transmetallate displace ox. add. M + (insert) (β-elim.)
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1 Chapter IV. Transition Metal σ-alkyl Complexes I. General For much of the rest of this course it will be necessary to understand how σ-alkyl metal complexes are formed and how they react. This is summarized below. σ-alkyl transition metal complexes in synthesis. A. Preparation (-) + M(-) + X M X displace displace transmetallate ox. add. M' + MX 'X + M(0) M + insert insert ' M uc. attack cyclomet. M + uc L M + L + M B. Transformation C ox. X M '- (coupling) "M " ' (transmetallate) Me Z nuc. uc-' (ox. cleavage) 'CMe (insert) ' Z (insert) ' (β-elim.) + M- All of these form C-C bonds in unusual ways from unusual starting materials and hence are useful in organic synthesis.
2 II. σ-alkyl metal complexes from the reaction of carbanions with metal halides (MgX, Li + MX) A. rganocopper chemistry [eviews: Lipshutz rg. eact. 41, 135 (1992); Comprehensive rganometallic Chemistry II 12, 59 (1995)] 1. Background - ne of oldest transition metal reactions a. MgX + (Gilman/Kharasch 's) CuX cat b. Stoichiometric diorganocuprates (ouse, Corey, Posner 's) Li + CuI "Cu" + Li "Cu" + LiI insoluble yellow oligomer " 2 CuLi" soluble, unstable eactions (1) 2 CuLi + 'X ' ' = sp 3 1 > 2 >> 3 I > Br > Cl Ts work sp 2 also reactive, both halides and triflates Tf 2 CuLi CCl very reactive as are 's C usually not safe acidic 's, 's, C's, stable to cuprates C millions of examples
3 2. 2 CuLi + ketones > esters for esters: α or β alkylation slows, esp. Fail undergoes 1,2 General Problems: (a) XS reagent required (3-5 fold) and only 1 group transfers (b) thermally unstable (c) until recently, group couldn't contain reactive functional groups - more of this later.
4 2. ecent Trends a. "igher rder" Cuprates and Mixed "igher rder Cuprates" (1) Preparation CuC + 2Li [ 2 CuC]Li 2 Lipshutz claims C stays coordinated to Cu to give a 3-coordinate species with different chemistry. But, Penn-ahn [JACS 118, 8808 (1996); JACS 117, (1995); JC 60, 4310 (1995)] and Bertz and Snyder [JC 60, 4312 (1995); Chem. Comm. 815 (1996)] by EXAFS, XAES and ab initio claim Li Li C whatever, these have different 3 C Cu C reactivity and 3 stability from 2 CuLi Mixed commercially available CuC + S Li S CuC Li Li [(Thien)()CuC]Li 2 nly transfers important if is expensive, hard to make. (2) eactions More reactive, more stable than 2 CuLi, best for 2 X, epoxides.
5 (3) Applications [Kishi JACS 113, 9693 (1991)] S Me Me 1) TMS 2) Ac 2 Cu(C)Li 2 TMS Ac Me Me
6 S Cu(C)Li 2 TIPS Bu 3 Sn TIPS BF 3 Et 2, TF, -78 [Evans JACS 114, 2260 (1992); JACS 115, 4497 (1993)] SnBu 3 Unsymmetrical Biaryl Synthesis Lipshutz, J. Am. Chem. Soc. 113, 8161 (1991) 115, 9276 (1993) ArLi + CuC -78 ArCu(C)Li Ar'Li [ArCuAr']CLi 2 o scrambling at low temp. Ar =, ome, mme, pme, 2Cl-4CF 3, 1 aphth % ArAr' >96:4 Ar' = ome, pme, ome, 3F, 4Me elated Cu Cu + I I [Y. Yamamoto J.C.S. Chem. Comm (1999)]
7 Me Me TBDMS Me X (a) X = Br (b) X = Li 1) Me MeTBDMS Me X ' (a) X = Br (b) X = Li (c) X = Cu(C)Li, ) 2, TMEDA, -131 Me Me Me TBDMS Me ' Me Me TBDMS 58% Me Me Me Me calphostin C Me [Coleman Tet. Letters 34, 2225 (1993)] Me Bn Me 1) CuC TMEDA Me * Bn 2) 2, -78 Me Li [Coleman JACS 117, (1995)] Me Bn Me Bn Bn Me Me Bn 70% 8:1 mix.
