One-pot solvent-free preparation of 2-phenyl-1,3,2-aryldioxaborins on acidic alumina

Article abstract of DOI:10.1080/00397910600764741

One-pot, solvent-free, microwave-promoted preparation of 1,3,2-aryldioxaborines on the surface of acidic alumina is described. Copyright Taylor & Francis Group, LLC.

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One‐Pot Solvent‐Free Preparation of
2‐Phenyl‐1,3,2‐aryldioxaborins on Acidic
Alumina
a
b
b
b
M. Reza Naimi‐Jamal , Mojtaba Mirzaei , M. Bolourtchian & Ali Sharifi
a
Organic Research Laboratory, Faculty of Chemistry , Iran University of
Science and Technology , Narmak, Tehran, Iran
b
Chemistry and Chemical Engineering Research Center of Iran , Tehran, Iran
Published online: 16 Feb 2007.
To cite this article: M. Reza Naimi‐Jamal , Mojtaba Mirzaei , M. Bolourtchian & Ali Sharifi (2006) One‐Pot
Solvent‐Free Preparation of 2‐Phenyl‐1,3,2‐aryldioxaborins on Acidic Alumina, Synthetic Communications:
An International Journal for Rapid Communication of Synthetic Organic Chemistry, 36:18, 2711-2717, DOI:
10.1080/00397910600764741
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Synthetic Communications , 36: 2711–2717, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910600764741
One-Pot Solvent-Free Preparation
of 2-Phenyl-1,3,2-aryldioxaborins
on Acidic Alumina
M. Reza Naimi-Jamal
Organic Research Laboratory, Faculty of Chemistry, Iran University of
Science and Technology, Narmak, Tehran, Iran
Mojtaba Mirzaei, M. Bolourtchian, and Ali Sharifi
Chemistry and Chemical Engineering Research Center of Iran,
Tehran, Iran
Abstract: One-pot, solvent-free, microwave-promoted preparation of 1,3,2-aryldioxa-
borines on the surface of acidic alumina is described.
Keywords: Alumina, boronic acid, microwave irradiation, phenols, solvent-free
synthesis
INTRODUCTION
The 2-phenyl-1,3,2,-aryldioxaborins (4) have been found to be very useful and
versatile synthetic intermediatens to prepare saligenol derivatives. Although
direct derivatization of a phenol with an aldehyde is not ortho-specific and
results usually in a mixture of ortho-, para-, and poly substitution, 4 can be
[1]
readily oxidized to the corresponding a-hydroxyalkylphenols. It can be
also reduced to o-alkylphenols or transformed to alkylthiomethylphenol
[2]
and alkoxymethylphenol derivatives (Scheme 1). Chambers et al. have
reported the successful use of this substance as a stable precursor of quinine
Received in Poland February 3, 2006
Address correspondence to M. Reza Naimi-Jamal, Organic Research Laboratory,
Faculty of Chemistry, Iran University of Science and Technology, Narmak, 16846
Tehran, Iran. E-mail: naimi@iust.ac.ir
2
711

