Metal-free hypervalent iodine/TEMPO mediated oxidation of amines and mechanistic insight into the reaction pathways

Article abstract of DOI:10.1039/c8ra07451h

A highly efficient metal free approach for the oxidation of primary and secondary amines to their corresponding aldehydes and ketones using PhI(OAc)₂ in combination with a catalytic amount of TEMPO as an oxidizing agent is described. This protocol is rapid and provides diverse products under milder reaction conditions in excellent yields. In addition, the mechanistic study is well demonstrated by spectroscopic methods.

Full text of DOI:10.1039/c8ra07451h

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PAPER
Metal-free hypervalent iodine/TEMPO mediated
oxidation of amines and mechanistic insight into
the reaction pathways†
Cite this: RSC Adv., 2018, 8, 32055
ab
Ajay H. Bansode and Gurunath Suryavanshi *ab
A highly efficient metal free approach for the oxidation of primary and secondary amines to their
Received 6th September 2018
Accepted 8th September 2018
2
corresponding aldehydes and ketones using PhI(OAc) in combination with a catalytic amount of TEMPO
as an oxidizing agent is described. This protocol is rapid and provides diverse products under milder
reaction conditions in excellent yields. In addition, the mechanistic study is well demonstrated by
spectroscopic methods.
DOI: 10.1039/c8ra07451h
rsc.li/rsc-advances
in the classical way. These two methods required harsh reaction
conditions and an extra hydrolysis step to access the target
Oxidation reactions to access carbonyl functional groups are carbonyl compound (eqn (2), Scheme 1).
Introduction
10,11
fundamental transformations and play a most signicant role
In continuation of our interest in development of new
12
in synthetic organic chemistry. Carbonyl functionalities serve as methodologies using PhI(OAc)
2
and to address issues asso-
versatile building blocks in functional group interconversions, ciated with existing protocols for the conversion of amines to
and synthesis of complex molecules and are widely present in carbonyl compounds, herein we report an efficient, rapid, mild,
natural products and biologically active compounds. The metal free and environment friendly protocol involving non-
conventional way to synthesize aldehydes and ketones involves metallic, less toxic and affordable hypervalent iodine
1
oxidation of primary and secondary alcohols, which has been (PhI(OAc)
) in combination with TEMPO as an oxidizing agent
2
successfully exploited in academic and industrial research. In for the rst time without any external oxygen source (eqn (3),
13,14
an alternative method, amine precursors were also successfully Scheme 1).
used to access carbonyl compounds due to their ability to
Hypervalent iodine compounds such as (diacetoxyiodo)
(PhI(OAc) ), [bis(triuoroacetoxy)] benzene
undergo oxidation reactions, and their natural and commercial benzene
availability. The oxidation of amines is also used as a powerful
tool to produce different synthetic intermediates: imines,
2
2
nitriles, oximes and amides. In the last two decades, several
protocols reported the synthesis of carbonyl compounds from
3
4
amines using metal reagents/catalysts such as KMnO ,
4
5
6
7
2 7
ZnCr O , nicotinium dichromate, palladium, copper and
8
ruthenium. These traditional methods suffer from their own
limitations, such as use of stoichiometric amounts of reagents/
catalysts, inherent toxicity of metals, high temperature and
limited substrate scope.
In addition, Voltrova et al. showed that catalytic copper and
ascorbic acid in open air condition can be used for oxidation of
amines, which is limited to primary amine substrates (eqn (1),
9
Scheme 1). De Luca et al. and Davis et al. developed metal free
methods using NCS/Et N and DEAD via an imine intermediate
3
a
Chemical Engineering & Process Development Division, CSIR-National Chemical
Laboratory, Dr Homi Bhabha Road, Pune-411008, India. E-mail: gm.suryavanshi@
ncl.res.in
b
Academy of Scientic and Innovative Research (AcSIR), New Delhi 110 025, India
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c8ra07451h
1
Scheme 1 Oxidation of amine to aldehyde.
