Synthesis of quinazoline based chiral ligands and application in the enantioselective addition of phenylacetylene to aldehydes

Article abstract of DOI:10.1016/j.tet.2014.08.067

Five novel 4-phenylquinazolinols were synthesised in three steps. Their application as ligands in the titanium tetraisopropoxide promoted catalytic enantioselective addition of phenylacetylene to a variety of aldehydes gave propargylic alcohols. Under the

Full text of DOI:10.1016/j.tet.2014.08.067

Tetrahedron xxx (2014) 1e4
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Synthesis of quinazoline based chiral ligands and application in the
enantioselective addition of phenylacetylene to aldehydes
,
Idris Karakaya a, Semistan Karabuga b, Ramazan Altundas c, Sabri Ulukanli a
*
a Department of Chemistry, Faculty of Science and Letters, Osmaniye Korkut Ata University, 80000 Osmaniye, Turkey
b Department of Chemistry, Faculty of Science and Letters, Kahramanmaras Sutcu Imam University, 46100 Kahramanmaras, Turkey
c Department of Chemistry, Faculty of Science, Ataturk University, 25240 Erzurum, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Five novel 4-phenylquinazolinols were synthesised in three steps. Their application as ligands in the
titanium tetraisopropoxide promoted catalytic enantioselective addition of phenylacetylene to a variety
of aldehydes gave propargylic alcohols. Under the optimised reaction conditions, the best enantiose-
lectivity was obtained using L-lactic acid derived 4-phenylquinazolinol and apart from the cyclo-
hexylcarbaldehyde derivative, 16 propargylic alcohols were then synthesised in moderate to excellent
enantiomeric excess from 53% to 97%.
Received 26 June 2014
Received in revised form 8 August 2014
Accepted 27 August 2014
Available online xxx
Keywords:
Quinazolines
Ó 2014 Elsevier Ltd. All rights reserved.
Quinazolinones
Phenylacetylene
Asymmetric alkynylation
Propargylic alcohol
Diethylzinc and organozinc addition
1. Introduction
Catalytic asymmetric CeC bond formation is an intense research
area in the field of modern organic chemistry.1 Among the variety
of nucleophilic reactions, the asymmetric alkynylzinc addition to
aldehydes has been a particularly significant method for the syn-
thesis of propargylic alcohols, which are very useful precursors for
various organic compounds involving natural products, pharma-
ceuticals and macromolecules.2 In 1994, Ishizaki and Hoshino
published the first asymmetric alkynylzinc reagents addition to
aldehydes in the presence of chiral pyridyl alcohol ligand 13 (Fig. 1).
After this seminal report, many chiral ligands such as Salen,4 pyr-
idyl,5 amino alcohol,6e8 BINOL9e11 and sulfonamide alcohols10,12e14
and its derivatives15,16 have been emerged to obtain high enantio-
selectivity in CeC bond forming reactions. In 2000, Carreira and co-
workers discovered a highly enantioselective alkynylzinc addition
to aldehydes.17 This result was based on a stoichiometric approach
using Zn(OTf)2 and N-methylephedrine. A year later they came up
with a catalytic version of this approach.18 Another efficient
method was reported by Pu et al. using BINOL derivatives and Et2Zn
with Ti(OiPr)4.19 In the last decades, many types of catalytic
asymmetric reactions have been carried out with various
Fig. 1. Structure of some chiral heterocyclic ligands containing nitrogen (1e4) and
evaluated ligands (5aee).
heterocyclic ligands containing nitrogen such as pyridyl alcohols
1e3,20 quinazolinone21,22 and quinazoline alcohols 4aee23 (Fig. 1).
