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3 Schade, W.; Watanabe, T.; Bressel, B.; Reissig, H.-U. unpublished results.
4a
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Hosomi T.
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4b For fragmentations of 4H-5,6-dihydro-1,2-oxazines by N-alkylation followed by base treatment see: Lidor R.
Shatzmiller S.
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5 For a recent application of the Murahashi protocol see: Dugovic B.
Wiesenganger T.
Fisera L.
Hametner C.
Prónayová N.
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6
Conversion of syn
-1 into syn
-2.
1,2-Oxazine syn-1 (350 mg, 1.15 mmol) was dissolved in MeCN (7 mL). The solution was treated with methyl triflate (1.26 mL, 1.26 mmol) at 0 °C. The reaction mixture was stirred at r.t. for 6 h until the starting material disappeared. The reaction mixture was then cooled to 0 °C and treated with Et3N (0.47 mL, 3.95 mmol) and stirred for 1 h. Then, H2O (5 mL) was added to the mixture and extracted three times with CH2Cl2, dried (Na2SO4) and concentrated to yield 283 mg. The crude product was purified by column chromatography (silica gel, hexane-EtOAc, 2:1) to yield 323 mg (87%) of syn-2 as colourless crystals. Analytical data for (4S,4′S)-4-(benzylmethylamino)-4-(2′,2′-dimethyl-[1′,3′]dioxolan-4′-yl)-3-methoxybut-2-enal: mp 42-44 °C. [α]D
22 +118.2 (c 0.77, CHCl3). 1H NMR (500 MHz, CDCl3): δ = 1.38, 1.41 (2 s, 3 H each, Me), 2.39 (s, 3 H, Me), 3.51 (mc, 1 H, 5′-HB), 3.52 (d, J = 13.5 Hz, 1 H, NCH
2
Ph), 3.66 (s, 3 H, OMe), 3.90 (d, J = 13.5 Hz, 1 H, NCH
2
Ph), 3.97 (dd, J = 6.5, 8.6 Hz, 1 H, 5′-HA), 4.06 (d, J = 8.6 Hz, 1 H, 4-H), 4.65 (dt, J = 6.5, 8.6 Hz, 1 H, 4′-H), 5.50 (d, J = 7.5 Hz, 1 H, 2-H), 7.20-7.34 (m, 5 H, Ph), 9.47 (d, J = 7.5 Hz, 1 H, CHO) ppm. 13C NMR (126 MHz, CDCl3): δ = 25.3, 26.6 (2 q, Me), 38.9 (q, NMe), 55.4 (q, OMe), 58.9 (t, NCH2Ph), 63.8 (d, C-4), 66.9 (t, C-5′), 73.6 (d, C-4′), 107.4 (d, C-2), 109.7 (s, C-2′), 127.0, 128.2, 128.6, 138.5 (3 d, s, Ph), 174.4 (s, C-3), 189.6 (s, CHO) ppm. IR (KBr): ν = 3085-3030 (=C-H), 2985-2795 (C-H), 1660 (C=O), 1605 (C=C) cm-1. MS (EI, 80 eV, 100 °C): m/z (%) = 319 (4) [M]+, 218 (14) [M - C5H9O2]+, 91 (100) [CH2Ph]+. Anal. Calcd for C18H25NO4 (319.4): C, 67.69; H, 7.89; N, 4.39. Found: C, 67.38; H, 7.65; N, 4.36. HRMS (EI, 80 eV, 100 °C): m/z calcd for C18H25NO4: 319.17834; found: 319.17744.
7 For related reaction conditions see: Sosnicki JG.
Monatsh. Chem.
2000,
131:
475
8 Conversion of syn-2 into syn-11: Aldehyde syn-2 (250 mg, 0.78 mmol) and hydrazine hydrate (0.40 mL, 9.50 mmol) were dissolved in dry EtOH (6 mL). TFA (58 µL, 0.78 mmol) was added and the mixture was stirred under reflux for 2 h. EtOH was removed in vacuo and H2O (5 mL) was added to the residue which was extracted three times with CH2Cl2, dried (Na2SO4) and concentrated to yield 243 mg (quant.) of syn-11 as colourless crystals. Analytical data for (1S,4′S)-benzyl-[(2′,2′-dimethyl-[1′,3′]dioxolan-4′-yl)-(2H-pyrazol-3-yl)methyl]methylamine: mp 68-70 °C. [α]D
22 -30.7 (c 1.72, CHCl3). 1H NMR (500 MHz, CDCl3): δ = 1.40, 1.42 (2 s, 3 H each, Me), 2.23 (s, 3 H, NMe), 3.47 (d, J = 13.3 Hz, 1 H, NCH
2
Ph), 3.58 (t, J = 7.7 Hz, 1 H, 5′-HB), 3.83 (d, J = 13.3 Hz, 1 H, NCH
2
Ph), 3.97 (mc, 1 H, 5′-HA), 3.90 (d, J = 6.5 Hz, 1 H, 1-H), 4.69 (td, J = 6.5, 7.7 Hz, 1 H, 4′-H), 6.17 (d, J = 2.2 Hz, 1 H, 4′′-H), 7.21-7.38 (m, 5 H, Ph), 7.50 (d, J = 2.2 Hz, 1 H, 5′′-H) ppm. 13C NMR (126 MHz, CDCl3): δ = 25.4, 26.6 (2 q, Me), 38.5 (q, NMe), 59.2 (t, NCH2Ph), 61.9 (d, C-1), 67.6 (t, C-5′), 75.5 (d, C-4′), 105.1 (d, C-4′′), 109.7 (s, C-2′), 127.0, 128.2, 129.2, 138.9 (3 d, s, Ph), 174.4 (s, C-3′′), 135.6 (d, C-6′′) ppm. IR (KBr): ν = 3260 (NH), 3085-3030 (=C-H), 2985-2800 (C-H), 1675 (C=C). cm-1. MS (EI, 80 eV, 110 °C): m/z (%) = 301 (0.4) [M]+, 286 (1) [M - CH3]+, 234 (0.3) [M - C3H3N3]+, 210 (0.3) [M - C7H7]+, 200 (91) [M - C5H9O2]+, 91 (100) [CH2Ph]+. HRMS (EI, 80 eV, 110 °C): m/z calcd for C17H23N3O2: 301.17902; found: 301.17854.
9 Similar reactions of 2-aminobenzimidazole with carbohydrate derivatives: Bari A.
Feist H.
Michalik D.
Michalik M.
Peseke K.
Synthesis
2004,
2863
10 For synthesis of amino acids with pyrazolyl substituents see: De Luca L.
Giacomelli G.
Porcheddu A.
Spanedda AM.
Falorni M.
Synthesis
2000,
1295