Enantioselective Diels–Alder Reaction Induced by Chiral Supramolecular Lewis Acid Catalysts Based on CN···B and PO···B Coordination Bonds

Abstract

Chiral supramolecular boron Lewis acid catalysts were prepared from chiral 3-phosphoryl-1,1′-bi-2-naphthols, (2-cyanophenyl)boronic acids, and tris(pentafluorophenyl)borane, bound through CN···B and PO···B coordination bonds. In particular, the coordinated tris(pentafluorophenyl)boranes increase the Lewis acidity of the active center in the manner of a Lewis acid assisted Lewis acid catalyst system. A possible cavity in these catalysts was highly suitable for several Diels–Alder probe reactions of acroleins with cyclic or acyclic dienes, which gave the corresponding adducts in good to high yields and high enantio­selectivities.

Key words

supramolecular catalysts - asymmetric catalysis - Diels–Alder reactions - Lewis acids - dienes - aldehydes

• References and Notes

• 1 Lehn J.-M. Science 1985; 227: 849

For recent reviews on supramolecular catalysis, see:
• 2a Ma L, Abney C, Lin W. Chem. Soc. Rev. 2009; 38: 1248
• 2b Corma A, García H, Llabrés i Xamena FX. Chem. Rev. 2010; 110: 4606
• 2c Meeuwissen J, Reek JN. H. Nat. Chem. 2010; 2: 615
• 2d Raynal M, Ballester P, Vidal-Ferran A, van Leeuwen PW. N. M. Chem. Soc. Rev. 2014; 43: 1660
• 2e Raynal M, Ballester P, Vidal-Ferran A, van Leeuwen PW. N. M. Chem. Soc. Rev. 2014; 43: 1734
• 2f Brown CJ, Toste FD, Bergman RG, Raymond KN. Chem. Rev. 2015; 115: 3012

For reviews on acid–base combination chemistry, see:
• 3a Kanai M, Kato N, Ichikawa E, Shibasaki M. Synlett 2005; 1491
• 3b Ishihara K, Sakakura A, Hatano M. Synlett 2007; 686
• 3c Ishihara K. Proc. Jpn. Acad., Ser. B 2009; 85: 290
• 3d Shibasaki M, Kanai M, Matsunaga S, Kumagai N. Acc. Chem. Res. 2009; 42: 1117

For anomalous endo-selective Diels–Alder reactions of α-substituted acroleins, see:
• 4a Hatano M, Mizuno T, Izumiseki A, Usami R, Asai T, Akakura M, Ishihara K. Angew. Chem. Int. Ed. 2011; 50: 12189
• 4b Hatano M, Ishihara K. Chem. Commun. 2012; 48: 4273

For anomalous exo-selective Diels–Alder reactions of α-nonsubstituted acroleins, see:
• 5a Maruoka K, Imoto H, Yamamoto H. J. Am. Chem. Soc. 1994; 116: 12115
• 5b Kündig EP, Saudan CM, Alezra V, Viton F, Bernardinelli G. Angew. Chem. Int. Ed. 2001; 40: 4481
• 5c Kano T, Tanaka Y, Maruoka K. Org. Lett. 2006; 8: 2687
• 5d Hayashi Y, Samanta S, Gotoh H, Ishikawa H. Angew. Chem. Int. Ed. 2008; 47: 6634
• 5e Sibi MP, Nie X, Shackleford JP, Stanley LM, Bouret F. Synlett 2008; 2655

For reviews on the Diels–Alder reaction, see:
• 6a Kagan HB, Riant O. Chem. Rev. 1992; 92: 1007
• 6b Du H, Ding K In Handbook of Cyclization Reactions . Ma S. Wiley-VCH; Weinheim: 2010. Chap. 1, 1
• 6c Ishihara K, Sakakura A In Science of Synthesis, Stereoselective Synthesis 3: Stereoselective Pericyclic Reactions, Cross Coupling, C–H and C–X Activation. Evans PA. Thieme; Stuttgart: 2011. Chap. 3.2, 67

