Divergent synthesis of 2,6-diaryl-substituted 5,7,8-trimethyl-1,4- benzoxazines via microwave-promoted palladium-catalyzed Suzuki-Miyaura cross coupling and biological evaluation

Article abstract of DOI:10.1016/j.tet.2012.10.009

An efficient palladium-catalyzed Suzuki-Miyaura cross-coupling protocol effected in a mixture of DME/water (2:1) enables the reaction of sterically hindered and electron rich 6-chloro or 6-bromo-1,4-benzoxazines(ones) with a variety of aryl, vinyl or alkylboronic acids. Coupling is effected with catalyst loading of 5 mol % using sealed-vessel microwave processing. The resulting compounds exhibit potent activity against Toxoplasma gondii tachyzoite proliferation.

Full text of DOI:10.1016/j.tet.2012.10.009

Tetrahedron 68 (2012) 10302e10309
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Divergent synthesis of 2,6-diaryl-substituted 5,7,8-trimethyl-1,4-benzoxazines via
microwave-promoted palladium-catalyzed SuzukieMiyaura cross coupling and
biological evaluation
,
,
b
,
,d
Eftychia N. Koini a y, Nicolaos Avlonitis a y, Erica S. Martins-Duarte c, Wanderley de Souza c
,
Rossiane C. Vommaro c, Theodora Calogeropoulou a
,
*
a Institute of Biology, Medicinal Chemistry and Biotechnology, National Hellenic Research Foundation, 48 Vassileos Constantinou Avenue, 11635 Athens, Greece
b Centre for Inflammation Research, The Queen’s Medical Research Institute, MRC/University of Edinburgh, 47 Little France Crescent, EH16 4TJ Edinburgh, UK
c
ꢀ
ꢀ
~
Laboratorio de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, UFRJ, CCS, Bloco G, Av. Carlo, Chagas Filho, Cidade Universitaria, Ilha do Fundao,
21941-902 Rio de Janeiro, RJ, Brazil
d
ꢀ
Instituto Nacional de Metrologia, Qualidade e Tecnologia-Inmetro, Xerem, Duque de Caxias, Rio de Janeiro, RJ, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 June 2012
Received in revised form 12 September 2012
Accepted 2 October 2012
Available online 9 October 2012
An efficient palladium-catalyzed SuzukieMiyaura cross-coupling protocol effected in a mixture of DME/
water (2:1) enables the reaction of sterically hindered and electron rich 6-chloro or 6-bromo-1,4-
benzoxazines(ones) with a variety of aryl, vinyl or alkylboronic acids. Coupling is effected with cata-
lyst loading of 5 mol % using sealed-vessel microwave processing. The resulting compounds exhibit
potent activity against Toxoplasma gondii tachyzoite proliferation.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
6-Halo-1,4-benzoxazines
2,6-Diaryl-substituted-1,4-benzoxazines
Microwave-assisted synthesis
SuzukieMiyaura cross coupling reaction
Toxoplasma gondii
1. Introduction
benzoxazines and 2-aryl-5,7,8-trimethyl-1,4-benzoxazines.3 We
therefore investigated a straightforward route towards this end via
The 2H-1,4-benzoxazine-3-(4H)-one and 3,4-dihydro-2H-1,4-
benzoxazine systems are considered as privileged scaffolds for
the development of potential new drugs and have been extensively
employed in the synthesis of a variety of biologically active com-
pounds, such as herbicides, fungicides, KATP channel openers, car-
diovascular, anti-diabetic, neuroprotective, anxiolytic agents and
antidepressants.1 Recently we reported that 5,7,8-trimethyl-1,4-
benzoxazine aminoamide derivatives possess activity against
reperfusion arrhythmias.2 The 5,7,8-trimethyl-1,4-benzoxazine
core can be considered as a classical bioisostere of the 5,7,8-
trimethylbenzopyran nucleus of the well known chain breaking
antioxidant, vitamin E. As part of an ongoing lead optimization
project we sought a strategy that would enable rapid exploration of
structureeactivity relationships through the late-stage, divergent
installation of different C-6 substituents in 5,7,8-trimethyl-1,4-
SuzukieMiyaura cross coupling reaction of the corresponding 6-
halogen-substituted 5,7,8-trimethyl-1,4-benzoxazines/ones and
a variety of boronic acids. The palladium catalyzed SuzukieMiyaura
reaction represents one of the most highly prized processes in
synthetic chemistry and an extensively studied cross coupling re-
action for carbonecarbon bond formation.4 It has found wide ap-
plications in the synthesis of bioactive complex molecules because
of its mild reaction conditions and its compatibility with a broad
range of functional groups. Typically it involves reaction of an aryl
or vinyl halide or triflate with an aryl, vinyl or alkyl boron com-
pound to obtain biaryls, 1,3-dienes, alkyl/aryl-substituted alkenes
and alkyl-substituted aromatics. Recent significant advancements
in the area of phosphine catalyst ligand design and synthesis were
contributed by Beller,5 Buchwald,6 Hartwig,7 and others8 while Fu9
and co-workers extended the scope of the reaction to cross-
coupling to alkyl electrophiles. The reaction involves the palla-
dium catalyzed cross coupling of alkyl boranes to primary alkyl
halides and tosylates in the presence of catalysts with bulky elec-
tron rich phosphane ligands.10 During the last decade, advances in
the organoboron nucleophilic counterpart have emerged and more
* Corresponding author. Tel.: þ30 210 7273833; fax: þ30 210 7273831; e-mail
address: tcalog@eie.gr (T. Calogeropoulou).
y
These authors contributed equally to this work.
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.10.009

E.N. Koini et al. / Tetrahedron 68 (2012) 10302e10309
10303
Table 1
specifically the use of organotrifluoroborates developed by the
groups of Genet11 and Molander.12 Recently, Kwong et al. reported
on the palladium catalyzed SuzukieMiyaura coupling of aryl
mesylates to aryl-, heteroaryl-, alkenyl-, and alkyl-trifluoroborate
salts13 while, Molander and Beaumard reported the Suzuki-type
cross coupling of aryl- and heteroaryl mesylates with potassium
aminomethyltrifluoroborates and amidomethyltrifluoroborates.14
SuzukieMiyaura cross coupling of 6-halo-3,5,6-trimethyl-2-nitrophenol and aryl
boronic acids. Optimization studies
2. Results and discussion
Entry Halo phenol ArB(OH)2 Product Reaction conditions (% isolated yielda)
Microwave irradiation Normal heating
In this work we examined the SuzukieMiyaura coupling reaction
of 6-halogen-substituted 5,7,8-trimethyl-1,4-benzoxazinones, 6-
bromo-5,7,8-trimethyl-1,4-benzoxazines and of 4-halogen-
substituted 3,5,6-trimethyl-2-nitrophenol, prepared using our
previously described halogenation procedure.15 2-Nitrophenols
have been widely used as the starting materials in the synthesis of
3,4-dihydro-2H-1,4-benzoxazines and 2H-1,4-benzoxazin-3-(4H)-
ones16 therefore, the biaryls obtained through the SuzukieMiyaura
cross coupling reactions could allow for increased structural di-
versity of the resulting heterocyclic derivatives. Alternatively, 1,4-
benzoxazine derivatives are synthesized via cyclocondensation of
aminophenols with dihalo derivatives17 or with substituted halo-
geno acyl bromides followed by reduction of the resulting lactams,
or by epoxide opening with o-halosulfonamides followed by cycli-
zation18 or by epoxide opening with aminophenols followed by
cyclocondensation19 or by domino aziridine ring opening with o-
iodophenols followed by the copper catalyzed Goldberg coupling
cyclization.20 3,4-Dihydro-3-oxo-2H-1,4-benzoxazine derivatives
have been prepared from o-aminophenols by a one-pot microwave-
assisted O-alkylation with substituted halogeno acyl bromides and
spontaneous cyclization21 or by microwave-assisted reductive N-
arylmethylation followed by regioselective O-alkylation with 2-
bromoalkanoates and spontaneous cyclization22 or via an Ugi four
component reaction followed by intramolecular O-alkylation.23
To achieve our goal we compared the effects of thermal versus
microwave-assisted conditions for the SuzukieMiyaura coupling
reactions. Microwave enhanced synthesis has emerged as a pow-
erful tool due to the high-speed construction of versatile chemical
entities.24 Several examples have been reported for its application
for the palladium catalyzed SuzukieMiyaura cross coupling re-
action.25 Previous synthetic efforts towards simple 6-aryl-2,4,4-
