Organocopper Reagents
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1 rganocopper eagents General Information!!! why organocopper reagents? - Efficient method of C-C bond formation - Cu less electropositive than Li or Mg, so -Cu bond less polarized - consequences: 1. how higher selectivity than -MgX and Li reagents Cl > > Ts > I > Br > Cl >> ' > ' > CN 2. 1,4-addition preferred in α,β-unsaturated compounds 3. -Cu reacts with alkyl, vinyl, and aryl halides
2 rganocopper eagents General Information!!! reactivity Cu ' or ' Cu ' "Cu" ' ' X ' ' ' Cl 2 CuLi ' '
3 rganocopper eagents tructure & Properties!!! Copper Catalyzed Grignard [MgX, CuI]: - Catalytic in copper; only slight excess of Grignard reagent required rganocopper Complexes [Cu]: - Participate in conjugate addition reactions - equires Lewis acid additives like BF 3 Et 2 - olubility may be a problem Lower rder Cuprates [ 2 CuLi]: - Most commonly used - Participate in conjugate addition, substitution, and alkyne addition reactions - Gilman reagents (homocuprates) - Mixed lower order cuprates also known: CuLi (heterocuprates)
4 rganocopper eagents tructure & Properties: Lower rder Cuprates!!! Kharasch (1941) MgX CuI (cat) MgX or Li Gilman (1952) Gilman reagents Li + CuI (1 eq) (1 eq) Et 2 or TF Cu + LiI Li (1 eq) < - 40 C < - 40 C insoluble bright yellow 2 Cu Li soluble colorless (blueish)
5 rganocopper eagents tructure & Properties!!! Lower rder Cyanocuprate [Cu(CN)Li]: - Participate in conjugate addition and substitution reactions with allyl derivatives - nly a single equivalent of Li required for preparation Li + CuCN Et 2 Cu(CN)Li igher rder Cuprates [ 2 Cu(CN)Li 2 ]: Lipshutz reagents - Participate in conjugate addition, substitution, and alkyne addition reactions - More reactive in substitution reactions than lower order cuprates - Increased stability similar to heterocuprates Et 2 2 Li + CuCN 2 Cu(CN)Li 2 higher order cuprate soluble
6 rganocopper eagents Ligand Transfer!! Gilman reagents - nly one group transfers; second group is wasted eterocuprates - Can incorporate a non-transferable or dummy ligand Cu ' Li - elative rate of ligand transfer: C=C > Ph > > Et > ipr > tbu >> Ph, 2 N, alkyne, etc. - Common non-transferable ligands: ' Ph 2 P tbu 3 ic 2 - Preparation of mixed cuprates + CuI Et 2 + LiI Li or TF Cu (1 eq) Cu Li (1 eq) (1 eq) Li
7 rganocopper eagents Conjugate Addition eactions!!! ' Y 2 CuLi Et 2, -40 C ' Y (Y ) mechanism Li 2 CuLi (ET) 2 Cu Li III Cu reductive elimination + Cu I Cu oxidative addition
8 rganocopper eagents Conjugate Addition eactions!!! 2 CuLi ' Y Et 2, -40 C ' Y (Y ) order of reactivity > > CN >> > - α,β-unsaturated aldehydes poor substrates react 1,2 2 C N 2 CuLi Et 2, -20 C 2 C N 71%
9 rganocopper eagents Conjugate Addition eactions!!! additives - Can enhance reactivity in hindered systems TM Bu 2 CuLi, TMCl TF, -78 C, 5 min 99% Bu 2 CuLi TF, -78 C, 1 h 28% 2 CuLi BF 3 Et 2 70% 2 CuLi no reaction J. Am. Chem. oc. 1989, 111, 1351.
10 rganocopper eagents Conjugate Addition eactions!!! additives - Can impact regioselectivity TM Bu 2 CuLi TMCl, -78 C Bu 2 CuLi ( =, alkyl) 2 CuLi TMCl - Can impact stereoselectivity 2 CuLi TF, -78 to 0 C 61% dr 92:8 2 CuLi, TMCl TF, -78 C, 2min 70% only product
11 rganocopper eagents Conjugate Addition eactions!!! enolate trap E -trap 2 CuLi E C-trap E -trap: E + = 3 icl, () 2 P()Cl C-trap: E + = X, C, halogen
12 rganocopper eagents Conjugate Addition eactions!!! enolate trap on oxygen TM 2 CuLi TMCl Pd(Ac) 2 Bn Bn Bn P(Et) 2 Tf 2 CuLi 2 CuLi Cl P(Et) 2 Tf 2 Li/N 3 tbu ' 2 CuLi Pd(Ac) 2 PPh 3 ' 2 CuLi '
13 rganocopper eagents Conjugate Addition eactions!!! enolate trap on carbon 2 CuLi; ' 'X ' = methyl, allyl, benzyl, propargyl α-halocarbonyls, C Bu 3 PCu TB TB (C 2 ) 4 C 3 I MPA C 2 C 2 C 2 TB (-)-PGE 2 J. Am. Chem. oc. 1988, 110, 4726.
