One-Pot Synthesis of 3-Substituted 3,4-Dihydro-1,2,3-benzotriazine Derivatives Based on the Reaction of o-Bromobenzyl Azides with Butyllithium

Article abstract of DOI:10.1002/hlca.201500234

An efficient one-pot procedure for the preparation of 3-substituted 3,4-dihydro-1,2,3-benzotriazines 2, 3, and 4 from o-bromobenzyl azides 1 is described. The reaction of these azides with BuLi in THF at -78 generates o-lithiobenzyl azides via the Br/Li e

Full text of DOI:10.1002/hlca.201500234

Helv. Chim. Acta 2016, 99, 33 – 36
33
FULL PAPER
One-Pot Synthesis of 3-Substituted 3,4-Dihydro-1,2,3-benzotriazine Derivatives Based on
the Reaction of o-Bromobenzyl Azides with Butyllithium
by Kazuhiro Kobayashi* and Yuuki Chikazawa
Division of Applied Chemistry, Department of Chemistry and Biotechnology, Graduate School of Engineering, Tottori
University, 4-101 Koyama-minami, Tottori 680 – 8552, Japan
(phone/fax: þ 81-857-315263; e-mail: kkoba@chem.tottori-u.ac.jp)
An efficient one-pot procedure for the preparation of 3-substituted 3,4-dihydro-1,2,3-benzotriazines 2, 3, and 4 from o-
bromobenzyl azides 1 is described. The reaction of these azides with BuLi in THF at À 788 generates o-lithiobenzyl azides via the
Br/Li exchange. These lithium compounds immediately undergo intramolecular cyclization to give the corresponding (dihydro-
1,2,3-benzotriazinyl)lithium intermediates, which are trapped with a variety of acylating agents or BnBr at N(3) exclusively to
provide the desired products in moderate to good yields.
Introduction. – In recent years, much attention has been
paid to compounds with the 1,2,3-benzotriazine structure
because of their biological activities [1]. However, to date,
there have been only a few efficient procedures for the
practical synthesis of 3-substituted 3,4-dihydro-1,2,3-ben-
zotriazines [2 – 4]. For example, Igeta et al. have reported
the formation of 3,4-dihydro-1,2,3-benzotriazine deriva-
tives by the reaction of 1,2,3-benzotriazine 3-oxides with
Scheme 1
PhMgBr [2]. Recently, the synthesis of 3-acyl-4-alkyl-3,4- whereas the yield of the product using di-tert-butyl
dihydro-1,2,3-benzotriazines by cyclization of acylated o- dicarbonate is somewhat lower than those using the other
triazenylbenzylamines was described by Reingruber et al. acylating agents, as can be seen from Entry 5. The
[4]. As part of our study on the preparation of benzene- substituents at the 4-position of the products give little
fused heterocyclic compounds utilizing o-functionalized influence on the yields. The 3-acyalted 3,4-dihydro-1,2,3-
benzyl azides [5], we now wish to report the treatment of o- benzotriazine structure of 2 was determined on the basis of
1
bromobenzyl azides 1 with BuLi followed by addition of their spectral data (IR, H- and 13C-NMR, and MS) and
acylating agents affording 3-acyl-3,4-dihydro-1,2,3-benzo- elemental analyses. Especially, the IR and 1H-NMR
triazines 2 and 3 in a one-pot procedure. We also spectral data of 1-(4-phenyl-1,2,3-benzotriazin-3(4H)-yl)-
demonstrate that the use of a haloalkane, such as BnBr, ethanone (2l) are identical to those reported previously by
makes possible to provide 3-benzyl-3,4-dihydro-1,2,3- Golik and Taub [3]. These authors synthesized this
benzotriazines 4. This is a rare example of the addition compound by the reaction of diazotized N-acetyl-2-amino-
of organometals to the azide terminal nitrogen, though benzhydrylamines with Na2CO3.
the formation of 3-alkyl-3,4-dihydro-1,2,3-benzotriazin-
Pentanedioyl chloride proved to be usable in the
4-imines by the reaction of 2-azidobenzonitrile with present reaction. Thus, the reaction of 1a with BuLi under
Grignard reagents has been described [6].