In our previous report,23 we synthesised a series of (1S,10S)-4,40-
biquinazoline alcohols 4aee from commercially available chiral
a-
hydroxy acids and -amino acids in a few steps. Their application as
a
ligands in enantioselective phenylacetylene addition to aldehydes
furnished good yields with moderate enantioselectivities. In this
respect, we describe here the synthesis of a series of quinazoline
alcohols 5aee containing a phenyl group at their 4-position. The
addition of phenylacetylene to aromatic aldehydes was then
* Corresponding author. Tel.: þ90 3288271818; fax: þ90 3288250097; e-mail
address: sabriulukanli@osmaniye.edu.tr (S. Ulukanli).
http://dx.doi.org/10.1016/j.tet.2014.08.067
0040-4020/Ó 2014 Elsevier Ltd. All rights reserved.
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2
I. Karakaya et al. / Tetrahedron xxx (2014) 1e4
studied with the aim of determining the catalytic effects of these
ligands.
3 and 4). To identify the appropriate ligand, the synthesised qui-
nazolines 5aee were then examined in the condition mentioned
above. Although the better differentiated tert-leucine derived chiral
centre containing ligand 5c gave the least enantioselectivity (Table
1, entry 6), interestingly, the least bulky chiral centre bearing one 5a
was still the best ligand choice (Table 1, entry 2). Additionally, 1,3-
diphenylprop-2-yn-1-ol was accomplished between 45 and 60%
enantioselectivities (Table 1, entries 5, 7 and 8) with the other li-
gands (5b, 5d and 5e). In order to seek a more efficient catalytic
system, we studied the effect of several reaction parameters such as
the choice of solvent, the reaction temperature and the amount of
the chiral ligand used. As a result of increasing the amount of ligand
2. Results and discussion
The quinazolinones 6aee were prepared from
a-hydroxy acids
and -amino acids in four steps in high yields and without a need
a
for chromatography (Scheme 1).23 Enantiomerically pure quina-
zolinones 6aee were treated with Ac2O in the presence of pyridine
as a base to protect the alcohols followed by exposing them to
POCl3 and N,N-diethyl aniline in order to obtain chloroquinazolines
7aee (Scheme 1).
Scheme 1.
With chloroquinazolines 7aee in hand, the synthesis of chiral 4-
phenylquinazoline alcohols was carried out via Suzuki coupling
reactions with phenylboronic acid in the presence of 2 mol % of
Pd(PPh3)4 at reflux. Except for 5d (72% ee), the other chiral 4-
phenylquinazolines 5aec and 5e were obtained in enantiopure
form (99% ee) and high yields (80e91%).
First of all, we carried out the alkynylation of benzaldehyde in
the presence of 10 mol % of ligand 5a both with and without
Ti(OiPr)4 in dry THF at 0 ꢀC under nitrogen atmosphere for 24 h. As
can be seen in Table 1, in the absence of Ti(OiPr)4 the reaction yield
was moderate but the enantioselectivity too low (Table 1, entry 1).
Pleasingly, the loading of 25% Ti(OiPr)4 into the reaction conditions
increased both enantiomeric excess and yield enormously (Table 1,
entry 2). However a rise in ees and yields was not observed sub-
stantially when 10 and 40 mol % Ti(OiPr)4 was used (Table 1, entries
from 10 to 15 mol %, the ees remained the same. However, de-
creasing the amount of the ligand to 5 mol %, diminished slightly
the reaction ees and yields.
After these observations we turned our attention to solvent
screening in order to improve ees. No matter, which solvent was
used, we could not get any better enantioselectivity apart from in
THF. Decreasing the reaction temperature from 0 ꢀC to ꢁ10 ꢀC led to
an increase in ee, but it reduced the reaction yield (Table 2, entry 9).
Extending the reaction time from 24 to 40 h allowed us to increase
the reaction yield from 65 to 89% (Table 2, entry 10).
