Scandium-Catalyzed Asymmetric Reactions
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1 Scandium-Catalyzed Asymmetric eactions Jimmy Wu Evans Group Seminar February 11, 2005 I. Background II. eutral BIL Ligands III. Anionic BIL Ligands IV. Pybox Ligands V. Bip yridine Ligands VI. rganop hosp hate Ligands VII. Miscellaneous Ligands Leading eferences: Aspinall,. C. C hiral Lanthanide Complexes: Coordination Chemistry and Applications Chem. ev. 2002, 1807 Mikami, K.; Terada, M.; Matsuzawa,. Asymmetric C atalysis b y Lanthanide C omp lexes Angew. C hemie., Int. Ed. 2002, 3554.
2 Interesting Tidbits Sc Discovered in 1879 by Swedish chemisty Lars Fredrik ilson Silvery-white metal found more abundantly on the sun than on earth Thortveitite contains 35-40% Sc 2 3 while by-products of uranium ore processing contain 0.02% Sc 2 3 1st pound of scandium not produced until 1960 Shu Kobayashi was 1st to prepare Sc(Tf) 3
3 Atomic Structure 6s 2 5p 6 4f 0 Sc Coordination number 6 12 tal/ligand Interactions mostly electrostatic in nature o orbital restrictions Ligands are extremely labile Atomic radii: Sc(III) Å La(III) Å Lu(III) Å M classic chirality M(bidentate) 3 *L L* ScX n Chirality must reside on the ligand
4 A asure of Lewis Acidity Ln 3 Lewis Acidity M(Tf) 3 L 4 M(Tf) 2 L 2 (parent ion) M(Tf)L 2 F M(Tf) 2 L more L.A. metal retains 4 ligands less L.A. metal retains 3 ligands Tandem Mass Spectrometry Imamoto, T. Chem. Comm. 1999, 1703
5 eutral BIL Ligands: Kobayashi s Catalyst "chiral Sc catalyst" 4Å MS, DCM entry cat. yield (%) endo/exo ee (%) : : : : : : n-pr : :22 75 chiral Sc catalyst = Sc(Tf) 3, ()-BIL, 1,2,6-trimethylpiperidine Kobayashi, S. JC 1994, 3758
6 eutral BIL Ligands: Catalyst Structure and TS Proposed TS conditions tetramethylpiperidine (TMP) TMP ()-BIL TMP Sc(Tf) 3 TMP Sc(Tf) 3 ()-BIL wavenumber (cm -1 ) , , 956 Fritsch, J. J. ys. Chem. 1981, 556
7 eutral BIL Ligands: Turnover in Enantioselection tal Yb Sc Conditions 0 o C, 0.5 h 0 o C, 5.5 h 0 o C, 0.5 h; 23 o C, 5 h 0 o C, 5.5 h 0 o C, 5.5 h 40 o C, 3h 0 o C, 0.5 h 0 o C, 0.5 h; 23 o C, 3 h 0 o C, 0.5 h; 23 o C, 3 h 0 o C, 0.5 h; 23 o C, 3 h -78 o C, 0.5 h Additive A acac PAA A acac Yield endo/exo 89/11 87/13 86/14 89/11 85/15 93/7 84/16 80/20 83/17 90/10 89/11 ee (%) A PAA Kobayashi, S. TL 1994, 6325
8 eutral BIL Ligands: ationalizing Turnover ' 3 Yb ' 3 site A Both oxazolidinones are in rapid equilibrium at site A CP attacks from si face or Yb ' 3 ' 3 site A site B Site A is occupied by PAA xazolidinone binds site B CP attacks from re face Sc(Tf) prefers coordination number 7 Kobayashi, S. JACS 1994, 4083
9 eutral BIL Ligands: onlinear Effects Kobayashi, S. TL 1994, 6325
10 eutral BIL Ligands: Mukaiyama Michael Addition 5 mol% Sc(Tf) mol% ligand C, DCM, 0 o C TMS 1a: = 1b: = 2a: 2 = 2b: 2 = 2 Et 2 entry 1 2 a substrate 1a 2a 1a 2a yield (%) anti:syn >50:1 >50:1 ee (%) C Et b 2a 1a 2b : a eaction run without molecular seives Katsuki, T. Tetrahedron 1997, 17015
