Imino Diels-Alder reaction of boronates: A new route to 3,4-dihydroquinolines

Article abstract of DOI:10.1016/j.jorganchem.2005.03.024

The synthesis of a series of 3,4-dihydroquinolines (3b-e, 3h and 3i) by Imino Diels-Alder reactions involving sulfolene and boronates 2a-j derived from Schiff bases is described. The reactions are regioselective leading to 4-substituted dihydroquinolines

Full text of DOI:10.1016/j.jorganchem.2005.03.024

Journal of Organometallic Chemistry 690 (2005) 2975–2988
www.elsevier.com/locate/jorganchem
Imino Diels–Alder reaction of boronates: A new route
to 3,4-dihydroquinolines
a
Mario Rodrıguez , Ma. Eugenia Ochoa , Rosa Santillan , Norberto Farfan ,
a
a,
a
*
´
´
b
Victor Barba
a
´ ´ ´
Departamento de Quımica, Centro de Investigacion y de Estudios Avanzados del IPN, 07000, Apdo. Postal. 14-740, Mexico D.F., Mexico
´
´ ´ ´
Centro de Investigaciones Quımicas, Universidad Autonoma del Estado de Morelos, Av. Universidad 1001, C.P. 62210 Cuernavaca, Morelos, Mexico
b
Received 15 February 2005; revised 14 March 2005; accepted 14 March 2005
Available online 5 May 2005
Abstract
The synthesis of a series of 3,4-dihydroquinolines (3b–e, 3h and 3i) by Imino Diels–Alder reactions involving sulfolene and bor-
onates 2a–j derived from Schiff bases is described. The reactions are regioselective leading to 4-substituted dihydroquinolines with a
cis relative stereochemistry between the phenyl group on the boron atom and the vinyl substituent at position 4, as established by X-
ray diffraction analyses of 3b, 3e, 3h and 3i.
Boronates 2 containing substituents meta to the imino fragment lead to 4-ethenyl-dihydroquinolines while para substituted deriv-
atives are more reactive and lead to 4-cyclohexenylquinolines 4 formed by a second Diels–Alder reaction with excess of butadiene.
The results show that boronates derived from Schiff bases are electron deficient species that react with sulfolene providing a new
route to 3,4-dihydroquinolines. Moreover, polarization of the imine bond activates these system toward cycloaddition.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Dihydroquinoline; Quinoline; Boronate; X-ray; NMR; Imino–Diels–Alder
1. Introduction
vides access to tetrahydroquinolines. Similarly, acids
like HBF4, CF3CO2H and TsOH [6] have been em-
ployed for the reaction with Danishefskyꢀs diene where-
by the first one provides the best results. In other cases,
the use of Lewis acids has been combined with the pres-
ence of electron withdrawing substituents in the imine
fragment providing a substantial increase in the yield
of quinolines [4]. More recently, the use of polar solvents
such as fluorinated alcohols has been reported for the
preparation of tetrahydroquinolines [7].
A main drawback in the catalyzed IDA reaction is
that although the reaction is promoted by Lewis acids,
more than stoichiometric amounts are required. More-
over, the acids may be trapped by the nitrogen atoms
present in the reactants or products which, in some
cases, are sensitive to acid conditions [8].
Hetero Diels–Alder reactions constitute a powerful
method for the preparation of biologically interesting
heterocycles [1]. For instance, the Imino Diels–Alder
reaction (IDA) provides a rapid means for the construc-
tion of functionalized rings containing nitrogen. In re-
cent years the potential of this reaction has been
explored and increasing efforts have been directed to
activate imine systems toward cycloaddition by increas-
ing its electron-deficient character.
Concerning the reaction of arylimines with activated
dienophiles, the use of Lewis acid catalysts such as InCl3
[2], SmI2(THF)2 [3], BF3–Et2O or Yb(OTf)3 [4,5] pro-
*
Corresponding author. Tel.: +52 55 5061 3725; fax: +52 55 5061
It has been reported that arylimines can act as imino-
dienophile as well as azabutadiene systems, for this
3389.
E-mail address: rsantill@cinvestav.mx (R. Santillan).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.03.024

´
M. Rodrıguez et al. / Journal of Organometallic Chemistry 690 (2005) 2975–2988
2976
reason, they can undergo intramolecular Diels–Alder
reactions [9]. Lucchini [10] described the reaction of
b-ketoarylimines with 1,3-butadiene under BF3 cataly-
sis showing that, in this case, the imine behaves both,
as imino-dienophile and azabutadiene, thus leading to
two types of derivatives: tetrahydroquinolines and tet-
rahydropyridines. Hermitage [11] reported that these
arylimines react readily as dienophiles with a wide
range of activated dienes, and as dienes with a range
of deactivated dienophiles, employing Yb(OTf)3, as
the Lewis acid (Scheme 1). The same author reported
that, under Lewis-acid catalyzed conditions, this reac-
tion proceeds by a non-concerted mechanism [12].
There are also a few reports on the use of cationic
aza Diels–Alder reactions for the preparation of tetra-
hydroquinolines from arylimines and a-methylstyrene
in the presence of tris(4-bromophenylaminium)hexa-
chloroantimonate [13].
O
O
H
N
B
N
B
R
R
O
O
O
O
2
Scheme 2. Acetolysis of type 2 boronates to give dioxaborocines.
would increase the reactivity of arylimines towards the
IDA taking advantage of boron adducts. The results
show that boron adducts derived from Schiff bases are
electron deficient species that react with sulfolene pro-
viding a new route to 3,4-dihydroquinolines.
Owing to their electron-deficient character, simple
aza-dienes are less reactive toward common electron
deficient dienophiles. The basic concept of activation
in an IDA reaction is to utilize the lone pair of electrons
of the nitrogen atom in the coordination with the Lewis
acid. This coordination changes the FMOꢀs (frontier
molecular orbitals) of the imino-dienophile and the en-
ergy difference between the HOMOdiene and the
LUMOiminodienophile is thus reduced [1b]. As a conse-
quence, these molecules tend to undergo inverse electron
demand Diels–Alder reactions.
Continuing our studies on the reactivity of boronate
derivatives, we decided to explore the IDA reaction of
a series of boron adducts (2a–j). In previous studies it
had been reported that the C@N bond in these adducts
is polarized by coordination of nitrogen to the boron
atom through a N ! B dative bond, as evidenced by
formation of acetolysis products [14] (Scheme 2). Thus
the aim of this study is to investigate alternatives that
2. Results and discussion
Boronates (2a–j) were prepared according to the pro-
cedure reported in the literature by reaction of Schiff
bases (1a–j) with the corresponding phenylboronic acid
under reflux of THF. Compounds 2b, 2g, 2h and 2i
are new and were characterized by spectroscopic tech-
niques; the remaining derivatives (2a, 2c, 2d, 2e, 2f and
2j) have been previously described in the literature [14]
(Scheme 3).
In a first approximation, the formation of type 2
products was established by the observation of the
C@N stretching band in the IR spectra. For example,
boronates 2b and 2g show bands in 1663 and
1626 cmꢀ1, which are shifted to higher wavenumber
compared to the ligands (1629 and 1621 cmꢀ1), owing
to the formation of the N–B coordinative bond. As
1
additional evidence, the H NMR data show that the
signal corresponding to the azomethine group is shifted
to lower frequency in the boronate compared to the free
ligands (Dd = 0.34 in 2b and 0.47 ppm in 2g). The same
effect is observed in the 13C NMR spectra which show
that, upon complexation, the signals for C-7 are shifted
upfield (147.8 (2b) and 152.7 ppm (2g)) compared to the
signals in the corresponding ligands which appear at
163.8 and 164.9 ppm, respectively. The small differences
between 2b and 2g, are attributed to the substituents at
the aminophenol moiety, and are in agreement with the
shifts expected based on substituent chemical shift ef-
fects (SCS) and the data previously reported for 2c, 2d
and 2e [14]. The 11B NMR chemical shifts are in the
range between 7.9 and 8.7 ppm characteristic for tetra-
coordinated species [15]. In general, the mass spectra
of boronates (2b, 2g–i) show the peak for the molecular
ion and the base peak corresponds to loss of the arylbo-
ronic fragment.
OCH3
H3CO
TMSO
N
OCH3
EtO2C
O
Yb(OTf)3
65 %
N
CO2Et
OAc
OAc
Yb(OTf)3
H3CO
N
CO2Et
H
59 %
Scheme 1. Products from the reaction of an arylimine with two dienes.

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M. Rodrıguez et al. / Journal of Organometallic Chemistry 690 (2005) 2975–2988
2977
R1
12
R1
13
6
3
7
R2
R2
5
11
N
B
8
THF
1
N
10
9
4
O
B(OH)2
O
2
HO
OH
o
1a-j
m
p
R3
R1
H
R2
H
R3
H
R3
a
b
c
d
e
f
p-tBu
Me
Cl
NO2
H
H
H
H
H
H
H
H
H
2a-j
SO2
Toluene
Me
H
g
h
i
H
Cl
NO2
H
NO2
H
H
H
CO2Me
CO2Me
CO2Me
18
15
19
20
j
H
17
16
16
4a
R1
15
4
R1
5
R2
4
5
4a
R2
R1
3
6
7
3
14
11
6
1
N
14
R2
13
12
1
N
2
8a
13
12
9
8
2
8a
7
9
8
O
B
O
O
N
B
10
NaOH
O
10
o
11
OH
o
OH
m
p
R3
m
p
R3
3b-e, h, i
Scheme 3. Synthesis of 2,3-dihydroquinolines 3 and quinolines 4 from boron adducts (2).
4a, c,d, f, g, j
5b, 5d
The X-ray diffraction analysis of 2b confirmed the
heterocyclic structure (Fig. 1). Selected bond distances
and angles, torsion angles and TetraHedral Character
(THC) are listed in Table 1, while Table 2 summarizes
the crystallographic data. The distance for the N ! B
˚
dative bond is 1.569 (13) A being smaller than that re-
ported for boronate 2a and similar to 2d [14]. The bond
distances for this type of compounds are in the range
˚
from 1.586(2) to 1.681(5) A [14,16] and [17].
The IDA reaction of boronates 2a–j was carried out
in a sealed ampule using 6 equivalents of sulfolene, tol-
uene as solvent and stirring 12–22 h at 120 ꢁC under N2
atmosphere in the dark. Boronates 2b, 2e, 2h and 2i
afforded the 3,4-dihydroquinolines 3b, 3e, 3h and 3i;
compounds 2c and 2d afforded a mixture of the corre-
sponding dihydroquinolines 3c–d and traces of quino-
lines 4c and 4d while boronates 2a, 2f, 2g and 2j
yielded the 4-substituted quinolines 4a, 4f, 4g and 4j
(Scheme 3) in low yields.
It is important to mention that NMR analyses of the
crude reaction mixture showed that the products are
formed in good yields; however, the presence of an allylic
system, as well as the boronate moiety lead to extensive
decomposition upon purification by chromatographic
Fig. 1. Perspective view for the molecular structure of boronate 2b.
Ellipsoids are shown at the 50% probability level.

