Synthesis, x-ray structure and photo chemistry of 2-(methyl(1-phenylvinyl) carbamoyl)phenyl acetate

Article abstract of DOI:10.1007/s10870-011-0227-z

2-(Methyl(1-phenylvinyl)carbamoyl)phenyl acetate (SM), empirical formula C₁₈H₁₇NO₃, crystallizes in the triclinic space group, P-1, with unit cell parameters α= 9.10870(10) A , b = 10.56940(10) A , c = 16.1340(2) A , a = 7

Full text of DOI:10.1007/s10870-011-0227-z

J Chem Crystallogr (2012) 42:214–221
DOI 10.1007/s10870-011-0227-z
ORIGINAL PAPER
Synthesis, X-ray Structure and Photo Chemistry
of 2-(Methyl(1-Phenylvinyl)Carbamoyl)Phenyl Acetate
Sujit Kumar Dehury
Received: 23 June 2011 / Accepted: 17 November 2011 / Published online: 26 November 2011
Ó Springer Science+Business Media, LLC 2011
Abstract 2-(Methyl(1-phenylvinyl)carbamoyl)phenyl ace-
tate (SM), empirical formula C18H17NO3, crystallizes in
the triclinic space group, P-1, with unit cell parameters
Introduction
Aromatic enamides are an interesting class of conjugated
systems possessing a marked degree of hexatrienic char-
acter. Therefore, photochemical electrocyclic ring closure
reactions are possible which would potentially give zwit-
terionic intermediates [1–3] (Scheme 1). This research
recognizes that the zwitterionic intermediates could elim-
inate leaving group anions. The goal is therefore to syn-
thesize the suitable target molecules that can expel leaving
group anions from zwitterions generated by a photochem-
ical electrocyclization process.
˚
a = 9.10870(10) A, b = 10.56940(10) A, c = 16.1340(2)
˚
˚
A, a = 78.0590(10)°, b = 89.5080(10)°, c = 86.6830(10)°,
Z = 4. The 2-(methyl(1-phenylvinyl)carbamoyl)phenyl
acetate (SM) molecule, upon irradiation of UV-light below
˚
3,000 A, releases acetate group to give six membered
cyclic lactam 1 as the major product. The quantum yield
for the lactam 1 was found to be 0.053. An alternate con-
rotatory 6-pi electron photochemically allowed electrocy-
clic ring closure reaction also occurs upon irradiation to
give a six-membered cyclic zwitterionic intermediate which
retains acetate as leaving group. A [1,5]-H shift would then
give the isomerized product 2. The quantum yield for the
lactam 2 was found to be 0.026. A minor oxidation product
lactam 3 that retains the leaving group also formed, likely
from loss of a proton and tautomerization of enol. The loss
of one hydrogen molecule is the driving force for revival of
aromaticity in the minor product 3. The quantum yield for
the lactam 3 was found to be 0.012. The low value of total
quantum yield (0.091) for photocyclization of SM can be
explained as the photoproducts absorb light in competition
with the photoreactant.
The research has practical importance for solving
problems in biological studies. Biological studies are
confronted by the problem of instantly delivering biologi-
cal reagents in order to trigger a specific biological process
on a cellular level under physiological conditions. A pro-
tecting group is chosen that inactivates biological reagent
or the bioeffector molecule until it is needed. The bioef-
fector is released by a short pulse of light within the cell to
nearly instantaneously initiate the biological process to be
studied [4–7]. The reagent or leaving group to be expelled
should be a biologically important molecule.
Although a number of photo cleavable protecting groups
are currently available for use in studies of biological
processes, no single type meets all of the requirements
needed for use in a given application. Therefore, there is
still the need for the development of new photo removable
leaving groups that can fulfill specific requirements for
practical applications [8, 9]. The proposed research
described herein focuses upon a new strategy for the
elimination of acetate leaving group from photogenerated
zwitterionic intermediates.