the conditions as described above was followed by treat-
ment with pentanedioyl dichloride (2 :2 :1 molar ratio) to
Results and Discussion. – Our one-pot synthesis of 2 result in the formation of bis(3,4-dihydro-1,2,3-benzotria-
from 1 was conducted according to the procedure illus- zin-3-yl)pentane-1,5-dione (3) in a reasonable yield as
trated in Scheme 1. Thus, compounds 1, readily prepared outlined in Scheme 2.
from the respective o-bromobenzyl bromides, were treated
Introduction of an alkyl group at the 3-position of 3,4-
with BuLi in THF at À 788. Acylating agents were then dihydro-1,2,3-benzotriazine was subsequently carried out,
added at the same temperature to result in the exclusive as illustrated in Scheme 3. After the treatment of 1 with
isolation of the 3-acylated products 2 after aqueous workup BuLi as described above for the preparation of 2, BnBr was
and the subsequent purification by column chromatogra- added. However, benzylation proceeded slowly even at
phy on SiO2. The results are compiled in the Table, which room temperature, and the corresponding desired products
indicate the present reaction is general for a range of 4 were isolated in low-to-moderate yields after column
acylating agents and that the yields are generally fair, chromatography on SiO2 from rather complicated mixtures
DOI: 10.1002/hlca.201500234
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Helv. Chim. Acta 2016, 99, 33 – 36
Table. Preparation of 3-Acyl-3,4-dihydro-1,2,3-benzotriazines 2
Entry
1
R2COX or (R2CO)2O
2
Yield [%]a)
1
2
3
4
5
6
7
8
9
1a (R1 ¼ H)
BzCl
2a
2b
2c
2d
2e
2f
2g
2h
2i
83
57
72
62
41
74
71
64
57
56
62
54
1a
2-ClÀC6H4COCl
EtOCOCl
Ac2O
(t-BuOCO)2O
BzCl
2-MeÀC6H4COCl
4-ClÀC6H4COCl
EtOCOCl
Ac2O
EtOCOCl
Ac2O
1a
1a
1a
1b (R1 ¼ Me)
1b
1b
1b
1b
10
11
12
2j
2k
2l [3]
1c (R1 ¼ Ph)
1c
a) Yields of isolated products.
Scheme 2
In conclusion, we have succeeded in the development
of a convenient one-pot method for the preparation of 3-
substituted 3,4-dihydro-1,2,3-benzotriazines from o-bro-
mobenzyl azides using BuLi and acylating agents or BnBr.
The present method may be of use in organic synthesis due
to the ready availability of the starting materials, and may
provide interesting pharmacophores. Further work on the
preparation of related heterocycles by utilizing o-bromo-
benzyl azides is currently under way in our laboratory.
Scheme 3
of products. The structure of 4 was elucidated by NOESY
analyses of 4b, which revealed an interaction between the
4-Me H-atoms and one of the benzyl H-atoms.
Experimental Part
A probable pathway from 1 to 2 – 4 is illustrated in
Scheme 4. Thus, o-lithiobenzyl azides 5 are generated by
the Br/Li exchange between 1 and BuLi. These undergo
immediate cyclization by intramolecular attack on the
terminal N of the azide moiety to provide tautomeric
benzotriazinide anion intermediates 6 and 7, which are
trapped exclusively at the N(3) (i.e. 7) by adding acylating
agents or BnBr to give rise to 3-acylated or benzylated
products 2 – 4. This regioselectivity possibly arises from the
difference of the nucleophilic reactivity between the N(3)
and N(1).
General. All org. solvents used in this study were dried over
appropriate drying agents and distilled prior to use. TLC: Merck silica
gel 60 PF254. Column chromatography (CC): Wako Gel C-200E. M.p.:
Laboratory Devices MEL-TEMP II melting-point apparatus; uncor-
rected. IR Spectra: PerkinÀElmer Spectrum65 FT-IR spectrophotom-
1
eter; n˜ in cmÀ1. H- and 13C-NMR Spectra: JEOL ECP500 FT NMR
spectrometer (at 500 and 125 MHz, resp.); in CDCl3; d in ppm rel. to
Me4Si as internal standard, J in Hz. HR-MS: Thermo Scientific Exactive
(DART or ESI, pos.) or JEOL JMS-T100GCV (EI, TOF; 70 eV)
spectrometer; in m/z. Elemental analyses: Elementar Vario EL II
instrument.