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M. Rodrıguez et al. / Journal of Organometallic Chemistry 690 (2005) 2975–2988
2978
Table 1
Selected bond lengths, bond angles, torsion angles and THC value for 2b, 3b, 3e, 3h, 3i, 4c and 4d
Compound
2ba
3b
3e
3h
3i
4c
4d
˚
Bond lengths (A)
N(1)–B(1)
N(1)–C(8a)
N(1)–C(2)
O(1)–B(1)
1.569(13)
1.411(8)
1.292(6)
1.496(6)
1.364(5)
1.496(6)
1.333(7)
1.595(7)
1.577(5)
1.382(5)
1.298(5)
1.475(5)
1.353(5)
1.479(6)
1.365(5)
1.590(6)
1.566(4)
1.391(4)
1.298(3)
1.463(4)
1.363(4)
1.530(4)
1.349(3)
1.593(5)
1.575(3)
1.391(3)
1.308(3)
1.466(3)
1.345(3)
1.516(3)
1.347(3)
1.603(4)
1.576(3)
1.392(3)
1.297(3)
1.462(3)
1.362(3)
1.508(3)
1.354(2)
1.608(3)
1.578(5)
1.359(4)
1.321(4)
1.472(5)
1.361(4)
1.509(5)
1.358(4)
1.596(5)
1.590(3)
1.387(2)
1.367(2)
1.470(3)
1.433(3)
1.608(3)
1.356(3)
1.620(3)
O(1)–C(10)
O(2)–B(1)
O(2)–C(8)
B(1)–CPh
Bond angles (ꢁ)
O(1)–B(1)–N(1)
O(1)–B(1)–O(2)
O(1)–B(1)–CPh
O(2)–B(1)–N(1)
O(2)–B(1)–CPh
N(1)–B(1)–CPh
C(10)–O(1)–B(1)
B(1)–O(2)–C(8)
C(2)–N(1)–C(8a)
C(2)–N(1)–B(1)
C(8a)–N(1)–B(1)
106.6(5)
110.5(6)
113.3(7)
100.3(7)
112.3(4)
112.8(7)
115.9(4)
107.4(6)
129.5(6)
122.9(7)
107.0(5)
104.9(3)
113.6(4)
113.5(4)
100.0(4)
113.0(4)
110.7(3)
117.3(3)
109.8(3)
122.9(3)
126.1(4)
108.3(3)
105.6(2)
113.5(2)
113.9(3)
98.4(2)
106.2(2)
113.0(3)
112.8(2)
99.03(19)
111.3(2)
113.7(2)
119.42(19)
109.69(18)
122.2(2)
126.3(2)
108.50(19)
106.02(17)
113.96(18)
113.13(18)
99.53(16)
103.2(3)
115.1(3)
112.3(3)
98.3(3)
103.11(16)
113.79(17)
112.32(17)
100.15(15)
112.22(17)
114.38(17)
115.28(15)
108.32 (15)
124.21(15)
127.47(16)
107.21(16)
109.9(2)
114.5(3)
115.2(2)
108.0(2)
122.6(3)
127.1(2)
108.7(2)
110.96(17)
112.37(18)
117.26(17)
108.85(15)
122.96(18)
126.99(18)
107.75(15)
110.2(3)
116.9(3)
115.9(3)
108.7(3)
122.0(3)
127.2(3)
109.8(3)
Torsion angles (ꢁ)
O(1)–B(1)–N(1)–C(2)
O(2)–B(1)–N(1)–C(8a)
C(4a)–C(4)–C(15)C(16)
N(1)–C(8a)–C(8)–O(2)
36.3(7)
ꢀ20.5(7)
31.7(6)
ꢀ12.3(4)
0.5(7)
30.5(3)
28.1(3)
29.4(3)
ꢀ35.7(5)
14.7(4)
ꢀ37.3(3)
13.4(2)
ꢀ17.8(3)
ꢀ1.5(6)
ꢀ1.9(3)
ꢀ13.2(2)
124.5(4)
ꢀ1.7(2)
ꢀ15.1(2)
ꢀ128.8(4)
ꢀ41(3)
ꢀ91.7(5)
ꢀ83.7(3)
ꢀ2.3(6)
74.4
ꢀ3.7(5)
70.1
ꢀ3.4(4)
62.2
ꢀ2.6(3)
66.16
THC (%)
68.0
70.5
71.3
a
For compound 2b the numbering scheme is different: C(2) = C(7), C(8a) = C(8), C(8) = C(13), C(10) = C(1), O(1) = O(2), O(2) = O(1).
procedures, this has been observed previously in the liter-
ature [4]. Nonetheless, for type 3 derivatives the yields
were improved by extraction with a saturated NH4Cl
solution and successive washings with hexane.
comparison with values reported in the literature [19].
The same procedure was used for the assignment of
the aliphatic protons: H-3a (2Jgauche = 1.2 Hz) and H-
3b (2Janti = 7.4 ppm) based on observed couplings with
H-4 [19].
Formation of 4-cyclohexenyl substituted quinolines 4
can be explained by a second Diels–Alder reaction of the
vinylic substituent in type 3 compounds with excess of
butadiene present in the reaction medium under pres-
sure, since butadiene is not an active diene and therefore
requires strong reaction conditions [18], even when the
second IDA reaction is followed by aromatization.
The results show that boronates substituted at posi-
tion 11 (R2) favor formation of quinolines (4), while
substituents meta to the imino fragment (R1) lead to
dihydroquinolines as the major products.
1
Unambiguous assignment of the 13C and H spectra
for all compounds was based on one and two dimen-
sional techniques (COSY, HETCOR and HMBC). The
13C NMR spectra of 3,4-dihydroquinoline derivatives
(3b–3e, 3h and 3i) showed the presence of two new ali-
phatic signals corresponding to C-3 and C-4, in the
range between 31.8 and 36.4 ppm, as well as vinylic car-
bons in the range from 135.2 to 137.9 (C-15) and 116.0
to 117.3 (C-16). The signal corresponding to C-4a ap-
pears in the range from 123.8 to 124.7 ppm which was
shifted 10 ppm upfield with regard to the corresponding
signal (C-13) in the boronate. Also the signal ascribed to
C-5 in 3,4-dihydroquinolines was shifted around 17 ppm
upfield with regard to the boronate (C-12). The 11B
NMR spectra of 3,4-dihydroquinolines showed signals
between 7.8 and 8.6 ppm, characteristic for tetracoordi-
ated boron atoms [15].
1
The H NMR spectra of 3,4-dihydroquinolines 3b–e,
3h, 3i show the disappearance of the signal for the imine
proton (H-7). Evidence for the formation of the IDA ad-
duct was obtained from the ABX systems assigned to
the allylic system (H-16a, H-16b and H-15), and the
AMX system from the aliphatic protons (H-3a, H-3b
and H-4). Individual assignment of the vinylic H-16a
(5.09–5.19 ppm) and H-16b (4.99–5.14 ppm) signals
was performed based on coupling constants with H-15
The X-ray diffraction analysis of 3b, 3e, 3h and 3i
(Fig. 2) established the structure for the 3,4-dihydro-
quinolines derivatives. Selected bond distances, angles,
3
(3Jcis = 10 Hz, Jtrans = 17 Hz), H-4 (4J = 1.3 Hz), and