Keywords X-ray ꢀ 2-(Methyl(1-phenylvinyl)
carbamoyl)phenyl acetate ꢀ Photochemistry ꢀ
Enamide ꢀ Lactam ꢀ Quantum yield
S. K. Dehury (&)
Department of Chemistry, Institute of Technical Education
and Research (ITER), Siksha O Anusandhan University,
Bhubaneswar 751030, Orissa, India
The zwitterionic intermediates would be generated
photochemically via an electro cyclic ring closure reaction
e-mail: sujitam@rediffmail.com
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J Chem Crystallogr (2012) 42:214–221
215
Scheme 1 Zwitterionic
intermediate that eliminate
leaving group anions
R
N
R
N
R
N
Ar
Ar
Ar
O
O
O
hv
R
R
X
R
R
R
R
X
X
zwitterionic
intermidiate
X
Ar
= Chromophoric
group
R
N
R
N
Ar
O
Ar
O
R = H
- H +
R
R
R
of certain conjugated aromatic enamides. The electrocyclic
ring closure can be considered to be a photochemically
allowed 6-pi electron conrotatory process [10–12] in the
excited state. The type of leaving group to be eliminated
from the zwitterionic elimination would be the carboxylate
group.
Experimental
Synthesis of Photoreactant SM
The synthesis of SM involves the acylation of imine of
acetophenone with o-acetylsalicyloyl chloride. The imi-
neInt1 was initially prepared from the reaction of
methylamine in ethanol with acetophenone in presence of
KOH as a dehydrating agent. KOH seems to provide the
driving force for the reaction that leads to a net forward
direction. The synthesis of title compound (SM) is repre-
sented in Eq. 1.
The chief advantage in the use of electrocyclic reactions
to generate zwitterions is that chromophores (Ar) can be
incorporated which would absorb at long wavelengths [13–
15]. It should be possible to affect electrocyclization (and
subsequent elimination of the leaving group) by use of long
wavelengths of light. For example, visible light has long
COCl
OAc
CH3
N
O
N
O
CH3NH2
ð1Þ
OAc
KOH
Et3N/C6H6
Int 1
SM
Synthesis of (E)-N-(1-phenylethylidene)methanamine
(Int1)
been used to achieve electrocyclic reaction in photochro-
mic molecules.
In this article, we report the photochemistry of
2-(methyl(1-phenylvinyl)carbamoyl)phenyl acetate (SM)
which bear acetate leaving group. Under aqueous condi-
tions, the acetate leaving group is expelled upon irradiation
of light (\300 nm) to give cyclic lactam as the major
process.
40 g (0.33 mol) of acetophenone was taken in a round
bottom flask. Then 13.4 g (0.43 mol) of methylamine in
ethanol was added dropwise via a syringe. 15 g KOH
(0.26 mol) pellets were added and the mixture was stir-
red at room temperature for 4 h. The reaction mixture
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J Chem Crystallogr (2012) 42:214–221
Fig. 1 Molecular scheme of
2-(methyl(1-phenylvinyl)
carbamoyl)phenyl acetate (SM)
was filtered and the filtrate was extracted with ether. The
ether extract was washed 3 times. The organic layer was
dried over sodium sulphate and concentrated in vacuum
to give oil. The oil was distilled to give 24.5 g of ace-
tophenone and imine mixture. One gram of mixture
contains 1.17 mmol of imine (Int1) by 1H NMR spec-
troscopy. The spectral data for imine (Int1) in the
CH3
N
O
OAc
SM
Crystal Structure of Title Compound (SM)
1
mixture: H NMR (CDCl3) d 2.14 (s, 3H), 3.28 (s, 3H),
7.2–7.9 (m, 5H).
The crystal structure of compound (SM) was obtained from
modern X-ray Diffractometer (Brucker-APEX2) with CCD
˚
camera and Cu-Ka (k = 1.54178 A) at 100(2) K. The data
Synthesis of 2-(Methyl(1-
collection for structure SM was carried out by APEX2
v2.1-4 (Bruker 2007). The cell refinement and structure
refinement was carried out by SAINT v7.23A (Bruker
2005) and SHELXL-97 v.97-2 (Sheldrick 1993–1997)
respectively. In Fig. 2, the X-ray structure of enamide
(SM) is shown with atomic labeling. The data complete-
ness was found to be low (0.921) which may be due to
imperfections present in the crystal during crystal growth.
CheckCIF was carried out to identify the outliers as well as
unusual parameters.