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a
(PhI(OCOCF
3 2
)
), Dess–Martin periodinane (DMP), 2-iodox- Table 1 Optimization of reaction conditions
ybenzoic acid (IBX) and their derivatives were extensively used
15,16
as oxidants and co-oxidants in organic transformations.
Using hypervalent iodine reagent oxidation of amine was well
1
7a–e
18a,b
established for conversion to imines,
and aromatization of pyrrolidine, dihydropyridine rings. Very
recently, Galletti et al. reported NaIO /TEMPO mediated
conversion of benzylamines to carbonyls via imine formation
aldehydes,
ketones
19
4
20
2 3
and in situ hydrolysis using H O/CH CN as solvent. However,
PhI(OAc)
(equiv.)
2
TEMPO
(equiv.)
these methods suffer from limitations such as higher temper-
b
b
Entry
Temp (time)
Yield
ature, long reaction time and sequence, substrate selectivity and
17–20
extra step for imine hydrolysis to form an aldehyde.
In this
ꢀ
1
2
3
4
5
6
7
8
9
1
1
1
1
0.5
1
1
1
—
1
1
1
0.5
1
0.25
0.1
—
1
0 C (30 min)
40
65
context we envisioned that, PhI(OAc) in combination with
2
rt (30 min)
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
TEMPO used as an oxidizing agent to convert amine functional
groups into corresponding carbonyl compounds at room
temperature, with short reaction time and no use of external
0 C to rt (20 min)
0 C to rt (20 min)
0 C to rt (20 min)
0 C to rt (20 min)
0 C to rt (20 min)
0 C to rt (20 min)
0 C to rt (20 min)
90
90
40
90
90
oxygen source (such as H
2
O or O
2
) with excellent yields.
c
NRc
NR
Result and discussion
a
Reaction conditions unless otherwise specied: 1a (1 equiv.),
ꢀ
To test our hypothesis, initially, p-methoxy benzyl amine (1a) PhI(OAc)2 (1 equiv.), TEMPO (0.1 equiv.),
0
C to rt, 20 min,
b
c
anhydrous CH
Cl
2 2
.
Isolated yields in percentage. Starting material
was treated with PhI(OAc) (1 equiv.) and TEMPO (1 equiv.) in
2
(
1a) recovered; rt ¼ room temperature; NR: no reaction.
ꢀ
anhydrous CH Cl for 30 min at 0 C, which furnished the p-
2
2
methoxy benzaldehyde (2a) in 40% yield along with 50% of
unreacted amine 1a (entry 1), when we raised the reaction
temperature to rt, the expected p-methoxy benzaldehyde (2a)
was obtained in 65% yield along with decomposition of the
starting material 1a in 30 min (entry 2). Hence, we carried out
pyridin-3-yl-methanamine were well participated to give 2i, 2j
and 2k respectively. To our delight, under identical conditions
alkyl and dialkyl substituted amines (3-phenylpropan-1-amine,
ꢀ
the same reaction for 10 min at 0 C followed by room
temperature for another 10 min, to our delight, this small
modication to the reaction conditions afforded the desired
oxidation product 2a in the excellent yield of 90% (entry 3). The
output of the reaction was not much affected when we reduced
the amount of TEMPO (0.5 equiv.), but the yield was dropped to
2
40% using 0.5 equiv. of PhI(OAc) (entries 4 and 5). Further
reduction of TEMPO to 0.25 and 0.1 equiv. also furnished the
product in good yields (entries 6 and 7). Then we veried the
reaction without using TEMPO or PhI(OAc)2, which led to the
unchanged starting material (1a) (entries 8 and 9). Ultimately,
the reaction conditions of PhI(OAc)
equiv.) in anhydrous CH Cl
2
(1 equiv.) and TEMPO (0.1
for 10 min at 0 C followed by room
ꢀ
2
2
temperature for another 10 min were found to be ideal for this
transformation (entry 7) (Table 1).