Table 2
Reaction optimisation for asymmetric alkynylation of benzaldehyde
Entry
Solvent
Temp (ꢀC)
eea (%)
Yieldb (%)
Config.c
1
2
3
4
5
6
7
8
Hexane
THF
0
0
0
0
0
0
0
25
ꢁ10
L10d
ꢁ20
17
78
51
27
7
54
35
70
84
84
80
17
98
75
96
38
71
70
95
65
89
50
R
R
R
R
R
R
R
R
R
R
R
Diethyl ether
Dichloromethane
Chloroform
Toluene
1,4-Dioxane
THF
THF
THF
THF
Table 1
Asymmetric alkynylation of benzaldehyde catalysed by 5aee
9
10
11
Entry
Ligand (mol %)
eea (%)
Yieldb (%)
Config.f
a
Determined by chiral HPLC (Chiralcel OD-H).
Isolated yields.
The absolute configurations of adducts were assigned in accordance with
b
c
1
2
3
4
5
6
7
8
9
10
5a (10)c
5a (10)
5a (10)d
5a (10)e
5b (10)
5c (10)
5d (10)
5e (10)
5a (15)
5a (5)
14
78
70
77
45
4
54
60
78
74
64
98
90
91
70
75
93
80
90
87
R
R
R
R
R
R
R
R
R
R
literature.24
d
The reaction was conducted for 40 h.
The addition of phenylacetylene to a series of aldehydes was
carried out under the optimised reaction conditions (THFas a solvent,
10% 5a, 25% Ti(OiPr)4 at ꢁ10 ꢀC for 40 h) (Table 2, entry 10). As shown
in Table 3, 17 aldehydes were then converted into their propargylic
alcohols in good to excellent yields (67e98%). While propargylic al-
cohols derived from aromatic aldehydes (Table 3, entries 1e13) gave
highly enantioselective results up to 97%, aliphatic ones afforded
moderate enantioselectivities (from 53 to 76% ee). Interestingly,
a
Determined by chiral HPLC (Chiralcel OD-H).
Isolated yields.
b
c
d
e
f
Without Ti(OiPr)4.
Ti(OiPr)4: 10 mol %.
Ti(OiPr)4: 40 mol %.
The absolute configurations of adducts were assigned in accordance with
literature.24
among
the
aldehydes
tested
in
the
reaction,
the
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I. Karakaya et al. / Tetrahedron xxx (2014) 1e4
3
Table 3
127.3, 127.2, 121.8, 69.8, 23.4; HRMS calculated for C16H14N2O:
251.1186. Found: 251.1187.
Enantioselective addition of phenylacetylene to aldehydes using ligand 5a
4.2. (S)-2-Methyl-1-(4-phenylquinazolin-2-yl)propan-1-ol 5b
General procedure
1
was followed using (S)-1-(4-
Entry Aldehyde
Product eea (%) Yieldb (%) Config.c
chloroquinazolin-2-yl)-2-methylpropyl acetate 7b (4.50 g,
16.10 mmol), phenylboronic acid (2.06 g, 16.95 mmol), Pd(PPh3)4
(371 mg, 0.32 mmol) and Na2CO3 (16 mL, 2 M in water) in a solution
in mixture of DME (15 mL) and ethanol (15 mL). The crude product
was purified by column chromatography (hexane-EtOAc, 7:1), and
then crystallised on addition of ethanol to give (S)-2-methyl-1-(4-
1
Benzaldehyde
8a
8b
8c
8d
8e
8f
84
88
75
86
78
83
87
80
97
91
89
91
88
76
53
67
13
89
75
98
73
67
96
95
78
76
98
77
94
85
74
68
70
82
R24
R25
R26
R24
R27
R24
R24
R28
R24
R24
R24
R25
R29
NA
R30
R31
S31
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
2-Methoxybenzaldehyde
3-Methoxybenzaldehyde
4-Methoxybenzaldehyde
2-Chlorobenzaldehyde
3-Chlorobenzaldehyde
4-Chlorobenzaldehyde
3-Bromobenzaldehyde
4-Bromobenzaldehyde