1-Bromo-2-(1-bromoethyl)benzene [7], 1-bromo-2-[chloro(phe-
nyl)methyl]benzene [8], and 1-azidomethyl-2-bromobenzene (1a) [9]
were prepared according to the appropriate reported procedures. BuLi
was supplied by Asia Lithium Corporation. All other chemicals used in
this study were commercially available.
Scheme 4
1-(1-Azidoethyl)-2-bromobenzene (1b) [10]. Representative Pro-
cedure. A soln. of 1-bromo-2-(1-bromoethyl)benzene (2.4 g, 9.1 mmol)
in DMSO (20 ml) containing NaN3 (0.65 g, 10 mmol) was stirred
overnight at r.t. H2O (50 ml) was added and the mixture was extracted
with AcOEt (3 Â 25 ml). The combined extracts were washed with
H2O (3 Â 25 ml) and brine (20 ml), dried (Na2SO4), and concentrated
by evaporation. The residue was purified by CC (SiO2) to afford 1b
(1.8 g, 86%). Colorless liquid. Rf (CH2Cl2/hexane 1:40) 0.36. IR (neat):
1
2094. H-NMR: 1.51 (d, J ¼ 6.9, 3 H); 5.11 (q, J ¼ 6.9, 1 H); 7.17 (td,
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Helv. Chim. Acta 2016, 99, 33 – 36
35
J ¼ 7.4, 1.7, 1 H); 7.36 (ddd, J ¼ 8.0, 7.4, 1.7, 1 H); 7.47 (dd, J ¼ 7.4, 1.7,
1 H); 7.57 (dd, J ¼ 8.0, 1.7, 1 H).
1 H); 7.29 (d, J ¼ 8.0, 1 H); 7.34 (ddd, J ¼ 8.0, 7.4, 1.1, 1 H); 7.46 (td, J ¼
7.4, 1.1, 1 H); 7.51 (td, J ¼ 7.4, 1.1, 1 H); 7.72 (dd, J ¼ 7.4, 1.1, 1 H).
13C-NMR: 19.47; 22.43; 44.60; 125.03; 125.37; 125.68; 127.56; 127.62;
129.02; 129.81; 130.25; 132.45; 134.80; 135.43; 136.18; 173.06. HR-ESI-
MS: 266.1288 ([M þ H]þ, C16H16N3Oþ; calc. 266.1293). Anal. calc. for
C16H15N3O (265.31): C 72.43, H 5.70, N 15.84; found: C 72.30, H 5.82, N
15.90.
1-[Azido(phenyl)methyl]-2-bromobenzene (1c). Colorless oil. Rf
(CH2Cl2/hexane 1:5) 0.36. IR (neat): 2100. 1H-NMR: 6.16 (s, 1 H); 7.19
(ddd, J ¼ 8.0, 7.4, 1.7, 1 H); 7.30 – 7.38 (m, 6 H); 7.49 (dd, J ¼ 8.0, 1.7,
1 H); 7.57 (dd, J ¼ 8.0, 1.1, 1 H). Anal. calc. for C13H10BrN3 (288.14): C
54.19, H 3.50, N 14.58; found: C 54.07, H 3.68, N 14.28.