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M. Rodrıguez et al. / Journal of Organometallic Chemistry 690 (2005) 2975–2988
2979
Table 2
Crystallographic data for compounds 2b, 3b, 3e, 3h, 3i, 4c and 4d
Compounda
2b
3b
3e
3h
3i
4c
4d
Crystal data
Formula
C
23H22BNO2
C27H26BNO2
C23H17BN2O4 C25H19BNClO3 C50H38B2N4O10 C28H24BN O2 C27H21BNClO2
0.4 · 0.4 · 0.3 0.15 · 0.35 · 0.45
Crystal size
FW (g/mol)
Space group
0.24 · 0.24 · 0.18 0.24 · 0.24 · 0.18 0.2 · 0.2 · 0.3 0.25 · 0.25 · 0.3 0.4 · 0.4 · 0.5
355.23
P21/n
407.3
P21/c
396.20
P21/c
427.70
P21/c
876.46
ꢀ
417.29
P21/n
437.71
P21/n
P1
Cell parameters
˚
a (A)
˚
8.219(5)
17.731(5)
12.880(5)
90.0
8.8579(8)
19.661(3)
12.5186(10)
90.0
10.922(2)
13.491(2)
12.901(3)
90.0
12.4738(3)
13.7940(4)
12.6889(4)
90.0
12.350(5)
12.596(5)
13.987(5)
83.080 (5)
89.246 (5)
84.590 (5)
2150.4 (14)
2
12.447(3)
14.893(2)
13.056(3)
90.0
12.4926(2)
14.9250(3)
13.9250(3)
90.0
b (A)
˚
c (A)
a (ꢁC)
b (ꢁC)
92.335 (5)
90.0
93.459(7)
90.0
90.929 (16)
90.0
93.4600 (10)
90.0
93.459(7)
90.0
117.2410(10)
90.0
c (ꢁCꢀ) 3
˚
V (A
)
1875.5 (15)
4
1.258
2176.2 (5)
4
1.243
1900.6 (6)
4
1.385
2179.32 (11)
4
1.304
2147.6 (7)
4
1.291
2308.38 (8)
4
1.259
Z
dcalcd (g/cm3)
1.354
Data collectionb
Limit of h
Total reflections
2–26
3934
2–26
4541
4261
2–27
4047
3844
3–28
9094
4920
3–28
16085
9562
2–26
4547
4356
2–27
9161
4922
Unique reflections 2002
Refinement
R/Rw (F)c
0.041/0.221
R/Rw (F2) (all data) 0.065/0.102
0.044/0.274
0.102/0.172
0.92
0.054/0.179
0.120/0.166
0.98
0.052/0.103
0.129/0.155
1.02
0.060/0.129
0.152/0.190
1.02
0.0564/0.2251 0.0520/0.0821
0.1230/0.1756 0.1220/0.1403
Goodness-of-Fit
Number of
variables
1.05
234
0.907
386
1.022
374
384
328
357
736
ꢀ3
˚
Dqmin (e Aꢀ3
)
ꢀ0.10
ꢀ0.20
ꢀ0.31
ꢀ0.26
ꢀ0.42
ꢀ0.198
ꢀ0.359
˚
Dqmax (e A
)
0.10
0.17
0.56
0.26
0.40
0.229
0.304
a
´
SHELXS-1993, version 1.8.
b
c
T = 295 K, kMo Ka = 0.71073 radiation.
P
P
P
P
2
2 1=2
R ¼ ðkF okF ckÞ= j F o j; Row ¼ ½ wðj F o j ꢀ j F c j Þ = w j F oj ꢁ
.
torsion angles and values for the THC are listed in Table
1, while Table 2 summarizes crystallographic data for all
compounds. The distance for the N ! B bond in 3,4-
dihydroquinolines 3b, 3e, 3h and 3i showed values from
tons which were assigned to the cyclohexenyl fragment
as well as olefinic protons around 5.90 ppm for H-17
and H-18. The aromatic region shows signals character-
istic for the quinoline system, a singlet for H-3 in the
range between 7.59 and 7.79 ppm. The 13C NMR spec-
tra show two sets of signals for several carbon atoms
in the quinoline fragment, indicative of the existence
of two diastereoisomers.
The X-ray analysis of 4c and 4d established the struc-
ture of the quinoline derivatives. Table 2 summarizes
crystallographic data for the two compounds and Table
1 contains selected bond distances, angles, torsion angles
and values for the THC.
˚
1.566(4) to 1.577(5) A, in agreement with values re-
ported for boronates [14]. The angles around the boron
atom have values close to a tetrahedron (Table 2). The
THC character was evaluated using the method de-
scribed by Ho¨pfl [17] showing an average value of 70%
(Table 1) which is smaller than that observed in previ-
ously reported boronates [14] due to an increase in the
annular tension of the dihydroquinoline ring. The angles
around the O(2)–B(1)–N(1) fragment, which are part of
the five membered-rings, are smaller that other angles
around the boron atom. The vinyl substituent and the
phenyl group attached to boron are cis, and in turn these
groups are perpendicular to the plane of the quinoline
ring (Fig. 2). This allows to conclude that the IDA reac-
tion on boron adducts provides the endo product.
As mentioned above, in the case of boronates 2a, 2c,
2d, 2f, 2g, and 2j, excess of sulfolene led to formation of
quinolines 4a, 4c, 4d, 4f, 4g and 4j, which are obtained
by a second Diels–Alder reaction with butadiene.
The N ! B bond lengths for compounds 4c and 4d
˚
are 1.578(5) and 1.590(3) A, respectively, which are sig-
nificantly shorter than those reported for boronates de-
rived from 8-hydroxyquinoline and diphenylboronic
1.61(1), 9-BBN 1.637(3) [20] or diethylboronic acid
˚
1.636(5) A [21].
The torsion angle for the NCCO fragment in the five-
membered boroxazolidine ring of 4c (ꢀ3.4ꢁ) and 4d
(ꢀ2.6ꢁ) showed a value closer to that of boronate 2b
ꢀ2.3(6) than to those reported for derivatives prepared
from 8-hydroxyquinoline and diphenylboronic acid
(ꢀ0.7) [20]. The five-membered ring in 4c and 4d is
1
The H NMR spectra of quinolines 4a, 4c, 4d, 4f, 4g
and 4j showed signals corresponding to aliphatic pro-

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M. Rodrıguez et al. / Journal of Organometallic Chemistry 690 (2005) 2975–2988
2980
Fig. 2. Perspective view of the molecular structures for compounds 3b, 3e, 3h, 3i, 4c and 4d.
nearly planar with a deviation of the boron atom from
˚
the plane of the hydroxyquinoline ring with torsion an-
gles of C(4a)–C(4)–C(15)–C(16) ꢀ91.7ꢁ (5) and ꢀ83.7ꢁ
(3) in 4c and 4d, respectively.
The 3,4-dihydroquinolines adducts 3b and 3d, were
hydrolyzed under basic conditions to give dihydroquin-
olines 5b and 5d in quantitative yields (Scheme 3). The
products were analyzed by NMR, which shows that
the hydrogens at position 3 undergo deuterium ex-
change upon standing in methanol-d6. The 13C NMR
the plane of ꢀ0.094 and 0.088 A, respectively. Also,
for the six-membered ring, the deviation of the oxygen
˚
atom is 0.235 and ꢀ0.257 A for 4c and 4d.
The cyclohexenyl substituent shows a half-chair con-
formation with a torsion angle of 5.2ꢁ for the C17–C18–
C19–C20 fragment and 54.56ꢁ for C–16–C15–C20–C19,
with C-15 out of the plane of the six-membered ring
(Fig. 2). The cyclohexenyl group is perpendicular to

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M. Rodrıguez et al. / Journal of Organometallic Chemistry 690 (2005) 2975–2988
2981
R1
R1
R1
R1
H
R2
R2
R2
H
R2
N
B
N
B
N
B
N
B
O
O
O
O
O
O
O
O
∆
R3
R3
R3
R3
2a-2g
Scheme 4. Mechanism proposed for the formation of dihydroquinolines and quinolines from boronates and sulfolene.
spectra showed that C-10 is shifted 6.0 ppm upfield com-
pared to the IDA adducts, while the chemical shifts for
the remaining signals are fairly constant.
Concerning the reaction mechanism, it has been re-
ported that IDA reaction of arylimines with some
dienophiles, employing a Lewis acid as catalyst, are
reaction of the vinylic fragment; while meta substituted
derivatives lead to dihydroquinolines. Moreover, polar-
ization of the imine bond in boronates activates these
systems toward cycloaddition, providing a new route
to dihydroquinoline synthesis. Further studies using
other electron rich dienophiles are in progress.
non-concerted processes [12]. An HOMOdienophile
–
LUMO2-azabutadiene controlled asynchronous process
(inverse electron demand) has been proposed, although
a stepwise zwitterionic mechanism is possible for polar
dienophiles or for catalyzed processes [11,12,22,23],
since experimental evidence indicates that the concerted
pathway is 2.7 kcal molꢀ1 below the stepwise alterna-
tive [24].
In the case of the boronates studies herein, the thermal
IDA reaction of boronates 2a–2g with sulfolene may be
rationalized by initial cycloaddition of sulfolene to the 2-
azabutadiene system, followed by aromatization to give
dihydroquinolines 3b–e, 3h and 3i (Scheme 4). In turn,
compounds 4c and 4d are formed by Diels–Alder reac-
tion of the vinyl fragment with excess sulfolene followed
by aromatization to give the corresponding quinoline.
4. Experimental
4.1. Instrumentals
NMR studies were obtained on Bruker 300 Avance
DPX and JEOL eclipse +400 spectrometers. Standards
were BF3 Æ OEt2(11B). Chemical shifts are stated in parts
per million. IR spectra were recorded on a Perkin–Elmer
16F-PC FT-IR spectrophotometer. Mass spectra were
determined on a HP 5989 A equipment. Elemental anal-
yses were realized on a Thermofinnigan Flash 1112 C,
H, N, S, O instrument. Melting points were obtained
on Electrothermal 9200 equipment and are uncorrected.
4.2. X-ray crystallography
3. Conclusions
X–ray diffraction studies of single crystal were real-
ized on a KAPPA CCD diffractometer. Solution and
refinement: direct method SHELXS-92 for structure solu-
tion and the SHELXL-97 [25] software package for refine-
ment and data output.
Boron adducts derived from Schiff bases provide a
new route for the synthesis of 3,4-dihydroquinolines
and quinolines. The reaction proceeds by inverse elec-
tron demand because the 2-azabutadiene system present
in the boronates is electron deficient and it reacts with
butadiene, an electron-activated dienophile. The reac-
tion is regioselective, as expected for hetero Diels–Alder
reactions yielding the 4-substituted derivatives. Further-
more, only one stereoisomer was isolated showing a cis
disposition between the vinyl substituent and the phenyl
group. Additionally, the reaction is sensitive to stereo-
electronic effects and substituents para to the imine
bond, in the fragment derived from the aminophenol, in-
crease the reactivity and lead to further Diels–Alder
4.2.1. Materials
Starting materials and solvents were commercially
available. [2-(2-Hydroxybenzyliden)amino]-phenol (1a),
[2-(2-hydroxybenzyliden)amino]-4-methylphenol (1c),
[2-(2-hydroxybenzyliden)amino]-4-chlorophenol
[2-(2-hydroxybenzyliden)amino]-4-nitrophenol
[2-(2-hydroxybenzyliden)amino]-5-methylphenol
(1d),
(1e),
(1f),
2-phenyl-40-methylbenzo[d]benzo[h]-6-aza-1,3-dioxa-2-
boracyclonon-6-ene (2c), 2-phenyl-40-chlorobenzo[d]-
benzo[h]-6-aza-1,3-dioxa-2-boracyclonon-6-ene
(2d),

