Chemoselectivity in the reaction of 2-diazo-3-oxo-3-phenylpropanal with aldehydes and ketones

Article abstract of DOI:10.1002/hlca.201200532

The chemoselectivity in the reaction of 2-diazo-3-oxo-3-phenylpropanal (1) with aldehydes and ketones in the presence of Et₃N was investigated. The results indicate that 1 reacts with aromatic aldehydes with weak electron-donating substituents and cyclic ketones under formation of 6-phenyl-4H-1,3-dioxin-4-one derivatives. However, it reacts with aromatic aldehydes with electron-withdrawing substituents to yield 1,3-diaryl-3-hydroxypropan-1-ones, accompanied by chalcone derivatives in some cases. It did not react with linear ketones, aliphatic aldehydes, and aromatic aldehydes with strong electron-donating substituents. A mechanism for the formation of 1,3-diaryl-3-hydroxypropan-1-ones and chalcone derivatives is proposed. We also tried to react 1 with other unsaturated compounds, including various olefins and nitriles, and cumulated unsaturated compounds, such as N,N′-dialkylcarbodiimines, phenyl isocyanate, isothiocyanate, and CS₂. Only with N,N′-dialkylcarbodiimines, the expected cycloaddition took place. Copyright

Full text of DOI:10.1002/hlca.201200532

Helvetica Chimica Acta – Vol. 96 (2013)
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Chemoselectivity in the Reaction of 2-Diazo-3-oxo-3-phenylpropanal with
Aldehydes and Ketones
by Jiantao Zhang and Jiaxi Xu*
State Key Laboratory of Chemical Resource Engineering, Department of Organic Chemistry, Faculty of
Science, Beijing University of Chemical Technology, Beijing 100029, P. R. China
(phone/fax: þ 86-10-64435565; e-mail: jxxu@mail.buct.edu.cn)
The chemoselectivity in the reaction of 2-diazo-3-oxo-3-phenylpropanal (1) with aldehydes and
ketones in the presence of Et3N was investigated. The results indicate that 1 reacts with aromatic
aldehydes with weak electron-donating substituents and cyclic ketones under formation of 6-phenyl-4H-
1,3-dioxin-4-one derivatives. However, it reacts with aromatic aldehydes with electron-withdrawing
substituents to yield 1,3-diaryl-3-hydroxypropan-1-ones, accompanied by chalcone derivatives in some
cases. It did not react with linear ketones, aliphatic aldehydes, and aromatic aldehydes with strong
electron-donating substituents. A mechanism for the formation of 1,3-diaryl-3-hydroxypropan-1-ones
and chalcone derivatives is proposed. We also tried to react 1 with other unsaturated compounds,
including various olefins and nitriles, and cumulated unsaturated compounds, such as N,N’-dialkylcar-
bodiimines, phenyl isocyanate, isothiocyanate, and CS2. Only with N,N’-dialkylcarbodiimines, the
expected cycloaddition took place.
1. Introduction. – a-Diazo-b-dicarbonyl compounds react with various unsaturated
bonds yielding different heterocyclic compounds [1 – 9]. Recently, we reported on the
synthesis of a series of 2,3,6-trisubstituted 2H-1,3-oxazin-4(3H)-one derivatives in
satisfactory-to-good yields by reaction of imines and 2-diazo-3-oxo-3-phenylpropanal
(1) in the presence of the catalytic amount of Et3N under mild conditions [9g][10]. The
reaction is metal-free, mild, and highly regioselective. To extend the application of 2-
diazo-3-oxo-3-phenylpropanal (1) to cycloaddition reactions with unsaturated com-
pounds, we explored its reaction with aldehydes and ketones and found that the
cycloaddition reaction shows a different chemoselectivity depending on the structural
feature of aldehydes and ketones. The mechanism of the formation of 1,3-diaryl-3-
hydroxypropan-1-ones and chalcone derivatives is also discussed.