trimethyl-1,4-dihydro-2H-benzo[d][1,3]oxazines involved thermal
conditions for the SuzukieMiyaura cross-coupling reaction.26
Furthermore, the microwave assisted palladium-catalyzed intra-
molecular direct arylation of suitably N-substituted 1,4-
benzoxazinones has been reported.27 However, to the best of our
knowledge, no reports on the synthesis of 6-aryl-1,4-benzoxazines/
ones with the extremely sterically hindered 5,7,8-trimethyl-1,4-
benzoxazine/one core, under microwave-assisted conditions have
appeared in the literature. Initially we focused our efforts in finding
the optimum conditions for the SuzukieMiyaura coupling of 4-
chloro- and 4-bromo-3,5,6-trimethyl-2-nitrophenol with neutral
and electron rich aryl boronic acids (Table 1) using conventional
heating. Our experimentation was focused in the use of a number of
bases Ba(OH)2, Cs2CO3, K3PO4, Na2CO3, solvents (THF, DMF), various
reaction times and temperature, while Pd(PPh3)4 was used as cat-
alyst. However, we were not able to detect any coupling product
with 4-chloro-3,5,6-trimethyl-2-nitro phenol (1a) and phenyl or 2-
methoxyphenyl boronic acid (Table 1, entries 1 and 2). Conversely,
the more reactive 4-bromo-substituted analogue (1b) afforded the
coupling products in isolated yields ranging between 54 and 82%
(Table 1, entries 3e6). Fine tuning of the reaction parameters led to
the use of controlled microwave irradiation using a closed vessel
and we were gratified to obtain the desired biaryls from 4-chloro-
3,5,6-trimethyl-2-nitro phenol (1a) in around 70% yield (Table 1,
entries 1 and 2). It should be noted that compound 1a is a sterically
1
2
3
4
5
6
1a
1a
1b
1b
1b
1b
2a
2b
2a
2b
2c
2d
3a
3b
3a
3b
3c
3d
A (71)
A (77)
B (90)
B (50)
B (51)
B (73)
d
d
C (82)
C (55)
C (63) D (72)
D (54)
a
Isolated yield after purification by flash chromatography (A) 1a (1 equiv),
ArB(OH)2 (1.5 equiv), Na2CO3 (1.5 equiv), Pd(PPh3)4 (5 mol %), Toluene,
mw,
T¼160 ꢀC, t¼5 min (B) 1b (1 equiv), ArB(OH)2 (1.5 equiv), Na2CO3 (1.5 equiv),
Pd(PPh3)4 (5 mol %), 2:1 DME/H2O,
m
w, T¼160 ꢀC, t¼5 min (C) 1b (1 equiv), ArB(OH)2
(1.5 equiv), Cs2CO3 (1.5 equiv), Pd(PPh3)4 (10 mol %), DMF, T¼100 ꢀC, t¼2 h (D) 1b
(1 equiv), ArB(OH)2 (1.5 equiv), Cs2CO3 (1.5 equiv), Pd(PPh3)4 (10 mol %), THF,
T¼80 ꢀC, t¼20 h.
demanding substrate, while 2-methoxyphenyl boronic acid, an
electron rich ortho-substituted aryl boronic acid, properties, which
do not favour productive coupling between the two partners. As an
example, reaction of mesitylboronic acid with iodobenzene re-
quires heating at 80 ꢀC and strong base (Ba(OH)2) due to the steric
hindrance during the transmetalation to the palladium (II) com-
plex.28 Furthermore, the conventional heating approach, suffers
from long reaction times at an elevated temperature regime
(2e20 h and 80e100 ꢀC) and the necessity to employ double the
quantity of palladium catalyst to obtain acceptable yields for these
difficult substrates. Conversely, employing sealed-vessel micro-
wave heating an improved protocol was obtained that allows per-
forming the reaction in only 5 min at 160 ꢀC using 5 mol %
palladium catalyst, Na2CO3 as base and almost equimolar boronic
acid stoichiometry. Finally, utilization of an aqueous solvent system
(DME/water 2:1) renders the reaction more environmentally
friendly. The yields of microwave-assisted SuzukieMiyaura cross
coupling of 4-bromo-3,5,6-trimethyl-2-nitrophenol (1b) and phe-
nyl or 4-methoxyphenyl boronic acid were superior to conven-
tional heating (Table 1, entries
3 and 6), while with 2-
methoxyphenyl boronic acid was lower due to dehalogenation of
the starting bromo-nitrophenol 1b (Table 1, entry 4). Furthermore,
in the case that 3-methoxyphenyl boronic acid was used as cou-
pling partner the yield was slightly lower under microwave irra-
diation conditions (Table 1, entry 5).
We then explored the SuzukieMiyaura coupling reaction of 6-
halo-5,7,8-trimethyl-1,4-benzoxazinones using our optimized mi-
crowave-assisted conditions. However, the yields of the cross cou-
pling of 6-chloro- and 6-bromo-substituted analogues 4a and 4b
with 2-methoxyphenyl boronic acid were low probably due to steric
hindrance of the boronic acid counterpart (Table 2, entries 1,3). It is
well-known that SuzukieMiyaura coupling is sensitive to steric
hindrance. In addition, electron-rich chloroarenes are more difficult
substrates than electron-poor ones.29 Cross coupling of 6-chloro
substituted 4a and 3-methoxyphenyl boronic acid was effected in
low yield (Table 2, entry 2), which was markedly increased to 67%
when the 6-bromo derivative 4b was used (Table 2, entry 4) and
was improved further to 86% when 4-methoxyphenyl boronic acid
was employed as the nucleophilic partner and Cs2CO3 as base
(Table 2, entry 5). Gratifyingly, SuzukieMiyaura coupling reactions
with 2-phenyl-6-bromo-5,7,8-trimethyl-1,4-benzoxazinone (4c)

10304
E.N. Koini et al. / Tetrahedron 68 (2012) 10302e10309
Table 2
entry 1). The byproduct of the reaction was the debrominated 1,4-
benzoxazine analogue of 6.
Microwave-promoted SuzukieMiyaura cross coupling of 6-halo-3,5,6-trimethyl-1,4-
benzoxazinones and aryl boronic acids
In the SuzukieMiyaura cross couplingreactiontheroleof thebase
is to facilitate the slow transmetalation of the boronic acid. Usually, in
the case of sterically hindered boronic acids, a mild base like Na2CO3
is preferable in order to avoid elimination of the boronic acid group.
However, switching to the stronger base Ba(OH)2 was necessary in
orderto increase the yield of the desired product 7a (Table 3, entry 1).
Accordingly, Cs2CO3 was employed as base when 4-methoxyphenyl
boronic acid (2d) was employed as coupling partner to obtain ana-
logue 7c (Table 3, entry 3). It has been previously reported that the
presence of nitrogen heterocyclic moieties, that are valuable struc-
tural motifs in medicinal chemistry, leads to low reactivity in cou-
pling reactions due to the binding of the heteroatom of the substrate
and product to the metal complex. Even though binding is reversible,
the large excess of substrate can lead to a strong inhibitory effect.30
However, in our case the corresponding 6-bromo-1,4-
benzoxazine derivative 6 exhibited good reactivity resulting to the
corresponding 6-aryl or 6-heteroaryl derivatives in high to excellent
yields thus, allowing the generation of a small compound library,
which was further investigated for its biological activity against
Toxoplasma gondii tachyzoites (Table 4). T. gondii, the causative agent
of toxoplasmosis, is a ubiquitous opportunistic pathogen that infects
individuals worldwide and a wide range of animals including all
warm blooded animals.31 It is a leading cause of severe congenital,
neurologic and ocular disease in humans, exacerbated when
immunodepression of the host takes place due to chemotherapy,
radiotherapy and HIV infection. Throughout the world, new T. gondii
infection during pregnancy can lead to devastating disease for the
foetus and newborn infant, later impacting on the child’s health and
development and potentially on his/her later productivity.32 Fur-
thermore, T. gondii is designated as an NIAID Category B biowarfare
(priority) pathogen, in large part due to its danger to both humans
and livestock, its persistence in the environment, and the ease with
which it disseminates. The treatment of choice for toxoplasmosis is
the combined administration of pyrimethamine with either sulfa-
diazine or clindamycin. Since no vaccine for humans is available, and
hypersensitivity and toxicity limit the use of the few available drugs
safer and more effective medicines to treat toxoplasmosis are ur-
gently needed. Compounds 7aek inhibited T. gondii tachyzoite
proliferation showing IC50 values in the low micromolar range
Entry
6-Halo-5,7,8-trimethyl-1,
4-benzoxazinone
ArB(OH)2
Product
Yield (%)a
1
2
3
4
5
6
7
8
4a
4a
4b
4b
4b
4c
4c
4c
2b
2c
2b
2c
2d
2a
2c
2d
5a
5b
5a
5b
5c
5d
5e
5f
24
18
15
67
86b
97
85b
91
a
Isolated product after purification by flash chromatography.