3-Methylbenzaldehyde
4-Methylbenzaldehyde
1-Naphthaldehyde
8g
8h
8i
8j
8k
8l
phenylquinazolin-2-yl)propan-1-ol 5b as
a colourless solid
(4.08 g, 91%). Mp: 69e70 ꢀC; [
a
]
D
ꢁ5.29 (c 1.7, CH2Cl2); ee: 99%;
retention time 5.1 min, Chiralcel OD-H, 90:10 n-hexane-i-PrOH,
flow rate of 1 mL/min, 254 nm; IR (KBr, cmꢁ1) 3455, 3061, 2959,
2928, 1613, 1487, 1143, 1019; 1H NMR (400 MHz, CDCl3, ppm)
d 8.12
Furfural
Crotonaldehyde
Propionaldehyde
Isobutyraldehyde
8m
8n
8o
8p
(d, J¼7.5 Hz, 1H), 8.08 (d, J¼8.4 Hz, 1H), 7.94e7.58 (m, 7H), 4.92 (dd,
J¼5.6, 3.4 Hz, 1H), 4.46 (d, J¼5.6 Hz, 1H), 2.54e2.46 (m, 1H), 1.17 (d,
J¼7.0 Hz), 0.77 (d, J¼6.8 Hz, 1H); 13C NMR (100 MHz, CDCl3, ppm)
d
168.6, 166.1, 150.5, 137.1, 133.9, 130.1, 128.6, 128.4, 127.4, 127.2,
Cyclohexanecarbaldehyde 8r
121.7, 34.0, 19.9, 15.4, 0.02; HRMS calculated for C16H14N2O:
279.1499. Found: 279.1503.
a
Determined by chiral HPLC (Chiralcel OD-H).
Isolated yields.
The absolute configurations of adducts were assigned in accordance with
b
c
literature.
4.3. (S)-2,2-Dimethyl-1-(4-phenylquinazolin-2-yl)propan-1-
ol 5c
cyclohexanecarbaldehyde corresponding adduct accomplished nei-
ther a good enantioselectivity nor the same sense of stereoselectivity.
General procedure
1
was followed using (S)-1-(4-
chloroquinazolin-2-yl)-2,2-dimethylpropyl acetate 7c (2.30 g,
7.85 mmol), phenylboronic acid (1.01 g, 8.24 mmol), Pd(PPh3)4
(180 mg, 0.157 mmol) and Na2CO3 (17.3 mL, 2 M in water) in a so-
lution in mixture of DME (15 mL) and ethanol (15 mL). The crude
product was purified by column chromatography (hexane/EtOAc,
7:1), and then crystallised on addition of ethanol to give (S)-2,2-
dimethyl-1-(4-phenylquinazolin-2-yl)propan-1-ol 5c as a colour-
3. Conclusions
In summary, we successfully prepared novel chiral quinazolinols
(5aee) from commercially available starting materials in a few
steps. Among these ligands, quinazolinol 5a exhibited high catalytic
activity and asymmetric induction in the alkynylation of aldehydes.
It is of note that the best enantioselectivity (75%) of propargylic
alcohols obtained in our earlier report23 is the worst one in this
present work for aromatic aldehydes. Application of these ligands
in other catalytic enantioselective reactions is currently under in-
vestigation in our laboratory.
less solid (1.84 g, 80%). Mp: 101e103 ꢀC; [
a
]
D þ7.08 (c 2.4, CH2Cl2);
ee: 99%; retention time 5.0 min, Chiralcel OD-H, 90:10 n-hexane/i-
PrOH, flow rate of 1 mL/min, 254 nm; IR (KBr, cmꢁ1) 3459, 3062,
2957, 2866, 1614, 1565, 1546, 1487, 1391, 1068; 1H NMR (400 MHz,
CDCl3, ppm)
d
8.15 (d, J¼8.4 Hz,1H), 8.10 (d, J¼8.5 Hz,1H), 7.92e7.58
(m, 7H), 4.73 (d, J¼7.6 Hz,1H), 4.47 (d, J¼7.6 Hz,1H),1.06 (s, 9H); 13
C
NMR (100 MHz, CDCl3, ppm) d 167.4, 165.3, 150.5, 137.1, 133.8, 130.1,
4. Experimental section
130.1, 128.6, 127.3, 127.1, 121.8, 80.9, 30.9, 26.3; HRMS calculated for
16H14N2O: 293.1655. Found: 293.1653.
