Oxidative Conversion of Imines into 2-Azadienes

Abstract

Several 2-azadienes were prepared by treatment of im­ines derived from diphenylmethanamine and ketones with sodium hydride in DMF under an air atmosphere.

Key words

imines - oxygen - azadienes - oxidations - heterocycles

References and Notes

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9

Analytical Data for N -(Diphenylmethylene)-1-(pyrrolidin-1-yl)ethenamine (3) IR (KBr pellet): 3450, 3059, 2972, 2877, 1715, 1628 (s), 1490, 1445, 1341, 1317, 1278, 1239, 1183, 1157, 1074, 1030, 969, 919, 872, 783, 765, 699, 639 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 7.68 (d, 2 H, ArH), 7.50-7.30 (m, 8 H, ArH), 4.94 (s, 1 H, =CHH), 4.70 (s, 1 H, =CHH), 3.51 (m,
2 H, NCH₂), 3.29 (m, 2 H, NCH₂), 1.81-1.76 (m, 4 H, NCH₂CH ₂). ^¹³C NMR (100 MHz, CDCl₃): δ = 169.1, 166.1, 151.5, 139.2, 136.2, 132.6, 131.0, 130.2, 129.5, 129.2, 129.0, 128.4, 128.3, 128.1, 126.1, 105.8 (C=CHH), 48.9 (NCH₂), 46.0 (NCH₂), 26.4 (NCH₂ CH₂), 24.2 (NCH₂ CH₂). MS (ESI-TOF): m/z = 305.2 [M + H]⁺.

11

Analytical Data for 2,2,4-Triphenyl-2,5-dihydro-oxazole (7) IR (KBr pellet): 3058, 3027, 2925, 2850,, 2603, 2359, 1817, 1726, 1662, 1631 (C=N), 1578, 1550, 1531, 1490, 1446, 1363, 1313, 1285, 1230, 1209, 1065, 1028, 963, 941, 919, 869, 799, 758, 692, 643, 561, 535 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 7.87-7.84 (m, 2 H, ArH), 7.61-7.57 (m, 4 H, ArH), 7.49-7.42 (m, 3 H, ArH), 7.36-7.31 (m, 4 H, ArH), 7.29-7.24 (m, 2 H, ArH), 5.19 (s, 2 H, CH₂). ^¹³C NMR (100 MHz, CDCl₃): δ = 166.9 (C=N), 144.2, 131.7, 131.1, 128.9, 128.3, 128.2, 127.8, 126.4, 113.9 (CPh₂), 74.2 (CH₂). MS (ESI-TOF): m/z = 300.2 [M + H]⁺.

15

Typical Experimental Procedure for the Synthesis of 2-Azadienes: Benzhydrylidene-[1-(4-methoxyphenyl)-vinyl]amine (6d)
A solution of imine 4d (200 mg, 0.634 mmol, 1 equiv) in anhyd DMF (6.3 mL) was placed under a dry air atmosphere. A suspension of NaH (84 mg of a 60% dispersion in mineral oil, 2.1 mmol, 3.3 equiv) in anhyd DMF (2.1 mL) was added, and the reaction mixture was stirred at r.t. for 2 d. Cold H₂O was then added, the aqueous layer was extracted three times with CH₂Cl₂ and the combined organic layers dried over MgSO₄. After filtration and concentration under vacuum, the residue obtained was purified by column chromatography (silica gel, 96:4 cyclohexane-EtOAc containing 4% Et₃N), to give 2-azadiene 6d as an off-white solid (129 mg, 65%); mp 137-139 ˚C. IR (KBr pellet): 3052, 3021, 2965, 2929, 2837, 2046, 1960, 1901, 1820, 1660, 1622, 1604, 1569, 1509, 1443, 1414, 1312, 1291, 1249, 1178, 1150, 1121, 1094, 1073, 1028, 998, 966, 938, 834, 812, 788, 770, 746, 700, 670, 647, 615, 579, 553 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 7.79-7.75 (m, 2 H, ArH), 7.46-7.44 (m, 3 H, ArH), 7.42-7.38 (m, 2 H, ArH), 7.34-7.27 (m, 3 H, ArH), 7.13-7.09 (m, 2 H, ArH), 6.86-6.82 (m, 2 H, ArH), 4.70 (s, 1 H, CHH), 4.03 (s, 1 H, CHH), 3.80 (s, 3 H, OCH₃). ^¹³C NMR (100 MHz, CDCl₃): δ = 167.5 (C=N), 159.6, 154.4, 139.4, 136.2, 130.9, 130.8, 130.2, 129.4, 128.8, 128.6, 128.5, 128.4, 128.3, 128.3, 127.9, 126.9, 113.7, 94.0 (CH₂), 55.4 (OCH₃). HRMS (ESI-TOF): m/z calcd for C₂₂H₂₀NO [M + H]⁺: 314.1545; found: 314.1547.