Cs2CO3 (1.5 equiv) was used as base instead of Na2CO3.
b
and phenyl or 3-methoxyphenyl or 4-methoxyphenyl boronic acid
were effected in almost quantitative yields (Table 2, entries 6e8).
Capitalizing on the excellent results of the SuzukieMiyaura
cross
coupling
of
2-phenyl-6-bromo-5,7,8-trimethyl-1,4-
benzoxazinone (4c) we applied our optimized conditions to the
corresponding 1,4-benzoxazine derivative (6) and a variety of aryl-
and heteroarylboronic acids to investigate further the synthetic
scope of the reaction (Table 3).
Table 3
Microwave-promoted SuzukieMiyaura cross coupling of 2-phenyl-6-bromo-5,7,8-
trimethyl-1,4-benzoxazine with various boronic acids
(0.86e4.5
mM, Table 4). The most active compounds were 6-
Entry
1
RB(OH)2
Product
Yield (%)a
(3-methoxyphenyl)-5,7,8-trimethyl-2-phenyl-3,4-dihydro-2H-1,4-
benzoxazine (7b) and 6-(4-butylphenyl)-5,7,8-trimethyl-2-phenyl-
2b R¼o-MeOPh
7a
47b
55d
80b
83c
81b
88b
90b
85b
84b
85b
87b
55b
3,4-dihydro-2H-1,4-benzoxazine (7j) with IC50¼1.21ꢁ0.04
mM and
2
3
4
5
6
7
8
9
2c R¼m-MeOPh
2d R¼p-MeOPh
2e R¼(E)-styryl
2f R¼4-vinylphenyl
2g R¼2-furyl
7b
7c
7d
7e
7f
7g
7h
7i
0.86ꢁ0.4 M, respectively, after 72 h.
m
3. Conclusions
2h R¼2-thienyl
2i R¼2-naphthyl
2j R¼p-CF3Ph
In summary, we have developed a convenient and efficient
strategy for the synthesis of 6-substituted-5,7,8-trimethyl-1,4-
benzoxazines(ones) via microwave-assisted SuzukieMiyaura
cross coupling with a variety of boronic acids. This approach allows
for the rapid incorporation of aryl, heteroaryl and alkyl function-
alities into this heterocyclic privileged scaffold. Furthermore, our
results demonstrate that 2-phenyl-6-aryl-5,7,8-trimethyl-1,4-
benzoxazines are very active against T. gondii tachyzoite pro-
liferation in vitro and suggest further investigation of this class of
molecules as potential agents against toxoplasmosis.
10
11
2k R¼p-butylphenyl
2l R¼butyl
7j
7k
a
Isolated yield.
b
c
Base: Na2CO3.
Base: Cs2CO3.
Base: Ba(OH)2.
d
The reaction conditions remained general across electron de-
ficient (Table 3, entry 9), electron rich (Table 3, entries 1, 2, 3, 5, 10)
and neutral hindered (Table 3, entry 8) aryl boronic acids, an
alkenylboronic acid (Table 3, entry 4), heteroarylboronic acids
(Table 3, entries 6, 7) and even an alkylboronic acid, albeit in
moderate yield (Table 3, entry 11). As previously observed in the
case of compound 5a, coupling with 2-methoxyphenyl boronic acid
(2b) was effected in moderate yield due to steric hindrance (Table 3,
4. Experimental section
4.1. General remarks
1H NMR spectra were recorded at 600 or 300 MHz, 13C NMR
spectra at 150.9 or 75.5 MHz and 19F NMR spectra at 564.8 MHz. 1H

E.N. Koini et al. / Tetrahedron 68 (2012) 10302e10309
10305
and 13C NMR spectra are internally referenced to residual solvent
signals (CDCl3). 19F NMR spectra are referenced to CCl3F. Data for 1H
NMR are reported as follows: chemical shift (d ppm), integration,
Table 4
Growth inhibition of T. gondii tachyzoites RH strain by 6-substituted 2-phenyl-5,7,8-
trimethyl-1,4-benzoxazines after 48 and 72 h of treatment
multiplicity (s¼singlet, d¼doublet, dd¼doublet of doublet,
ddd¼doublet of doublet of doublet, m¼multiplet) and coupling
constant. Data for 13C NMR are reported in terms of chemical shift
Compounds
IC50 (mM)
48 h
72 h
(d
ppm). Melting points (ꢀC) are uncorrected. Reactions were per-
OMe
H
N
formed in a microwave reactor CEM Discover LabMate. IR spectra
were obtained on an ATR-IR spectrometer. Thin-layer chromatog-
raphy (TLC) was performed on glass plates coated with silica gel
(0.2 mm, 60 F254) and flash chromatography using silica gel
(200e400 mesh).
1.41ꢁ0.64a,c
2.65ꢁ0.53a,c
O
7a
OMe
H
4.2. Experimental procedures
N
0.90ꢁ0.32b
1.21ꢁ0.04a
O
4.2.1. 6-Bromo-5,7,8-trimethyl-2-phenyl-2H-benzo[b][1,4] oxazin-
3(4H)-one (4c). To a solution of 5,7,8-trimethyl-2-phenyl-2H-1,4-
benzoxazin-3(4H)-one (0.001 mol) in petroleum ether (10 mL)
7b
MeO
was added
a mixture of CH3COOH/H2O2 (30%)/HBr (48%)
H
N
(6.50 mmol:6.50 mmol:2.50 mmol) and the reaction was stirred at
room temperature for 1 h. After dilution with EtOAc (50 mL), the
organic layer was separated, washed with NaHCO3 (50 mL, satd
aq), brine (50 mL), dried (Na2SO4) and the solvent evaporated in
vacuo. Purification of the crude product by flash chromatography
(10% acetone/petroleum ether 40e60 ꢀC) gave the title compound
4c (0.225 g, 65%) as a white solid, mp 210e212 ꢀC (recrystallized
from EtOAc); Rf (20% EtOAc/petroleum ether 40e60 ꢀC/4:1) 0.35;
1.81ꢁ0.9a
2.13ꢁ0.86a
1.33ꢁ0.39b
1.64ꢁ0.5a
O
7c
H
N
2.27ꢁ 0.80a
2.07ꢁ0.83a
O
nmax(neat) 3212, 3140, 1681, 1578, 1228 cmꢂ1
; dH (300 MHz, CDCl3)
7d
8.88 (1H, s, NH), 7.41e7.33 (5H, m, Ph), 5.70 (1H, s, CHPh), 2.35
(6H, s, 2Me), 2.27 (3H, s, Me); dC (75.5 MHz, CDCl3) 166.4, 140.3,
135.1, 132.6, 129.0, 128.9, 126.8, 124.3, 123.2, 121.5, 121.4, 78.2, 20.6,
17.6, 13.3; MS (EI), m/z 347 (90, [Mþ2]þ), 345 (89, Mþ), 118 (100);
HRMS (ESIþ): MHþ, found 346.0444. C17H17Br79NO2 requires
346.0437.