With optimized conditions in hand, initially, the substrate
scope for this methodology was examined using a series of
diverse aromatic and aliphatic primary amines (Scheme 2).
Commercially available aryl and heteroaryl amines possessing
electron donating and electron withdrawing substituents were
provided corresponding aldehydes in excellent yields without
signicant discrimination in the output (2b–e). Naphthalen-1-
ylmethanamine also well reacted and gave the corresponding
aldehyde 2f in good yield of 91%. p-Xylylamine also a good
substrate for this reaction, which delivered the tereph-
thalaldehyde (2g) in 85% yield. The benzylamine with dioxolane
protection is well tolerated in these reaction conditions and
gave 2h in 85% yield. Heteroaryl amines like furan-2-
Scheme 2 Oxidation of primary amines to aldehydes and ketones.
Reaction conditions unless otherwise specified: amine 1 (1 equiv.),
ꢀ
PhI(OAc)
2
(1 equiv.), TEMPO (0.1 equiv.), 0 C to rt, 20 min, anhydrous
a
ylmethanamine, (5-bromofuran-2-yl) methanamine and CH
Cl
2 2
, PhI(OAc)
2
(2 equiv.), TEMPO (0.2 equiv.).
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n-propylamine, n-heptylamines and isobutylamine) well toler-
ated and furnished corresponding aldehydes in excellent yields
(2l–o). Next the reactivity of diverse alpha-disubstituted primary
amine derivatives were examined to obtained corresponding
ketones. Highly hindered alpha substituted benzyl amine and
tetrahydronaphthalene derived amines provided corresponding
ketones 2p and 2q in good yields of 83% and 87%. Phenyl and
tolyl substituted amines gave 2r and 2s respectively. Cycloalkyl
derived amines furnished 2t–v in good yields, even hindered 2-
adamantyl amine was converted into 2-adamantanone (2w) in
80% yield.
Scheme 4 Comparative study on symmetrical secondary amines.
Aer successful studies involving primary amines, we were
curious to know the reactivity of secondary amines in this PhI(OAc)
oxidation protocol. Several alkyl–aryl and dialkyl amines were
subjected to slightly modied reaction conditions of 2 equiv. of
Reaction conditions unless otherwise specified: amine 1 (1 equiv.),
ꢀ
2
(1 equiv.), TEMPO (0.1 equiv.), anhydrous CH
2
Cl
2
, 0 C to rt,
20 min.
2 2 2
PhI(OAc) and 0.2 equiv. of TEMPO in dry CH Cl
. The oxida- hydroxyamine species I to regenerate oxoammonium species A
tions of N-methyl-aryl amine substrates were quite interesting, and re-enters in catalytic cycle, expels iodobenzene and acetic
which would generate possible two products of aryl-aldehydes acid which was used in further reaction sequence. Imine C then
and formaldehyde based on the choice of oxidation sites. To converted into corresponding aldehyde via two probable path-
our surprise, aryl-aldehydes were obtained exclusively in good ways. In the path-I, imine intermediate C will react with acetic
yield (2b, 2x and 2y), which could be due to the more reactivity acid and forms the amino acetate intermediate D. Intermediate
of the benzylic position of substrates. This selectivity is in D would react with another 1 mole of acetic acid to give the
3–11
contrast with other oxidizing agents used in earlier reports.
corresponding acetate intermediate E, which further reacts to
Isobutyl-methylamine also well reacted under identical condi- give desired aldehyde 2 via releasing the acetic anhydride and
tions to provide corresponding isobutyraldehyde 2o in excellent ammonia. In an alternate path II, imine C will react with ben-
yield of 89% (Scheme 3). Oxidation of symmetrical amines such zylamine (1b) with exertion of ammonia to provide secondary
22
as dibenzylamine using PhI(OAc) (1 equiv) and TEMPO (0.1 imine F, which will react with acetic acid to provide the amino-
2
equiv) in dry CH Cl provided the mixture of benzaldehyde (2b) acetate intermediate G. Under acidic condition as in the path I,
2
2
and benzyl amine (1b) in 1 : 1 ratio in the good yield of 90% intermediate G delivers the aldehyde 2 and benzylamine which
yield. Equivalent results were obtained in the oxidation of dii- re-enters the catalytic cycle.