11 eutral BIL Ligands: More Useful Transformations Cbz 10 mol% [Sc(()-BIL)](Tf) 3 24 mol% i-pr 2 Et, 4Å MS, DCM, -78 > 0 o C Cbz 92% yield, 90% ee, 94:6 endo Bn 20 mol% Sc(Tf) 20 mol% ligand A or B 4 Å MS Bn endo Bn exo Ligand A; 92:8 endo, 83% ee (,S,) Ligand B; 97:3 endo, 31% ee (,S,) A B Wipf, P. TL 2000, 8747 hta, T. JMC 2000, 603, 6
12 Anionic BIL Ligands: Asymmetric Strecker Bn 10 mol% catalyst Bn Ar C or TMSC, toluene, C Ar entry substrate yield (%) XC ee (%) 1 Ar = ; = 80 TMSC 91 2 Ar = ; = 95 C 81 3 Ar =!-aphthyl; = 45 TMSC 65 4 Ar =!-aphthyl; = 80 C 86 5 Ar = ; = 70 TMSC 45 Li Sc Sc[()-BIL) 2 ]Li Vallée, Y. Tetrahedron: Asymm. 2001, 1147
13 Anionic BIL Ligands: ther Applications TMSC 10 mol% catalyst toluene, -20 o C, 2d C quant. yield 84% ee CEt CEt 10 mol% catalyst toluene, -20 o C, 3d EtC EtC 60% yield, 37% ee Li Sc Sc[()-BIL) 2 ]Li Vallée, Y. Tetrahedron: Asymm. 2001, 1147
14 Anionic BIL Ligands: Y[(,,)-BIL 3 )]Li 3 thf 6 1: Y[(,,)-BIL 3 )] Li 3 thf 6 Shibasaki, M. ACIEE 2004, 4493
15 Pybox Ligands: azarov eaction X C, 0 o C or T 3 Å MS X Trauner, D. JACS 2004, 9544
16 Pybox Ligands: azarov chanism Asymmetric Protonation LA LA e - conrotatory LA 2 3 LA 3 2 asymmetric protonation 2 3
17 Pybox Ligands: 1,3-Dipolar Cycloaddition h 2 (Ac) 4 i-pr Sc (Tf) 3 10 mol% i-pr C 2 Ar endo C 2 4Å MS DCM, -10 o C Ar exo C 2 Ar entry Ar yield endo/exo ee (%) 1 2 a :12 55: : : F : Cl : Br :37 83 a no molecular seives used Suga,. JACS 2002, 14836
18 Pybox Ligands: 1,3-Dipolar Cycloadditions Pyruvates C 2 i-pr Sc (Tf) 3 i-pr 10 mol% h 2 (Ac) 4 DCM, -10 o C C 2 endo C 2 exo entry additive yield (%) endo/exo ee (%) 1 no 84 12: pyruvic acid 88 4: Bn no 82 18: Bn pyruvic acid 88 7:97 87 Suga,. JACS 2002, 14836
19 Pybox Ligands: Evans Group thodology 2 Sc (Tf) 3 A Et 3 Si 2 10 mol% A Et Et Si 3 6 examples 90-98% ee 7 examples 85-94% ee SbF 6 Cl Sc Cl Sc B, = C, = t Bu X TMS 2 X = S, Aryl Et X = S (10 mol% B) X = Ar (10 mol% C) X 2 Et X = S, 2 = ; 7 examples 90-94% ee, >92:8 syn:anti X = Ar, = 2 ; 6 examples 91-98% ee (Tf) 3 D X Y 2 P 10 mol% D then, DBU X Y 2 13 examples 80 - >99% ee Evans, D. A. JACS 2001, Evans, D. A. L 2002, 3375 Evans, D. A. JACS 2003, 10780
20 Pybox Ligands: Evans Group thod. Unpublished esults mol% A or D examples 92 99% ee 9 24:1 syn/anti TMS 10 mol% A or D 8 examples 93 99% ee 10 99:1 anti/syn X Y 2 3 Catalyst D Z examples 90 98% ee Sc Sc (Tf) 3 A (Tf) 3 D Unpublished results
21 Pybox Ligands: X-ay Cystallography Y 2 1 E Y Sc (Tf) 3 X (Tf) 3 X E Pybox 1-E-2 ( o ) 1-E (Å) La i-pr La* Bn Sm* Eu Yb Yb* Sc* i-pr i-pr orephedrine E[(S,S)-Pybox](Tf) 3 E = La, Sm, Eu, Yb Pybox =, Bn, i-pr, Inda, orephedrine Sc* Inda *Crystals solved by Evans group Aspinall,. C. JMC 2002, 151 Evans, D. A. JACS 2001, Evans, D. A. JACS 2003, Evans, D. A. unpublished results