H
N
O
7e
H
N
O
S
1.64ꢁ0.40b
2.07ꢁ0.47a
1.79ꢁ0.37a
2.15ꢁ0.62a
4.2.2. 6-Bromo-3,4-dihydro-5,7,8-trimethyl-2-phenyl-2H-benzo[b]
[1,4]oxazine (6). To a solution of benzoxazinone 4c (0.346 g,
0.001 mol) in anhydrous THF (2 mL) was added drop wise at 0 ꢀC
a solution of borane dimethyl sulfide complex (24.0 mmol,
2.28 mL). The resulting mixture was stirred at room temperature
for 12 h and the reaction was quenched by the drop wise addition of
water at 0 ꢀC until gas evolution ceased. After dilution with EtOAc
(50 mL), the organic layer was separated, washed with brine
(50 mL), dried (Na2SO4) and the solvent evaporated in vacuo. Pu-
rification of the crude product by flash chromatography (3% ace-
tone/hexane) afforded the title compound 6 (0.249 g, 75%) as a white
solid, mp 122e124 ꢀC (recrystallized from hexane/EtOAc); Rf (20%
acetone/petroleum ether 40e60 ꢀC) 0.40; nmax(neat) 3413, 1601,
O
7f
H
N
O
7g
H
N
3.00ꢁ0.96a
1.60ꢁ0.29a
1.83ꢁ0.19a
1.57ꢁ0.35b
O
7h
1383, 1124 cmꢂ1
; dH (300 MHz, CDCl3) 7.44e7.35 (5H, m, Ph), 5.03
F3C
(1H, dd, J 8.7, 2.1 Hz, CHPh), 3.61 (1H, dd, J 12.0, 2.1 Hz, CH2CHPh),
3.31 (1H, dd, J 12.0, 8.7 Hz, CH2CHPh), 2.37 (3H, s, Me), 2.30 (3H, s,
Me), 2.25 (3H, s, Me); dC (75.5 MHz, CDCl3) 141.9, 139.5, 129.4, 128.8,
128.3, 126.9, 126.3, 123.9, 120.7, 119.9, 75.6, 48.4, 20.2, 17.6, 13.0; MS
(EI), m/z 333 (95, [Mþ2]þ), 331 (96, Mþ), 242 (100), 240 (100);
HRMS (FABþ): Mþ, found 331.0556. C17H18Br79NO requires
331.0572.
H
N
O
7i
H
N
1.69ꢁ0.79a
4.5ꢁ0.67b
0.86ꢁ0.40b
2.31ꢁ0.18b
O
4.3. General procedure for the microwave assisted Suzu-
kieMiyaura cross coupling reaction, synthesis of compounds
3ae3d, 5ae5f, 7ae7k
7j
H
N
To a thick-wall borosilicate glass vial (5 mL) were sequentially
added the appropriate 4-halo-2,3,5-trimethyl-6-nitrophenol (1a or
1b), or 6-halo-5,7,8-trimethyl-1,4-benzoxazinone (4a or 4b), or 6-
bromo-2-phenyl-5,7,8-trimethyl-1,4-benzoxazinone (4c) or 6-
bromo-5,7,8-trimethyl-1,4-benzoxazine (6) (0.001 mol), Pd(PPh3)4
O
7k
Results were expressed as the meanꢁstandard deviation of athree or btwo different
experiments. cThe less polar rotamer was evaluated.

10306
E.N. Koini et al. / Tetrahedron 68 (2012) 10302e10309
(5 mol %), aryl boronic acid (1.50 mmol), Na2CO3 (1.50 mmol) and
a mixture of DME/H2O (2:1, 1 mL). The mixture was degassed with
argon, the reaction vial was sealed, was placed in a CEM Discover
LabMate microwave reactor and was irradiated at 160 ꢀC for 5 min.
After cooling to room temperature, the mixture was diluted with
dichloromethane, dried (Na2SO4) and the solvent evaporated in
vacuo. Purification of the crude product by flash chromatography
afforded the title compounds 3ae3d, 5ae5f, 7ae7k.
m/z: 287 (100, Mþ); HRMS (ESIꢂ): [MꢂH]ꢂ, found 286.1077.
C16H16NO4 requires 286.1085.
4.3.5. 6-(2-Methoxyphenyl)-5,7,8-trimethyl-2H-1,4-benzoxazin-
3(4H)-one (5a). Following the general procedure described above
using 2-methoxyphenyl boronic acid (2b) and 6-chloro-5,7,8-
trimethyl-2H-benzo[b][1,4]oxazin-3(4H)-one (4a)3 or 6-bromo-
5,7,8-trimethyl-2H-benzo[b][1,4]oxazin-3(4H)-one (4b),15 the title
compound 5a was obtained (0.071 g, 24%) or (0.046 g, 15%), re-
spectively, as a white solid after purification by flash chromatog-
raphy (20% EtOAc/petroleum ether 40e60 ꢀC). Mp 209e211 ꢀC
(recrystallized from EtOAc); Rf (25% EtOAc/petroleum ether
4.3.1. 2,3,6-Trimethyl-5-nitro[1.10-biphenyl]-4-ol (3a). Following the
general procedure described above, using phenyl boronic acid (2a)
and 4-chloro-2,3,5-trimethyl-6-nitrophenol (1a)15 or 4-bromo-
2,3,5-trimethyl-6-nitrophenol (1b)15 the title compound 3a was
obtained (0.181 g, 71%) or (0.230 g, 90%), respectively, as a yellow
solid after purification by flash chromatography (2% Et2O/petro-
leum ether 40e60 ꢀC). Mp 84 ꢀC; Rf (5% Et2O/petroleum ether
40e60 ꢀC) 0.24; nmax(neat) 3215, 3144, 1682, 1461, 1405, 1239 cmꢂ1
;
dH (300 MHz, CDCl3) 8.34 (1H, s, NH), 7.38e7.32 (1H, m, Ph),
7.01e6.94 (3H, m, Ph), 4.59 (2H, s, OCH2), 3.75 (3H, s, OMe), 2.19
(3H, s, Me), 1.89 (6H, s, 2Me); dC (75.5 MHz, CDCl3) 166.2, 156.8,
141.1, 132.5, 131.3, 131.2, 129.3, 128.6, 122.5, 122.2, 120.7, 119.9, 110.8,
67.1, 55.5, 17.0, 13.8, 12.1; MS (EI), m/z 297 (100, Mþ); HRMS (FABþ)
[M]þ, found 297.1361. C18H19NO3 requires 297.1365.
40e60 ꢀC) 0.30; nmax(neat) 3500e3300 (br), 1581, 1522, 1249 cmꢂ1
;
dH (300 MHz CDCl3) 10.20 (1H, s, OH), 7.46e7.34 (3H, m, Ph),
7.08e7.06 (2H, m, Ph), 2.27 (3H, s, Me), 2.16 (3H, s, Me), 1.96 (3H, s,
Me); dC (75.5 MHz CDCl3) 151.3, 144.0, 140.2, 135.8, 134.6, 130.5,
129.6, 128.8, 127.3, 124.1, 19.3, 19.0, 12.3; MS (EI), m/z: 257 (100,
Mþ); HRMS (ESIꢂ): [MꢂH]ꢂ, found 256.0975. C15H14NO3 requires
256.0979.
4.3.6. 6-(3-Methoxyphenyl)-5,7,8-trimethyl-2H-1,4-benzoxazin-
3(4H)-one (5b). Following the general procedure described above
using 3-methoxyphenyl boronic acid (2c) and 4a or 4b, the title
compound 5b was obtained (0.054 g, 18%) or (0.199 g, 67%), re-
spectively, as a white solid after purification by flash chromatog-
raphy (15% EtOAc/petroleum ether 40e60 ꢀC), mp 231e232 ꢀC
(recrystallized from EtOAc); Rf (25% EtOAc/petroleum ether
40e60 ꢀC) 0.31; nmax(neat) 3205, 3144, 1679, 1587, 1463, 1407,
4.3.2. 20-Methoxy-2,3,6-trimethyl-5-nitro[1.10-biphenyl]-4-ol
(3b). Following the general procedure described above, using 2-
methoxyphenyl boronic acid (2b) and 4-chloro-2,3,5-trimethyl-6-
nitrophenol (1a) or 4-bromo-2,3,5-trimethyl-6-nitrophenol (1b)
the title compound 3b was obtained (0.220 g, 77%) or (0.143 g, 50%),
respectively, as a yellow solid after purification by flash chroma-
tography (1% Et2O/1% CH2Cl2/petroleum ether 40e60 ꢀC). Mp
135e137 ꢀC; Rf (5% Et2O/petroleum ether 40e60 ꢀC) 0.25; nmax(neat)
1240 cmꢂ1
; dH (300 MHz, CDCl3) 8.26 (1H, s, NH), 7.35e7.30 (1H, m,
Ph), 6.90e6.87 (1H, m, Ph), 6.68e6.62 (2H, m, Ph), 4.59 (2H, s,
OCH2), 3.81 (3H, s, OMe), 2.19 (3H, s, Me), 1.91 (6H, s, 2Me); dC
(75.5 MHz, CDCl3) 165.9, 159.6, 142.4, 141.1, 136.2, 130.8, 129.5,
122.6, 122.1, 122.0, 119.1, 115.2, 112.2, 67.2, 55.2, 17.3, 13.9, 11.9; MS
(EI), m/z 297 (100, Mþ); HRMS (FABþ): [M]þ, found 297.1394.
