Vanadium-Catalyzed Oxidation of tert-Butyl N-Hydroxycarbamate to tert-Butyl Nitrosoformate and Its Diels–Alder Reaction with Simple and 
Functionalized Dienes

Yujiro Hoshino; Kenzo Suzuki; Kiyoshi Honda

doi:10.1055/s-0032-1317148

Synlett, Table of Contents

Synlett 2012; 23(16): 2375-2380
DOI: 10.1055/s-0032-1317148

letter

Vanadium-Catalyzed Oxidation of tert-Butyl N-Hydroxycarbamate to tert-Butyl Nitrosoformate and Its Diels–Alder Reaction with Simple and Functionalized Dienes

Yujiro Hoshino*

Graduate School of Environment and Information Sciences, Yokohama National University, 79-7 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan, Fax: +81(45)3394434 Email: yhoshino@ynu.ac.jp

,

Kenzo Suzuki

Graduate School of Environment and Information Sciences, Yokohama National University, 79-7 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan, Fax: +81(45)3394434 Email: yhoshino@ynu.ac.jp

,

Kiyoshi Honda

Graduate School of Environment and Information Sciences, Yokohama National University, 79-7 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan, Fax: +81(45)3394434 Email: yhoshino@ynu.ac.jp

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Abstract

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Abstract

A general and efficient vanadium-catalyzed oxidation of tert-butyl N-hydroxycarbamate to tert-butyl nitrosoformate using alkyl hydroperoxides as terminal oxidants has been developed. The intermediate nitroso compound was trapped by in situ Diels–Alder reaction with simple and functionalized dienes, providing general access to a variety of functionalized 3,6-dihydro-2H-1,2-oxazines.

Key words

nitroso Diels–Alder reaction - catalysis - oxidation - functionalized dienes - vanadium catalyst

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References

References and Notes

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10 Typical Procedure for the Vanadium-Catalyzed Oxidation of tert-Butyl N-Hydroxycarbamate and in situ Diels–Alder Reaction with (E,E)-Hexa-2,4-dien-1-ol (1a) To a solution of tert-butyl N-hydroxycarbamate (0.564 g, 4.1 mmol), (E,E)-hexa-2,4-dien-1-ol (0.246 mL, 2.1 mmol), and VO(Oi-Pr)₃ (5.0 μL, 0.021 mmol) in CH₂Cl₂ (4.2 mL) was added 80% CHP (0.39 mL, 2.1 mmol) at ambient temper-ature. After stirring for 1 h, H₂O (2 mL) was added to the mixture. A sat. Na₂SO₃ solution was slowly added to the resulting mixture. After stirring for 1 h, the reaction mixture was transferred to a separatory funnel, and the aqueous phase was extracted with CH₂Cl₂ (5 × 5 mL). The combined organic phases were washed with brine, dried over anhyd Na₂SO₄, filtered, and concentrated under reduced pressure. Flash chromatographic purification (eluent: hexane–Et₂O = 3:1 to 2:1) of the residue provided 2a and 3a (0.480 g, 99%) as a mixture of two regioisomers. The mixture was separated by column chromatography on silica gel (hexane–EtOAc = 9:1) to give pure 2a and 3a. The structure was deduced from two-dimensional NMR spectroscopy (HMBC and HMQC).¹³ (3R*,6R*)-N-tert-Butoxycarbonyl-6-hydroxymethyl-3-methyl-3,6-dihydro-2H-1,2-oxazine (2a) ¹³ TLC: R_f = 0.26 (hexane–EtOAc = 1:1). IR (neat): 3407, 2978, 1698, 1369, 1169, 1119, 1066 cm^–1. ¹H NMR (300 MHz, CDCl₃): δ = 1.32 (d, J = 9.0 Hz, 3 H), 1.47–1.49 (m, 1 H), 1.50 (s, 9 H), 3.67 (dd, J = 6.6, 12.6 Hz, 1 H), 3.77 (dd, J = 3.0, 12.3 Hz, 1 H), 4.41–4.46 (m, 1 H), 4.64–4.68 (m, 1 H), 5.69 (dt, J = 10.2, 1.8 Hz, 1 H), 5.92 (ddd, J = 10.2, 4.5, 2.4 Hz, 1 H). (3S*,6S*)-N-tert-Butoxycarbonyl-3-hydroxymethyl-6-methyl-3,6-dihydro-2H-1,2-oxazine (3a) ¹³ TLC: R_f = 0.38 (hexane–EtOAc = 1:1). IR (neat): 3445, 2979, 1704, 1369, 1166, 1113, 1088 cm^–1. ¹H NMR (300 MHz, CDCl₃): δ = 1.26 (d, J = 6.6 Hz, 3 H), 1.50 (s, 9 H), 1.65 (s, 1 H), 3.72–3.77 (m, 2 H), 4.47–4.52 (m, 1 H), 4.65–4.68 (m, 1 H), 5.78 (ddd, J = 10.2, 4.2, 2.1 Hz, 1 H), 5.85 (td, J = 1.5, 10.2 Hz, 1 H).