22 Bipyridine Ligands: Epoxide penings by Alcohols 2 10 mol% Sc(Tf) 3, DCM, r.t. 2 entry 2 yield (%) ee (%) Et nbu allyl PMB !-aphthyl tolyl % yield, 54% ee PMB PMB 93% yield, 49% ee Schneider, C. ACIEE 2004, 5691
23 Bipyridine Ligands: Epoxide penings by Amines amine 10 mol% Sc(Tf) 3, DCM, r.t. 2 entry amine yield (%) ee (%) C p-anisidine Bn !-aphthyl tolyl % yield, 54% ee % yield, 60% ee Schneider, C. ACIEE 2004, 5691
24 Bipyridine Ligands: X-ay Structures Complete loss of enantioselectivity Free hydroxyl groups are essential Sc (Br) 2 Co Cl Cl Kobayashi, S. JACS 2004, Bolm, C. ACIEE 1990, 205
25 Bipyridine Ligands: ydroxymethylation aq. TMS mol% 10 mol% Sc(Tf) 3 2 /DME = 1/9, -20 o C 3 2 TMS = ; 80%yield, 90% ee = Et; 66% yield, 88% ee TMS TBS 53% yield, 80% ee TMS 73% yield, 92% ee TMS 90% yield, 90% ee TMS TMS ( ) n TMS TMS 84% yield, 94% ee n = 0; 50% yield, 85% ee n = 1; 68% yield, 91% ee n = 2; 62% yield; 90% ee 26% yield, 78% ee 63% yield, 60% ee TMS 59% yield, 80% ee TMS S 24% yield, 94% ee Kobayashi, S. JACS 2004, 12236
26 rganophosphate Ligands: eteroconjugate Additions 2 ()-BP P toluene, rt, >98% yield 3 Sc 10 mol% 5 mol% a- TF, 2h, rt >99% yield, 94% ee 94% yield, 99% ee Cl 98% ee 94% ee 99% ee Cl 98% ee 2 C F 99% ee 94% ee 98% ee 98% ee Inanaga, J. Tetrahedron 2002, 8321
27 rganophosphate Ligands: eteroconjugate Addition II 2 10 mol% [Sc(BP)3 ) (Tf)3 toluene, r.t. 2 Inanaga, J. Tetrahedron 2002, 8321
28 rganophosphate Ligands: etero-d.a. & Catalyst ecovery P E reuse TMS DCM, rt; then TFA 3 10 mol% 10 mol% Sc complex evaporate then dilute with Et 2 entry metal yield (%) ee (%) 1 Sc precipitate elute with TF eluent TFA Yb Er Y complex run 1 2 product yield (%) ee (%) Dy Sm La Inanaga, J. Tetrahedron 2003, 10509
29 Bisimine/Diol Ligands: Diels-Alder 10 mol% Sc(Tf) ligand, 2,6-lutidine 0 o C 89:11 endo/exo, 81% yield, 85% ee without lutidine: 45% ee 82:18, 71% yield, 34% ee without lutidine: 29% ee = ; 86:14, 71% yield, 69% ee without lutidine: 23% ee = I-Pr; 81:19, 82% yield, 9% ee 75:25, 69% yield, 3% ee = ; 90:10, 80% yield, 68% ee = I-Pr; 91:9, 86% yield, 71% ee 86:14, 65% yield, 83% ee without lutidine: 14% ee 80:20, 84% yield, 29% ee Fe 90:10, 99% yield, 91% ee without lutidine: 19% ee Fukuzawa, S. TL 2003, 3671 Fukuzawa, S. L 2002, 707
30 -xide Ligands: Michael Addition 5 mol% C () mol% Sc(Tf) 3, DCM, r.t. C () entry Acceptor Yield (%) ee (%) 1 MVK C 2 MVK i-pr MVK i-bu MVK MVK acrolein Proposed TS akajima, M. Tetrahedron 2003, 7307
31 Summary Compared to main group TM catalysis, asymmetric Sc mediated transformations is relatively new BIL and Pybox ligands are most widely used in asymmetric scandium catalysis Tertiary amines form -bonds to Sc-BIL complexes Molecular sieves often influence selectivities in unpredictable ways
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