C18H19NO3 requires 297.1365.
3400e3300 (br), 1581, 1522, 1341, 1249 cmꢂ1
; dH (300 MHz CDCl3)
10.29 (1H, s, OH), 7.41e7.35 (1H, m, Ph), 7.06e6.94 (3H, m, Ph), 3.74
(3H, s, OMe), 2.27 (3H, s, Me), 2.16 (3H, s, Me), 1.95 (3H, s, Me); dC
(75.5 MHz CDCl3) 156.7, 151.5, 144.7, 134.6, 132.1, 131.4, 131.1, 129.1,
128.5, 123.9,121.0, 110.9, 55.5, 18.9,18.5, 12.4; MS (EI), m/z: 287 (100,
Mþ); HRMS (ESIꢂ): [MꢂH]ꢂ, found 286.1079, C16H16NO4 required
286.1085; HRMS (ESIþ): [MþNa]þ found 310.1054. C16H17NNaO4
requires 310.1050.
4.3.7. 6-(4-Methoxyphenyl)-5,7,8-trimethyl-2H-1,4-benzoxazin-
3(4H)-one (5c).3 Following the general procedure described above
using 4-methoxyphenyl boronic acid (2d), 4b, and Cs2CO3
(1.50 mmol) the title compound 5c was obtained (0.256 g, 86%) as
a white solid after purification by flash chromatography (15%
EtOAc/petroleum ether 40e60 ꢀC), mp 211e213 ꢀC (recrystallized
from EtOAc); Rf (25% EtOAc/petroleum ether 40e60 ꢀC) 0.29; dH
(300 MHz, CDCl3) 8.34 (1H, s, NH), 6.94 (4H, ABq, DdAB¼0.04,
JAB¼9.0 Hz), 4.59 (2H, s, OCH2), 3.85 (3H, s, OMe), 2.19 (3H, s, Me),
1.90 (6H, s, 2Me); dC (75.5 MHz, CDCl3) 165.7, 158.4, 140.9, 136.0,
133.2, 131.4, 130.6, 122.6, 122.1, 119.3, 113.8, 67.2, 55.2, 17.4, 13.9,
12.0; MS (EI), m/z 297 (100, Mþ); HRMS (FABþ): [M]þ, found
297.1352. C18H19NO3 requires 297.1365.
4.3.3. 30-Methoxy-2,3,6-trimethyl-5-nitro[1.10-biphenyl]-4-ol
(3c). Following the general procedure described above using 4-
bromo-2,3,5-trimethyl-6-nitrophenol (1b) and 3-methoxyphenyl
boronic acid (2c) the title compound 3c was obtained (0.146 g,
51%) as a yellow solid after purification by flash chromatography
(2% Et2O/1% CH2Cl2/petroleum ether 40e60 ꢀC). Rf (5% Et2O/pe-
troleum ether 40e60 ꢀC) 0.32; nmax(neat) 3500e3250 (br), 1576,
1519, 1223, 1182 cmꢂ1
; dH (300 MHz, CDCl3) 10.19 (1H, s, OH),
7.37e7.32 (1H, m, Ph), 6.93e6.89 (1H, m, Ph), 6.66e6.60 (2H, m,
Ph), 3.82 (3H, s, OMe), 2.26 (3H, s, Me), 2.17 (3H, s, Me), 1.97 (3H, s,
Me); dC (75.5 MHz, CDCl3) 159.9, 151.3, 143.9, 141.6, 135.6, 130.4,
129.8, 124.1, 121.9, 119.6, 115.2, 112.6, 55.2, 19.2, 18.9, 12.3; MS (EI),
m/z: 287 (100, Mþ); HRMS (ESIꢂ): [MꢂH]ꢂ, found 286.1079.
C16H16NO4 requires 286.1085.
4.3.8. 5,7,8-Trimethyl-2,6-diphenyl-2H-1,4-benzoxazin-3(4H)-one
(5d). Following the general procedure described above using
phenyl boronic acid (2a) and 4c the title compound 5d was obtained
(0.333 g, 97%) as a white sticky solid after purification by flash
chromatography (10% EtOAc/cyclohexane); Rf (20% EtOAc/cyclo-
hexane) 0.38; nmax(neat) 3210, 3144, 1680, 1460, 1406, 1235 cmꢂ1
;
4.3.4. 40-Methoxy-2,3,6-trimethyl-5-nitro[1.10-biphenyl]-4-ol
(3d).3 Following the general procedure described above using 4-
bromo-2,3,5-trimethyl-6-nitrophenol (1b) and 4-methoxyphenyl
boronic acid (2d) the title compound 3d was obtained (0.209 g,
73%) as a yellow solid after purification by flash chromatography
(2% Et2O/1% CH2Cl2/petroleum ether 40e60 ꢀC); Rf (5% Et2O/pe-
troleum ether 40e60 ꢀC) 0.30; dH (300 MHz, CDCl3) 10.16 (1H, s,
OH), 6.97 (4H, s, Ph), 3.86 (3H, s, OMe), 2.26 (3H, s, Me), 2.17 (3H, s,
Me), 1.97 (3H, s, Me); dC (75.5 MHz CDCl3) 158.6, 151.1, 144.4, 135.4,
134.6, 132.3, 130.8, 130.5, 123.9, 114.1, 55.2, 19.2, 18.9, 12.3; MS (EI),
dH (300 MHz, CDCl3) 8.23 (1H, s, NH), 7.50e7.33 (8H, m, Ph),
7.08e7.03 (2H, m, Ph), 5.72 (1H, s, CHPh), 2.25 (3H, s, Me), 1.88 (3H,
s, Me), 1.86 (3H, s, Me); dC (75.5 MHz, CDCl3) 165.7, 141.0, 140.0,
136.3, 135.3, 130.9, 129.6, 128.7, 128.6, 128.4, 126.8, 126.7, 122.7,
121.8, 118.8, 78.2, 17.4, 14.0, 12.1; HRMS (ESIþ): [MþH]þ, found
344.1649. C23H22NO2 requires 344.1645.
4.3.9. 6-(3-Methoxyphenyl)-5,7,8-trimethyl-2-phenyl-2H-1,4-
benzoxazin-3(4H)-one (5e). Following the general procedure de-
scribed above using 3-methoxyphenyl boronic acid (2c), 4c, and

E.N. Koini et al. / Tetrahedron 68 (2012) 10302e10309
10307
Cs2CO3 (1.50 mmol), the title compound 5e was obtained (0.317 g,
85%) as a white solid after purification by flash chromatography
(15% EtOAc/petroleum ether 40e60 ꢀC), mp 156e159 ꢀC (recrys-
tallized from petroleum ether 40e60 ꢀCeEtOAc); Rf (30% EtOAc/
petroleum ether 40e60 ꢀC) 0.47; nmax(neat) 3207, 3144, 1679, 1462,
1.0 Hz, Ph), 6.76e6.70 (2H, m, Ph), 5.13 (1H, dd, J 8.9, 2.3 Hz, CHPh),
3.83 (3H, s, OMe), 3.65 (1H, dd, J 11.8, 2.3 Hz, CH2CHPh) 3.38 (1H, dd,
J 11.8, 8.9 Hz, CH2CHPh), 2.26 (3H, s, Me), 1.95 (3H, s, Me), 1.87 (3H, s,
Me); dC (75.5 MHz, CDCl3) 159.5, 143.6, 141.7, 139.7, 134.5, 129.1,
128.5, 128.0, 126.1, 125.3, 122.5, 122.4, 122.2, 119.0, 115.4, 111.9, 75.5,
55.2, 48.4, 17.0, 14.3, 11.9; MS (EI), m/z 359 (100, Mþ); HRMS (FABþ):
[M]þ, found 359.1887. C24H25NO2 requires 359.1885.
