Asymmetric Lewis Base Strategies for Heterocycle Synthesis
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1 Asymmetric Lewis Base trategies for eterocycle ynthesis Dr Andrew mith EatCEM, chool of Chemistry, University of t Andrews 1st cottish-japanese ymposium of rganic Chemistry, University of Glasgow Friday 9 th eptember 2011
2 AD group research rganocatalysis Probe new reactivity rganocatalysis TB Catalyst development -heterocyclic carbenes Isothioureas Catalytic enolate chemistry
3 AD group research rganocatalysis Probe new reactivity rganocatalysis TB Catalyst development -heterocyclic carbenes Isothioureas Catalytic enolate chemistry TB azolium enolate ammonium enolate
4 Lewis base catalysis: ammonium enolate chemistry mono-substituted in-situ generated "ketene enolates" 99% ee Wynberg et al. J. Am. Chem. oc., 1982, 104, 166 up to 99% ee Lectka et al. J. Am. Chem. oc., 2006, 128, 1810 up to 99% ee Lectka et al. J. Am. Chem. oc., 2008, 130, J. rg. Chem. 2010, 75, 969 Cl 3 C 1 F 1 1 Cl X or Y/ 3 1 ammonium enolate Fe For reviews 1. "ketene enolate" chemistry Lectka et al. Tetrahedron, 2009, 65, For ammonium enolates Gaunt and Johansson, Chem. ev., 2007, 107, di-substituted enolates from isolable ketenes Cl 1 1 C 2 C 2 up to 94% ee Fu et al. Angew. Chem. Int. Ed., 2007, 46, 977 up to 93% ee Fu et al. Angew. Chem. Int. Ed., 2008, 47, 7048 up to 96% ee Fu et al. Angew. Chem. Int. Ed., 2009, 48, 2391
5 AD group research rganocatalysis Probe new reactivity rganocatalysis Catalyst development TB -heterocyclic carbenes Isothioureas Catalytic enolate chemistry TB azolium enolate
6 Typical rganocatalytic organocatalytic C reactivity C reactivity Generation of enolate equivalents Cl 1 Cl 1 unstable 1 bench stable 1 base - Cl 1 asymmetric catalysis base azolium enolate Bode, ovis (halide) cheidt (aryloxy) azolium enolate AD / Ye azolium enolate AD Chem. Commun, 2011, 47,
7 Typical rganocatalytic organocatalytic C reactivity C reactivity Generation of enolate equivalents Cl 1 Cl 1 unstable 1 bench stable 1 base - Cl 1 asymmetric catalysis base azolium enolate Bode, ovis (halide) cheidt (aryloxy) azolium enolate AD / Ye azolium enolate AD Chem. Commun, 2011, 47,
8 Typical rganocatalytic organocatalytic C reactivity C reactivity Generation of enolate equivalents Cl 1 Cl 1 unstable 1 bench stable 1 base - Cl 1 asymmetric catalysis base azolium enolate Bode, ovis (halide) cheidt (aryloxy) azolium enolate AD / Ye azolium enolate AD Chem. Commun, 2011, 47,
9 Typical rganocatalytic organocatalytic C reactivity C reactivity Generation of enolate equivalents Cl 1 Cl 1 unstable 1 bench stable 1 base - Cl 1 asymmetric catalysis base azolium enolate Bode, ovis (halide) cheidt (aryloxy) azolium enolate AD / Ye azolium enolate AD Chem. Commun, 2011, 47,
10 Applications of C-generated enolates from ketenes Cl C 6 Cl 5 Ts up to 60% ee Eur. J. rg. Chem., 2010, 5863 up to 90% ee rg. Biomol. Chem., 2008, 6, 1108 Cl Cl up to 84% ee Adv. ynth. Cat., 2009, 351, 3001 Cl Cl Cl Ts Cl ' ' azolium enolate Generally - 2-aryl substituted arylalkyl ketenes show moderate reactivity ' Ts ' = C 2 Et ' ' = C C 2 Et C 2 Et up to 91% ee Ye et al, J. rg. Chem., 2009, 74, 7585 C Ts up to 95% ee Ye et al, Angew. Chem. Int. Ed, 2010, 49, 8412 up to 97% ee Ye et al, Angew. Chem. Int. Ed, 2009, 48, 192
11 AD group research Catalytic generation of ammonium enolates from acids rganocatalysis Probe new reactivity rganocatalysis Catalyst development LB* ne-pot domino Lewis base catalysis enolate E-X -heterocyclic carbenes Isothioureas ew Asymmetric Transformations E X X E acyl donor
12 Catalytic generation of enolates from acids: literature - omo C 2 + = or Lewis base Br Tf Mukaiyama reagent (1.5 eq) i-pr 2 Et, C 2 Cl 2, rt 82% yield >19:1 dr 92% ee aldol and lactonisation Ac LB Lewis base (LB) derived enolate aldol and lactonisation PPY 48% yield >19:1 dr J. Am. Chem. oc., 2001,123, rg. Lett., 2006, 8, J. Am. Chem. oc., 2008,130, Angew. Chem. Int. Ed., 2010, 49, 9479.