2. Results and Discussion. – 2-Diazo-3-oxo-3-phenylpropanal (1) was previously
prepared from 2-diazoacetophenone and the VilsmeierꢀHaack reagent [9a], which was
synthesized from DMF and (COCl)2 [11]. However, the overall yield was low. The
diazo transformation is a general method for the preparation of a-diazo-b-diketones
and a-diazo-b-oxo alkanoates from the corresponding b-diketones and b-oxo
alkanoates under basic conditions [2]. We attempted to synthesize 2-diazo-3-oxo-3-
phenylpropanal (1) by this method. 3-Oxo-3-phenylpropanal was prepared from
acetophenone and HCOOEt by Claisen condensation. It was converted to 2-diazo-3-
ꢀ 2013 Verlag Helvetica Chimica Acta AG, Zꢁrich

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Helvetica Chimica Acta – Vol. 96 (2013)
Scheme 1. Reactions of 2-Diazo-3-oxo-3-phenylpropanal (1) with Ketones and Aldehydes
oxo-3-phenylpropanal (1) by the treatment with TsN3 in the presence of K2CO3 in a
high yield (Scheme 1).
2-Diazo-3-oxo-3-phenylpropanal (1) was reacted with various ketones, however,
only with cycloalkanones 2 (cyclopentanone (2a) and cyclohexanone (2b)), the
corresponding spiro 6-phenyl-4H-1,3-dioxin-4-one derivatives 3a and 3b were formed
in the presence of Et3N (Scheme 1). On the other hand, aromatic ketones (acetophe-
none and benzophenone) and aliphatic linear ketones (acetone, heptan-2-one, and
heptan-4-one) did not undergo the desired cycloaddition. Instead, the benzoylketene
generated from 1 dimerized to 3-benzoyl-6-phenyl-2H-pyran-2,4(3H)-dione (4’),
which tautomerized to give 3-benzoyl-4-hydroxy-6-phenyl-2H-pyran-2-one (4) [12].
The reaction of 1 with various aldehydes was attempted as well. No desired
cycloaddition was observed with aliphatic aldehydes. However, diverse products were
obtained with aromatic aldehydes 5, depending on the electronic characters of the
aromatic aldehydes (Table). We found that 1 reacted with aromatic aldehydes with
weak electron-donating substituents to generate 6-phenyl-4H-1,3-dioxin-4-one deriv-
atives 6. However, it reacted with aromatic aldehydes with electron-withdrawing
substituents to yield 1,3-diaryl-3-hydroxypropan-1-ones 7, accompanied by chalcone
derivatives 8 in some cases.
On the basis of the above results, we propose the mechanism of the chemoselective
reaction of 1 with aromatic aldehydes as depicted in Scheme 2. Diazo compound 1 is
converted in the presence of Et3N to benzoylketene, which undergoes [4 þ 2] or [2 þ 2]
cycloaddition chemoselectively with different aromatic aldehydes to give rise to 6-
phenyl-4H-1,3-dioxin-4-one derivatives 6 or 3-benzoyl-b-lactones 9, respectively.
However, 3-benzoyl-b-lactones 9 are unstable under the reaction conditions and
undergo elimination of CO2 to afford chalcone derivatives 8. Lactones 9 are hydrolyzed
to b-oxo alkanoic acids 10 during workup, which undergo a decarboxylation to form 3-
hydroxy-1-phenylalkan-1-ones 7. The different cycloadditions result in the chemo-

Helvetica Chimica Acta – Vol. 96 (2013)
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Table. Reactions of 2-Diazo-3-oxo-3-phenylpropanal (1) with Aromatic Aldehydes
Entry
ArCHO
Ar
Yield [%]
6
7
8
4
1
2
3
4
5
6
7
8
9
5a
5b
5c
5d
5e
5f
5g
5h
5i
4-MeOꢀC6H4
4-Me2NꢀC6H4
4-MeꢀC6H4
Ph
–
–
80
71
21
–
–
–
–
–
–
–
–
–
–
10
11
10
16
27
16
19
–
–
–
–
–
14
–
–
–
–
46
33
46
45
n.d.a)
n.d.
37
36
44
40
33
4-FꢀC6H4
2-ClꢀC6H4
4-ClꢀC6H4
2,6-Cl2ꢀC6H3
2-O2NꢀC6H4
4-O2NꢀC6H4
2-Cl-5-O2NꢀC6H3
Pyridin-4-yl
10
11
12
5j
5k
5l
35
19
20
–
–
a) n.d. ¼ Not determined.
selective formation of various products in the reaction. However, it is not completely
clear so far why different aromatic aldehydes undergo [4 þ 2] or [2 þ 2] cycloaddition
chemoselectively with benzoylketene.