Phenylvinyl)Carbamoyl)Phenyl Acetate (SM)
19 g of distilled mixture contains 3.0 g (22.3 mmol) of
imine (Int1) was taken in a round bottom flask. 70 ml of
triethyl amine was added to it. 8.8 g of o-acetylsalicyloyl
chloride in 70 ml of benzene was added at 5–8 °C to the
above mixture solution. The reaction mixture was warmed
to room temperature and refluxed for 5 h. Upon cooling,
triethylamine hydrochloride precipitate was filtered. The
filtrate was concentrated in vacuo and the residue was
dissolved in benzene. The benzene solution was washed
with NaHCO3, brine solution, dried over Na2SO4, and
concentrated in vacuo to give 21.58 g crude oil. The resi-
due was chromatographed on silica gel (76% yield), eluting
with 33% ethyl acetate in hexane to obtain colorless,
crystalline amide after crystallization from 25% ethyl
Photolysis Result
At lower concentrations, the compound SM has kmax below
˚
3,000 A. The compound was thus photolysed without a
Pyrex filter. From 1H NMR spectroscopy, it was found that
three photo-products were formed as a result of the pho-
tochemical reaction as shown in Eq. 2.
1
acetate in hexane. The spectral data were as follows: H
NMR (CDCl3) d 2.23 (s, 3H), 3.15 (s, 3H), 5.04 (s, 1H),
CH3
N
O
CH3COOH
+
hv
CH3
N
H
O
1
OAc
hv
ð2Þ
CH3
CH3
SM
N
O
+ H2
OAc
N
O
+
H
H
OAc
H
H
3
2
5.23 (s, 1H), 6.8–7.5 (m, 9H); 13C NMR (CDCl3) d 21.64,
36.41, 112.74, 123.44, 125.54, 126.49, 128.05, 129.20,
129.26, 129.35, 129.66, 130.66, 136.61, 148.62, 168.55,
169.55 (Fig. 1).
Photolysis of SM in 50% H2O and CH3CN gave lactam
1 as major product and lactam 3 as minor oxidation
1
product. All three lactams were characterized by H and
13C NMR Spectroscopy. HPLC analyses were performed
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J Chem Crystallogr (2012) 42:214–221
217
Fig. 2 X-ray strucrure of 2-(methyl(1-phenylvinyl)carbamoyl)phenyl acetate (SM)
Table 1 Crystal data and
Empirical formula
C18 H17 N O3
295.33
structure refinement for
Compound (SM)
Formula weight
Temperature
100(2) K
˚
1.54178 A
Wavelength
Crystal system
Space group
Triclinic
P-1
˚
a = 9.10870(10) A
Unit cell dimensions
a = 78.0590(10)°
˚
b = 10.56940(10) A
b = 89.5080(10)°
c = 86.6830(10)°
˚
c = 16.1340(2) A
3
˚
1517.11(3) A
Volume
Z
4
Density (calculated)
Absorption coefficient
F(000)
1.293 Mg/m3
0.716 mm-1
624
Crystal size
0.55 9 0.45 9 0.40 mm3
Theta range for data collection
Index ranges
2.80–67.29°
-10 B h B 10, -12 B k B 12, 0 B l B 19
25399
Reflections collected
Independent reflections
Completeness to theta = 67.29°
Absorption correction
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I [ 2r(I)]
R indices (all data)
Extinction coefficient
Largest diff. peak and hole
5005 [R(int) = 0.0169]
92.10%
Semi-empirical from equivalents
0.7628 and 0.6943
Full-matrix least-squares on F2
5005/0/534
1.045
R1 = 0.0311, wR2 = 0.0793
R1 = 0.0318, wR2 = 0.0798
0.0083(4)
-3
˚
0.262 and -0.166 eꢀA