8 Me Me Me Br 1) tbuli, -78 Me Me Me Br 2) CuC 3) 2 Me Me Me Me Me Me [Lipshutz Tet. Lett. 35, 815 (1994); Tet. Lett. 38, 1087 (1997)] elated C 2 Et SnMe 3 5 eq CuCl C 2 Et SnMe 3 Cl DMF min 94% Cl many related SnMe 3 SnMe 3 CuCl couple [Piers JACS 118, 1215 (1996); Tetrahedron 54, (1998)] SnBu 3 Bu 3 Sn PdCl 2 CuI DMF [eathcock JC 61, 700 (1996)]
9 I Me 3 Sn Me 2 3 Me Cu S 69% C 2 [Paterson, Angew. Chem. Int. Ed. Engl. 39, 1308 (2000)] ' ' Me
10 b. Functionalized Cuprates (1) From "Cu(0)" LI + aphthalene TF rt, 2 h Li + [dark green] CuI P 3 0 (Cu) n ( 3 P) y [reddish black] [ieke JC 58, 2483 (1993)] Br(C 2 ) 3 C CCl -36 to rt C(C 2 ) 3 C (79%) Br(C 2 ) 3 C 2 Et "Cu(0)" functionalized cuprate* -78 to rt (90%) C 2 Et Br(C 2 ) 6 Cl * FG FG C 2 Cu LiX or C 2 Cu(X)Li -78 to -20 (78%) (C 2 ) 7 Cl C(C 2 ) 6 Br (Cu) n (PBu 3 ) y -45 to rt (C 2 ) 6 C (83%)
11 Li + S Cu(C)Li TF, -78 "(Cu) n (L) y " [Lipshutz Tet. Lett. 28, 9451 (1989)] CuC nlix (X = Cl, Br) Li p TF, -100 "(Cu) n (L) y " [ieke Tet. Lett. 34, 3063 (1993)] Ac Cl "(Cu) n (L) y " TF -100 functionalized allylic cuprate Ac X ArI "Cu(0)" ["XArCu"] 'X XAr' (79%) aaphth + CuX XAr = Br [JC 60, 2361 (1995)] F no benzyne formation vs Li 'X = MeI, BnBr, CCl, etc.
12 (2) From Transmetallation (a) From Zinc L n Zn- or Zn-X [X = halide] + L Cu L n [L = ligand on Cu(I)] Cu Zn X() L Cu L n + L Zn X() functionalized Cu(I) reagent ZnCl 2 + Liaphth FG I Zn(0) TF, FG ZnI (>85%) [Knochel Chem. ev. 93, 2117 (1993)] Zn/Cu in situ C 2 Me I C 2 Me(x's) Tf Zn, CuI ))), rt, 40 min Et/ 2 (7:3) Tf (65%) [Castedo JC 58, 118 (1993)]
13 FG C 2 ZnI (FG 1) neat, 25-50, 2-20 h C 2 ) 2 Zn + + EtI 1.5 Et 2 Zn CuI (0.3 eq) 2) 50, 0.1 mmg, 1 h + Et 2 Zn Preformed Cu(C)ZnX nlix Cu(C)(Znr) nlix ZnX + CuC nlix 2 Zn + CuC nlix 2 C 2 Me 1) (Et) 2 P Cu(C)ZnI TF, 4 h, -78 to rt 2) ef reaction (Et) 2 P Me 2 C (78%) [Angew. Chem. Int. Ed. 28, 351 (1989)] 1) IZn(C)Cu (C 2 ) 5 C 2 Me Si Si 2) TMS-Cl, TF hydrolysis C 2 Me Si JC 56, 3205 (1991) (78%) Si