1,2,3-Benzotriazin-3(4H)-yl(phenyl)methanone (2a). Representa-
tive Procedure. To a stirred soln. of 1a (0.21 g, 1.0 mmol) in THF at
À 788 was added BuLi (1.6m in hexane, 1.0 mmol) dropwise. After
5 min, a soln. of BzCl (0.14 g, 1.0 mmol) in THF (2 ml) was added
slowly. H2O (20 ml) was then added, and the mixture was warmed to r.t.
and extracted with AcOEt (3 Â 10 ml). The combined extracts were
washed with aq. 10% NaOH, H2O, and brine (10 ml each), then dried
(Na2SO4), and finally concentrated by evaporation. The residual solid
was recrystallized from hexane/CH2Cl2 to give 2a (0.20 g, 83%). Pale-
(4-Chlorophenyl)(4-methyl-1,2,3-benzotriazin-3(4H)-yl)metha-
none (2h). White solid. M.p. 72 – 748 (hexane/CH2Cl2). IR (KBr): 1673.
1H-NMR: 1.39 (d, J ¼ 6.9, 3 H); 5.62 (q, J ¼ 6.9, 1 H); 7.18 (dd, J ¼ 7.4,
1.7, 1 H); 7.42 (d, J ¼ 8.6, 2 H); 7.48 – 7.54 (m, 2 H); 7.68 (d, J ¼ 8.6, 2 H);
7.77 (dd, J ¼ 7.4, 1.1, 1 H). 13C-NMR: 21.93; 45.26; 125.44; 125.56;
127.38; 128.19; 129.06; 131.78; 131.83; 132.56; 136.38; 137.93; 170.29.
HR-ESI-MS: 286.0742 ([M þ H]þ, C15H13ClN3Oþ; calc. 286.0747).
Anal. calc. for C15H12ClN3O (285.73): C 63.05, H 4.23, N 14.71; found: C
62.97, H 4.18, N 14.65.
Ethyl 4-Methyl-1,2,3-benzotriazine-3(4H)-carboxylate (2i). Yellow
oil. Rf (AcOEt/hexane 1:7) 0.27. IR (neat): 1723. 1H-NMR: 1.31 (d, J ¼
6.3, 3 H); 1.43 (t, J ¼ 7.4, 3 H); 4.41 – 4.52 (m, 2 H); 5.34 (q, J ¼ 6.3,
1 H); 7.09 (dd, J ¼ 6.9, 1.7, 1 H); 7.42 – 7.48 (m, 2 H); 7.73 (d, J ¼ 6.9, 2.2,
1 H). 13C-NMR: 14.41; 22.25; 46.34; 63.55; 125.23; 125.28; 127.29;
129.00; 132.13; 136.11; 153.85. HR-ESI-MS: 220.1079 ([M þ H]þ,
C11H14N3Oþ2 ; calc. 220.1086). Anal. calc. for C11H13N3O2 (219.24): C
60.26, H 5.98, N 19.17; found: C 60.26, H 6.04, N 19.06.
1
yellow solid. M.p. 103 – 1058. IR (KBr): 1672. H-NMR: 4.92 (s, 2 H);
7.18 (dd, J ¼ 6.3, 2.3, 1 H); 7.44 – 7.51 (m, 4 H); 7.54 (t, J ¼ 7.4, 1 H); 7.74
(dd, J ¼ 6.9, 2.3, 1 H); 7.78 (dd, J ¼ 6.9, 1.7, 2 H). 13C-NMR: 38.88;
119.26; 126.28; 127.79; 127.91; 129.22; 130.37; 131.69; 132.24; 133.03;
136.29; 171.94. HR-ESI-MS: 238.0973 ([M þ H]þ, C14H12N3Oþ; calc.
238.0980). Anal. calc. for C14H11N3O (237.26): C 70.87, H 4.67, N 17.71;
found: C 70.81, H 4.70, N 17.64.
1,2,3-Benzotriazin-3(4H)-yl(2-chlorophenyl)methanone (2b).
White solid. M.p. 101 – 1028 (hexane/CH2Cl2). IR (KBr): 1687.
1H-NMR: 5.00 (s, 2 H); 7.17 (d, J ¼ 7.4, 1 H); 7.34 – 7.50 (m, 6 H); 7.70
(d, J ¼ 7.4, 1 H). 13C-NMR: 38.59; 118.34; 126.39; 126.62; 128.39;
128.84; 129.31; 129.48; 130.95; 131.33; 132.47; 134.67; 135.76; 170.69.
HR-ESI-MS: 272.0585 ([M þ H]þ, C14H11ClN3Oþ; calc. 272.0590).