2
712
M. R. Naimi-Jamal et al.
Scheme 1.
methides in inter- and intramolecular cycloaddition reactions under pyrolytic
[
conditions.
3]
The general procedure for the preparation of 4 includes refluxing a mixture
of a phenol, phenylboronic acid, and an aldehyde in benzene or toluene with
[1,2]
azeotropic removal of water using a Dean–Stark trap.
The presence of
catalytic amounts of a carboxylic acid, such as acetic or propionic acid, is
crucial for the reaction to take place. Less reactive reactants need stronger
acidic catalysts, such as trichloroacetic acid, for the completion of the
[
1]
reaction. Another method for the synthesis of 4 is cyclic esterification of
boronic acids with suitably constituted diols; however, this method needs
the preparation of the corresponding diols, which makes this method
[
4]
a lengthy and unattractive one.
With regards to the environmental damages caused by employing
organic solvents in chemical processes, there is a huge interest in using
[
5]
solvent-free reactions.
solvents by carrying out organic reactions on the surface of solid supports
Efforts for complete elimination of organic
[6]
have been extensively documented. Active surfaces of solid supports,
[
7]
[8]
[9]
such as montmorillonite, clayfen, and alumina, serve as suitable
alternatives for the organic solvents. The role of solid surfaces is not just
limited of being good reaction media; in most cases they catalyze different
kinds of organic reactions, too. Therefore, for the reactions taking place on
the solid media, vigorous conditions are unnecessary in most cases. In this
way, selectivity of the reactions increases, and the amount of unwanted
by-products in the course of reactions decreases. Alumina, among other
solid supports, seems to be a very interesting reagent, as it can be
modified in a variety of ways that enhance its application as acidic or
[
9a]
basic catalyst.
irradiation, which reduces the reaction times from several hours to just
These reactions are usually promoted by microwave
[
10]
a few minutes.

2-Phenyl-1,3,2-aryldioxaborins
2713
Scheme 2.
In continuation of our interest in developing solvent-free methods for
[
11]
the preparation of organic compounds,
one-pot, three-component preparation of 2-phenyl-1,3,2,-aryldioxaborins 4,
we report here a solventless,
on the surface of acidic Al O without using of organic solvents
3
2
(Scheme 2).
RESULTS AND DISCUSSION
In this procedure, phenol, benzaldehyde, phenylboronic acid, and acidic
alumina were mixed, ground together, and irradiated in a microwave oven.
Monitoring of the reaction progress by thin layer chromatography (TLC)
revealed the formation of a new substance, which was later confirmed to be
4
a. After 15 min of irradiation, the yield of the product was 75%, which is
by far higher than the conventional preparation method reported by Nagata
et al. (49%) in which a benzene solution of reactants with up to seven times
[1]
excess amounts of aldehyde must be refluxed for 20 h. Because acidic
alumina serves also as the catalyst, the use of an additional carboxylic acid,
such as propionic or trichloroacetic acid is unnecessary. On the other hand,
heating of the same reaction mixture (ground reactants with acidic alumina)
in a regular oven at 80 8C for up to 24 h yields only 11% of the corresponding
product. The method tolerates different aromatic and aliphatic aldehydes as
well as naphtols and substituted phenols (Table 1). For instance, the
reaction of b-naphtol (1b), 1-octanal (2d), and phenylboronic acid (3)
affords 4d with 70% yield in 10 min. Paraformaldehyde or formalin both
can be used as a formaldehyde source for this reaction.
The advantages of the solid support preparation of 4 compared to the con-
ventional solvent-based method can be summarized as follows: 1) higher
yields (65–95%); 2) dramatically shorter reaction times (2–20 min, instead
of several hours); 3) elimination of toxic solvents, such as benzene or
toluene; and 4) elimination of huge excess amounts of aldehydes and
carboxylic acids as catalysts.
In summery, acidic alumina combined with microwave irradiation is an
efficient method for a one-pot, three-component preparation of 1,3,2-

2
714
M. R. Naimi-Jamal et al.
Table 1. Synthesis of 1,3,2-aryldioxaborins on acidic alumina
Time
(min)
Yield
(%)
a
Entry
Phenol
Aldehyde
Product
0
1
2
3
4
1a, R ¼ H
1a
2a, R ¼ Ph
4a
4b
4c
4d
15
10
20
10
75
86
72
70
0
2b, R ¼ H
0
1a
2c, R ¼ p-NO
2
Ph
7
C H15CHO
2
d
5
6
7
8
1b
1b
1b
2b
2c
2a
2b
4e
b
4
10
15
15
90
85
65
77
4f
b
4g
4h
4i
9
2b
2c
15
8
88
86
b
1
0
4j
1
1
1e
2b
4k
2
95
a
The structures of the all known products were characterized with comparison
1
of their melting points, or H NMR, with those in the literature.
b
For new compounds 4f, 4g, and 4j, all spectral data are reported.
aryldioxaborins in a short period of time and in an environmentally friendly,
solvent-free method.
EXPERIMENTAL
Melting points were determined on a hot stage or oil bath apparatus without
1
13
correction. H NMR (80 MHz or 300 MHz) and C NMR (75 MHz)
spectra were recorded on a Bruker 80-MHz or Bruker WP 300-MHz in
CDCl using TMS as internal standard. High resolution mass spectrometry
3
(HRMS) was obtained on a Finnigan MAT system MAT 212.