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2982
2-phenyl-40-nitrobenzo[d]benzo[h]-6-aza-1,3-dioxa-2-bo-
racyclonon-6-ene (2e), 2-phenyl-30-methylbenzo[d]ben-
zo[h]-6-aza-1,3-dioxa-2-boracyclonon-6-ene (2f) and
2-[(4-acetyl)phenyl]-benzo[d]-benzo[h]-6-aza-1,3-dioxa-
2-boracyclonon-6-eno (2j) were prepared as described
in the literature [14].
119.4 (C-1), 119.2 (C-5), 116.8 (C-3), 115.1 (C-12),
110.8 (C-10). Anal. Calc. for C13H10N2O4: C, 60.46;
H, 3.87; N, 10.85. Found: C, 60.42; H, 3.98; N, 10.81%.
4.2.3. General procedure for the preparation of boron
adducts 2b, 2g, 2h, 2i
An equimolar amount of phenylboronic acid (or
4-acetylphenylboronic) was added to a solution of the
tridentate ligand in THF (usually about 15 ml for 2–
3 mmol). The mixture was refluxed for 1 h (for 2b and
2g) or 8 h (for 2h and 2i), the solvent and the water
formed during the reaction were removed with a
Dean-Stark trap. The solid was collected by filtration
and washed with small amounts of an ethyl acetate/hex-
ane mixture (1:9).
4.2.2. General procedure for the preparation of Schiff
bases 1b and 1g
Equimolar quantities of the corresponding o-amino-
phenol and salicylaldehyde were heated under reflux in
methanol for 30 min. The solvent and water formed dur-
ing the reaction were removed with a Dean-Stark trap to
yield a solid, which was washed with a hexane/ethyl ace-
tate mixture (9:1) and used without further purification.
4.2.2.1. [2-(2-Hydroxybenzyliden)amino]-4-tert-butyl-
phenol (1b). The title compound was prepared from
1.00 g (6.05 mmol) of 2-amino-4-tert-butyl-phenol and
0.73 g (6.05 mmol) of salicylaldehyde to give 1.46 g
(90% yield) of 1b as a brown solid. M.p.: 139–139 ꢁC.
4.2.3.1. [2-Phenyl-40-tert-butylbenzo[d]benzo[h]-6-aza-
1,3-dioxa-2-boracyclonon-6-ene (2b). The title com-
pound was prepared from 1.00 g (2.81 mmol) of 1b
and phenylboronic acid (0.34 g 2.81 mmol), to give
1.05 g (80% yield) of 2b as an orange solid. M.p.: 203–
ꢀ
ꢀ
IR mmax (KBr) 3453, 2960, 1629 (C@N), 1527, 1486,
205 ꢁC. IR mmax (KBr) 2962, 1623 (C@N), 1455, 1176,
1486, 1285, 1220, 1147 cmꢀ1. MS (70 eV) m/z (%) 269
(M+, 61), 254 (100), 212 (2), 176 (6), 160 (12), 148 (4),
132 (15), 120 (7), 77 (6), 51 (3).1H NMR (300 MHz,
CDCl3) d:12.47 (1H, br, OH), 8.69 (1H, s, H-7); 7.46
(1H, dd, J = 7.6, 1.6 Hz, H-6), 7.41 (1H, ddd, J = 8.2,
7.5, 1.6 Hz, H-4), 7.26 (1H, dd, J = 8.5, 2.3 Hz, H-11),
7.13 (1H, d, J = 2.3 Hz, H-13), 7.04 (1H, d, J = 8.2 Hz,
H-3), 6.99 (1H, td, J = 7.5, 1.3 Hz, H-5), 6.97 (1H, d,
J = 8.5 Hz, H-10), 5.79 (1H, br, OH), 1.35 (9H, s,
C(CH3)3). 13C NMR (75 MHz, CDCl3) d:163.8 (C-7),
160.7 (C-2), 147.8 (C-12), 144.3 (C-9), 135.3 (C-8),
133.8 (C-4), 132.8 (C-6), 125.9 (C-11), 119.7 (C-5),
119.5 (C-1), 117.4 (C-3), 115.6 (C-10), 115.5 (C-13),
34.6 (C(CH3)3), 31.7 (C(CH3)3). Anal. Calc. for
C17H19NO2: C, 75.83; H, 7.06; N, 5.20. Found: C,
75.83; H, 7.42; N, 5.26%.
961, 752 cmꢀ1. MS (70 eV) m/z (%) 355 (M+, 10), 340
(3), 278 (M+–C6H5, 100), 262 (40), 248 (9), 222 (3),
1
117 (7), 77 (3), 51 (2). H NMR (400 MHz, CDCl3):
8.35 (1H, s, H-7), 7.53 (1H, dd, J = 8.3, 7.5 Hz, H-4),
7.46 (1H, d, J = 1.3 Hz, H-13), 7.40 (1H, d, J = 8.8 Hz,
H-11), 7.26–7.39 (3H, m, H-o, 6), 7.21 (1H, d,
J = 8.3 Hz, H-3), 7.13–7.19 (3H, m, H-m, p), 7.04 (1H,
d, J = 8.8 Hz, H-10), 6.93 (1H, t, J = 7.5 Hz, H-5),
1.34 (9H, s, C(CH3)3). 13C NMR (75 MHz, CDCl3)
d:157.4 (C-2), 156.6 (C-9), 147.8 (C-7), 142.9 (C-12),
137.6 (C-4), 131.3 (C-o), 131.3 (C-6), 130.0 (C-8),
129.9 (C-11), 127.8 (C-p), 127.4 (C-m), 120.3 and 120.2
(C-3 and C-5), 119.3 (C-1), 114.5 (C-10), 111.7 (C-13),
34.6 (C(CH3)3), 31.6 (C(CH3)3). 11B NMR (96 MHz,
CDCl3) d: 7.9 ppm (h1/2 = 288 Hz). Anal. Calc. for
C23H22NO2B: C, 77.74; H, 6.19; N, 3.94. Found: C,
77.34; H, 6.30; N, 3.99%.
4.2.2.2. [2-(2-Hydroxybenzyliden)amino]-5-nitrophenol
(1g). The title compound was prepared from 3.00 g
(19.58 mmol) of 2-amino-5-nitrophenol and 2.39 g
(19.60 mmol) of salicylaldehyde, to give 3.60 g (90%
4.2.3.2. 2-Phenyl-50-nitrobenzo[d]benzo[h]-6-aza-1,3-
dioxa-2-boracyclonon-6-ene (2g). The title compound
was prepared from 3.00 g (11.62 mmol) of 1g and phen-
ylboronic acid (1.42 g, 11.61 mmol), to give 1.05 g (92%
yield) of 2g as an orange solid. M.p.: 227–228 ꢁC. IR
ꢀ
yield) of 1 g as a red solid. M.p.: 220 ꢁC. IR mmax
(KBr) 3453, 2924, 2344, 1621 (C@N), 1523, 1344,
1215, 763 cmꢀ1 MS (70 eV) m/z (%) 258 (M+, 100),
241 (9), 211 (32), 183 (10), 165 (31), 120 (8), 107 (5),
ꢀ
mmax (KBr) 3443, 2924, 2853, 1626 (C@N), 1526, 1339,
1181, 956, 758 cmꢀ1. MS (70 eV) m/z (%) 344 (M+,
14), 268 (17), 267 (M+–C6H5, 100), 221 (46), 193 (1).
1H NMR (300 MHz, CDCl3) d:8.54 (1H, s, H-7), 7.93
(1H, d, J = 2.2 Hz, H-10), 7.87 (1H, dd, J = 8.6,
2.2 Hz, H-12), 7.69 (1H, ddd, J = 8.6, 7.1, 1.5 Hz, H-
4), 7.58 (1H, d, J = 8.6 Hz, H-13), 7.50 (1H, dd,
J = 7.8, 1.6 Hz, H-6), 7.32–7.26 (3H, m, H-o, H-3),
7.22–7.15 (3H, m H-m, p), 7.04 (1H, ddd, J = 1.1, 7.2,
7.8 Hz, H-5). 13C NMR (75 MHz, CDCl3) d: 159.0 (C-
9), 158.7 (C-2), 152.7 (C-7), 150.4 (C-11), 140.4 (C-4),
1
94 (15), 78 (10). H NMR (300 MHz, CDCl3) d:13.04
(1H, s, OH), 10.72 (1H, s, OH), 9.01 (1H, s, H-7), 7.79
(1H, dd, J = 9.4, 2.4 Hz, H-12), 7.77 (1H, d,
J = 2.4 Hz, H-10), 7.68 (1H, dd, J = 7.8, 1.3 Hz, H-6),
7.52 (1H, d, J = 9.4 Hz, H-13), 7.44 (1H, td, J = 7.8,
1.3 Hz, H-4), 7.01 (1H, td, J = 7.8, 1.3 Hz, H-5), 6.97
(1H, d, J = 7.8, H-3). 13C NMR (75 MHz, CDCl3)
d:164.9 (C-7), 160.7 (C-2), 151.2 (C-9), 145.9 (C-11),
142.0 (C-8), 134.0 (C-4), 132.7 (C-6), 120.6 (C-13),

