H (OH) R1 6 8 5 Negishi, E. et al. Org. Lett. 2001, 3, 3253 or OR2 HO O OH OH O C5H7O(OH)4 O 2 HO R = H or Ac HO TMC-151 A-F Negishi, E.
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