Diastereoselectivity in Diels–Alder Cycloadditions of Erythrose Benzylidene-acetal 1,3-Butadienes with Maleimides

Abstract

Maleimides were combined with d-erythrose benzylidene-acetal 1,3-butadienes to study the facial selectivity of the Diels–Alder cycloadditions. The selectivity was found to range from moderate to good. The reaction diastereotopicity can be reversed with the temperature. Simultaneous coordination of the diene, having a free hydroxy group, and maleimide to a chiral bimetallic Lewis acid catalyst (LACASA–DA reaction) occurs with complete diastereocontrol to give a single adduct, using an extra chiral inductor either (R)- or (S)-BINOL.

Key words

maleimides - d-erythrose benzylidene-acetal 1,3-butadiene - Diels–Alder cycloaddition - selectivity

• References and Notes

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• 4 Analytical Data for Some Typical Compounds Compound 5a: [α]_D ²⁰ –92.4 (c 0.45, EtOAc). IR (Nujol): ν_max = 3441, 1690, 1457 cm^–1. ¹H NMR (400 MHz, CDCl₃): δ = 2.22–2.32 (1 H, m, H-7), 2.75–2.90 (2 H, m, H-7 and H-3a), 3.35 (1 H, tdd, J = 11.6, 5.8, 3.5 Hz, H-4), 3.60 (1 H, td, J = 11.2, 0.8 Hz, H-6′), 3.83 (1 H, br s, H-5′), 3.96 (1 H, dt, J = 15.0, 7.5 Hz, H-7a), 4.28 (1 H, t, J = 9.0 Hz, H-4′), 4.36 (1 H, ddd, J = 11.0, 5.1, 2.3 Hz, H-6′), 5.52 (1 H, s, H-2′), 6.02–6.13 (1 H, m, H-6), 6.17 (1 H, dt, J = 9.4, 3.2 Hz, H-5), 7.11–7.18 (2 H, m, Ph), 7.32–7.54 (8 H, m, Ph) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 24.27 (C-7), 39.23 (C-3a), 40.41 (C-4), 41.43 (C-7a), 66.44 (C-5′), 71.89 (C-6′), 80.46 (C-4′), 101.10 (C-2′), 126.06 (C-H, Ph), 126.42 (C-H, Ph), 128.13 (C-6), 128.23 (C-H, Ph), 128.83 (C-H, Ph), 128.94 (C-H, Ph), 129.12 (C-H, Ph), 130.14 (C-5), 131.56 (Cq, Ph), 137.49 (Cq, Ph), 178.53 (C=O), 179.81 (C=O) ppm. ESI-HRMS: m/z calcd for C₂₄H₂₃NNaO₅: 428.1467; found: 428.1468. Compound 6a: [α]_D ²⁰ –118.2 (c 0.45, EtOAc). IR (Nujol): ν_max = 3442, 1690, 1411, 1072 cm^–1. ¹H NMR (400 MHz, CDCl₃): δ = 2.17–2.31 (1 H, m, H-7), 2.64–2.76 (1 H, m, H-4), 2.83 (1 H, ddd, J = 15.4, 7.0, 1.6 Hz, H-7), 3.27 (1 H, td, J = 8.0, 1.6 Hz, H-3a), 3.65 (1 H, t, J = 10.4 Hz, H-6′), 3.81 (2 H, dd, J = 9.0, 5.5 Hz, H-7a and H-5′), 4.27 (1 H, dd, J = 10.8, 5.1 Hz, H-6′), 4.44 (1 H, t, J = 9.6 Hz, H-4′), 5.64 (1 H, s, H-2′), 6.02 (1 H, ddt, J = 12.9, 6.5, 3.3 Hz, H-6), 6.41 (1 H, dt, J = 9.4, 3.5 Hz, H-5), 7.19–7.22 (2 H, m, Ph), 7.35–7.40 (4 H, m, Ph), 7.43–7.47 (2 H, m, Ph), 7.50–7.52 (2 H, m, Ph) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 25.00 (C-7), 39.50 (C-3a), 40.09 (C-7a), 41.32 (C-4), 68.05 (C-5′), 71.24 (C-6′), 79.47 (C-4′), 100.79 (C-2′), 126.08 (C-H, Ph), 126.54 (C-H, Ph), 127.54 (C-6), 128.19 (C-H, Ph), 128.60 (C-H, Ph), 128.85 (C-H, Ph), 129.08 (Cq, Ph), 130.62 (C-5), 131.89 (Cq, Ph), 137.70 (Cq, Ph), 177.21 (C=O), 179.05 (C=O) ppm. ESI-HRMS: m/z calcd for C₂₄H₂₃NNaO₅: 428.1473; found: 428.1468
• 5 Compound 5a: H-5: 6.40 (dt, J = 3.2, 9.2 Hz); H-2′: 5.64 (s). Compound 5b: H-5: 6.38 (dt, J = 3.6, 9.2 Hz); H-2′: 5.66 (s). Compound 5c: H-5: 6.34 (dt, J = 3.6, 9.2 Hz); H-2′: 5.67 (s). Compound 5d: H-5: 6.28 (dt, J = 3.6, 9.2 Hz); H-2′: 5.67 (s). Compound 6a: H-5: 6.17 (dt, J = 3.2, 9.2 Hz); H-2′: 5.51 (s). Compound 6b: H-5: 6.12 (dt, J = 3.6, 9.6 Hz); H-2′: 5.54 (s). Compound 6c: H-5: 6.16 (br s),* H-2′: 5.42 (s). Compound 6d: H-5: 6.08 (br t, 2.0 Hz),* H-2′: 5.42 (s). * These signals coincide with H-6
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• 8 Preparation of Solution A A solution of diene 1 (0.05 g, 0.22 mmol) in dry toluene (1.0 mL) was added to a solution of Me₂Zn (1.2 M) in toluene (178 μL, 0.22 mmol) at 0 °C and stirred for 5 min. Preparation of Solution B A solution of (S)-BINOL (0.061 g; 0.22 mmol) in dry toluene (1.0 mL) was added to a solution of MeMgBr (1.4 M in toluene–THF; 152 μL, 0.22 mmol) at 0 °C and stirred for 5 min. Solution A was added to solution B, the mixture diluted with dry toluene (1.8 mL) and stirred for 5 min. This mixture was refrigerated at –78 °C and a solution of maleimide (3; 0.02 g, 0.22 mmol) in dry toluene (1.5 mL) was then added. The temperature was allowed to rise gradually to r.t. The reaction was complete after 17 d and was quenched with an aq sat. solution of NaHCO₃ (1 mL), filtered through a pad of Celite, and the Celite was washed with EtOAc (4 × 10 mL). The filtrates were combined and concentrated under reduced pressure to give a yellow oil that was submitted to ‘dry-flash’ chromatography using a mixture of PE (40–60)–Et₂O. (S)-BINOL was recovered (0.035 g, 57%) from PE–Et₂O (1:1), and the product was eluted with PE–Et₂O (1:2.3; 0.024 g, 33%)