14 rganocopper eagents Conjugate Addition eactions!!! stereochemistry - 3,5-selectivity 2 CuLi - 3,4-selectivity 2CuLi
15 rganocopper eagents Conjugate Addition eactions!!! stereochemistry - 2,3-selectivity 2 CuLi + usually trans
16 rganocopper eagents Conjugate Addition eactions!!! stereochemistry - exocyclic enones 2 CuLi BF 3 Et 2 tbu - fused ring systems (6,4-, 6,5-, 6,6-) 2 CuLi
17 rganocopper eagents Conjugate Addition eactions!!! stereochemistry of alkylation - 6-membered ring systems (stereoelectronic) 1. Bu 2 CuLi 2. I - 5-membered ring systems (steric) I 2CuLi
18 rganocopper eagents Conjugate Addition eactions!!! stereochemistry of alkylation - intramolecular alkylation Br Br 2 CuLi
19 rganocopper eagents Conjugate Addition eactions!!! addition / elimination processes C 2 2 CuLi C 2 X X C 2 2 CuLi C 2 X = Ph, Cl, Br, Ac X
20 rganocopper eagents Conjugate Addition to Alkynes!!! C 2 2 CuLi C 2 E + Cu C 2 E E + = +, NB, C, epoxides conditions cis : trans ratio TF, -100 C 97 : 3 TF, -78 C 92 : 8 Et 2, -30 C (3 hr) 24 : 76 - alkenyl copper reagent is configurationally unstable at higher temperatures cis C trans
21 rganocopper eagents Conjugate Addition to Alkynes!!! equilibration of alkenyl copper C 2 2 CuLi TF, -78 C C 2 Cu warm Cu C 2 E + 25 C 0 C -30 C rapid slow observable E C 2 Corey J. Am. Chem. oc. 1969, 91, Fried J. Am. Chem. oc. 1969, 91, Klein J. Chem. oc., Perkin Trans. 2, 1973, 1971.
22 rganocopper eagents Carbocupration of Alkynes!!! 2 CuLi E + TF, -78 C Cu E E + = +, I 2, C, epoxide, X examples PrMgBr CuBr 2 Pr Cu Pr - intramolecular alkylation
23 rganocopper eagents Carbocupration of Alkynes!!! examples - directed addition altered regiochemistry 2 CuLi I C 2 Et Cu MPA Et 2 C - chelation to alkoxide trans addition MgBr CuI Cu I 2 I
24 rganocopper eagents Alkylation eactions!!! X ' 2 CuLi ' X = Ts, Ms, halide, epoxide - works best with higher order cuprates Br Bu 2 Cu(CN)Li 2 TF, -50 C 95% (70% with lower order cuprate) Pr 2 Cu(CN)Li 2 TF, 0 C 86% (30% with lower order cuprate)
25 rganocopper eagents Alkylation eactions!!! N 2 Addition 2 CuLi 2 CuLi Ac Ac Pv 2 CuLi Pv Pv
26 rganocopper eagents Alkylation eactions!!! N 2 Addition 2 CuLi Cl Cl CPh 3 CPh 3 TM tbucu(cn)li TM 3 +
27 Umpolung What is it?!!! Polarity eversal! δ - C δ+ δ + C δ- C Nu - E + - ow do you do that? CN
28 Umpolung Dithianes!!! Properties, Preparation, Utility - pk a 31 - anion stabilized by empty d orbitals on - deprotonation requires strong base nbuli; BF 3 Et 2 X nbuli nbuli NT E + E
29 Umpolung Dithianes!!! Properties, Preparation, Utility ' ' ' Et Et 'X 'C ' Cl ' ' " ' C 2 ' ' " '
30 Umpolung Dithianes!!! Properties, Preparation, Utility gcl 2 a(ni) ' ' ' ' ' ' ' ' ' " ' ' " ' ' ' '
31 Umpolung Dithianes!!! Properties, Preparation, Utility nbuli nbuli, MPA N Li N Ph TF MPA, -78 C N N Ph Li/N 3 N N Ph TiCl 4 N N N N uleine
32 Umpolung Dithianes!!! Properties, Preparation, Utility CN - = TM, EE - deprotonation requires strong base CN LDA CN E + CN E TMCN TM CN NaCN CN EE CN p 6 pts (cat)
33 Umpolung Cyanohydrins!!! Properties, Preparation, Utility TM CN Ph C LDA; TM CN Ph Bu 4 NF or 3 + Ph EE CN LDA; EE CN 3 + Br NC EE LDA; EE CN LDA; quench at -78 C quench at 0 C NC EE
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