As a strong Lewis base moiety, a phosphoryl group (P=O) is highly attractive in asymmetric catalysis. Shibasaki pioneered the development of catalytic asymmetric cyanosilylation and a Strecker-type reaction in which Me₃SiCN is effectively activated by coordination of a phosphoryl group; see:
• 7a Hamashima Y, Sawada D, Kanai M, Shibasaki M. J. Am. Chem. Soc. 1999; 121: 2641
• 7b Takamura M, Hamashima Y, Usuda H, Kanai M, Shibasaki M. Angew. Chem. Int. Ed. 2000; 39: 1650
• 7c Takamura M, Funabashi K, Kanai M, Shibasaki M. J. Am. Chem. Soc. 2000; 122: 6327
• 7d Hamashima Y, Kanai M, Shibasaki M. J. Am. Chem. Soc. 2000; 122: 7412
• 7e Funabashi K, Ratni H, Kanai M, Shibasaki M. J. Am. Chem. Soc. 2001; 123: 10784

We have used the coordinating P=O moiety in some catalytic processes; see:
• 8a Hatano M, Miyamoto T, Ishihara K. Adv. Synth. Catal. 2005; 347: 1561
• 8b Hatano M, Miyamoto T, Ishihara K. Synlett 2006; 1762
• 8c Hatano M, Miyamoto T, Ishihara K. J. Org. Chem. 2006; 71: 6474
• 8d Hatano M, Takagi E, Ishihara K. Org. Lett. 2007; 9: 4527
• 8e Hatano M, Miyamoto T, Ishihara K. Org. Lett. 2007; 9: 4535
• 8f Hatano M, Ishihara K. Chem. Rec. 2008; 8: 143
• 8g Hatano M, Ikeno T, Matsumura T, Torii S, Ishihara K. Adv. Synth. Catal. 2008; 350: 1776
• 8h Hatano M, Mizuno T, Ishihara K. Chem. Commun. 2010; 46: 5443
• 8i Hatano M, Mizuno T, Ishihara K. Synlett 2010; 2024
• 8j Hatano M, Mizuno T, Ishihara K. Tetrahedron 2011; 67: 4417
• 8k Hatano M, Gouzu R, Mizuno T, Abe H, Yamada T, Ishihara K. Catal. Sci. Technol. 2011; 1: 1149
• 8l Hatano M, Goto Y, Izumiseki A, Akakura M, Ishihara K. J. Am. Chem. Soc. 2015; 137: 13472
• 8m Hatano M, Ishihara H, Goto Y, Ishihara K. Synlett DOI: 10.1055/s-0035-1560369

Yamamoto developed the pioneering concept of combined acid catalysis. For reviews, see:
• 9a Ishibashi H, Ishihara K, Yamamoto H. Chem. Rec. 2002; 2: 177
• 9b Yamamoto H, Futatsugi K. Angew. Chem. Int. Ed. 2005; 44: 1924
• 9c Yamamoto H, Futatsugi K In Acid Catalysis in Modern Organic Synthesis . Vol. 1. Yamamoto H, Ishihara K. Wiley-VCH; Weinheim: 2008: 1
• 10 Focante F, Mercandelli P, Sironi A, Resconi L. Coord. Chem. Rev. 2006; 250: 170
• 11 Dichloromethane was essential for inducing good reactivity and enantioselectivity in this catalytic system. Toluene, as another nonpolar solvent, was also effective in promoting the reaction, although the enantioselectivity decreased significantly (~60% ee). In contrast, the use of coordinative polar solvent such as Et₂O or THF resulted in almost no catalytic activity.
• 12 In the ESI-MS (positive mode) analysis of catalyst 2c, a peak for [2a + H₂O + H]⁺ was observed. See the Supporting Information.
• 13 When we compared the catalytic activity of 10, which has a phosphoryl moiety, to that of 11, which has a 3,5-[3,5-(F₃C)₂C₆H₃]₂C₆H₃ moiety, 10 showed a higher yield. This tendency should be correlated to the reaction using 2c or 7a in the presence of a competing 5 mol% of B(C₆F₅)₃ (see footnotes a in Figures 2 and 3).
• 14 The position of the CN group influenced the enantioselectivity. The use of (3-cyanophenyl)boronic acid or (4-cyanophenyl)boronic acid in place of (2-cyanophenyl)boronic acid in catalyst 10 gave exo-(2S)-5a in ~80% yield with 9% and 11% ee, respectively.
• 15 Because cyclopentadiene 3 is too reactive to permit the evaluation of meaningful differences in catalytic activity in 14a–d, we used cyclohexa-1,3-diene (12).
• 16 ¹H and ¹³C NMR (CD₂Cl₂) analyses of 14 and 4a at room temperature did not show clear interactions, because a somewhat broad chart was observed.