Anal. calc. for C14H10ClN3O (271.70): C 61.89, H 3.71, N 15.47; found: C
61.66, H 3.88, N 15.43.
1-(4-Methyl-1,2,3-benzotriazin-3(4H)-yl)ethanone (2j). Beige sol-
1
id. M.p. 52 – 538 (hexane/CH2Cl2). IR (KBr): 1700. H-NMR: 1.28 (d,
J ¼ 6.9, 3 H); 2.58 (s, 3 H); 5.57 (q, J ¼ 6.9, 1 H); 7.10 (dd, J ¼ 6.3, 1.7,
1 H); 7.43 – 7.48 (m, 2 H); 7.73 (dd, J ¼ 6.9, 2.3, 1 H). 13C-NMR: 21.86;
22.66; 44.05; 124.98; 125.64; 127.31; 128.88; 132.21; 136.15; 173.19. HR-
ESI-MS: 190.0975 ([M þ H]þ, C10H12N3Oþ; calc. 190.0980). Anal. calc.
for C10H11N3O (189.21): C 63.48, H 5.86, N 22.21; found: C 63.28, H
5.88, N 22.08.
Ethyl 4-Phenyl-1,2,3-benzotriazine-3(4H)-carboxylate (2k). White
solid. M.p. 75 – 778 (hexane/CH2Cl2). IR (KBr): 1725. 1H-NMR: 1.37 (t,
J ¼ 6.9, 3 H); 4.32 – 4.46 (m, 2 H); 6.30 (s, 1 H); 7.09 (dd, J ¼ 6.9, 1.7,
1 H); 7.18 (d, J ¼ 6.9, 2 H); 7.24 – 7.29 (m, 3 H); 7.41 – 7.47 (m, 2 H); 7.80
(dd, J ¼ 7.4, 1.7, 1 H). 13C-NMR: 14.32; 53.73; 63.73; 122.83; 126.59;
126.68; 127.79; 128.34; 128.84; 129.17; 132.41; 135.38; 141.34; 153.86.
HR-MS (DART): 282.1233 ([M þ H]þ, C16H16N3Oþ2 ; calc. 282.1242).
Anal. calc. for C16H15N3O2 (281.31): C 68.31, H 5.37, N 14.94; found: C
68.21, H 5.41, N 14.76.
Ethyl 1,2,3-Benzotriazine-3(4H)-carboxylate (2c). Pale-yellow sol-
1
id. M.p. 93 – 958 (hexane/CH2Cl2). IR (KBr): 1718. H-NMR: 1.43 (t,
J ¼ 7.4, 3 H); 4.46 (q, J ¼ 7.4, 2 H); 4.76 (s, 2 H); 7.07 (dd, J ¼ 4.6, 3.4,
1 H); 7.41 – 7.44 (m, 2 H); 7.70 (dd, J ¼ 4.6, 4.0, 1 H). 13C-NMR: 14.43;
39.85; 63.66; 119.04; 125.90; 127.81; 129.18; 132.03; 136.04; 154.29. HR-
ESI-MS: 206.0923 ([M þ H]þ, C10H12N3Oþ2 ; calc. 206.0929). Anal. calc.
for C10H11N3O2 (205.21): C 58.53, H 5.40, N 20.48; found: C 58.29, H
5.43, N 20.27.
1-(1,2,3-Benzotriazin-3(4H)-yl)ethanone (2d). White solid. M.p.
1
119 – 1218 (hexane/CH2Cl2). IR (KBr): 1693. H-NMR: 2.59 (s, 3 H);
4.80 (s, 2 H); 7.09 (dd, J ¼ 6.3, 2.9, 1 H); 7.41 – 7.45 (m, 2 H); 7,70 (dd,
J ¼ 6.3, 2.9, 1 H). 13C-NMR: 21.58; 38.18; 118.63; 126.30; 127.98; 129.17;
132.11; 135.81; 173.71. HR-ESI-MS: 176.0816 ([M þ H]þ, C9H10N3Oþ;
calc. 176.0824). Anal. calc. for C9H9N3O (175.19): C 61.70, H 5.18, N
23.99; found: C 61.70, H 5.21, N 23.81.