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J Chem Crystallogr (2012) 42:214–221
˚
Table 2 Selected bond lengths (A), Bond and Torsion angles (°) for compound (SM)
˚
Bond lengths (A)
Bond angles (°)
Torsion angles (°)
O(1)–C(7)
1.2297(14)
1.4686(15)
1.4368(15)
1.3962(17)
1.3974(17)
1.5033(16)
1.3279(17)
1.4878(16)
1.2001(15)
1.3618(14)
1.4006(14)
1.3616(15)
1.2283(14)
1.1973(15)
1.3650(15)
1.3949(15)
1.3650(15)
1.4415(15)
1.4676(15)
1.3982(17)
1.3987(17)
1.4873(16)
1.3257(18)
C(8)–O(3)–C(2)
118.74(9)
C(6)–C(1)–C(2)–C(3)
3.06(17)
177.39(11)
-173.32(10)
1.01(17)
N(1)–C(10)
N(1)–C(17)
C(1)–C(2)
C(7)–N(1)–C(17)
126.08(10)
116.99(10)
116.47(10)
117.20(11)
120.77(10)
121.78(10)
121.11(11)
120.07(10)
118.77(10)
123.11(11)
120.87(10)
123.78(11)
115.35(10)
125.08(10)
118.13(10)
115.79(9)
C(7)–C(1)–C(2)–C(3)
C(7)–N(1)–C(10)
C(6)–C(1)–C(2)–O(3)
C(17)–N(1)–C(10)
C(2)–C(1)–C(6)
C(7)–C(1)–C(2)–O(3)
C(1)–C(6)
C(8)–O(3)–C(2)–C(3)
121.22(11)
-62.19(15)
168.08(10)
-3.81(16)
-14.37(16)
173.74(10)
-41.83(16)
132.24(12)
140.59(11)
-45.33(15)
176.42(10)
-52.47(16)
119.46(13)
126.90(12)
-61.18(13)
54.00(15)
C(1)–C(7)
C(2)–C(1)–C(7)
C(8)–O(3)–C(2)–C(1)
C(17)–C(18)
C(11)–C(17)
O(2)–C(8)
C(6)–C(1)–C(7)
C(17)–N(1)–C(7)–O(1)
C(10)–N(1)–C(7)–O(1)
C(17)–N(1)–C(7)–C(1)
C(10)–N(1)–C(7)–C(1)
C(2)–C(1)–C(7)–O(1)
O(1)–C(7)–N(1)
O(1)–C(7)–C(1)
O(3)–C(8)
N(1)–C(7)–C(1)
O(3)–C(2)
O(2)–C(8)–O(3)
N(1)–C(7)
C(18)–C(17)–N(1)
C(18)–C(17)–C(11)
N(1)–C(17)–C(11)
C(7A)–N(1A)–C(17A)
C(7A)–N(1A)–C(10A)
C(17A)–N(1A)–C(10A)
C(6A)–C(1A)–C(2A)
C(6A)–C(1A)–C(7A)
O(1A)–C(7A)–C(1A)
N(1A)–C(7A)–C(1A)
C(18A)–C(17A)–N(1A)
N(1A)–C(17A)–C(11A)
C(6)–C(1)–C(7)–O(1)
O(1A)–C(7A)
O(2A)–C(8A)
O(3A)–C(8A)
O(3A)–C(2A)
N(1A)–C(7A)
N(1A)–C(17A)
N(1A)–C(10A)
C(1A)–C(6A)
C(1A)–C(2A)
C(11A)–C(17A)
C(17A)–C(18A)
C(2)–C(1)–C(7)–N(1)
C(6)–C(1)–C(7)–N(1)
C(2)–O(3)–C(8)–C(9)
C(7)–N(1)–C(17)–C(18)
C(10)–N(1)–C(17)–C(18)
C(7)–N(1)–C(17)–C(11)
C(10)–N(1)–C(17)–C(11)
C(8A)–O(3A)–C(2A)–C(1A)
C(17A)–N(1A)–C(7A)–O(1A)
C(10A)–N(1A)–C(7A)–O(1A)
C(10A)–N(1A)–C(17A)–C(11A)
117.42(11)
120.96(11)
119.58(10)
118.58(10)
119.58(11)
115.50(10)
-166.30(11)
1.72(16)
64.03(13)
on a 14.6 9 250 mm Partisil ODS-2 column eluting with
75:25 (v/v) methanol and water as solvent for quantum
yield determination.
Results and Discussion
The title compound, C18H17NO3, consists of a phenylvinyl
group in conjugation with N-methyl substituted benzamide
moiety. The crystal data and structure refinement details
are provided in Table 1. CheckCIF results tell us that dif-
fractions were collected as low as theta value of 0.921.
Absorption corrections were given as multi-scan process
and reflection counts are less than 95% complete. The
selected bond lengths, bond and torsion angles are reported
in Table 2. The bond length of vinyl group C(17)–C(18) in
˚
compound (SM) is found to be 1.3279(17)A which is very
close to the theoretical value for a double bond.