sobutylamine (7) and gave isobutyraldehyde (2o) and isobutyl-
To further understand the proposed mechanistic sequence,
amine (1o) in 1 : 1 ratio in excellent yield of 85% (Scheme 4).
a few supporting experiments were carried out and described in
Based on earlier reports and results obtained in this work, Scheme 5. To verify, the probable formation of amino acetate
21
a plausible reaction mechanism was proposed. Initially, TEMPO intermediate D, we have prepared the same using known liter-
23
was converted into oxoammonium species A using PhI(OAc) as ature procedure and subjected to standard reaction conditions
2
2
oxidant. The reaction of benzylamine (1) with oxoammonium of PhI(OAc) (1 equiv.) and TEMPO (0.1 equiv.). To our delight,
species A could provide the intermediate B via attack of lone the expected aldehyde 2 was isolated in 90% yield. The possible
pair of nitrogen from benzyl amine on electron decient hydrolysis of imine intermediate C, which could directly deliver
nitrogen of oxoammonium A. Then, intermediate B could the aldehyde without the intervention of path I and/or path II
undergo reductive elimination which provide the reactive imine was established by performing the reaction of amino acetate or
˚
C through the abstraction of proton from benzylic position of amine under optimized conditions using 4 A-MS.
intermediate B. Further PhI(OAc)2 was used for oxidation of
The formation of imine C and amino acetate D intermediates
and release of acetic anhydride and ammonia as by-products in
1
this reaction was established by time dependent H NMR
analysis. A standard reaction using benzyl amine in a sealed
3
NMR tube in CDCl under inert atmosphere was studied.
1
Analysis of H NMR at 0 h without adding reagents were
analysed, showed peaks at 1.5 (s, –NH ), 3.97(s, benzylic –CH ),
2
2
7.2–7.6 (m, aromatic 5H), belongs to benzyl amine. To the same
NMR tube, PhI(OAc)
2
(1 equiv.) and TEMPO (0.1 equiv.) were
ꢀ
1
added at 0 C, as soon as the addition was completed, H NMR
was recorded, in which we found that, peak at 3.97 ppm belongs
to benzylic proton of benzyl amine was disappeared and new
peaks for intermediates were clearly indicative. We found out
a singlet at 10.1 ppm, which clearly show that the peak of
benzaldehyde proton and doublet at 7.98 ppm is for ortho
proton of benzaldehyde. In addition, we found signals related to
Scheme 3 Oxidation of secondary amines to aldehydes. Reaction
conditions unless otherwise specified: amine 1 (1 equiv.), PhI(OAc)
2
(2
ꢀ
equiv), TEMPO (0.2 equiv), anhydrous CH
2 2
Cl , 0 C to rt, 20 min.
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1
Initially, we took H NMR of our intermediate amino acetate
D in CDCl , which showed peaks at 2.4 ppm (s, –CH ), 7.68 ppm
3
3
(
s, benzylic –CH), 10.22 ppm (bs, NH ). In same NMR tube we
2
ꢀ
added PhI(OAc) (1 equiv.) and TEMPO (0.1 equiv.) at 0 C, as
soon as addition completed we took H NMR. We found out that
2
1
3 2
peak at 2.4 (s, –CH ), 7.68 (s, benzylic –CH), 10.22 (bs, NH ) was
disappeared and new peaks at 2.10 ppm for acetic acid, 2.2 ppm
for acetic anhydride are clearly indicative (Fig. 2).