Scheme 2. Proposed Reaction Mechanism of the Chemoselective Reaction of 2-Diazo-3-oxo-3-phenyl-
propanal (1a) and Aromatic Aldehydes
To investigate the generality of the cycloaddition of 1 and other unsaturated
compounds, we attempted to react 1 with olefins (such as styrene, cyclohexene, 1-
phenylpropene, cyclopenadiene, 1,1-dichloroethene, vinyl acetate, and butyl vinyl
ether) and nitriles (including benzonitrile, 2-chlorobenzonitrile, acetonitrile, and ethyl
cyanoacetate). In all cases, no desired reaction occurred, only 3-benzoyl-6-phenyl-2H-
pyran-2,4(3H)-dione, dimer of benzoylketene, was obtained in each of the reactions.
The reaction of 1 with cumulated unsaturated compounds, including N,N’-dicyclohex-
ylcarbodiimide (DCC; 11a), N,N’-diisopropylcarbodiimide (DIC; 11b), phenyl
isocyanate, phenyl isothiocyanate, and CS2, was also attempted. With 11a and 11b,
the desired cycloadducts, 3-cyclohexyl-2-(cyclohexylimino)-6-phenyl-2H-1,3-oxazin-

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4(3H)-one (12a) and 3-isopropyl-2-(isopropylimino)-6-phenyl-2H-1,3-oxazin-4(3H)-
one (12b), respectively, were formed (Scheme 3). However, no desired reaction
occurred with phenyl isocyanate, phenyl isothiocyanate, and CS2.
Scheme 3. Reaction of 2-Diazo-3-oxo-3-phenylpropanal (1) and N,N’-Dialkylcarbodiimides
3. Conclusions. – The chemoselectivity of the reaction of 2-diazo-3-oxo-3-phenyl-
propanal (1) with aldehydes and ketones in the presence of Et3N was investigated. The
results indicate that 2-diazo-3-oxo-3-phenylpropanal (1) reacted with aromatic
aldehydes with weak electron-donating substituents and cyclic ketones to generate 6-
phenyl-4H-1,3-dioxin-4-one derivatives. With aromatic aldehydes with electron-with-
drawing substituents, however, 1 furnished 1,3-diaryl-3-hydroxypropan-1-ones, accom-
panied by chalcone derivatives in some cases. For linear aliphatic and aromatic ketones,
aliphatic aldehydes, and aromatic aldehydes with strong electron-donating substituents,
no cycloaddition reaction was observed. A mechanism of the formation of 1,3-diaryl-3-
hydroxypropan-1-ones and chalcone derivatives has been proposed (Scheme 2). 2-
Diazo-3-oxo-3-phenylpropanal (1) was also attempted to react with other unsaturated
compounds, such as different olefins and nitriles, and cumulated unsaturated
compounds, including N,N’-dialkylcarbodiimides, phenyl isocyanate, phenyl isothio-
cyanate, and CS2. Only N,N’-dialkylcarbodiimides undergo the expected cycloaddition
reaction.
Experimental Part
General. Column chromatography (CC): silica gel (200 – 300 mesh) with petroleum ether (PE) and
AcOEt as the eluent. M.p.: Yanaco MP-500; uncorrected. IR Spectra: Nicolet Avatar 330 FT-IR
spectrometer; in KBr; ˜n in cmꢀ1. 1H- and 13C-NMR spectra: Bruker AV 400 at 400 MHz in CDCl3; d in
ppm rel. to Me4Si as internal standard, J in Hz. HR-ESI-MS: LC/MSD TOF mass spectrometer; in m/z.