2-Phenyl-1,3,2-aryldioxaborins
2715
General Procedure for the Preparation of 2-Phenyl-1,3,2-
aryldioxaborins Promoted by Microwave Oven
Phenol (1 mmol), aldehyde (1.2 mmol), phenylboronic acid (1.2 mmol), and
acidic alumina (1 g) were carefully mixed and ground together in a mortar.
The mixture was transferred to a 25-mL flask and irradiated in a microwave
oven for the given time. The progress of reaction was monitored by TLC
and GC. After cooling to room temperature, the reaction mixture was
washed with ether and filtered, and the solvent was evaporated on a rotary
evaporator. The crude product was purified by crystallization (dichloro-
methane/petrol 1:2). The structures of the all known products were being
1
characterized with comparison of their melting points, or H NMR, with
those in the literature. For new compounds 4f, 4g, and 4j, all spectral data
are reported.
Data
1
4
(
f. Mp: 178–180 8C. H NMR (CDCl ): d ¼ 6.87 (s, 1H), 7.30–7.60
3
1
3
m, 8Harom), 7.90–8.20 (m, 7H
). C NMR (CDCl ): d ¼ 72.2, 115.1,
arom
3
1
1
19.3, 122.0, 124.2 (2C), 124.7, 127.4, 127.8 (2C), 128.6, 128.9, 129.8,
30.5, 130.7, 131.9, 134.5 (2C), 147.2, 147.8, 148.5. MS (EI): m/z ¼ 259.1
þ
(
100), 381.1 (60) [M ]. HRMS (EI): m/e calcd. for C H BNO :
2
3
16
4
3
81.1172; found: 381.1171.
1
4
g. Mp: 144–146 8C. H NMR (CDCl ): d ¼ 6.80 (s, 1H), 7.10–7.15
3
(
(
(
m, 2Harom), 7.20–7.60 (m, 10H
), 7.70–7.90 (m, 3H
), 7.95-8.10
arom
arom
1
3
d, 1Harom). C NMR (CDCl ): d ¼ 73.4, 109.5, 119.2, 122.6, 124.3, 127.7
3
2C), 128.4 (2C), 128.6, 128.8 (2C), 129.0, 129.8, 130.0, 130.1, 131.5,
34.5 (2C), 142.0, 147.1, 153.0. MS (EI): m/e ¼ 259.1 (100), 336.1 (68)
1
þ
[
M ]. HRMS (EI): m/z calcd. for C H BO : 336.1322; found: 336.1320.
2
3
17
2
1
4
j. Mp: 173–175 8C. H NMR (CDCl ): d ¼ 6.48 (s, 1H), 6.95 (d, 1Harom),
3
7
.40–7.70 (m, 8H
), 7.80 (d, 1H
), 8.10–8.30 (m, 4H
), 8.55
arom
arom
arom
1
3
(
d, 1Harom). C NMR (CDCl ): d ¼ 74.6, 117.6, 121.8, 123.1, 123.2, 124.1
3
(
2C), 125.1, 126.6, 127.2, 127.7, 127.9 (2C), 128.3 (2C), 132.0, 134.2,
34.6 (2C), 143.8, 147.9, 149.2. MS (EI): m/e ¼ 259.1 (100), 381.1 (94)
1
þ
[
M ]. HRMS (EI): m/z calcd. for C H BNO : 381.1172; found: 381.1173.
2
3
16
4
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