1408, 1237 cmꢂ1
; dH (300 MHz, CDCl3) 8.32 (1H, s, NH), 7.50e7.30
(6H, m, Ph), 6.89e6.87 (1H, m, Ph), 6.68e6.61 (2H, m, Ph), 5.72 (1H,
s, CHPh), 3.81 (3H, s, OMe), 2.26 (3H, s, Me), 1.91 (3H, s, Me), 1.89
(3H, s, Me); dC (75.5 MHz, CDCl3) 165.9, 159.6, 142.5, 140.0, 136.1,
135.3, 130.8, 129.4, 128.5, 126.7, 122.6, 122.1, 121.9, 119.0, 115.1, 112.3,
112.1, 78.1, 55.2, 17.3, 14.0, 12.1; MS (EI), m/z 373 (100, Mþ); HRMS
(ESIþ): [MþH]þ, found 374.1753. C24H24NO3 requires 374.1751.
4.3.13. 3,4-Dihydro-6-(4-methoxyphenyl)-5,7,8-trimethyl-2-phenyl-
2H-benzo[b][1,4]-oxazine (7c). Following the general procedure
described above using 4-methoxyphenyl boronic acid (2d), ben-
zoxazine 6, and Cs2CO3 (1.50 mmol) the title compound 7c was
obtained (0.298 g, 83%) as a white solid after purification by flash
chromatography (5% acetone/hexane), mp 175e176 ꢀC; Rf (10%
EtOAc/petroleum ether 40e60 ꢀC) 0.26; nmax(neat) 3412,1596,1514,
4.3.10. 6-(4-Methoxyphenyl)-5,7,8-trimethyl-2-phenyl-2H-1,4-
benzoxazin-3(4H)-one (5f). Following the general procedure de-
scribed above using 4-methoxyphenyl boronic acid (2d) and 4c, the
title compound 5e was obtained (0.340 g, 91%) as a white solid after
purification by flash chromatography (15% EtOAc/petroleum ether
40e60 ꢀC), mp 207e209 ꢀC (recrystallized from petroleum ether
40e60 ꢀCeEtOAc 7:3); Rf (30% EtOAc/petroleum ether 40e60 ꢀC)
1468, 1337, 1277, 1235, 1028 cmꢂ1
; dH (600 MHz CDCl3) 7.47 (2H, d, J
7.5 Hz, Ph), 7.42 (2H, d, J 7.5 Hz, Ph), 7.37e7.34 (1H, m, Ph), 7.05 (2H,
dd, J 7.5, 0.7 Hz, Ph), 6.95 (2H, d, J 7.5 Hz, Ph), 5.11 (1H, d, J 8.2 Hz,
CHPh), 3.85 (3H, s, OMe), 3.62 (1H, d, J 11.6 Hz, CH2CHPh), 3.37e3.33
(1H, m, CH2CHPh), 2.22 (3H, s, Me), 1.91 (3H, s, Me), 1.83 (3H, s, Me);
dC (75.5 MHz, CDCl3) 158.0, 141.6, 139.7, 134.4, 134.2, 131.0, 130.9,
128.5, 128.0, 126.1, 125.8, 122.1, 119.5, 113.5, 75.5, 55.2, 48.4, 17.1,
14.4, 11.9; MS (EI), m/z 359 (100, Mþ); HRMS (ESIþ): [MþNa]þ,
found 382.1785. C24H25NNaO2 requires 382.1778.
0.47; nmax(neat) 3201, 3139, 1675, 1464, 1395, 1243 cmꢂ1
; dH
(300 MHz, CDCl3) 8.41 (1H, s, NH), 7.49e7.47 (2H, m, Ph), 7.39e7.30
(3H, m, Ph), 7.00e6.91 (4H, m, Ph), 5.72 (1H, s, CHPh), 3.84 (3H, s,
OMe), 2.24 (3H, s, Me), 1.89 (3H, s, Me), 1.88 (3H, s, Me); dC
(75.5 MHz, CDCl3) 166.0, 158.3, 139.9, 136.0, 135.4, 133.3, 131.3,
130.6, 128.6, 128.5, 126.7, 122.5, 121.8, 119.5, 113.7, 78.1, 55.2, 17.4,
14.1, 12.2; MS (EI), m/z 373 (100, Mþ); HRMS (FABþ): [M]þ, found
373.1669. C24H23NO3 requires 373.1678.
4.3.14. (E)-3,4-Dihydro-5,7,8-trimethyl-2-phenyl-6-styryl-2H-benzo
[b][1,4]oxazine (7d). Following the general procedure described
above using trans-2-phenylvinylboronic acid (2e) and benzoxazine
6 the title compound 7d was obtained (0.288 g, 81%) as a yellow solid
after purification by flash chromatography (20% EtOAc/hexane), mp
132e135 ꢀC; Rf (10% EtOAc/petroleum ether 40e60 ꢀC) 0.33;
4.3.11. 3,4-Dihydro-6-(2-methoxyphenyl)-5,7,8-trimethyl-2-phenyl-
2H-benzo[b][1,4]-oxazine (7a). Following the general procedure
described above using 2-methoxyphenyl boronic acid (2b), ben-
zoxazine 6, and Na2CO3 (1.50 mmol) or Ba(OH)2 (1.50 mmol) the
title compound 7a was obtained (as a mixture of rotamers) (0.169 g,
47%) or (0.198 g, 55%), respectively, after purification by flash
chromatography (5% EtOAc/hexane).
nmax(neat) 3387, 1595, 1468, 1448, 1379, 1339, 1108 cmꢂ1
; dH
(600 MHz, CDCl3) 7.52e7.35 (9H, m, Ph), 7.28e7.25 (1H, m, Ph), 7.14
(1H, d, J 16.5 Hz, CH]), 6.45 (1H, d, J 16.5 Hz, CH]), 5.10 (1H, d, J 8.7,
CHPh), 3.63 (1H, d, J 11.8 Hz, CH2CHPh), 3.35e3.23 (1H, m,
CH2CHPh), 2.24 (3H, s, Me), 2.23 (3H, s, Me), 2.18 (3H, s, Me); dC
(75.5 MHz, CDCl3) 141.7, 139.6, 137.7, 134.0, 130.1, 128.6, 128.5, 128.4,
128.3, 128.0, 127.3, 126.2, 126.1, 125.6, 122.4, 119.0, 75.5, 48.3, 16.8,
14.2, 11.9; MS (EI), m/z: 355 (100, Mþ); HRMS (ESIþ): [M]þ, found
355.1935. C25H25NO requires 355.1931; [MþH]þ, found 356.2007.
C25H26NO requires 356.2009.
Less polar: sticky solid; Rf (10% EtOAc/petroleum ether
40e60 ꢀC) 0.32; nmax(neat) 3370, 1578, 1495, 1279, 1237, 1109 cmꢂ1
;
dH (300 MHz, CDCl3) 7.50e7.32 (6H, m, Ph), 7.07e6.98 (3H, m, Ph),
5.14 (1H, dd, J 9.1, 2.3 Hz, CHPh), 3.77 (3H, s, OMe), 3.61 (1H, dd, J
11.8, 2.3 Hz, CH2CHPh), 3.40e3.33 (1H, m, CH2CHPh), 2.24 (3H, s,
Me), 1.91 (3H, s, Me), 1.83 (3H, s, Me); dC (75.5 MHz CDCl3) 157.1,
141.9, 139.9, 131.7, 130.5, 130.4, 128.5, 128.1, 128.0, 127.9, 126.1, 125.8,
122.1, 120.5, 119.6, 110.7, 75.6, 55.5, 48.4, 16.8, 14.1, 12.0; MS (EI), m/z
359 (100, Mþ); HRMS (FABþ): [M]þ, found 359.1879. C24H25NO2
requires 359.1885.