Reaction of 2-Diazo-3-oxo-3-phenylpropanal (1) with Unsaturated Compounds in the Presence of
Et3N: General Procedure. To a soln. of 1 (87 mg, 0.5 mmol) and an aldehyde, ketone, or carbodiimide
(0.5 mmol) in CH2Cl2 (1 ml) was added a drop of Et3N (30 mg, 0.3 mmol) under stirring in an ice-water
bath or at r.t. N2 was liberated immediately, and TLC monitoring indicated that the reaction was
complete. After stirring for 2 to 5 s, the residue was separated by CC (AcOEt/PE(60 – 908) 1:10 to 1:20)
to afford product(s).
9-Phenyl-6,10-dioxaspiro[4.5]dec-8-en-7-one (3a). Colorless oil. M.p. 54 – 568 ([13]). Yield: 42 mg
(36%). IR: 1722 (C¼O). 1H-NMR: 1.51 – 2.31 (m, 4 CH2); 5.93 (s, CH); 7.47 – 7.50 (m, 2 arom. H); 7.55
(m, arom. H); 7.71 – 7.73 (m, 2 arom. H). 13C-NMR: 18.4; 23.2; 36.7; 58.5; 67.3; 71.0; 88.4; 92.3; 116.3;
126.4; 128.9; 132.2.
4-Phenyl-1,5-dioxaspiro[5.5]undec-3-en-2-one (3b). Colorless oil. M.p. 54 – 558 ([13]). Yield: 37 mg
(30%). IR: 1721 (C¼O). 1H-NMR: 1.49 – 3.51 (m, 5 CH2); 5.91 (s, CH); 7.47 – 7.55 (m, 2 arom. H); 7.56

Helvetica Chimica Acta – Vol. 96 (2013)
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(m, arom. H); 7.74 – 7.76 (m, 2 arom. H). 13C-NMR: 22.5; 24.7; 33.8; 91.5; 107.3; 126.4; 128.9; 132.1; 162.0;
164.6.
3-Benzoyl-4-hydroxy-6-phenyl-2H-pyran-2-one (4). Yellow crystals. M.p. 169 – 1708 ([12b]: 169 –
1708). Yield: 67 mg (46%). 1H-NMR: 6.66 (s, CH); 7.43 – 7.92 (m, 10 arom. H); 15.94 (s, C¼COH).
2-(4-Methylphenyl)-6-phenyl-4H-1,3-dioxin-4-one (6c). Yield: 106 mg (80%). Colorless crystals.
M.p. 109 – 1108. IR: 1724 (C¼O). 1H-NMR: 2.45 (s, Me); 6.09 (s, C¼CH); 6.56 (s, CH); 7.31 – 7.79 (m, 9
arom. H). 13C-NMR: 21.4; 93.2; 100.5; 126.7; 128.9; 129.4; 130.2; 130.9; 132.5; 140.6; 163.2; 168.3. HR-
ESI-MS: 267.1014 ([M þ H]þ, C17H15O3þ ; calc. 267.1016).
2,6-Diphenyl-4H-1,3-dioxin-4-one (6d). Yield: 90 mg(71%). Colorless crystals. M.p. 103 – 1058 ([13]:
103 – 1058). IR: 1680 (C¼O). 1H-NMR: 6.11 (s, C¼CH); 6.60 (s, CH); 7.47 – 7.81 (m, 10 arom. H).
13C-NMR: 93.3; 100.4; 126.7; 126.7; 128.7; 129.0; 130.5; 132.6; 163.0; 168.2.
2-(4-Fluorophenyl)-6-phenyl-4H-1,3-dioxin-4-one (6e). Yield: 28 mg (21%). Colorless crystals. M.p.
152 – 1538. IR: 1733 (C¼O). 1H-NMR: 6.08 (s, C¼CH); 6.55 (s, CH); 7.16 – 7.77 (m, 9 arom. H).
13C-NMR: 93.3; 99.7; 115.7; 116.0; 126.7; 128.8; 128.9; 129.0; 132.6; 162.8; 168.2; 172.1. HR-ESI-MS:
271.0771 ([M þ H]þ, C16H12FOþ3 ; calc. 271.0765).
3-(2-Chlorophenyl)-3-hydroxy-1-phenylpropan-1-one (7f). Yield: 13 mg(10%). Colorless crystals.