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2983
136.2 (C-8), 132.6 (C-6), 131.4 (C-o), 128.8 (C-p), 128.0
4.2.4. General procedure for the Imino Diels–Alder
reaction of boron adducts
(C-m), 121.4 and 121.1 (C-5, C-3), 119.3 (C-1), 115.5 and
115.3 (C-12, C-13), 110.8 (C-10). 11B NMR (96 MHz,
CDCl3) d: 8.7 ppm (h1/2 = 152 Hz). Anal. Calc. for
C19H13N2O4B: C, 66.27; H, 3.77; N, 8.13. Found: C,
65.98; H, 3.84; N, 7.96%.
Boron adducts 2a–2j (1 equiv), sulfolene (3 equiv),
2 ml of toluene and traces of hydroquinone were placed
in a sealed ampule and heated for 12–22 h at 120 ꢁC un-
der nitrogen atmosphere and protected from light. The
solvent was removed under vacuum and the product ex-
tracted with a CH2Cl2-saturated NH4Cl solution. The
organic phase was dried over Na2SO4, and evaporated
under vacuum. Samples for elemental analysis were ob-
tained by purification on silica gel (70–230 mesh) using
hexane–ethylacetate (95:5).
4.2.3.3. 2-(4-Acetylphenyl)-40-chlorobenzo[d]benzo[h]-
6-aza-1,3-dioxa-2-boracyclonon-6-ene (2h). The title
compound was prepared from 1d (2.50 g, 10.09 mmol)
and 4-acetylphenylboronic acid (1.82 g, 11.0 mmol) to
give 3.21 g (85% yield) as a yellow solid. M.p.: 213–
ꢀ
215 ꢁC. IR mmax (KBr) 3339, 3035, 1672 (C@O), 1619
(C@N), 1548, 1469, 1268, 1182, 957, 824, 759 cmꢀ1
.
4.2.4.1. Phenyl[2(20-hydroxyphenyl-O)-4-ethenyl-5-tert-
buthyl-8-(3,4-dihydroquinolate)O0,N))]boron (3b). The
title compound was prepared from 2b (1.00 g,
2.80 mmol) and sulfolene (1.00 g, 8.40 mmol), heating
for 12 h, to give 1.00 g (87% yield) of 3b. M.p.: 363–
MS (70 eV) m/z (%); 375 (M+, 1), 258 (37), 257 (24),
1
256 (M+-C6H4COCH3, 100), 221(11), 77(10), 42(8). H
NMR (CDCl3, 300 MHz) d: 8.42 (1H, s, H-7), 7.72
(2H, d, J = 8.2 Hz, H-m), 7.61 (1H, ddd, J = 8.5, 7.5,
1.6 Hz, H-4), 7.49 (1H, d, J = 2.2 Hz, H-13), 7.44 (1H,
dd, J = 7.8, 1.6 Hz, H-6), 7.39 (2H, d, J = 8.2 Hz,
H-o), 7.32 (1H, dd, J = 8.7, 2.2 Hz, H-11), 7.24 (1H, d,
J = 8.5 Hz, H-3), 7.04 (1H, d, J = 8.7 Hz, H-10), 7.00
(1H, td, J = 7.5, 1.0 Hz, H-5), 2.50 (3H, s, Me). 13C
NMR (CDCl3, 75.5 MHz) d: 198.7 (C@O), 157.6 (C-
2), 157.3 (C-9), 150.1 (C-7), 139.1 (C-4), 136.8 (C-8),
132.6 (C-11), 131.9 (C-6), 131.5 (C-o), 131.2 (C-p),
127.5 (C-m), 124.6 (C-12), 121.1 (C-5), 120.6 (C-3),
119.1 (C-10), 116.3 (C-1), 115.6 (C-13), 26.8 (Me).11B
NMR (CDCl3, 96.3 MHz) d: 8.0 ppm.(h1/2 = 219 Hz).
Anal. Calc. for C21H15BNO3Cl: H, 3.99; C, 67.11; N,
3.72. Found: H, 4.00; C, 67.15; N, 3.66%.
ꢀ
364 ꢁC. IR mmax (KBr) 3047, 2920, 1629 (C@N), 1551,
1463, 1325, 1186, 1015, 956, 755 cmꢀ1. MS (70 eV) m/z
(%) 407 (M+, 1), 330 (100), 300 (7), 283 (5), 129 (9), 97
1
(7), 57 (16). H NMR (400 MHz, CDCl3) d:7.52 (1H,
ddd, J = 8.5, 7.1, 1.5 Hz, H-12); 7.49 (1H, dd, J = 7.9,
1.5 Hz, H-14), 7.38–7.42 (2H, m, H-o), 7.35 (1H, d,
J = 8.7 Hz, H-6), 7.24 (3H, dd, J = 8.5, 1.0 Hz, H-11),
7.16-7.19 (3H, m, H-m, p), 6.92 (1H, ddd, J = 7.9, 7.1,
1.0 Hz, H-13), 6.88 (1H, d, J = 8.7 Hz, H-7), 5.95 (1H,
ddd, J = 17.1, 10.3, 5.2 Hz, H-15), 5.16 (1H, ddd,
J = 10.3, 1.7, 0.8 Hz, H-16a), 4.99 (1H, ddd, J = 17.1,
1.7, 0.8 Hz, H-16b), 4.43–4.38 (1H, m, H-4), 3.51 (1H,
dd, J = 19.5, 1.7 Hz, H- 3a), 2.76 (1H, dd, J = 19.5,
6.4 Hz, H-3b), 1.40 (9H, s, Me). 13C NMR (100.5 MHz,
CDCl3) d:158.7 (C-2), 156.9 (C-10), 153.9 (C-8), 138.0
(C-5), 137.9 (C-15), 137.2 (C-12), 131.1 (C-o), 130.1 (C-
8a), 129.3 (C-6), 127.5 (C-p), 127.3 (C-m, 14), 124.7 (C-
4a), 120.9 (C-11), 119.8 (C-13), 118.5 (C-9), 117.3 (C-
16), 111.8 (C-7), 36.4 (C-4), 35.4 (C-Me), 33.1 (C-3), 31.9
(C-Me). 11B NMR (96 MHz, CDCl3) d: 7.9 ppm
(h1/2 = 77 Hz). Anal. Calc. for C27H26NO2B: C, 79.61;
H, 6.39; N, 3.43. Found: C, 80.01; H, 6.71; N, 3.57%.
4.2.3.4. 2-(4-Acetylphenyl)-40-nitrobenzo-[d]benzo[h]-
6-aza-1,3-dioxa-2-boracyclonon-6-ene (2i). The title
compound was prepared from 1e (3.00 g, 11.6 mmol)
and 4-acetylphenylboronic acid (2.10 g, 12.80 mmol) to
ꢀ
give 2.62 g (58% yield). M.p.: 218–220 ꢁC. IR mmax
(KBr) 3089, 3043, 2984, 1676 (C@O), 1631(C@N),
1512, 1465, 1333, 1273, 1182, 920 cmꢀ1. MS (70 eV) m/z
386 (M+, 2), 267 (M+-C6H4COCH3, 100), 268 (16),
1
222 (10), 221(68), 220 (25), 76 (10), 43 (12). H NMR
(CDCl3, 300 MHz) d: 8.67 (1H, s, H-7), 8.47 (1H, s,
H-13), 8.33 (1H, dd, J = 9.0, 1.5 Hz, H-11), 7.74 (2H,
d, J = 8.2 Hz, H-m), 7.69 (1H, dd, J = 8.1, 7.5 Hz, H-
4), 7.54 (1H, d, J = 7.5 Hz, H-6), 7.39 (2H, d,
J = 8.2 Hz, H-o), 7.27 (1H, d, J = 8.1 Hz, H-3), 7.17
(1H, d, J = 9.0 Hz, H-10), 7.07 (1H, t, J = 7.5 Hz, H-
5), 2.52 (3H, s, Me). 13C NMR (CDCl3, 75.5 MHz) d:
198.6 (CO), 163.5 (C-12), 158.0 (C-2), 152.6 (C-7),
140.4 (C-9), 140.1 (C-4), 137.1 (C-p), 132.5 (C-6),
131.3 (C-o), 130.8 (C-8), 128.7 (C-11), 127.6 (C- m),
121.6 (C-5), 120.8 (C-3), 119.0 (C-1), 114.9 (C-10),
112.0 (C-13), 26.8 (Me). 11B NMR (CDCl3,
86.68 MHz) d: 8.2 ppm (h1/2 = 385 Hz). Anal. Calc. for
C21H15N2BO5: C, 65.32; H, 3.92; N, 7.25. Found: C,
65.37; H, 3.84; N, 7.20%.
4.2.4.2. Phenyl[2(20-hydroxyphenyl-O)-4-ethenyl-5-met-
hyl-8-(3,4-dihydroquinolate) O0, N))] boron (3c). The
title compound was prepared from 2c (1.00 g,
3.19 mmol) and sulfolene (1.13 g, 9.60 mmol), heating
for 22 h, to give 0.90 g (77% yield) of 3c. M.p.: 164–
165 ꢁC and 4c in traces. IR
ꢀmmax (KBr) 2920, 1623
(C@N), 1462, 1265, 1188, 920, 760 cmꢀ1. MS (70 eV)
m/z (%) 365 (M+, 0.2), 288 (100), 273 (22), 260 (16), 77
(10), 51(2). 1H NMR (400 MHz, CDCl3) d:7.52 (1H,
ddd, J = 8.4, 7.6, 1.3 Hz, H-12); 7.47 (1H, dd, J = 7.6,
1.3 Hz, H-14), 7.40–7.38 (2H, m, H-o), 7.26 (1H, d,
J = 8.4 Hz, H-11), 7.17–7.15 (3H, m, H-m, p), 7.10 (1H,
d, J = 8.2 Hz, H-6), 6.92 (1H, td, J = 7.6, 1.0 Hz, H-13),
6.84 (1H, d, J = 8.2 Hz, H-7), 5.93 (1H, ddd, J = 17.0,