4.3.15. 3,4-Dihydro-5,7,8-trimethyl-2-phenyl-6-(4-vinylphenyl)-2H-
benzo[b][1,4]oxazine (7e). Following the general procedure de-
scribed above using 4-vinylphenylboronic acid (2f) and benzox-
azine 6 the title compound 7e was obtained (0.313 g, 88%) as
a yellow solid after purification by flash chromatography (20%
EtOAc/hexane), mp 179e182 ꢀC; Rf (10% EtOAc/petroleum ether
40e60 ꢀC) 0.38; nmax(neat) 3406, 1628, 1595, 1467, 1337, 1276,
More polar: sticky solid; Rf (10% EtOAc/petroleum ether
40e60 ꢀC) 0.25; nmax(neat) 3403, 1460, 1338, 1238, 1109 cmꢂ1
; dH
(300 MHz CDCl3) 7.51e7.30 (6H, m, Ph), 7.04e6.97 (3H, m, Ph), 5.13
(1H, dd, J 9.0, 2.3 Hz, CHPh), 3.76 (3H, s, OMe), 3.63 (1H, dd, J 11.8,
2.3 Hz, CH2CHPh), 3.34 (1H, dd, J 11.8, 9.0 Hz, CH2CHPh), 2.22 (3H, s,
Me), 1.89 (3H, s, Me), 1.81 (3H, s, Me); dC (75.5 MHz, CDCl3) 157.1,
141.9, 139.8, 131.8, 130.6, 130.5, 128.5, 128.1, 127.9, 127.8, 126.1, 125.9,
122.1, 120.4, 119.8, 110.7, 75.3, 55.5, 48.4, 16.8, 14.1, 12.0; MS (EI), m/z
359 (Mþ, 100); MS (EI), m/z 359 (100, Mþ); HRMS (ESIþ): [M]þ,
found 359.1883. C24H25NO2 requires 359.1880; [MþH]þ, found
360.1947. C24H26NO2 requires 360.1958.
1101 cmꢂ1
; dH (600 MHz CDCl3) 7.49e7.42 (6H, m, Ph), 7.38e7.36
(1H, m, Ph), 7.12 ( 2H, d, J 7.2 Hz, Ph), 6.79 (1H, dd, J 17.6, 10.9 Hz,
CH]CH2), 5.81 (1H, d, J 17.6 Hz, CH]CH2), 5.27 (1H, d, J 10.9 Hz,
CH]CH2), 5.13 (1H, d, J 8.9 Hz, CHPh), 3.64 (1H, d, J¼11.8 Hz,
CH2CHPh), 3.38e3.35 (1H, m, CH2CHPh), 2.24 (3H, s, Me), 1.93 (3H,
s, Me),1.84 (3H, s, Me); dC (75.5 MHz, CDCl3) 141.9,141.7,139.7,136.7,
135.5, 134.3, 130.2, 128.5, 128.1, 128.0, 126.1, 126.0, 125.3, 122.2,
119.0, 113.3, 75.5, 48.4, 17.1, 14.4, 11.9; MS (EI), m/z: 355 (100, Mþ);
HRMS (FABþ): [M]þ, found 355.1920. C25H25NO requires 355.1936.
4.3.12. 3,4-Dihydro-6-(3-methoxyphenyl)-5,7,8-trimethyl-2-phenyl-
2H-benzo[b][1,4]-oxazine (7b). Following the general procedure
described above using 3-methoxyphenyl boronic acid (2c) and
benzoxazine 6 the title compound 7b was obtained (0.288 g, 80%) as
a white gummy solid after purification by flash chromatography
(10% EtOAc/hexane); Rf (10% EtOAc/petroleum ether 40e60 ꢀC)
4.3.16. 6-(Furan-2-yl)-3,4-dihydro-5,7,8-trimethyl-2-phenyl-2H-
benzo[b][1,4]oxazine (7f). Following the general procedure de-
scribed above using 2-furanboronic acid (2g) and benzoxazine 6 the
title compound 7f was obtained (0.288 g, 90%) as an oil after puri-
fication by flash chromatography (5% EtOAc/hexane); Rf (10%
EtOAc/petroleum ether 40e60 ꢀC) 0.40; nmax(neat) 3379, 1598,
0.35; nmax(neat) 3412, 1597, 1578, 1465, 1340, 1230, 1102 cmꢂ1
(600 MHz, CDCl3) 7.50e7.29 (6H, m, Ph), 6.87 (1H, ddd, J 8.2, 2.6,
; dH
1468, 1331, 1273, 1118, 1103 cmꢂ1
; dH (600 MHz, CDCl3) 7.46 (1H, m,

10308
E.N. Koini et al. / Tetrahedron 68 (2012) 10302e10309
furyl), 7.42e7.36 (4H, m, Ph), 7.32e7.30 (1H, m, Ph), 6.43 (1H, dd, J
2.7, 1.9 Hz, furyl), 6.17 (1H, d, J 2.7 Hz, furyl), 5.06 (1H, dd, J 8.8,
1.9 Hz, CHPh), 3.58 (1H, dd, J¼11.7, 1.9 Hz, CH2CHPh), 3.29 (1H, dd,
J¼11.7, 8.8 Hz, CH2CHPh), 2.17 (3H, s, Me), 1.97 (3H, s, Me), 1.89 (3H,
s, Me); dC (75.5 MHz, CDCl3) 153.5, 143.1, 141.3, 139.5, 128.5, 128.3,
128.15, 128.07, 126.1, 123.8, 122.4, 121.7, 110.3, 109.1, 75.6, 48.1, 16.8,
14.1, 11.9; MS (EI), m/z: 320 (100, Mþ); HRMS (ESIþ): [MþH]þ, found
320.1658. C21H22NO2 requires 320.1645.
1450, 1339, 1276, 1102 cmꢂ1
; dH (600 MHz CDCl3) 7.48e7.47 (2H, m,
Ph), 7.43e7.40 (2H, m, Ph), 7.36e7.34 (1H, m, Ph), 7.20 (2H, d, J
7.7 Hz, Ph), 7.04e7.02 (2H, m, Ph), 5.12 (1H, dd, J 9.0, 2.0 Hz, CHPh),
3.62 (1H, dd, J 11.8, 2.0 Hz, CH2CHPh), 3.35 (1H, dd, J 11.8, 9.0 Hz,
CH2CHPh), 2.66 (2H, t, J 7.8 Hz, PhCH2CH2CH2CH3), 2.23 (3H, s, Me),
1.90 (3H, s, Me), 1.82 (3H, s, Me), 1.69e1.63 (2H, m,
PhCH2CH2CH2CH3), 1.43e1.37 (2H, m, PhCH2CH2CH2CH3), 0.96 (3H,
t, J 7.4 Hz, PhCH2CH2CH2CH3), dC (75.5 MHz, CDCl3) 141.6, 140.7,
139.8, 139.3,134.7,129.8,129.7,128.5,128.1,127.9,126.1,125.5,122.1,
119.2, 75.5, 48.4, 35.4, 33.7, 22.5, 17.1, 14.4, 14.0, 11.9; MS(EI), m/z:
385 (100, Mþ); HRMS (ESIþ): [MþH]þ, found 386.2496. C27H32NO
requires 386.2478.
4.3.17. 3,4-Dihydro-5,7,8-trimethyl-2-phenyl-6-(thiophen-2-yl)-2H-
benzo[b][1,4]oxazine (7g). Following the general procedure de-
scribed above using 2-thienylboronic acid (2h) and benzoxazine 6
the title compound 7g was obtained (0.285 g, 85%) as an oil after
purification by flash chromatography (5% EtOAc/hexane); Rf (10%
EtOAc/petroleum ether 40e60 ꢀC) 0.44; nmax(neat) 3385, 1595,
4.3.21. 6-Butyl-3,4-dihydro-5,7,8-trimethyl-2-phenyl-2H-benzo[b]