Our main goal is to nd out in which form –NH is going out
2
either ammonia or amide. To prove our side product, we carried
out ammonia trapping experiment. In this we took two neck RB
(
(
A) equipped with magnetic needle contenting Benzyl amine
500 mg, 4.67 mmol) and dry CH Cl (5 mL). Other side single
2
2
neck RB (B) having water and small pieces of pH paper. To
connect this two RB's, we used silicon pipe having one side
connecter connected to two neck RB (A) and other side dropper
which dipped in single neck RB (B) (as shown in picture below).
Reaction start with addition of PhI(OAc) (1.5 g, 4.67 mmol) and
2
ꢀ
TEMPO (72 mg, 0.467 mmol) at 0 C for 10 minutes followed by
ꢀ
1
0 minutes at room temperature. When we did reaction at 0 C
for 10 minutes neither bubbling nor color change observed in
ꢀ
RB-B. When we increase temperature form 0 C to room
temperature of RB-A and within 5 minutes in RB-B bubbling as
well as color change of pH paper from yellow to purple was
observed. With time span of 5 to 10 minutes at room temper-
ature vigorous bubbling and color changed to purple. In addi-
tion to this intense smell of ammonia was observed. Bubbling
and color change of pH paper yellow to purple clearly indicate
formation of ammonia (pH: 11.6 and purple on pH paper)
Scheme 5 Plausible reaction mechanism & control experiments.
imine intermediates, amino acetate intermediate as well while
performing the analysis (as shown in Fig. 1).
In addition, we carried out GC-MS study to prove our
hypothesis that oxygen is not coming from out sources and it is
(Fig. 3).
from PhI(OAc) . We performed reaction in air tight GC-MS vial
2
to avoid the contamination with atmospheric oxygen. To our
delight, we found out peak corresponding to benzaldehyde and
intermediate F. Generation of benzaldehyde in reaction mixture
Experimental section
General procedure
itself, without additional hydrolysis clearly indicates that no All reaction carried out under nitrogen atmosphere with dry
external oxygen source is required and PhI(OAc)
is acting as an solvents kept anhydrous condition. Anhydrous CH Cl was
oxygen source in this reaction. In addition, release of ammonia distilled from P . Yields are calculated by chromatographical
2
2
2
O
2 5
was detected using well-known ammonia test.
isolation. Thin layer chromatography was performed using
1
1
Fig.
1
Time dependent
H
NMR experiment for mechanistic Fig. 2 Time dependent H NMR experiment for mechanistic deter-
determination.
mination on intermediate.
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concentrated under reduced pressure. The residue was puried
by column chromatography on silica gel and 2% ethyl acetate in
petroleum ether as an eluting solvent to afford the desired
aldehyde and 25% ethyl acetate in petroleum ether as an eluting
solvent to afford the desired amine.
General procedures to convert secondary amine to aldehyde.
To the solution of amine (1.0 mmol) was added PhI(OAc)
2
(2
ꢀ
mmol) in 4 mL of dry CH
and followed by addition of TEMPO (0.2 mmol) at 0 C. The
2
Cl
2
at 0 C under nitrogen atmosphere
ꢀ
ꢀ
resulting mixture was stirred at 0 C for 10 min. Then reaction
mixture was gradually allowed to stir at room temperature for
Fig. 3 Mechanistic study (ammonia trapping experiments).
1
0 min. The progress of reaction was monitored by TLC. The
reaction mixture was quenched by water (5 mL) and extracted
commercially prepared silica gel plates, and visualization was with CH Cl
(3 ꢁ 5 mL). The organic layers were combined,
effect with short wavelength UV light (254 nm). Column chro- wash with brine, dried over Na SO and concentrated under
matography performed on 100–200 mesh size silica gel.
reduced pressure. The residue was puried by column chro-
The H and C NMR spectra were recorded on Bruker matography on silica gel and 2% ethyl acetate in petroleum
2
2
2
4
1
13
1
13
advance 500 ( H 500 MHz, C 125 MHz) or Bruker advance 400 ether as an eluting solvent to afford the desired aldehyde.