14 (Et) 2 P "IZn(X)Cu C 2 Me" TBDMS TBDMS C 2 Me Tetrahedron 47, 1861 (1991) TBDMS TBDMS (97%) IZn Boc C 2 Bn CuC 2LiCl TF, -10 to 0 IZn(C)Cu Boc C 2 Bn Zn/Cu (1.7 eq.) /DMA (15:1) sonication 30 min I Boc C 2 Bn 1 2 X X = Cl, Br, Ts 1 =,, C 2 Br, C 2 Me 2 =, Me, C 2 Me 3 =, C 2 Cl Boc [Jackson, J. Chem.Soc., Chem. Comm. 319 (1992)] Can be made catalytic in Cu FGZnI 1) 1.4 MeLi cat. Me 2 CuCLi 2 1) 2 Eq. TMSCl FG = Cl(C 2 ) 4, C(C 2 ) 5, (C 2 ) 3, Et 2 C(C 2 ) 3 2) 1 (32-65%) FG C 2 Bn good yield large scale [Lipshutz JACS 117, 6126 (1995)]
15 ZnCl 2 TMS Et Et C 2 Zn + C 2 Et CuBr SMe 2 (10-25 mol %) MPA, TMS Cl TF, rt, 4-6 h C 2 Et from zinc homoenolate C 2 Et cat. Cu(I) 2 Zn (89%) Me 2 cat. Cu(I) C 2 Et Me 2 TBDMS TBDMS Me cat. Cu(I) (71%) C 2 Me (72%) [Crimmins JC 58, 1038 (1993)]
16 C 2 Et Zn(C 2 C 2 C 2 Et) 2 cat. CuBr Me 2 S (10 mol %) MPA, TF, Et 2 TMS-Cl C 2 Et Me 3 Si (52%) hν [Crimmins JACS 115, 3146 (1993)] C2 Et Carbocupration of Alkynes Me 3 Si FGZnI + Me 2 CuCLi 2 "FGCu(C)LiZnMe 2 Li" ' " FG E E + FG CuC ' " ' " FG = Et, Et 2 C, C, Cl, E + = +, Br, Me 3 SnCl ' = Bu,, " = SMe, [ao, Knochel J. Am. Chem.Soc. 1991, 113, 5735]
17 " I Zn ' ''' " 1) Me 2 CuCLi 2 2) E + ' E ''' " " 55-76% ' "X ' S 2 " S 2 CuMgX 2 + 'C C ' CuMgX 2 D + ' D C 2 1 ' C 2 I 2 ' I (a) Alexakis, A.; Commercon, A.; Coulentianos, C.; ormant, J.F. Pure Appl. Chem. 1983, 55, (b) ormant, J.F.; Alexakis, A. Synthesis 1981, 841. (c) Asymmetric induction in Michael additions 1 MgX 1 CuBF 3 + S 1 ppolzer elv. Chim Acta 72, 1337 (1989) eview Tetrahedron 43, 1969 and 4057 (1987)
18 BuCuI SiMe 3 Bu Me 93% 98% de J. rganomet. Chem. 391, C19 (1990). CuI, MeLi L*, C 3 /TF 6 6 (-) Muscone 89% 100% opt. purity L* = J. Chem. Soc. Perkins I, 1445 (1991).
19 Then 1) MgBr CuBr Me 2 S 2) BnBr Bn 50-89% [ruby Tet. Letters 34, 2561 (1993) JC 60, 5509 (1995)] >99% ee Bn 1) MgX / CuI 2) 2 Pd/C + 2 C 3 [egedus, Lander JACS 116, 8126 (1994)] = t-bu, adamantyl, pme, TMSC 2, cyclohexyl 89-98% yield 88-97% ee ( ) n Bu 2 CuLi L* Et 2-78 ( ) n Bu L* = [ossiter JC 60, 8422 (1995)] n = 2, % yield 92-97% ee + 2 CuLi [Smith JACS 117, (1995)] 1) 2) AcCl MPA 89%
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