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10.0, 6.8 Hz, H-15), 5.09 (1H, dd, J = 9.8, 1.2 Hz, H-
16a), 5.06 (1H, dd, J = 17.0, 1.2 Hz, H-16b), 3.92 (1H,
dt, J = 7.2, 1.2 Hz, H-4), 3.48 (1H, d, J = 19.8 Hz, H-
3a), 2.80 (1H, dd, J = 19.8, 7.7 Hz, H-3b), 2.23 (3H, s,
Me). 13C NMR (100.5 MHz, CDCl3) d: 158.5 (C-2),
157.0 (C-10), 154.1 (C-8), 137.0 (C-12), 137.0 (C-15),
133.0 (C-6), 131.0 (C-o), 128.5 (C-8a), 127.6 (C-p), 127.4
(C-m), 127.2 (C-14), 125.3 (C-5), 124.2 (C-4a), 121.1 (C-
11), 119.9 (C-13), 118.8 (C-9), 116.0 (C-16), 112.1 (C-7),
35.0 (C-4), 32.6 (C-3), 16.4 (Me). 11B NMR (96 MHz,
CDCl3) d: 7.9 ppm (h1/2 = 58 Hz). Anal. Calc. for
C24H20NO2B: C, 78.90; H, 5.47; N, 3.80. Found: C,
78.85; H, 5.60; N, 3.80%.
J = 17.0, 10.4, 6.1 Hz, H-15), 5.18 (1H, dd, J = 10.4,
1.4 Hz, H-16a), 5.14 (1H, dd, J = 17.1, 1.4 Hz, H-16b),
4.93 (1H, td, J = 6.1, 1.5 Hz, H-4), 3.65 (1H, d,
J = 20.2 Hz, H-3a), 2.80 (1H, dd, J = 20.2, 7.5 Hz, H-
3b). 13C NMR (75 MHz, CDCl3) d:162.7 (C-2), 160.6
(C-8), 157.3 (C-10), 138.7 (C-12), 137.2 (C-5), 135.3 (C-
15), 130.8 (C-o), 129.9 (C-6), 129.7 (C-8a), 128.2 (C-p),
127.9 (C-14), 127.7 (C-m), 123.8 (C-4a), 121.3 (C-11),
120.7 (C-13), 118.1 (C-9), 117.0 (C-16), 112.3 (C-7), 35.0
(C-4), 31.8 (C-3). 11B NMR (96 MHz, CDCl3) d:8.6 ppm
(h1/2 = 58 Hz). Anal. Calc. for C23H17N2O4B: C, 69.69;
H, 4.29; N, 7.07. Found: C, 70.05; H, 4.35; N, 7.27%.
4.2.4.5. p-Acetylphenyl[2(20-hydroxyphenyl-O)-4-eth-
enyl-5-chloro-8-(3,4-dihydroquinolate) O0, N))]boron
(3h). The title compound was prepared from 2h
(1.00 g, 2.70 mmol) and sulfolene (0.94 g, 8.0 mmol),
heating for 20 h, to give 0.81 g (71% yield) of 3h.
4.2.4.3. Phenyl[2(20-hydroxyphenyl-O)-4-ethenyl-5-chl-
oro-8-(3,4-dihydroquinolate)O0, N))] boron (3d). The
title compound was prepared from 2d (1.00 g,
2.99 mmol) and sulfolene (1.10 g, 9.00 mmol), heating
for 12 h, to give 0.90 g (83% yield) of 3d. M.p.: 184–
ꢀ
M.p.: 197–198ꢁC. IR mmax (KBr) 2997, 1682 (C@N),
ꢀ
185 ꢁC and 4d in traces. IR mmax (KBr) 3078, 2921, 1601
1549, 1461, 1359, 1267, 1183, 1127, 1076, 1043, 993,
912, 821, 760, 727, 596 cmꢀ1. MS (70 eV) m/z 427
(M+, 4), 308 (100), 257 (24), 293 (18), 280(15), 76(10),
43(14). 1H NMR (CDCl3, 400 MHz) d: 7.76 (2H, d,
J = 8.2 Hz, H-m), 7.60 (1H, td, J = 8.0, 1.4 Hz, H-12),
7.54 (1H, dd, J = 8.0, 1.4 Hz, H-14), 7.45 (2H, d,
J = 8.3 Hz, H-o), 7.29 (1H, d, J = 8.4 Hz, H-6), 7.27
(1H, d, J = 8.0 Hz, H-11), 6.99 (1H, t, J = 8.5 Hz, H-
13), 6.89 (1H, d, J = 8.4 Hz, H-7), 5.95 (1H, ddd,
J = 16.7, 10.4, 6.2 Hz, H-15), 5.18 (1H, dd, J = 10.2,
1.0 Hz, H-16a), 5.12 (1H, dd, J = 16.8, 1.3 Hz, H-16b),
4.14 (1H, ddd, J = 7.5, 6.2, 1.3 Hz, H-4), 3.60 (1H, d,
J = 20.1 Hz, H-3a), 2.90 (1H, dd, J = 20.1, 7.7 Hz, H-
3b), 2.51 (3H, s, Me). 13C NMR (CDCl3, 67.9 MHz)
d: 198.6 (CO), 160.5 (C-2), 156.9 (C-10), 154.4 (C-8),
138.1 (C-12), 136.6 (C-p), 135.7 (C-15), 131.9 (C-6),
131.1 (C-o), 129.4 (C-8a), 127.6 (C-14), 127.5 (C-m),
124.2 (C-4a), 121.5 (C-5), 121.2 (C-11), 120.5 (C-13),
118.4 (C-9), 116.6 (C-16), 113.7 (C-7), 34.9 (C-4), 32.3
(C-3), 26.6 (Me). 11B NMR (CDCl3, 96.3 MHz) d:
7.8 ppm (h1/2 = 96 Hz). Anal. Calc. for C25H19NO3B:
C, 70.17; H, 4.44 N, 3.27. Found: C, 70.34; H, 4.54;
N, 3.18%.
(C@N), 1534, 1469, 1289, 1142, 917, 814, 743 cmꢀ1. MS
(70 eV) m/z (%) 385 (M+, 1), 362 (3), 308 (100), 293 (20),
1
272 (11), 245 (7), 77 (7), 51 (7). H NMR (400 MHz,
CDCl3) d: 7.57 (1H, ddd, J = 8.4, 7.1, 1.5 Hz H-12), 7.51
(1H, dd, J = 8.0, 1.7 Hz, H-14), 7.38 (2H, dd, J = 6.5,
3.0 Hz, H-o), 7.28 (1H, d, J = 8.4 Hz, H-11), 7.27 (1H, d,
J = 8.7 Hz, H-6), 7.20–7.18 (3H, m, H-m, p), 6.96 (1H,
ddd, J = 7.8, 7.1, 1.1 Hz, H-13), 6.88 (1H, d, J = 8.7 Hz,
H-7), 5.95 (1H, ddd, J = 17.0, 10.2, 6.4 Hz, H-15), 5.17
(1H, dd, J = 10.2, 1.2 Hz, H-16a), 5.15 (1H, dd,
J = 17.0, 1.2 Hz, H-16b), 4.12 (1H, ddd, J = 7.6, 6.3,
1.2 Hz, H-4), 3.35 (1H, dd, J = 20.0, 1.2 Hz, H-3a), 2.86
(1H, dd, J = 20.0, 7.6 Hz, H-3b). 13C NMR (75 MHz,
CDCl3) d:160.2 (C-2), 157.2 (C-10), 154.7 (C-8), 138.0
(C-12), 136.0 (C-15), 131.8 (C-6), 131.1 (C-o), 129.8 (C-
8a), 128.0 (C-p), 127.7 (C-m), 127.6 (C-14), 124.2 (C-4a),
121.4 (C-11), 121.3 (C-5), 120.4 (C-13), 118.7 (C-9),
116.8 (C-16), 113.7 (C-7), 35.1 (C-4), 32.4 (C-3). 11B
NMR (96 MHz, CDCl3) d:8.2 ppm (h1/2 = 48 Hz). Anal.
Calc. for C23H17NO2BCl: C, 71.68; H, 4.41; N, 3.63.
Found: C, 71.66; H, 4.48; N, 3.98%.
4.2.4.4. Phenyl[2(20-hydroxyphenyl-O)-4-ethenyl-5-nitro-
8-(3,4-dihydroquinolate)O0, N))] boron (3e). The title
compound was prepared from 2e (1.00 g, 2.90 mmol)
and sulfolene (1.00 g, 8.70 mmol), heating for 12 h, to
give 0.80 g (70% yield) of 3e. M.p.: 215–217 ꢁC. IR ꢀmmax
(KBr) 3071, 3045, 3007, 1639 (C@N), 1511, 1464, 1331,
1289, 1189, 907, 750 cmꢀ1. MS (70 eV) m/z (%) 396 (M+,
1), 319 (100), 272 (23), 246 (31), 77 (11), 51 (7). 1H NMR
(400 MHz, CDCl3) d:8.30 (1H, d, J = 9.0 Hz, H-6); 7.62
(1H, ddd, J = 8.4, 7.2, 1.5 Hz, H-12), 7.56 (1H, dd,
J = 7.2, 1.2 Hz, H-14), 7.32–7.29 (3H, m, H-11 y-o),
7.19–7.16 (3H, m, H-m, p), 7.00 (1H, td, J = 7.2, 1.2 Hz,
H-13), 6.96 (1H, d, J = 9.0 Hz, H-7), 6.05 (1H, ddd,
4.2.4.6. p-Acetylphenyl[2(20-hydroxyphenyl-O)-4-eth-
enyl-5-nitro-8-(3,4-dihydroquinolate) O0, N))]boron
(3i). The title compound was prepared from 2i
(1.00 g, 2.59 mmol) and sulfolene (0.92 g, 7.77 mmol),
heating for 12 h, to give 0.85 g (75% yield) of 3i. M.p.:
ꢀ
158–160 ꢁC. IR mmax (KBr) 3083, 2920, 1680 (C@O),
1626 (C@N), 1515, 1462, 1332, 1270, 1187, 909, 817,
760 cmꢀ1. MS (70 eV) m/z 438 (M+, 0.2), 320 (20), 319
(100), 273 (11), 272 (27), 271 (11), 246 (43), 245 (23).
1H NMR (CDCl3, 400 MHz) d: 8.31 (1H, d,
J = 9.2 Hz H-6), 7.76 (2H, d, J = 8.2 Hz, H-m), 7.64
(1H, ddd, J = 8.3, 7.3, 1.6 Hz, H-12), 7.60 (1H, dd,