13 Catalytic generation of enolates from acids: Michael-lactonisation activating agent (1.2 eq) isothiourea C 2 i-pr 2 Et (3.5 eq), C 2 Cl 2, rt activating agent isothiourea eq yield %, dr 99: %, dr 99:1 Et Br Tf.Cl %, dr 99:1 ee 97% 43%, dr 99:1 ee 97%.Cl %, dr 99:1 ee 97% Cl %, dr 80:20 ee 70% (ent) J. Am. Chem. oc., 2011,133, 2714
14 Catalytic generation of enolates from acids: Michael-lactonisation activating agent (1.2 eq) isothiourea C 2 i-pr 2 Et (3.5 eq), C 2 Cl 2, rt activating agent isothiourea eq yield %, dr 99: %, dr 99:1 Et Br Tf.Cl %, dr 99:1 ee 97% 43%, dr 99:1 ee 97%.Cl %, dr 99:1 ee 97% Cl %, dr 80:20 ee 70% (ent) J. Am. Chem. oc., 2011,133, 2714
15 Catalytic generation of enolates from acids: Michael-lactonisation activating agent (1.2 eq) isothiourea C 2 i-pr 2 Et (3.5 eq), C 2 Cl 2, rt activating agent isothiourea eq yield %, dr 99: %, dr 99:1 Et Br Tf.Cl %, dr 99:1 ee 97% 43%, dr 99:1 ee 97%.Cl %, dr 99:1 ee 97% Cl %, dr 80:20 ee 70% (ent) J. Am. Chem. oc., 2011,133, 2714
16 Catalytic generation of enolates from acids: Michael-lactonisation activating agent (1.2 eq) isothiourea C 2 i-pr 2 Et (3.5 eq), C 2 Cl 2, rt activating agent isothiourea eq yield %, dr 99: %, dr 99:1 Et Br Tf.Cl %, dr 99:1 ee 97% 43%, dr 99:1 ee 97%.Cl %, dr 99:1 ee 97% Cl %, dr 80:20 ee 70% (ent) J. Am. Chem. oc., 2011,133, 2714
17 Catalytic generation of enolates from acids: mechanism? C 2 (i) pivaloyl chloride, Et 3 lactonisation acyl ammonium C C 2 Ct-Bu mixed anhydride C acyl ammonium Michael addition deprotonation ammonium enolate J. Am. Chem. oc., 2011,133, 2714
18 Catalytic generation of enolates from acids: Generality.Cl 2 (C 3 ) 3 CCCl (1.2 eq) tetramisole.cl (20 mol%) 1 i-pr 2 Et (3.5eq), 1 C 2 C 2 Cl 2, rt 1 hour 2 61%, dr 99:1 ee 97% 81%, dr 99:1 ee 94% 94%, dr 99:1 ee 91% 99%, dr 99:1 ee 99% J. Am. Chem. oc., 2011,133, 2714
19 Catalytic generation of enolates from acids: Generality ' C 2 (C 3 ) 3 CCCl (1.2 eq) tetramisole.cl (5-20 mol%) i-pr 2 Et (3.5 eq), C 2 Cl 2, rt 15 minutes ' 1 hour ' C 2 C 2 C 2 C 2 C 2 98%, dr 99:1 ee 94% 87%, dr 96:4 ee 95% = 4-C %, dr 96:4 ee 94% = 4-ClC %, dr 97:3 ee 84% 2 C 2 73%, dr 99:1 ee 92% C 2 62%, dr 99:1 ee 94% 79%, dr 96:4 ee 96% C 2 C 2 75%, dr 98:2 ee 95% J. Am. Chem. oc., 2011,133, 2714
20 Catalytic generation of enolates from acids: Generality ' C 2 (C 3 ) 3 CCCl (1.2 eq) tetramisole.cl (5-20 mol%) i-pr 2 Et (3.5 eq), C 2 Cl 2, rt 15 minutes ' 1 hour ' C 2 C 2 C 2 C 2 C 2 98%, dr 99:1 ee 94% 87%, dr 96:4 ee 95% = 4-C %, dr 96:4 ee 94% = 4-ClC %, dr 97:3 ee 84% 2 C 2 73%, dr 99:1 ee 92% C 2 62%, dr 99:1 ee 94% 79%, dr 96:4 ee 96% C 2 C 2 75%, dr 98:2 ee 95% J. Am. Chem. oc., 2011,133, 2714