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12 Zeng W, Ballard TE, Melander C. Tetrahedron Lett. 2006; 47: 5923
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14 N-tert-Butoxycarbonyl-2-oxa-3-azabicyclo[2.2.1]hept-5-ene (2b) ¹⁶ TLC: R_f = 0.33 (hexane–Et₂O = 1:2). IR (neat): 2978, 1739, 1702, 1165 cm^–1. ¹H NMR (300 MHz, CDCl₃): δ = 1.47 (s, 9 H), 1.73 (d, J = 8.6 Hz, 1 H), 1.99 (td, J = 2.4, 8.6 Hz, 1 H), 4.98 (br s, 1 H), 5.21 (br s, 1 H), 6.40–6.42 (m, 2 H). N-tert-Butoxycarbonyl-2-oxa-3-azabicyclo[2.2.2]oct-5-ene (2c) ¹⁶ TLC: R_f = 0.51 (hexane–EtOAc = 3:1). IR (neat): 2976, 2936, 1736, 1695, 1158, 1073 cm^–1. ¹H NMR (300 MHz, CDCl₃): δ = 1.27–1.54 (m, 2 H), 1.47 (s, 9 H), 2.06–2.23 (m, 2 H), 4.73–4.75 (m, 2 H), 6.50–6.59 (m, 2 H). (3S*,6R*)-N-tert-Butoxycarbonyl-3,6-diphenyl-3,6-dihydro-2H-1,2-oxazine (2d) TLC: R_f = 0.39 (hexane–EtOAc = 5:1). IR (neat): 2978, 1700, 1392, 1368, 1166, 1094, 699 cm^–1. ¹H NMR (300 MHz, CDCl₃): δ = 1.49 (s, 9 H), 5.56 (br s, 1 H), 5.59 (br s, 1 H), 6.09 (d, J = 10.5 Hz, 1 H), 6.16 (ddd, J = 10.8, 4.5, 2.1 Hz, 1 H), 7.26–7.53 (m, 10 H). ¹³C NMR (75 MHz, CDCl₃): δ = 28.4, 79.0, 81.7, 126.4, 127.7, 127.8, 128.2, 128.5, 128.7, 129.0, 137.2, 139.2, 154.2. N-tert-Butoxycarbonyl-1,8-dimethyl-15-oxa-16-azatetracyclo[6.6.2.0^2,7.0^9,14]hexadec-2,4,6,9,11,13-hexaene (2e) ⁴ Mp 106–109 °C. TLC: R_f = 0.33 (hexane–EtOAc = 5:1). IR (KBr): 2981, 1707, 1460, 1288, 1159, 748 cm^–1. ¹H NMR (300 MHz, CDCl₃): δ = 1.21 (s, 9 H), 2.23 (s, 3 H), 2.56 (s, 3 H), 7.23–7.27 (m, 4 H), 7.34–7.38 (m, 2 H), 7.43–7.46 (m, 2 H). A 1:1 Mixture of N-tert-Butoxycarbonyl-4-methyl-3,6-dihydro-2H-1,2-oxazine (2f) and N-tert-Butoxycarbonyl-5-methyl-3,6-dihydro-2H-1,2-oxazine (3f) ¹³ TLC: R_f = 0.66 (hexane–EtOAc = 6:1). IR (neat): 2978, 2933, 1705, 1683, 1392, 1368, 1243, 1166, 1102 cm^–1. ¹H NMR (300 MHz, CDCl₃): δ = 1.50 [s, 9 H, 3 × CH₃ (3f)], 1.51 (s, 9 H, 3 × CH₃), 1.67 [br s, 3 H, CH₃-5 (3f)], 1.74 (br s, 3 H, CH₃-4), 3.94 (br s, 2 H, H-3), 4.02–4.05 [m, 2 H, H-3 (3f)], 4.26 [br s, 2 H, H-6 (3f)], 4.35–4.38 (m, 2 H, H-6), 5.51–5.55 [m, 1 H + 1 H, overlapped with H-5 and H-4 (3f)]. A 1:1 Mixture of N-tert-Butoxycarbonyl-4-(4-methyl-pent-3-enyl)-3,6-dihydro-2H-1,2-oxazine (2g) and N-tert-Butoxycarbonyl-5-(4-methylpent-3-enyl)-3,6-dihydro-2H-1,2-oxazine (3g) TLC: R_f = 0.64 (hexane–EtOAc = 6:1). IR (neat): 2976, 2929, 1727, 1703, 1366, 1162, 1092 cm^–1. ¹H NMR (300 MHz, CDCl₃): δ = 1.50 (s, 9 H + 9 H), 1.60 (s, 3 H + 3 H), 1.69 (s, 3 H + 3 H), 1.98–2.12 (m, 4 H + 4 H), 3.97 (br s, 2 H), 4.05 (br s, 2 H), 4.29 (br s, 2 H), 4.39 (br s, 2 H), 5.05–5.12 (m, 1 H + 1 H), 5.52 (br s, 1 H + 1 H). ¹³C NMR (75 MHz, CDCl₃): δ = 17.7, 25.6, 25.8, 25.9, 28.3, 32.7, 33.9, 44.9, 47.6, 68.0, 70.4, 81.4, 116.0, 117.6, 123.3, 132.3, 134.2, 135.5, 155.0. N-tert-Butoxycarbonyl-6-carboxy-3-methyl-3,6-dihydro-2H-1,2-oxazine (2h) TLC: R_f = 0.68 (MeOH). IR (KBr): 2977, 1748, 1686, 1370, 1156, 1121 cm^–1. ¹H NMR (300 MHz, CDCl₃): δ = 1.36 (d, J = 6.6 Hz, 3 H), 1.51 (s, 9 H), 4.43 (br s, 1 H), 5.16 (s, 1 H), 5.93–6.03 (m, 2 H). ¹³C NMR (75 MHz, CDCl₃): δ = 17.9, 28.3, 50.8, 75.9, 82.8, 121.9, 130.6 154.5, 170.5. N-tert-Butoxycarbonyl-6-ethoxycarbonyl-3-methyl-3,6-dihydro-2H-1,2-oxazine (2i) ¹⁷ TLC: R_f = 0.63 (hexane–EtOAc = 6:1). IR (neat): 2980, 1760, 1738, 1705, 1369, 1312, 1196, 1169, 1076, 1032, 716 cm^–1. ¹H NMR (300 MHz, CDCl₃): δ = 1.32 (t, J = 7.1 Hz, 3 H), 1.36 (d, J = 6.8 Hz, 3 H), 1.50 (s, 9 H), 4.27 (q, J = 7.2 Hz, 2 H), 4.46–4.48 (m, 1 H), 5.14–5.16 (m, 1 H), 5.90 (td, J = 1.3, 10.4 Hz, 1 H), 5.98 (ddd, J = 10.2, 4.3, 2.5 Hz, 1 H). N-tert-Butoxycarbonyl-6-methoxycarbonyl-3-hydroxy-methyl-3,6-dihydro-2H-1,2-oxazine (2j) TLC: R_f = 0.24 (hexane–EtOAc = 1:1). IR (neat): 3446, 2979, 1737, 1707, 1475, 1251, 1157, 1071, 1024 cm^–1. ¹H NMR (300 MHz, CDCl₃): δ = 1.50 (s, 9 H), 3.73–3.88 (m, 2 H), 3.82 (s, 3 H), 4.51–4.55 (m, 1 