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J = 7.3, 1.6 Hz, H-14), 7.41 (2H, d, J = 8.2 Hz, H-o),
7.29 (1H, d, J = 8.3 Hz, H-11), 7.03 (1H, td, J = 7.3,
1.1 H-13), 6.99 (1H, d, J = 9.2 Hz, H-7), 6.07 (1H,
ddd, J = 17.0, 10.3, 6.0 Hz, H-15), 5.19 (1H, dd,
J = 10.3, 1.4 Hz, H-16a), 5.12 (1H, dd, J = 17.0,
1.4 Hz, H-16b) 4.96 (1H, t, J = 6.0 Hz, H-4) 3.71 (1H,
d, J = 20.1 Hz, H-3a), 2.92 (1H, dd, J = 20.1, 7.3 Hz,
H-3b), 2.50 (3H, s, Me). 13C NMR (CDCl3, 100.5
MHz) d: 198.5 (CO), 163.0 (C-2), 160.3 (C-8), 157.0
(C-10), 138.9 (C-12), 137.3 (C-5), 136.8 (C-p), 135.2
(C-15), 130.9 (Co), 129.9 (C-6), 129.5 (C-8a), 127.9 (C-
14), 127.5 (C-m), 123.8 (C-4a), 121.3 (C-11),120.9
(C-13), 118.0 (C-9), 116.8 (C-16), 112.4 (C-7), 34.8 (C-
4),31.7 (C-3), 26.6 (Me). 11B NMR (CDCl3,
128.26 MHz) d: 8.1 ppm (h1/2 = 64 Hz). Anal. Calc. for
C25H19N2O5B: C, 68.49; H, 4.33; N, 6.39. Found: C,
68.87; H, 4.37; N, 6.31%.
(1H, dt, J = 7.7, 1.8 Hz, H-120), 7.35–7.29 (4H, m, H-
6, 11, o), 7.14–7.10 (3H, m, H-m, p), 7.00 (1H, d,
J = 7.7 Hz, H-7), 6.99 (1H, dt, J = 7.7, 1.0 Hz, H-13),
6.98 (1H, dt, J = 7.7, 1.1 Hz, H-130), 5.88 (2H, s, H-17,
H-18), 5.87 (2H, s, H-170, H-180), 4.12–4.03 (1H, m,
H-15), 2.80 (3H, s, Me), 2.54–1.91 (6H, m, H-16, 19,
20). 13C NMR (68 MHz, CDCl3) d:162.4 (C-4), 162.3
(C-40), 156.8 (C-10), 156.0 (C-8), 144.6 (C-2), 137.0 (C-
8a), 135.4 (C-12), 133.8 (C-6), 131.6 (C-o), 127.5 and
127.4 (C-17, C-p and C-m), 125.9 and 125.8 (C-18),
125.3 (C-14), 125.3 (C-4a), 122.0 (C-5), 121.7 (C-11),
120.1 (C-13), 118.7 (C-9), 115.1 (C-3), 109.8 (C-7),
37.0 (C-15), 33.7 (C-19), 33.2 (C-190), 30.3 (C-20), 29.9
(C-200), 25.1 (C-16), 25.5 (C-160), 22.9 (Me). 11B NMR
(96 MHz, CDCl3) d:8.8 ppm (h1/2 = 78 Hz). Anal. Calc.
for C28H24NO2B: C, 80.57; H, 5.75; N, 3.35. Found:
C, 80.56; H, 5.81; N, 3.81%.
4.2.4.7. Phenyl[2(20-hydroxyphenyl-O)-4-(30-cyclohexe-
nyl)-8-quinolate)-O0, N]boron (4a). The compound
was prepared as described previously heating for 22 h
in 67% yield determined by NMR, and purified by chro-
matography using hexane:ethyl acetate (95:5). M.p.:
4.2.4.9. Phenyl[2(20-hydroxyphenyl-O)-4-(30-cyclohexe-
nyl)-5-chloro-8- quinolate-O0, N)]boron (4d). M.p.:
232–233 ꢁC. MS (70 eV) m/z (%) 437 (M+, 0.2), 380
(2), 360 (100), 306 (77), 270 (36), 245 (5), 77 (14), 51
(11). 1H NMR (400 MHz, CDCl3) d: 7.77 (1H, d,
J = 8.5 Hz, H-14), 7.74 (1H, s, H-3), 7.72 (1H, s, H-
30), 7.56 (1H, d, J = 8.1, H-6), 7.55 (1H, dd, J = 8.1,
7.7 Hz, H-12), 7.34 (1H, d, J = 8.1, H-11), 7.30–7.28
(2H, m, H-o), 7.15–7.11 (3H, m, H-m, p), 7.02 (1H, d,
J = 8.4 Hz, H-7), 7.02 (1H, t, J = 7.7 Hz, H-13), 5.87
(2H, s, H-17, 18), 4.64–4.55 (1H, m, H-15), 2.63–1.85
(6H, m, H-16, 19, 20). 13C NMR (75 MHz, CDCl3)
d:161.8 (C-4), 161.7 (C-40), 156.9 (C-10), 156.8 (C-8),
145.8 (C-2), 137.2 (C-8a), 136.2 (C-12), 133.5 (C-6),
133.5 (C-60), 131.7 (C-o), 127.9 (C-p), 127.8 and 127.6
(C-17 and C-m), 126.0 and 125.8 (C-18), 125.7 (C-14),
123.2 (C-4a), 123.1 (C-4a), 121.9 (C-11), 120.5 (C-13),
118.5 (C-9), 116.1 (C-3), 116.0 (C-30), 110.6 (C-7), 36.4
(C-15), 36.3 (C-150), 33.3 (C-19), 32.7 (C-190), 30.4 (C-
20), 29.7 (C-200), 25.6 (C-16, C-160). 11B NMR
(96 MHz, CDCl3) d: 9.5 ppm (h1/2 = 77 Hz). Anal. Calc.
for C27H21NO2BCl: C, 74.05; H, 4.80; N, 3.20. Found:
C, 73.60; H, 5.00; N, 3.40%.
ꢀ
198–200 ꢁC. IR mmax (KBr) 3026, 2914, 1610, 1552,
1498, 1260, 1186, 1037, 907, 874, 755 cmꢀ1. MS
(70 eV) m/z 430 (M+–CH3, 0.1), 327 (25), 326 (100),
325 (26), 273(18), 272 (90), 271(25). 1H NMR
(400 MHz, CDCl3) d: 7.78 (1H, d, J = 7.5 Hz, H-14),
7.63 (1H, s, H-3), 7.62 (1H, s, H-30), 7.56 (1H, t,
J = 8.1 Hz, H-6), 7.53 (1H, t, J = 7.3 Hz, H-12), 7.39
(1H, d, J = 8.3 Hz, H-7), 7.35–7.33 (3H, m, H-11, o),
7.15-7.13 (3H, m, H-m, p), 7.01 (1H, dt, J = 7.5,
1.0 Hz, H-13), 5.88 (2H, s, H-17, 18) 3.67-3.66 (1H, m,
H-15), 2.58–1.99 (6H, m, H-16, H-19, H-20). 13C
NMR (100.53 MHz, CDCl3) d: 160.5 (C-4) 160.3 (C-
40), 157.6 (C-8), 156.7 (C-10), 145.5 (C-2), 136.9 (C-
8a), 135.5 (C-12), 131.7 (C-o), 131.2 (C-6), 127.7 (C-p),
127.5 (C-m and C-17, C-170), 125.9 (C-18), 125.7 (C-
180), 125.8 (C-4a), 125.7 (C-4a0), 125.3 (C1-14), 121.8
(C-11), 120.2 (C-13), 119.1 (C-9), 114.4 (C-3), 114.2
(C-30), 111.0 (C-7), 110.0 (C-5), 36.2 (C-15), 32.5 (C-
16), 31.8 (C-160), 28.9 (C-19), 28.3 (C-190), 25.4 (20),
25.3 (C-200). 11B NMR (96.3 MHz, CDCl3) d: 9.2 ppm
(h1/2 = 96 Hz). Anal. Calc. for C27H22NBO2: C, 80.39;
H, 5.46; N, 3.47. Found: C, 80.14; H, 5.64; N, 3.38%.
4.2.4.10. Phenyl[2(20-hydroxyphenyl-O)-4-(30-cyclohex-
enyl)-6-methyl-8- quinolate-O0, N)]boron (4f). Pre-
pared from 2f (0.80 g, 2.55 mmol) and sulfolene
(0.90 g, 7.66 mmol) after heating for 12 h. The little
compound decomposes extensively during chromato-
4.2.4.8. Phenyl[2(20-hydroxyphenyl-O)-4-(30-cyclohexe-
nyl)-5-methyl-8- quinolate) O0, N))] boron (4c). M.p.:
ꢀ
graphic purification. M.p.: 249–250 ꢁC, IR mmax (KBr)
ꢀ
215–216 ꢁC. IR mmax (KBr) 3025, 2921, 1611, 1554, 1505,
3023, 2919, 1614, 1553, 1497, 1460, 1380, 1187, 1035,
974, 906, 751, 701 cmꢀ1. MS (70 eV) m/z (%) 417 (M+,
0.2), 340 (100), 286 (73), 270 (9), 77 (9), 51 (7). 1H
NMR (400 MHz, CDCl3) d:7.76 (1H, d, J = 7.7 Hz, H-
14), 7.59 (1H, s, H-3), 7.51 (1H, t, J = 7.8 Hz, H-12),
7.36–7.33 (3H, m, H-11, o), 7.17 (1H, s, H-5), 7.15–
7.11 (3H, m, H-m, p), 6.99 (1H, t, J = 7.7 Hz, H-13),
1453, 1374, 1241,1181, 933, 751, 698 cmꢀ1. MS (70 eV)
m/z (%) 417 (M+, 0.3), 394 (3), 340 (100), 286 (54), 270
(19), 77(19), 43(15). 1H NMR (270 MHz, CDCl3)
d:7.78 (1H, dd, J = 7.9, 1.7 Hz, H-14), 7.77 (1H, dd,
J = 7.9, 1.8 Hz, H-140), 7.68 (1H, s, H-3), 7.67 (1H, s,
H-30), 7.51 (1H, ddd, J = 8.4, 7.7, 1.7 Hz, H-12), 7.52