21 Catalytic generation of enolates from acids: Generality ' C 2 (C 3 ) 3 CCCl (1.2 eq) tetramisole.cl (5-20 mol%) i-pr 2 Et (3.5 eq), C 2 Cl 2, rt 15 minutes ' 1 hour ' C 2 C 2 C 2 C 2 C 2 98%, dr 99:1 ee 94% 87%, dr 96:4 ee 95% = 4-C %, dr 96:4 ee 94% = 4-ClC %, dr 97:3 ee 84% 2 C 2 73%, dr 99:1 ee 92% C 2 62%, dr 99:1 ee 94% 79%, dr 96:4 ee 96% C 2 C 2 75%, dr 98:2 ee 95% J. Am. Chem. oc., 2011,133, 2714
22 Catalytic generation of enolates from acids: intermolecular reaction + C 2 isothiourea pivaloyl chloride (1.2 eq) i-pr 2 Et (3.5 eq), C 2 Cl 2 C 2.Cl 5 mol%, -30 C 67%, dr 95:5 ee 96% 20 mol%, rt 61%, dr 95:5 ee 82% (ent) 20 mol%, rt 68%, dr 95:5 ee 91% J. Am. Chem. oc., 2011,133, 2714
23 Catalytic generation of enolates from acids: intermolecular reaction + C 2 isothiourea pivaloyl chloride (1.2 eq) i-pr 2 Et (3.5 eq), C 2 Cl 2 C 2.Cl 5 mol%, -30 C 67%, dr 95:5 ee 96% 20 mol%, rt 61%, dr 95:5 ee 82% (ent) 20 mol%, rt 68%, dr 95:5 ee 91% J. Am. Chem. oc., 2011,133, 2714
24 Catalytic generation of enolates from acids: intermolecular reaction + C 2 isothiourea pivaloyl chloride (1.2 eq) i-pr 2 Et (3.5 eq), C 2 Cl 2 C 2.Cl 5 mol%, -30 C 67%, dr 95:5 ee 96% 20 mol%, rt 61%, dr 95:5 ee 82% (ent) 20 mol%, rt 68%, dr 95:5 ee 91% J. Am. Chem. oc., 2011,133, 2714
25 Catalytic generation of enolates from acids: Generality + C 2 (C 3 ) 3 CCCl (1.2 eq) isothiourea (10 mol%) i-pr 2 Et (3.5 eq), C 2 Cl 2, -30 C C 2 C 2 C 2 C 2 C 2 67%, dr 95:5 ee 97% 81%, dr 95:5 ee 99% 67%, dr 95:5 ee 97% 66%, dr 95:5 ee 87% Br C 2 C 2 C 2 C 2 62%, dr 90:10 ee 93% 76%, dr 95:5 ee 98% 72%, dr 96:4 ee 86% 73%, dr 93:7 ee 97% J. Am. Chem. oc., 2011,133, 2714
26 Catalytic generation of enolates from acids: Generality + C 2 (C 3 ) 3 CCCl (1.2 eq) isothiourea (10 mol%) i-pr 2 Et (3.5 eq), C 2 Cl 2, -30 C C 2 C 2 C 2 C 2 C 2 67%, dr 95:5 ee 97% 81%, dr 95:5 ee 99% 67%, dr 95:5 ee 97% 66%, dr 95:5 ee 87% Br C 2 C 2 C 2 C 2 62%, dr 90:10 ee 93% 76%, dr 95:5 ee 98% 72%, dr 96:4 ee 86% 73%, dr 93:7 ee 97% J. Am. Chem. oc., 2011,133, 2714
27 Catalytic generation of enolates from acids: Generality + C 2 (C 3 ) 3 CCCl (1.2 eq) isothiourea (10 mol%) i-pr 2 Et (3.5 eq), C 2 Cl 2, -30 C C 2 C 2 C 2 C 2 C 2 67%, dr 95:5 ee 97% 81%, dr 95:5 ee 99% 67%, dr 95:5 ee 97% 66%, dr 95:5 ee 87% Br C 2 C 2 C 2 C 2 62%, dr 90:10 ee 93% 76%, dr 95:5 ee 98% 72%, dr 96:4 ee 86% 73%, dr 93:7 ee 97% J. Am. Chem. oc., 2011,133, 2714
28 Catalytic generation of enolates from acids: Generality + 1 C 2 2 (C 3 ) 3 CCCl (1.2 eq) isothiourea (10 mol%) i-pr 2 Et (3.5 eq), C 2 Cl 2, -30 C 1 C 2 2 C 2 C 2 i-pr C 2 C 2 67%, dr 95:5 ee 97% 67%, dr 87:13 ee 99% 87%, dr 94:6 ee 97% 82%, dr 95:5 ee 99% C 2 C 2 C 2 C 2 Br 71%, dr 96:4 ee 98% 66%, dr 92:8 ee 99% 82%, dr 95:5 ee 99% 80%, dr 88:12 ee 96% J. Am. Chem. oc., 2011,133, 2714