1-(4-Phenyl-1,2,3-benzotriazin-3(4H)-yl)ethanone (2l). White sol-
id. M.p. 95 – 968 (hexane/CH2Cl2) ([3] 96 – 978). The spectral (IR and
1H-NMR) data for this product were identical to those reported in [3].
1,5-Bis(1,2,3-benzotriazin-3(4H)-yl)pentane-1,5-dione (3). Beige
solid. M.p. 147 – 1498 (hexane/CHCl3). IR (KBr): 1697. 1H-NMR:
2.24 (quint, J ¼ 7.4, 2 H); 3.13 (t, J ¼ 7.4, 4 H); 4.79 (s, 4 H); 7.09 (dd, J ¼
8.0, 1.7, 2 H); 7.41 – 7.43 (m, 4 H); 7.67 (dd, J ¼ 8.6, 2.3, 2 H). 13C-NMR:
19.61; 32.86; 38.27; 118.79; 126.31; 127.97; 129.14; 132.08; 135.95;
175.45. HR-ESI-MS: 385.1385 ([M þ Na]þ, C19H18N6NaO2þ ; calc.
385.1389). Anal. calc. for C19H18N6O2 (362.39): C 62.97, H 5.01, N
23.19; found: C 62.83, H 5.04, N 22.96.
3-Benzyl-3,4-dihydro-1,2,3-benzotriazine (4a). Yellow solid. M.p.
80 – 828 (hexane/CH2Cl2). IR (KBr): 1425, 1098. 1H-NMR: 4.22 (s,
2 H); 4.86 (s, 2 H); 6.82 (d, J ¼ 7.4, 1 H); 7.23 (td, J ¼ 7.4, 1.1, 2 H); 7.30 –
7.39 (m, 5 H); 7.46 (dd, J ¼ 8.0, 1.1, 1 H). 13C-NMR: 42.91; 60.41; 117.61;
125.35; 125.44; 128.12; 128.46; 128.78; 128.83; 129.50; 134.97; 126.91.
HR-EI-MS: 223.1106 (Mþ, C14H13Nþ3 ; calc. 223.1109). Anal. calc. for
C14H13N3 (223.27): C 75.31, H 5.87, N 18.82; found: C 75.02, H 5.84, N
18.67.
tert-Butyl 1,2,3-Benzotriazine-3(4H)-carboxylate (2e). Pale-yellow
1
solid. M.p. 83 – 848 (hexane/CH2Cl2). IR (KBr): 1714: H-NMR: 1.62
(s, 9 H); 4.71 (s, 2 H); 7.06 (dd, J ¼ 4.6, 4.0, 1 H); 7.40 (dd, J ¼ 7.4, 4.0,
1 H); 7.42 (dd, J ¼ 7.4, 3.4, 1 H); 7.67 (dd, J ¼ 5.1, 3.4, 1 H). 13C-NMR:
28.14; 39.68; 83.66; 119.38; 125.87; 127.49; 129.09; 131.74; 136.30;
152.85. HR-ESI-MS: 234.1237 ([M þ H]þ, C12H16N3O2þ ; calc.
234.1242). Anal. calc. for C12H15N3O2 (233.27): C 61.79, H 6.48, N
18.01; found: C 61.70, H 6.62, N 17.98.
(4-Methyl-1,2,3-benzotriazin-3(4H)-yl)(phenyl)methanone (2f).
Beige solid. M.p. 95 – 978 (hexane/CH2Cl2). IR (KBr): 1679, 1602.
1H-NMR: 1.40 (d, J ¼ 6.3, 3 H); 5.64 (q, J ¼ 6.3, 1 H); 7.17 (d, J ¼ 6.9,
1 H); 7.44 (t, J ¼ 7.4, 2 H); 7.47 – 7.53 (m, 3 H); 7.72 (d, J ¼ 7.4, 2 H); 7.76
(dd, J ¼ 7.4, 1.1, 1 H). 13C-NMR: 21.90; 45.15; 125.53 (2 overlapped Cs);
127.24; 127.85; 128.96; 130.29; 131.56; 132.38; 133.45; 136.43; 171.42.