1
13
1
24
1
(
H 400 MHz, C 100 MHz) or Bruker advance 200( H 200 MHz,
p-Anisaldehyde (2a). 54 mg (90%); colourless oil; H NMR
1
3
C 50 MHz), otherwise mentioned. Deuterated solvent CDCl + (200 MHz, CDCl
, ppm): d 3.89 (s, 3H), 6.99 (m, J ¼ 8.84 Hz, 2H),
3
3
1
3
CCl
4
(70 : 30) were used as internal standard and singlet at 7.83 (m, J ¼ 8.84 Hz, 2H), 9.88 (s, 1H); C NMR (50 MHz, CDCl
3
,
1
3
96.1 ppm in C NMR corresponds to carbon of CCl
4
. Solvent ppm): d 55.47, 114.28, 130.06, 131.93, 164.54, 190.39; HRMS
1
3
+
signal was used as reference for C NMR (CDCl
3
, 77.0 ppm) or (ESI) calcd for C
, 40.0 ppm). The following abbreviations
Benzaldehyde (2b). 194 mg, 88%; colourless oil; H NMR
, ppm): d 7.46–7.68 (m, 4H), 7.78–7.98 (m, 2H),
8 8 2
H O [M + H] 137.0597; found 137.0599.
1
3
24
1
C NMR (DMSO-d
6
were used to explain the multiplicities: s ¼ singlet, d ¼ doublet, (200 MHz, CDCl
3
3
1
t ¼ triplet, q ¼ quartet, m ¼ multiple, br ¼ broad. Chemical 10.02 (s, 1H); C NMR (50 MHz, CDCl3, ppm): d 128.9, 129.7,
+
shis are reported in ppm and referenced to residual solvent 134.3, 136.5, 191.9; HRMS (ESI) calcd for C
H O [M + H]
6
7
peak or TMS. Coupling constants are reported in hertz. High 107.0491; found 107.0495.
2
8
1
resolution mass spectra were recorded on a double focusing
magnetic sector mass spectrometer using EI at 70 eV. The GC (200 MHz, CDCl
analysis were done using Agilent 7890A GC coupled with mass 8.72 Hz, 2H), 10.17 (s, 1H); C NMR (50 MHz, CDCl
detector. All reagents were used as obtained commercially. The d 124.3, 130.5, 140.1, 151.2, 190.3; HRMS (ESI) calcd for
4-Nitrobenzaldehyde (2c). 20 mg, 86%; white solid; H NMR
3
, ppm): d 8.09 (m, J ¼ 8.84 Hz, 2H), 8.41 (m, J ¼
13
3
, ppm):
+
PhI(OAc)
General procedures to convert primary amine to aldehyde.
To the solution of amine (1.0 mmol) was added PhI(OAc) (1 (200 MHz, CDCl
2
and TEMPO were purchased by Sigma Aldrich.
C
7
H
5
NO
4-Formylbenzonitrile (2d). 50 mg, 85%; white solid; H NMR
, ppm): d 7.83–7.92 (m, 2H), 7.97–8.05 (m, 2H),
3
[M + H] 152.0342; found 152.0703.
2
6
1
2
3
13
ꢀ
mmol) in 2 mL of dry CH Cl at 0 C under nitrogen atmosphere 10.11 (s, 1H); C NMR (50 MHz, CDCl , ppm) d 117.6, 117.7,
3
and followed by addition of TEMPO (0.1 mmol) at 0 C. The 129.9, 132.9, 138.8, 190.7; HRMS (ESI) calcd for C
resulting mixture was stirred at 0 C for 10 min. Then reaction H] 132.0444; found 132.0443.