29 Catalytic generation of enolates from acids: Generality + 1 C 2 2 (C 3 ) 3 CCCl (1.2 eq) isothiourea (10 mol%) i-pr 2 Et (3.5 eq), C 2 Cl 2, -30 C 1 C 2 2 C 2 C 2 i-pr C 2 C 2 67%, dr 95:5 ee 97% 67%, dr 87:13 ee 99% 87%, dr 94:6 ee 97% 82%, dr 95:5 ee 99% C 2 C 2 C 2 C 2 Br 71%, dr 96:4 ee 98% 66%, dr 92:8 ee 99% 82%, dr 95:5 ee 99% 80%, dr 88:12 ee 96% J. Am. Chem. oc., 2011,133, 2714
30 Catalytic generation of enolates from acids: Generality + 1 C 2 2 (C 3 ) 3 CCCl (1.2 eq) isothiourea (10 mol%) i-pr 2 Et (3.5 eq), C 2 Cl 2, -30 C 1 C 2 2 C 2 C 2 i-pr C 2 C 2 67%, dr 95:5 ee 97% 67%, dr 87:13 ee 99% 87%, dr 94:6 ee 97% 82%, dr 95:5 ee 99% C 2 C 2 C 2 C 2 Br 71%, dr 96:4 ee 98% 66%, dr 92:8 ee 99% 82%, dr 95:5 ee 99% 80%, dr 88:12 ee 96% J. Am. Chem. oc., 2011,133, 2714
31 AD group research Catalytic generation of ammonium enolates from acids Intramolecular and Intermolecular "activation" catalyst Catalyst variation LB* ne-pot domino Lewis base catalysis enolate E-X Product derivatisation and mechanistic studies E X X E Electrophile variation acyl donor
32 AD group research rganocatalysis Probe new reactivity rganocatalysis Catalyst development -heterocyclic carbenes Boc then 4 Cl (aq) + Boc Isothioureas ew asymmetric transformations
33 erendipity Et [3+2] Et Et TF, 30 mins then 0.1M Cl (aq) Et 83% yield
34 erendipity Anticipated [3+2]-cycloaddition gave consistent by-product Et [3+2] Et eaction occurs in the absence of C catalyst Et TF, 30 mins then 0.1M Cl (aq) Et 83% yield
35 Literature precedent 1 eq 1 eq "1:1 adduct" "2:1 adduct" [3,3] o examples of asymmetric reactions sigmatropic rearrangement taudinger and Miescher, elv. Chim Acta., 1919, 2, 554 afiz and Taylor., J. Chem. oc., Perkin Trans. 1, 1980, 8, 1700
36 Asymmetric etero-claisen eactions then 1 4 Cl (aq) asymmetric induction? chiral auxiliary cleaved and regenerated on work-up Boc Mg 4 C 2 Cl 2 87% Boc (,Z) rg. Lett., 2009, 11, 3858
37 Asymmetric etero-claisen eactions then 1 4 Cl (aq) asymmetric induction? chiral auxiliary cleaved and regenerated on work-up Boc Mg 4 C 2 Cl 2 87% Boc (,Z) rg. Lett., 2009, 11, 3858
38 Asymmetric etero-claisen eactions then 1 4 Cl (aq) asymmetric induction? chiral auxiliary cleaved and regenerated on work-up Boc Mg 4 C 2 Cl 2 87% Boc (,Z) rg. Lett., 2009, 11, 3858
39 Asymmetric etero-claisen eactions: Generality 2 1 Boc 1 TF, -78 C 3 hours then 4 Cl (aq) 2 + Boc 78-91% yield 85%, 87% ee 80%, 81% ee 82%, 78% ee F 88%, 90% ee 91%, 86% ee 78%, 80% ee 91%, 90% ee 84%, 87% ee rg. Lett., 2009, 11, 3858
40 Asymmetric etero-claisen eactions: Generality 2 1 Boc 1 TF, -78 C 3 hours then 4 Cl (aq) 2 + Boc 78-91% yield 85%, 87% ee 80%, 81% ee 82%, 78% ee F 88%, 90% ee 91%, 86% ee 78%, 80% ee 91%, 90% ee 84%, 87% ee rg. Lett., 2009, 11, 3858