HR-ESI-MS: 252.1132 ([M þ H]þ, C15H14N3Oþ; calc. 252.1137). Anal.
calc. for C15H13N3O (251.28): C 71.70, H 5.21, N 16.72; found: C 71.44, H
5.32, N 16.51.
3-Benzyl-3,4-dihydro-4-methyl-1,2,3-benzotriazine (4b). Represen-
tative Procedure. Compound 1b (0.48 g, 2.1 mmol) in THF (12 ml) at
À 788 was treated with BuLi (1.6m in hexane; 2.1 mmol) as described
for the preparation of 2a. After BnBr (0.36 g, 2.1 mmol) was added, the
temp. was gradually warmed to r.t. and stirring was continued overnight
at the same temp. The resulting mixture was worked up as described for
the preparation of 2a and the crude product was purified by CC (SiO2)
(4-Methyl-1,2,3-benzotriazin-3(4H)-yl)(2-methylphenyl)metha-
none (2g). Pale-yellow solid. M.p. 78 – 818 (hexane/CH2Cl2). IR (KBr):
1680. 1H-NMR: 1.43 (d, J ¼ 6.9, 3 H); 2.33 (s, 3 H); 5.74 (q, J ¼ 6.9,
1 H); 7.18 (dd, J ¼ 7.4, 1.1, 1 H); 7.23 (t, J ¼ 7.4, 1 H); 7.24 (d, J ¼ 7.4,
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Helv. Chim. Acta 2016, 99, 33 – 36
to afford 4b (0.22 g, 44%). Yellow oil. Rf (AcOEt/hexane 1:4) 0.38. IR
(neat): 1446, 1102. 1H-NMR: 1.28 (d, J ¼ 6.3, 3 H); 4.45 (q, J ¼ 6.3,
1 H); 4.80 (d, J ¼ 14.9, 1 H); 5.23 (d, J ¼ 14.9, 1 H); 6.83 (d, J ¼ 7.4,
1 H); 7.25 (t, J ¼ 7.4, 1 H); 7.31 – 7.38 (m, 6 H); 7.48 (d, J ¼ 8.0, 1 H).
13C-NMR: 20.13; 48.16; 57.30; 122.77; 124.83; 128.02; 128.08; 128.51;
128.79; 128.81; 129.52; 135.83; 136.78. HR-ESI-MS: 238.1340 ([M þ
H]þ, C15H16N3þ ; calc. 238.1344). Anal. calc. for C15H15N3 (237.30): C
75.92, H 6.37, N 17.71; found: C 76.00, H 6.41, N 17.51.
3-Benzyl-3,4-dihydro-4-phenyl-1,2,3-benzotriazine (4c). Yellow
oil. Rf (AcOEt/hexane 1:5) 0.37. IR (neat): 1444, 1101. 1H-NMR:
4.32 (d, J ¼ 14.9, 1 H); 5.21 (d, J ¼ 14.9, 1 H); 5.36 (s, 1 H); 6.67 (d, J ¼
7.4, 1 H); 7.14 (td, J ¼ 7.4, 1.1, 1 H); 7.19 (dd, J ¼ 8.0, 1.7, 2 H); 7.28 – 7.38
(m, 9 H); 7.53 (dd, J ¼ 8.0, 1.1, 1 H). 13C-NMR: 56.66; 57.46; 120.81;
125.55; 126.55; 127.55; 128.08; 128.49; 128.55; 128.75; 128.78; 129.03;
129.63; 135.15; 135.41; 141.52. HR-MS (DART): 300.1491 ([M þ H]þ,
C20H18Nþ3 ; calc. 300.1500). Anal. calc. for C20H17N3 (299.37): C 80.24, H
5.72, N 14.04; found: C 80.00. H 5.73, N 13.86.
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This work was supported in part by JSPS KAKENHI Grant
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university for recording mass spectra and performing combustion
analyses.
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Received September 9, 2015
Accepted October 2, 2015
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