[1,4]oxazine (7k). Following the general procedure described above
using butylboronic acid (2l) and benzoxazine 6 the title compound
7k was obtained (0.170 g, 55%) as an oil after purification by flash
chromatography (5% EtOAc/hexane); Rf (10% EtOAc/petroleum
1496, 1421, 1343, 1114 cmꢂ1
; dH (600 MHz CDCl3) 7.47e7.40 (4H, m,
Ph), 7.36e7.33 (2H, m, Ph and thienyl), 7.08 (1H, dd, J 5.1, 3.4 Hz,
thienyl), 6.79 (1H, dd, J 3.4, 1.1 Hz, thienyl), 5.11 (1H, dd, J 8.9, 2.1 Hz,
CHPh), 3.62 (1H, dd, J 11.9, 2.1 Hz, CH2CHPh), 3.32 (1H, dd, J 11.9,
8.9 Hz, CH2CHPh), 2.21 (3H, s, Me), 2.00 (3H, s, Me), 1.91 (3H, s, Me);
dC (75.5 MHz, CDCl3) 143.1, 142.6, 139.5, 128.5, 128.3, 128.1, 127.7,
126.9, 126.8, 126.2, 126.1, 125.1, 122.3, 121.4, 75.6, 48.2, 17.1, 14.4,
11.9; MS (EI), m/z: 335 (100, Mþ); HRMS (ESIþ): [MþH]þ, found
336.1420. C21H22NOS requires 336.1417.
ether 40e60 ꢀC) 0.40; nmax(neat) 3390, 1499, 1259, 1104 cmꢂ1
; dH
(600 MHz, CDCl3) 7.45e7.39 (4H, m, Ph), 7.35e7.33 (1H, m, Ph), 5.04
(1H, dd, J 9.0, 1.9 Hz, CHPh), 3.59 (1H, dd, J 11.9, 1.9 Hz, CH2CHPh),
3.55 (1H, bs, 1H, NH), 3.29 (1H, dd, J 11.9, 9.0 Hz, CH2CHPh),
2.63e2.61 (2H, m, PhCH2CH2CH2CH3), 2.20 (6H, s, Me), 2.11 (3H, s,
Me), 1.47e1.42 (4H, m, PhCH2CH2CH2CH3), 0.98 (3H, t, J 7.0 Hz,
PhCH2CH2CH2CH3); dC (75.5 MHz, CDCl3) 140.7, 139.9, 131.6, 128.4,
128.3, 127.9, 126.1, 125.3, 122.3, 119.0, 75.4, 48.6, 32.5, 29.7, 23.2,
15.3, 14.0, 12.6, 12.0; MS(EI), m/z: 309 (100, Mþ); HRMS (ESIþ):
[MþH]þ, found 310.2171. C21H28NO requires 310.2165.
4.3.18. 3,4-Dihydro-5,7,8-trimethyl-6-(naphthalen-2-yl)-2-phenyl-
2H-benzo[I][1,4]oxazine (7h). Following the general procedure de-
scribed above using 2-naphthaleneboronic acid (2i) and benzox-
azine 6 the title compound 7h was obtained (0.319 g, 84%) as a white
solid after purification by flash chromatography (10% EtOAc/hex-
ane), mp 172e175 ꢀC; Rf (10% EtOAc/petroleum ether 40e60 ꢀC)
4.4. Biology, antiproliferative assays
0.38; nmax(neat) 3404, 1597, 1473, 1339, 1277, 1115, 1099 cmꢂ1
; dH
The antiproliferative activity of compounds 7aek was evaluated
utilizing tachyzoites of m2m3 strain expressing the yellow fluo-
rescent protein.33 Parasites of m2m3 strain were maintained in LLC-
MK2 (kidney, Rhesus monkey, Macaca mulatadATCC CCL7, Rock-
ville, MD/USA) cultures and freshly egressed parasites were col-
lected and used for experiments. Approximately 1ꢃ106 LLC-MK2
cells placed in a black with clear flat bottom 96- plate (Nalge Nunc
International, New York, USA) were infected with 1ꢃ106 parasites
resuspended in RPMI medium 1640 without phenol red (GibcoÒ,
InvitrogenÔ, USA) and supplemented with 2% of foetal bovine se-
rum. The compounds were added after 6 h of infection and the
antiproliferative effect was evaluated for 48 h and 72 h of treat-
ment. Plate fluorescence was read from the bottom in SpectraMax
Me2 Molecular Devices equipment. Excitation and emission wave-
lengths were 510 and 540 nm, respectively. All experiments were
performed together with untreated infected cultures (positive
control) and non-infected cultures (negative control-blank). For
IC50 (concentration for 50% growth inhibition) calculations, the
percentage of growth inhibition was plotted as a function of the
drug concentration by fitting the values to the non-linear curve
(600 MHz CDCl3) 7.90e7.82 (3H, m, Ph), 7.61 (1H, s, Ph), 7.51e7.48
(4H, m, Ph), 7.45e7.42 (2H, m, Ph), 7.38e7.36 (1H, m, Ph), 7.31e7.29
(1H, m, Ph), 5.16e5.13 (1H, m, CHPh), 3.65 (1H, dd, J 11.8, 2.2 Hz,
CH2CHPh), 3.38 (1H, dd, J 11.8, 9.3 Hz, CH2CHPh), 2.25 (3H, s, Me),
1.92 (3H, s, Me), 1.84 (3H, s, Me); dC (75.5 MHz, CDCl3) 141.8, 139.8,
139.7, 134.5, 133.5, 132.1, 128.8, 128.7, 128.6, 128.5, 128.4, 128.1,
127.9, 127.7, 127.6, 126.1, 126.0, 125.6, 122.3, 119.2, 75.6, 48.4, 17.2,
14.5, 12.0; MS (EI), m/z: 379 (100, Mþ); HRMS (ESIþ): [MþH]þ,
found 380.2010. C27H26NO requires 380.2009.
4.3.19. 6-(4-(Trifluoromethyl)phenyl)-3,4-dihydro-5,7,8-trimethyl-2-
phenyl-2H-benzo[b][1,4]oxazine (7i). Following the general pro-
cedure described above using 4-(trifluoromethyl)phenylboronic
acid (2j) and benzoxazine 6 the title compound 7i was obtained
(0.338 g, 85%) as a white solid after purification by flash chroma-
tography (5% EtOAc/hexane), mp 213e214 ꢀC; Rf (10% EtOAc/pe-
troleum ether 40e60 ꢀC) 0.40; nmax(neat) 3439, 1614, 1320,
1103 cmꢂ1
; dH (600 MHz, CDCl3) 7.67 (2H, d, J 7.7 Hz, Ph), 7.48e7.42
(4H, m, Ph), 7.38e7.35 (1H, m, Ph), 7.27 (2H, d, J 7.7 Hz, Ph), 5.12 (1H,
dd, J 8.8, 1.5 Hz, CHPh), 3.64 (1H, dd, J¼11.9, 1.5 Hz, CH2CHPh), 3.36
(1H, dd, J 11.9, 8.8 Hz, J CH2CHPh), 2.23 (3H, s, Me), 1.87 (3H, s, Me),
1.79 (3H, s, Me); dC (150 MHz, CDCl3) 146.2, 142.0, 139.5, 133.2,
130.4, 128.6 (q, J 32.3 Hz), 128.5, 128.3, 128.1, 126.1, 125.2 (d, J
3.62 Hz), 124.8, 124.4 (q, J 272.9 Hz), 122.5, 118.6, 75.6, 48.3, 17.1,
14.3, 11.9; dF (564.8 MHz, CDCl3) ꢂ62.3; MS (EI), m/z: 397 (100, Mþ);
HRMS (ESIþ): [MþH]þ, found 398.1726. C24H23F3NO requires
398.1726.
analysis where f¼minþ(maxꢂmin)/(1þ(x/EC50
)
Hillslope). The re-
gression analyses were performed by using Sigma Plot 8.0 software
(Systat Software Inc, Chicago, IL, USA).
Acknowledgements
We thank Eleni Siapi for obtaining HRMS spectra. We thank Dr.
Kyriakos Prousis and Mr. Giannis Christopoulos for obtaining the IR
spectra. Funding from the European Union (FP7-REGPOT-2009-1)
under grant agreement No. 245866 ‘ARCADE’, (FP6-TOK-DEV) un-
der grant agreement No. MTKD-CT-2004-014399 ‘SOPHOLIDES’
and COST Action CM0801 ‘New Drugs for Neglected Diseases’ is
gratefully acknowledged. This work was also supported by grants
from the Brazilian agencies CNPq and Faperj.
4.3.20. 6-(4-Butylphenyl)-3,4-dihydro-5,7,8-trimethyl-2-phenyl-2H-
benzo[b][1,4]oxazine (7j). Following the general procedure de-
scribed above using 4-butylphenylboronic acid (2k) and benzox-
azine 6 the title compound 7j was obtained (0.335 g, 87%) as an oil
after purification by flash chromatography (3% EtOAc/hexane); Rf
(10% EtOAc/petroleum ether 40e60 ꢀC) 0.49; nmax(neat) 3393, 1465,

E.N. Koini et al. / Tetrahedron 68 (2012) 10302e10309
10309
10. For a review, see: (a) Frisch, A. C.; Beller, M. Angew. Chem., Int. Ed. 2005, 44,
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Supplementary data
11. Darses, S.; Genet, J. P. Chem. Rev. 2008, 108, 288e325.
Copies of 1H NMR, 13C NMR and 19F NMR spectra and HPLC
chromatograms. Supplementary data related to this article can be
found at http://dx.doi.org/10.1016/j.tet.2012.10.009. These data in-
cludes MOL files and InChiKeys of the most important compounds
described in this article.
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