41 Asymmetric etero-claisen eactions: Generality 2 1 Boc 1 TF, -78 C 3 hours then 4 Cl (aq) 2 + Boc 78-91% yield 85%, 87% ee 80%, 81% ee 82%, 78% ee F 88%, 90% ee 91%, 86% ee 78%, 80% ee 91%, 90% ee 84%, 87% ee rg. Lett., 2009, 11, 3858
42 Asymmetric etero-claisen eactions: mechanism? nucleophilic addition ow does chiral auxiliary impose enantioselectivity? + hydrolysis and cyclization C 2 imino acid [3,3]- sigmatropic rearrangement C 2
43 ta to F
44 ta to F
45 ta to F
46 ta to F
47 ta to F
48 ta to F
49 eaction modelling March unpublished results
50 eaction modelling March Your project is an excellent one for us to study computationally, and we will be happy to do so!...!we look forward to collaborating with you and should have the answers to your questions, soon!! Ken ouk unpublished results
51 eaction modelling March Your project is an excellent one for us to study computationally, and we will be happy to do so!...!we look forward to collaborating with you and should have the answers to your questions, soon!! Ken ouk 6 months later... unpublished results
52 eaction modelling March Your project is an excellent one for us to study computationally, and we will be happy to do so!...!we look forward to collaborating with you and should have the answers to your questions, soon!! Ken ouk 6 months later... Your [3,3]-sigmatropic rearrangement is rather more challenging than we expected. unpublished results
53 eaction modelling March Your project is an excellent one for us to study computationally, and we will be happy to do so!...!we look forward to collaborating with you and should have the answers to your questions, soon!! Ken ouk 6 months later... Your [3,3]-sigmatropic rearrangement is rather more challenging than we expected. To put a long story short, we could locate a T for the rearranged product, but its geometry does not resemble a [3,3]-sigmatropic rearrangement transition structure at all - that's something we don't understand, as yet. Colin Lam unpublished results
54 eaction modelling...we could not find the intermediate that results from the nucleophilic addition of the nitrone onto the ketene... Colin Lam unpublished results
55 eaction modelling...we could not find the intermediate that results from the nucleophilic addition of the nitrone onto the ketene... Colin Lam nucleophilic addition unpublished results
56 eaction modelling In fact, we located two 3+2 Ts (one of them has the nitrone adding across the C=C bond of ketene, the other across the C= bond of ketene), which have much lower enthalpies of activation Colin Lam Angew. Chem., accepted
57 eaction modelling In fact, we located two 3+2 Ts (one of them has the nitrone adding across the C=C bond of ketene, the other across the C= bond of ketene), which have much lower enthalpies of activation Colin Lam [3+2] C=C Et Et Angew. Chem., accepted