The C(=O)H···O hydrogen-bonding interaction is well known, see:
• 17a Corey EJ, Lee TW. Chem. Commun. 2001; 1321
• 17b Corey EJ, Shibata T, Lee TW. J. Am. Chem. Soc. 2002; 124: 3808
• 17c Ryu DH, Lee TW, Corey EJ. J. Am. Chem. Soc. 2002; 124: 9992

Energy profiles and bond distances in boron Lewis acid complexes with coordinating substrates such as aldehydes, ketones, or pyridines have been studied; see:
• 18a Reetz MT, Huellmann M, Massa W, Berger S, Rademacher P, Heymanns P. J. Am. Chem. Soc. 1986; 108: 2405
• 18b LePage TJ, Wiberg KB. J. Am. Chem. Soc. 1998; 110: 6642
• 18c Wu D, Jia D, Liu L, Zhang L, Guo J. J. Phys. Chem. A 2010; 114: 11738
• 19 The previous supramolecular catalyst 1 was calculated to be in a similar C ₁-symmetric syn-conformation for two bulky tris(pentafluorophenyl)boranes.⁴
• 20 Other possible transition states are discussed in the Supporting Information, which also gives the results for other supramolecular catalysts.
• 21 Diels–Alder Reaction of Methacrolein (4a) with Cyclopenta-1,3-diene (3); Typical Procedure A solution of (R)-3-(5,5-dimethyl-2-oxido-1,3,2-dioxaphosphorinan-2-yl)-5,5′,6,6′,7,7′,8,8′-H₈-BINOL (22.1 mg, 0.050 mmol) and [2-cyano-5-(trifluoromethyl)phenyl]boronic acid (10.7 mg, 0.050 mmol) in CH₂Cl₂ (1 mL), THF (0.3 mL), and H₂O (9 μL, 0.5 mmol) was stirred at r.t. for 12 h in a Pyrex Schlenk tube under N₂. Volatile compounds were removed under reduced pressure, and powdered 4 Å MS (250 mg, used as received from a commercial source) was added. The resulting white solid was heated at 100 °C (bath temperature) and <5 torr for 2 h. The resulting substance was cooled to r.t. under N₂ and tris(pentafluorophenyl)borane (51.2 mg, 0.10 mmol) and freshly distilled CH₂Cl₂ (2 mL) were added under argon in a glove box. The pale-brown mixture was stirred at r.t. for 1 h, then cooled to –78 °C, and methacrolein 4a (95% purity, 43.4 μL, 0.50 mmol) was added. Freshly distilled cyclopenta-1,3-diene (3; 210 μL, 2.5 mmol) was then added over 15 min at –78 °C, and the mixture was stirred at –78 °C for 3 h. To quench the reaction, Et₃N (0.5 mL) was poured into the reaction mixture at –78 °C. The product mixture was directly purified by column chromatography [silica gel, pentane–Et₂O (100:1 to 8:1)]. Solvents were removed on a rotary evaporator at 15 °C and <200 torr to give 5a; yield: 60.8 mg (89%). ¹H NMR (400 MHz, CDCl₃): δ = 0.76 (d, J = 12.0 Hz, 1 H), 1.01 (s, 3 H), 1.39 (m, 2 H), 2.25 (dd, J = 12.0, 3.9 Hz, 1 H), 2.82 (br s, 1 H), 2.90 (br s, 1 H), 6.11 (dd, J = 6.0, 3.0 Hz, 1 H), 6.30 (dd, J = 6.0, 3.0 Hz, 1 H), 9.69 (s, 1 H). ¹³C NMR (100 MHz, CDCl₃): δ = 20.1, 34.6, 43.2, 47.6, 48.5, 53.9, 133.1, 139.6, 205.9. HRMS (EI): m/z [M]⁺ calcd for C₉H₁₂O: 136.0888; found: 136.0893. The endo/exo ratio of 5a was determined by ¹H NMR (CDCl₃) analysis: δ = 9.40 [s, 1 H, CHO (endo-5a)], 9.69 [s, 1 H, CHO (exo-5a)] (see ref. 4a). The enantioselectivity and absolute stereochemistry of 5a were determined by GC analysis according to the reported method (see ref. 4a).