Fig. 3 Plot of % chemical yield versus time in minutes
It is found that compound SM, in solid state is dimeric
in nature. SM can be cyclized at two ortho positions of the
aromatic ring where one of ortho position is occupied by
the acetate (OAc) leaving group and other ortho position by
hydrogen atom itself. This compound thus can be cyclized
photochemically at both the ortho-positions to give rise to
six-membered cyclic lactams in solution. The bond
distances from the alkene (phenyl vinyl group) to the two
˚
ortho positions for photocyclization are 3.39 and 3.99 A for
H and acetate ortho positions, respectively. It is found that
the alkene for cyclization is closer to the ortho position
where leaving group is not present. Hence, it can be con-
cluded that the likely pathway for cyclization would be
where no leaving group is present in solid state.
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J Chem Crystallogr (2012) 42:214–221
219
The quantum yield results were obtained for photolysis
at 270 nm for 15 h. The electrocyclic reaction which would
be required to form three products would have a total
quantum yield of 0.091. The highest quantum yield for the
process of formation of lactam 1 is found to be 0.053 where
the release of acetic acid takes place. The minor oxidation
product 3 has quantum yield value 0.012.
However, the overall low value of total quantum yield
value for the photolysis of SM can be explained from the
UV-spectra of the photolyzed starting material. Figure 4
shows that the photoproducts absorb light in competition
with the starting material. Since, lactam 1 and 3 have
stilbeneoid moiety present, they will definitely absorb light
at higher wavelengths in comparison to the photoreactant.
Hence, the absorption of light by co-products hinders the
process of effective photolysis of SM which gives rise to a
low total quantum yield value of 0.091.
The photoreactant SM undergoes cyclization to give rise
to three products via different mechanistic pathways. Photo
product 1 is formed via a zwitterionic intermediate where
the elimination of acetic acid takes place (Scheme 2). The
loss of proton from the molecule gives a neutral lactam
containing stilbenoid moiety as stable product. An alternate
electrocyclic ring closure reaction also occur upon irradi-
ation to give a six-membered cyclic zwitterionic interme-
diate which retains acetate as leaving group (Scheme 3). A
[1,5]-H shift would then give the isomerized product 2.
Interestingly, the product 3 is formed from the same
photoreactant (SM) via a zwitterionic intermediate where
the liberation of one molecule of hydrogen takes place due
Fig. 4 UV-spectra of photolyzed reactant at different intervals of
time
The Fig. 3 shows the plot of percentage of chemical
yield vs time for the photolysis of SM as starting material.
Within 30 min, 18% of starting material was converted into
photoproducts. After 150 min, 38% of the major product
was formed. It was found that the elimination of the ortho
acetate leaving group is the major process in comparison to
[1,5]-H shift, which forms lactam 1. The other minor
product was 3, which would be formed by an oxidation that
must occur at some stage of photolysis.
CH3
CH3
N
CH3
N
N
O
- OAc-
O
hv
O
H
AcO
AcO
H
- H+
CH3
CH3
N
O
N
O
+
AcOH
OAc
H
SM
1
Scheme 2 Mechanism for formation of lactam 1
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J Chem Crystallogr (2012) 42:214–221
CH3
N
CH3
N
CH3
O
O
N
O
hv
[1,5]-H
H
H
OAc
OAc
OAc
H
H
CH3
N
CH3
N
O
O
H
H
OAc
OAc
H
SM
2
Scheme 3 Mechanism for formation of lactam 2
CH3
CH3
N
CH3
N
N
O
O
OH
OAc
- H+
hv
OAc
OAc
H
H
H
Tautomerizes
CH3
CH3
CH3
N
N
O
H
N
O
O
Oxidation
OAc
OAc
H
- H2
OAc
H
H
SM
3
Scheme 4 Mechanism for formation of lactam 3
Acknowledgments The author thanks Dr. Mark G. Steinmetz for
his sincere help and stimulating discussions throughout the project
work and Dr. Sergey V. Lindeman for solving the crystal structure.
The author would like to thank Marquette University, USA for
financial support and for the use of research facilities.
to oxidation (Scheme 4). Loss of a proton can evidently
compete with [1,5]-H shift to give the oxidized lactam 3
after tautomerization of the enol.
Supporting Information Available
References
X-ray crystallographic files, in Cif format, for the structure
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CCDC, 12 Union Road, Cambridge, CB2 1EZ (fax: ?44-
1223-336033; email: deposit@ccdc.cam.uk or at: http://www.
ccdc.cam.ac.uk).
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