58 eaction modelling In fact, we located two 3+2 Ts (one of them has the nitrone adding across the C=C bond of ketene, the other across the C= bond of ketene), which have much lower enthalpies of activation Colin Lam [3+2] C=C Et Et Et [3+2] C= Et Angew. Chem., accepted
59 eaction modelling In fact, we located two 3+2 Ts (one of them has the nitrone adding across the C=C bond of ketene, the other across the C= bond of ketene), which have much lower enthalpies of activation Colin Lam [3+2] C=C Et Et Et [3+2] C= Et ring opening Et [3,3]- sigmatropic rearrangement Angew. Chem., accepted
60 eaction modelling: a pericyclic cascade 2 weeks later: I have some exciting results about the pathway of the hetero- Claisen reaction! We now find a low-energy T involving - bond cleavage.! This results in a seven-membered ring that is a formal [3,3]-sigmatropic transformation. Colin Lam Angew. Chem., accepted
61 eaction modelling: a pericyclic cascade 2 weeks later: I have some exciting results about the pathway of the hetero- Claisen reaction! We now find a low-energy T involving - bond cleavage.! This results in a seven-membered ring that is a formal [3,3]-sigmatropic transformation. Colin Lam Et [3+2] C= Et [3,3] Et tautomerisation and ring-opening + Et hydrolysis and cyclization Et C 2 Angew. Chem., accepted
62 eaction modelling: a pericyclic cascade 2 weeks later: I have some exciting results about the pathway of the hetero- Claisen reaction! We now find a low-energy T involving - bond cleavage.! This results in a seven-membered ring that is a formal [3,3]-sigmatropic transformation. Colin Lam Et [3+2] C= Et [3,3] Et asymmetric step tautomerisation and ring-opening + Et hydrolysis and cyclization Et C 2 Angew. Chem., accepted
63 eaction modelling: Asymmetric oxindole synthesis tereoselectivity a consequence of: allylic strain controls facial selectivity of nitrone addition of nitrone anti to substituent of ketene PG i face * * C- anti / inside anti to PG e face * * observed favoured Angew. Chem., accepted
64 Conclusions Cs and isothioureas are efficient Lewis base catalysts Future: further catalytic asymmetric applications of azolium and ammonium enolates TB TB azolium enolate ammonium enolate ne-pot synthesis of oxindoles from acids and the development of a catalytic variant?
65 Acknowledgements Dorine Belmessieri tuart Leckie Kenneth Ling Prof. Alex lawin (X-ray) Craig Campbell Pei-Pei Ye Edward ichmond Dr David Fox (Warwick) il Woods Carmen imal Chris Collett Caroline Joannesse Louis Morrill Eoin Gould Dr. AnnMarie ʼDonoghue (Durham) James Douglas Craig Johnston iobhan mith Prof. Douglas ilp The Carnegie Trust For the Universities of cotland
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