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6.96 (1H, s, H-7), 5.88 (2H, s, H-17, 18), 3.66–3.59 (1H,
m, H-15), 2.58 (3H, s, Me), 2.58–1.95 (6H, m, H-16, 19,
20). 13C NMR (75 MHz, CDCl3) d:159.5 (C-4), 159.3
(C-40), 157.3 (C-8), 156.5 (C-10), 144.4 (C-2), 142.3 (C-
6), 135.1 (C-12), 134.6 (C-8a), 131.6 (C-o), 127.5 (C-p),
127.4 (C-m), 127.3, 125.9 and 125.7 (C-17, C-18),
125.1 (C-14, 4a), 121.7 (C-11), 120.1 (C-13), 119.1 (C-
9), 114.4 (C-3), 114.2 (C-30), 111.8 (C-7), 110.1 (C-5),
36.0 (C-15), 32.5 (C-19), 31.7 (C-190), 28.8 (C-20), 28.2
(C-200), 25.3 (C-16, C-160), 23.6 (Me). 11B NMR
(96 MHz, CDCl3) d: 9.1 ppm (h1/2 = 64 Hz). Anal. Calc.
for C28H24NO2B: C, 80.57; H, 5.75; N, 3.35. Found: C,
80.46; H, 5.91; N, 3.23%.
(1H, s, H-30), 7.58 (1H, t, J = 7.8 Hz, H-6), 7.53 (1H,
dd, J = 8.4, 7.3 Hz, H-12), 7.42 (1H, d, J = 8.4 Hz,
H-o), 7.41 (1H, d, J = 6.6 Hz, H-5), 7.33 (1H, d,
J = 8.4 Hz, H-11), 7.12 (1H, d, J = 7.8 Hz, H-7), 7.02
(1H, dt, J = 7.3, 1.1 Hz, H-13), 5.88 (2H, s, H-17, 18)
3.68-3.60 (1H, m, H-15), 2.55-2.00 (6H, m H-16, H-
19, H-20), 2.48 (3H, s, Me). 13C NMR (100.53 MHz,
CDCl3) d:198.8 (CO), 160.8 (C-4) 160.7 (C-40), 157.2
(C-8), 156.2 (C-10), 145.5 (C-2), 136.3 (C-8a), 135.7
(C-12), 131.7 (C-o), 131.3 (C-6), 127.4 (C-17), 127.3
(C-m), 125.7 and 125.5 (C-18, C-180), 125.3 (C-14
and C-4a), 121.7 (C-13), 120.4 (C-11), 118.9 (C-9),
114.4 (C-3), 114.2 (C-3), 111.1 (C-7), 110.3 (C-5),
36.2 (C-15), 32.3 (C-16), 31.8 (C-160), 28.8 (C-19),
28.3 (C-190), 26.6 (Me). 25.2 (C-20). 11B NMR
(96.3 MHz, CDCl3) d: 8.0 ppm (h1/2 = 64 Hz). Anal.
Calc. for C29H24NBO3: H, 5.43; C, 78.22; N, 3.15.
Found: H, 5.57; C, 77.02; N, 3.06%.
4.2.4.11. Phenyl[2(20-hydroxyphenyl-O)-4-(30-cyclohex-
enyl)-6-nitro-8-quinolate-O0, N)]boron (4g). Prepared
from 2g (1.00 g, 2.90 mmol) and sulfolene (1.03 g,
8.72 mmol) after heating for 12 h. The little compound
decomposes extensively upon chromatographic purifi-
ꢀ
cation. M.p.: 221–223 ꢁC. IR mmax (KBr) 3021, 2919,
4.2.4.13. Hydrolysis of 3,4-dihydroquinolines adducts.
Equimolar quantities of the 3,4-dihydroquinoline
adduct and NaOH were stirred 10 min in CH2Cl2. The
yield was quantitative.
1608, 1553, 1498, 1338, 1314, 1251, 1192, 904, 863,
740 cmꢀ1. MS (70 eV) m/z (%) 448 (M+, 0.2), 371
(100), 341 (21), 317 (49), 271 (56), 245 (7), 77 (3),
44 (16). 1H NMR (300 MHz, CDCl3) d:8.45 (1H, d,
J = 1.5 Hz, H-7), 7.89 (1H, d, J = 0.7 Hz, H-5), 7.88
(1H, d, J = 0.7 Hz, H-50), 7.84 (1H, dt, J = 7.5,
1.8 Hz, H-14), 7.79 (1H, s, H-3), 7.78 (1H, s, H-30),
7.64 (1H, dd, J = 7.5, 8.3 Hz, H-12), 7.39 (1H, d,
J = 8.3 Hz, H-11), 7.35–7.33 (2H, m, H-o), 7.24–7.14
(3H, m, H-m, p), 7.09 (1H, t, J = 7.5 Hz, H-13), 5.93
(2H, s, H-17, 18), 3.77–3.65 (1H, m, H-15), 2.62–
1.99 (6H, m, H-16, 19, 20). 13C NMR (75 MHz,
CDCl3): 162.9 (C-4), 162.8 (C-40), 158.2 (C-8), 157.1
(C-10), 150.4 (C-6), 148.8 (C-2), 138.7 (C-8a), 137.3
(C-12), 131.7 (C-o), 128.3 (C-p), 127.8 (C-m), 127.6
(C-17), 125.9 (C-14), 125.5 and 125.3 (C-18, 180),
123.5 (C-4a), 123.4 (C-4a0), 122.1 (C-11), 120.9
(C-13), 118.6 (C-9), 116.4 (C-3), 116.2 (C-30), 109.0
(C-7), 104.7 (C-5), 36.5 (C-15), 32.8 (C-19), 32.1 (C-
190), 29.0 (C-20), 28.5 (C-200), 25.2 (C-16), 25.1
4.2.4.14. [2(20-Hydroxyphenyl]-4-ethenyl-5-tert-butyl-8-
hydroxy-3,4-dihydroquinoline (5b). The title com-
pound was prepared from 3b (0.20 g, 0.49 mmol)
and NaOH (0.02 g, 0.49 mmol) to give 157 mg
ꢀ
(99.5% yield) of 5b. M.p.: 220–221 ꢁC. IR mmax (KBr)
3443, 2963, 1601, 1529, 1495, 1257, 1142, 918, 823,
745, 559 cmꢀ1. MS (70 eV) m/z (%) 321 (M+, 30)
306 (14), 294 (100), 276 (11), 228 (4), 91 (3), 77 (2).
1H NMR (400 MHz, CDCl3) d:7.56 (1H, d,
J = 7.7 Hz, H-14); 7.29–7.18 (2H, m, H-12, 6), 6.90–
6.79 (3H, m, H-11, 7, 13), 5.71 (1H, ddd, J = 16.8,
10.9, 5.2 Hz, H-15), 4.95 (1H, d, J = 10.3 Hz, H-
16a), 4.68 (1H, d, J = 16.8 Hz, H-16b), 4.20 (1H, br,
H-4), 3.35 (1H, d, J = 16.5 Hz, H-3a), 2.70 (1H, d,
J = 6.2 Hz, H-3b), 1.38 (9H, s, C (CH3)3). Anal. Calc.
for C21H23NO2: C, 78.50; H, 7.16; N, 4.36. Found: C,
78.05; H, 7.43; N, 4.23%.
(160). 11B NMR (96 MHz, CDCl3) d:9.9 ppm (h1/2
=
48 Hz). Anal. Calc.. for C27H21-N2O4B: C, 71.56; H,
4.81; N, 6.42. Found: C, 71.76; H, 4.89; N, 6.51%.
4.2.4.15. [2(20-Hydroxyphenyl]-4-ethenyl-5-tert-butyl-8-
hydroxy-3,4-dihydroquinoline-d2 (5b-d2). The sample
undergoes deuterium exchange upon standing in deu-
terated methanol. MS (70 eV) m/z (%) 323 (M+, 46),
308 (24), 296 (100), 278 (17), 264 (7), 229 (5), 115
(10), 83 (16), 57 (28), 41 (45). 1H NMR (300 MHz,
methanol-d4) d:7.67 (1H, dd, J = 8.5, 1.6 Hz, H-14);
7.28 (1H, ddd, J = 8.5, 7.3, 1.6 Hz, H-12), 7.16 (1H,
d, J = 8.9 Hz, H-6), 6.78 (1H, d, J = 8.5 Hz, H-11),
6.72 (1H, d, J = 8.9 Hz, H-7), 6.63 (1H, t,
J = 7.3 Hz, H-13), 5.85 (1H, ddd, J = 16.0, 10.8,
4.4 Hz, H-15), 4.96 (1H, dd, J = 10.1, 1.5 Hz, H-
16a), 4.71 (1H, dd, J = 16.0, 1.4 Hz, H-16b), 4.33
4.2.4.12. p-Acetylphenyl[2(20-hydroxyphenyl-O)-4-(30-
cyclohexenyl)-8-quinolate)-O0, N]boron (4j). The
compound was prepared as described previously heat-
ing for 26 h, and purified by column chromatography
using hexane:ethyl acetate (95:5), it decomposes upon
ꢀ
purification. M.p.: 230–231 ꢁC. IR mmax (KBr) 1682,
1610, 1502, 1386,1254, 1180, 1037, 909, 820, 755,
703 cmꢀ1. MS (70 eV) m/z 430 (M+–CH3, 0.1), 327
(25), 326 (100), 325 (26), 273(18), 272 (90), 271(25).
1H NMR (400 MHz, CDCl3) d: 7.79 (1H, dd, J = 8.0,
1.7 Hz, H-14), 7.78 (1H, dd, J = 8.0, 1.7 Hz, H-140),
7.71 (1H, d, J = 8.4 Hz, H-m), 7.66 (1H, s, H-3), 7.65
(1H, dd, J = 2.2, 4.4 Hz, H-4), 1.39 (9H, s,
C

´
M. Rodrıguez et al. / Journal of Organometallic Chemistry 690 (2005) 2975–2988
2987
(CH3)3). 13C NMR (75 MHz, methanol-d4) d: 171.7
Acknowledgements
(C-2), 163.9 (C-10), 154.1 (C-8), 138.4 (C-15), 134.2
(C-12), 133.8 (C-5), 128.3 (C-14), 127.5 (C-4a), 126.8
(C-8a), 126.2 (C-6), 121.3 (C-11), 116.2 (C-9), 116.1
(C-7), 115.3 (C-16), 114.5 (C-13), 34.9 (C-4), 34.4
(C-3), 31.7 C(CH3)3), 31.3 C(CH3)3).
The authors thank CONACyT for financial support
and the scholarship to M. Rodriguez. Thanks are gi-
´
ven to Consejo Superior de la Investigacion Cientıfica
in Spain for the Cambridge Crystallographic Data
´
´
Base license, to V. Gonzalez and G. Uribe for
4.2.4.16.
[2(20-Hydroxyphenyl]-4-ethenyl-5-chloro-8-
NMR spectra, D. Castillo for IR spectra, and G.
Cuellar for MS.
hydroxy-3,4-dihydroquinoline (5d). The title com-
pound was prepared from 3d (0.20 g, 0.52 mmol) and
NaOH (0.02 g, 0.49 mmol) to give 152 mg (98% yield)
ꢀ
of 5d. M.p.: 209–210 ꢁC. IR mmax (KBr) 3443, 3077,
1601, 1535, 1478, 1288, 1141, 916, 813, 741, 561 cmꢀ1
.
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