M.p.: 78 – 808 ([14]: 808). IR: 1677 (C¼O), 3466 (OH). 1H-NMR: 3.18 (dd, J ¼ 9.6, 17.6, 1 H of CH2); 3.59
(dd, J ¼ 2.4, 17.6, 1 H of CH2); 3.87 (s, OH); 5.72 (dd, J ¼ 2.4, 9.6, CH); 7.25 – 8.00 (m, 9 arom. H).
13C-NMR: 45.4; 66.9; 127.3; 128.2; 128.6; 128.8; 129.4; 131.2; 133.8; 136.5; 140.4; 200.3.
3-(4-Chlorophenyl)-3-hydroxy-1-phenylpropan-1-one (7g). Yield: 15 mg (11%). Colorless crystals.
M.p. 99 – 1008 ([15]: 99.4 – 100.48). IR (KBr): 1724 (C¼O), 3446 (OH). 1H-NMR: 3.37 (dd, J ¼ 2.8, 17.2,
1 H of CH2); 4.04 (dd, J ¼ 9.6, 17.2, 1 H of CH2); 3.92 (s, OH); 6.19 (dd, J ¼ 2.8, 9.6, CH); 7.45 – 8.00 (m, 8
arom. H). 13C-NMR: 44.8; 66.5; 123.1; 123.4; 128.2; 128.9; 130.3; 134.1; 142.6; 199.6.
3-(2,6-Dichlorophenyl)-3-hydroxy-1-phenylpropan-1-one (7h). Yield: 15 mg (10%). Colorless
1
crystals. M.p. 150 – 1518. IR: 1643 (C¼O), 3243 (OH). H-NMR: 7.71 (d, J ¼ 18.8, ArCH); 7.66 (d, J ¼
18.8, COCH); 7.47 – 7.65 (m, 5 arom. H); 8.02 – 8.70 (m, 4 arom. H). HR-ESI-MS: 295.0288 ([M þ
H]þ, C15H13Cl2Oþ2 ; calc. 295.0287).
3-Hydroxy-3-(2-nitrophenyl)-1-phenylpropan-1-one (7i). Yield: 22 mg (16%). Colorless crystals.
M.p. 106 – 1078 ([16]: 106 – 1078). IR: 1678 (C¼O), 3509 (OH). 1H-NMR: 3.21 (dd, J ¼ 9.2, 17.6, 1 H of
CH2); 3.74 (dd, J ¼ 2.0, 17.6, 1 H of CH2); 4.01 (s, OH); 5.88 (dd, J ¼ 2.0, 9.2, CH); 7.45 – 8.00 (m, 9 arom.
H). 13C-NMR: 45.4; 66.9; 127.3; 128.2; 128.6; 128.8; 129.4; 131.2; 133.8; 136.5; 140.4; 200.3.
3-Hydroxy-3-(4-nitrophenyl)-1-phenylpropan-1-one (7j). Yield: 37 mg (27%). Colorless crystals.
M.p. 113 – 1148 ([15]: 114 – 114.78). IR: 1670 (C¼O), 3499 (OH). 1H-NMR: 3.38 (dd, J ¼ 9.6, 17.6, 1 H of
CH2); 3.58 (dd, J ¼ 4.0, 17.6, 1 H of CH2); 3.90 (s, OH); 5.71 (dd, J ¼ 4.0, 9.6, CH); 7.48 – 8.26 (m, 8 arom.
H). 13C-NMR: 47.0; 69.2; 123.8; 126.6; 128.2; 134.0; 136.2; 147.4; 150.3; 199.5.
3-(2-Chloro-5-nitrophenyl)-3-hydroxy-1-phenylpropan-1-one (7k). Yield: 25 mg (16%). Colorless
crystals. M.p. 120 – 1228. IR: 1681 (C¼O), 3466 (OH). 1H-NMR: 3.17 (dd, J ¼ 9.6, 17.6, 1 H of CH2); 3.58
(dd, J ¼ 2.0, 17.6, 1 H of CH2); 4.01 (s, OH); 5.71 (dd, J ¼ 2.0, 9.6, CH); 7.26 – 8.64 (m, 8 arom. H).
13C-NMR: 42.8; 67.7; 128.3; 128.7; 129.32; 129.5; 133.6; 134.8; 136.3; 136.6; 198.9. HR-ESI-MS: 306.0528
([M þ H]þ, C15H13ClNOþ4 ; calc. 306.0528).