C
4.1. General procedure 1 for the preparation of (S)-1-(4-
phenylquinazolin-2-yl)ethanol 5a
4.4. (S)-Phenyl(4-phenylquinazolin-2-yl)methanol 5d
General procedure was followed using (S)-(4-
To a solution of (S)-1-(4-chloroquinazolin-2-yl)ethyl acetate 7a
(5.00 g, 19.90 mmol) in DME (15 mL) and ethanol (15 mL) were
added phenylboronic acid (2.55 g, 20.94 mmol), Pd(PPh3)4 (454 mg,
0.39 mmol) and Na2CO3 (22 mL, 2 M in water). The resulting mix-
ture was then refluxed for 12 h, cooled to room temperature and
diluted with dichloromethane (150 mL). The mixture was washed
with water (3ꢂ75 mL). The organic layer was dried over Na2SO4,
and evaporated under reduced pressure. The crude product was
purified by column chromatography (silica gel, hexane/EtOAc, 7:1),
and then crystallised on addition of ethanol to give (S)-1-(4-
phenylquinazolin-2-yl)ethanol 5a as a colourless solid (4.48 g,
1
chloroquinazolin-2-yl)(phenyl)methyl acetate 7d (5.40 g,
17.26 mmol), phenylboronic acid (2.20 g, 18.12 mmol), Pd(PPh3)4
(396 mg, 0.34 mmol) and Na2CO3 (7.8 mL, 2 M in water) in a solu-
tion in mixture of DME (6 mL) and ethanol (6 mL). The crude
product was purified by column chromatography (hexane/EtOAc,
10:1), and then crystallised on addition of ethanol to give (S)-2,2-
dimethyl-1-(4-phenylquinazolin-2-yl)propan-1-ol 5d as a colour-
less solid (4.58 g, 85%). Mp: 102e106 ꢀC; [
ee: 72%; retention time 8.9 min (major), 11.7 min (minor), Chiralcel
OD-H, 90:10 n-hexane/i-PrOH, flow rate of 1 mL/min, 254 nm; IR
(KBr, cmꢁ1) 3423, 3058, 1613, 1565, 1547, 1389, 1058; 1H NMR
a
]
D þ54.33 (c 2.0, CH2Cl2);
90%). Mp: 85e87 ꢀC; [
a
]
þ7.5 (c 3.2, CH2Cl2); ee: 99%; retention
D
time 6.9 min, Chiralcel OD-H, 90:10 n-hexane/i-PrOH, flow rate of
1 mL/min, 254 nm; IR (KBr, cmꢁ1) 3232, 3048, 2978, 2909, 1613,
(400 MHz, CDCl3, ppm)
d
8.19e7.31 (m, 14H), 6.10 (d, J¼6.3 Hz, 1H),
1486, 1132, 1107; 1H NMR (400 MHz, CDCl3, ppm)
d
8.13 (d,
5.29 (d, J¼6.3 Hz, 1H); 13C NMR (100 MHz, CDCl3, ppm)
d 168.9,
J¼8.8 Hz, 1H), 8.09 (d, J¼8.4 Hz, 1H), 7.93e7.57 (m, 7H), 5.17e5.16
165.2, 150.7, 142.5, 136.9, 134.1, 130.2, 130.2, 128.6, 128.5, 128.2,
127.6, 127.5, 127.2, 126.9, 121.9, 75.5; HRMS calculated for
(m, 1H), 4.6 (s, 1H), 1.71 (d, J¼6.7 Hz, 1H); 13C NMR (100 MHz, CDCl3,
ppm)
d
168.9, 167.3, 150.7, 137.0, 134.0, 130.2, 130.0, 128.6, 128.4,
C16H14N2O: 313.1342. Found: 313.1335.