H), 5.52 (s, 1 H), 6.00 (ddd, J = 10.2, 3.9, 2.1 Hz, 1 H), 6.06 (td, J = 1.5, 10.5 Hz, 1 H). ¹³C NMR (75 MHz, CDCl₃): δ = 28.2, 52.8, 56.6, 63.0, 74.3, 82.8, 124.3, 125.7, 155, 167.6. N-tert-Butoxycarbonyl-3-[(triisopropylsilyloxy)methyl]-6-methoxycarbonyl-3,6-dihydro-2H-1,2-oxazine (2k) TLC: R_f = 0.77 (hexane–EtOAc = 1:1). IR (neat): 2943, 2867, 1766, 1740, 1710, 1367, 1109, 881, 681 cm^–1. ¹H NMR (300 MHz, CDCl₃): δ = 1.02–1.13 (m, 3 H), 1.06 (d, J = 3.9 Hz, 18 H), 1.49 (s, 9 H), 3.80 (s, 3 H), 3.82 (dd, J = 9.6, 7.8 Hz, 1 H), 3.97 (dd, J = 9.3, 6.6 Hz, 1 H), 4.48–4.49 (m, 1 H), 5.16–5.19 (m, 1 H), 6.02 (td, J = 1.8, 10.2 Hz, 1 H), 6.16 (ddd, J = 10.2, 4.2, 2.7 Hz, 1 H). ¹³C NMR (75 MHz, CDCl₃): δ = 11.9, 17.9, 28.3, 52.6, 55.8, 64.1, 74.7, 82.1, 123.2, 127.3, 154.1, 167.9. N-tert-Butoxycarbonyl-6-(N′-methoxy-N′-methyl-carbamoyl)-3-methyl-3,6-dihydro-2H-1,2-oxazine (2l) TLC: R_f = 0.25 (hexane–Et₂O = 1:2). IR (neat): 3592, 2979, 2934, 1681, 1369, 1172, 992, 714 cm^–1. ¹H NMR (300 MHz, CDCl₃): δ = 1.37 (d, J = 6.6 Hz, 3 H), 1.51 (s, 9 H), 3.24 (br s, 3 H), 3.84 (s, 3 H), 4.45–4.47 (m, 1 H), 5.53 (br s, 1 H), 5.86 (br s, 1 H), 5.99 (ddd, J = 10.5, 5.1, 2.4 Hz, 1 H). ¹³C NMR (75 MHz, CDCl₃): δ = 17.9, 28.4, 32.4, 50.7, 62.2, 74.3, 81.7, 122.3, 130.0, 154.2. N-tert-Butoxycarbonyl-3-[(tert-butyldimethylsilyloxy)-methyl]-6-methoxycarbonyl-3,6-dihydro-2H-1,2-oxazine (2m) TLC: R_f = 0.66 (hexane–EtOAc = 1:1). IR (neat): 2954, 2930, 2857, 1766, 1741, 1710, 1253, 1106, 834, 777 cm^–1. ¹H NMR (300 MHz, CDCl₃): δ = 0.07 (s, 6 H), 0.89 (s, 9 H), 1.49 (s, 9 H), 3.73 (dd, J = 9.9, 7.2 Hz, 1 H), 3.81 (s, 3 H), 3.88 (dd, J = 10.2, 7.2 Hz, 1 H), 4.46 (br s, 1 H), 5.16–5.19 (m, 1 H), 6.01 (td, J = 1.5, 10.2 Hz, 1 H), 6.11 (ddd, J = 10.5, 4.2, 2.7 Hz, 1 H). ¹³C NMR (75 MHz, CDCl₃): δ = –5.3, –5.3, 18.2, 25.6, 25.8, 28.3, 52.6, 55.8, 63.6, 74.7, 82.1, 123.5, 127.0, 154.2, 167.8.
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