3-Hydroxy-1-phenyl-3-(pyridin-4-yl)propan-1-one (7l) [17]. Yield: 22 mg (19%). Colorless oil.
1H-NMR: 3.35 (d, J ¼ 6.0, CH2); 4.21 (s, OH); 5.36 (t, J ¼ 6.0, CH); 7.37 (d, J ¼ 6.0, 2 arom. H); 7.47 (t, J ¼
7.6, 2 arom. H); 7.60 (t, J ¼ 7.2, arom. H); 7.95 (dd, J ¼ 7.2, 1.2, 2 arom. H); 8.57 (dd, J ¼ 1.2, 4.4, 2 arom.
H). 13C-NMR: 46.7; 68.6; 120.6; 128.1; 128.7; 133.7; 136.3; 149.7; 152.0; 199.4.
(2E)-3-(2-Chlorophenyl)-1-phenylprop-2-en-1-one (8f) [18]. Yield: 17 mg (14%). Colorless oil. M.p.
50 – 528. IR: 1663 (C¼O). 1H-NMR: 8.21 (d, J ¼ 16.0, ArCH); 7.52 (d, J ¼ 16.0, COCH); 7.34 – 8.06 (m, 9
arom. H).
(2E)-3-(2-Chloro-5-nitrophenyl)-1-phenylprop-2-en-1-one (8k). Yield: 66 mg (46%). Colorless
crystals. M.p. 152 – 1558 ([19]: 151 – 1528). IR: 1670 (C¼O). 1H-NMR: 8.18 (d, J ¼ 17.2, ArCH); 7.70
(d, J ¼ 17.2, COCH); 7.65 – 8.65 (m, 8 arom. H).
(2E)-1-Phenyl-3-(pyridin-4-yl)prop-2-en-1-one (8l). Yield: 35 mg (33%). Colorless crystals. M.p.
74 – 758 ([20]: 73 – 74.58). IR: 1667 (C¼O). 1H-NMR: 7.71 (d, J ¼ 18.8, ArCH); 7.66 (d, J ¼ 18.8, COCH);

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Helvetica Chimica Acta – Vol. 96 (2013)
7.47 – 7.65 (m, 5 arom. H); 8.02 – 8.70 (m, 4 arom. H). 13C-NMR: 122.0; 125.9; 128.5; 128.6; 133.1; 137.2;
141.3; 141.9; 150.4; 189.6.
3-Cyclohexyl-2-(cyclohexylimino)-6-phenyl-2,3-dihydro-4H-1,3-oxazin-4-one (12a). Yield: 155 mg
(88%). Colorless crystals. M.p. 123 – 1258 ([21]: 119 – 1208). IR: 1670 (C¼O). 1H-NMR: 1.24 – 2.63 (m, 10
CH2); 3.85 (m, CHN); 4.77 (m, CHN); 6.08 (s, CH); 7.48 – 7.54 (m, 3 arom. H); 7.70 – 7.73 (m, arom. H).
13C-NMR: 22.4; 25.5; 26.1; 26.4; 28.0; 33.9; 53.6; 54.5; 97.1; 125.6; 129.0; 131.6; 159.5; 162.1.
2,3-Dihydro-3-(1-methylethyl)-2-[(1-methylethyl)imino]-6-phenyl-4H-1,3-oxazin-4-one (12b).
Yield: 122 mg (89%). Colorless crystals. M.p. 47 – 488. IR: 1670 (C¼O). 1H-NMR: 1.21 (d, J ¼ 6.4,
NCHMe2); 1.48 (d, J ¼ 6.4, NCHMe2); 4.12 (sept., J ¼ 6.4, NCHMe2); 5.15 (sept., J ¼ 6.4, NCHMe2); 6.05
(s, CH); 7.45 – 7.71 (m, 5 arom. H). HR-ESI-MS: 272.1525 ([M þ H]þ, C16H20N2O2þ ; calc. 272.1525).
This work was supported by the National Natural Science Foundation of China (Nos. 21172017,
20972013, and 20772005) and the Beijing Natural Science Foundation (No. 2092022).
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Received September 16, 2012