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4
I. Karakaya et al. / Tetrahedron xxx (2014) 1e4
4.5. (S)-2-Phenyl-1-(4-phenylquinazolin-2-yl)ethanol 5e
General procedure was followed using (S)-1-(4-
chloroquinazolin-2-yl)-2-phenylethyl acetate 7e (5.00 g,
15.30 mmol), phenylboronic acid (1.96 g, 16.06 mmol), Pd(PPh3)4
(352 mg, 0.31 mmol) and Na2CO3 (15 mL, 2 M in water) in a solution
in mixture of DME (20 mL) and ethanol (20 mL). The crude product
was purified by column chromatography (hexane/EtOAc, 6:1), and
then crystallised on addition of ethanol to give (S)-2-phenyl-1-(4-
phenylquinazolin-2-yl)ethanol 5e as a colourless solid (4.24 g,
Supplementary data
1
Supplementary data associated with this article can be found in
the online version, at http://dx.doi.org/10.1016/j.tet.2014.08.067.
References and notes
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85%). Mp: 66e68 ꢀC; [
a
]
D ꢁ70.74 (c 2.7, CH2Cl2); ee: 99%; retention
time 6.2 min, Chiralcel OD-H, 90:10 n-hexane/i-PrOH, flow rate of
1 mL/min, 254 nm; IR (KBr, cmꢁ1) 3430, 3058, 1613, 1565, 1547,
1389, 1058; 1H NMR (400 MHz, CDCl3, ppm)
d
8.12 (d, J¼8.7 Hz, 1H),
8.06 (d, J¼8.4 Hz, 1H), 7.92e7.23 (m, 12H), 5.36e5.29 (m, 1H), 4.48
(d, J¼5.8 Hz, 1H), 3.51 (dd, J¼13.8, 3.95 Hz, 1H), 3.17 (dd, J¼13.8,
7.64 Hz, 1H); 13C NMR (100 MHz, CDCl3, ppm)
d 168.7, 165.7, 150.7,
138.2, 137.0, 134.0, 130.2, 130.08, 129.7, 128.6, 128.5, 128.1, 127.4,
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4.6. Typical procedure for catalytic asymmetric addition of
phenylacetylene to aldehydes
Under nitrogen atmosphere, phenylacetylene (1.96 mmol) and
diethylzinc (1.96 mmol, 1 M in hexane) were dissolved in freshly
distilled THF (3 mL) and refluxed for 1 h. The resulting solution was
brought to ambient temperature and following that a solution of
chiral ligand 5a (0.098 mmol) inTHF (3 mL) was added. After stirring
for 30 min, Ti(OiPr)4 (0.25 mmol) was added to the solution and
stirredfor a further 1 h. Finally, the mixturewas cooled to ꢁ10 ꢀC and
aldehyde (0.98 mmol in 2 mL THF) was added. After stirring for 40 h
at ꢁ10 ꢀC under a nitrogen atmosphere, the reaction was then
quenched with saturated ammonium chloride (10 mL). The aqueous
phase was extracted with ethyl acetate (3ꢂ20 mL), washed with
brine (3ꢂ20 mL), dried with anhydrous Na2SO4, filtered and con-
centrated under reduced pressure. The crude product was purified
bycolumn chromatography (silica gel, EtOAc/hexane 9:1) to give the
desired product. The enantiomeric excess was determined by chiral
HPLC using Chiralcel OD-H column.
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Acknowledgements
We would like to thank to Gokhan Bilsel at TUBITAK UME for the
HRMS measurements.
Please cite this article in press as: Karakaya, I.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2014.08.067