2
2
ꢀ
8
H
5
NO [M +
ꢀ
+
2
7
1
mixture was gradually allowed to stir at room temperature for
0 min. The progress of reaction was monitored by TLC. The (200 MHz, CDCl
reaction mixture was quenched by water (5 mL) and extracted 7.69–7.78 (m, 2H), 7.89–7.98 (m, 2H), 10.04 (s, 1H); C NMR (50
): d 127.4, 127.7, 128.5, 129.1, 130.3, 135.3, 139.8,
4-Phenylbenzaldehyde (2e). 85 mg, 86%; white solid; H NMR
1
3
, ppm): d 7.38–7.52 (m, 3H), 7.58–7.67 (m, 2H),
1
3
with CH Cl (3 ꢁ 5 mL). The organic layers were combined, MHz, CDCl
2
2
3
+
wash with brine, dried over Na SO and concentrated under 147.2, 191.93; HRMS (ESI) calcd for C13
H
10O [M + H] 183.0804;
2
4
reduced pressure. The residue was puried by column chro- found 183.0804.
24
1
matography on silica gel and 2% ethyl acetate in petroleum
1-Naphthaldehyde (2f). 195 mg, 91%; colourless oil; H NMR
ether as an eluting solvent to afford the desired aldehyde.
6
(200 MHz, DMSO-d , ppm): d 7.54–7.84 (m, 3H), 7.96–8.39 (m,
1
3
General procedures to convert secondary amine to aldehyde 3H), 9.18 (d, J ¼ 8.34 Hz, 1H), 10.42 (s, 1H); C NMR (101 MHz,
and amine. To the solution of amine (1.0 mmol) was added DMSO-d
6
, ppm): d 124.6, 125.9, 127.4, 129.2, 129.5, 130.2, 131.3,
ꢀ
+
PhI(OAc)
2
(1 mmol) in 2 mL of dry CH
2
Cl
2
at 0 C under 133.8, 135.7, 137.2, 194.9; HRMS (ESI) calcd for C11
H
8
O [M + H]
nitrogen atmosphere and followed by addition of TEMPO (0.1 157.0648; found 157.0647.
ꢀ
ꢀ
32
1
mmol) at 0 C. The resulting mixture was stirred at 0 C for
0 min. Then reaction mixture was gradually allowed to stir at (200 MHz, CDCl
room temperature for 10 min. The progress of reaction was (50 MHz, CDCl , ppm): d 130.1, 140.0, 191.1; HRMS (ESI) calcd
monitored by TLC. The reaction mixture was quenched by water for C [M + H] 135.0441; found 135.0439.
5 mL) and extracted with CH Cl
Piperonal (2h). 45 mg, 85%; white solid; H NMR (500 MHz,
and CDCl , ppm): d 6.03–6.11 (m, 2H), 6.88–6.96 (m, 1H), 7.29–7.35
Terephthalaldehyde (2g). 100 mg, 85%; white solid; H NMR
1
3
1
, ppm): d 8.06 (s, 4H), 10.14 (s, 2H); C NMR
3
3
+
8 6 2
H O
29
1
(
2
2
(3 ꢁ 5 mL). The organic layers
were combined, wash with brine, dried over Na
2
SO
4
3
1
3
(m, 1H) 7.36–7.44 (m, 1H), 9.77–9.83 (m, 1H); C NMR (126
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MHz, CDCl
3
, ppm): d 102.0, 106.9, 108.3, 128.49, 131.9, 148.7, 128.53, 133.00, 137.19, 197.60; HRMS (ESI) calcd for C
8
H
8
O [M +
+
+
153.0, 189.9; HRMS (ESI) calcd for C H O [M + H] 151.0390; H] 121.0648; found 113.0651.
8
6 3
28
1
found 151.0390.
4-Methylacetophenone (2s). 59 mg, 89%; colourless oil; H
24
1
Furfural (2i). 43 mg, 87%; colourless oil; H NMR (200 MHz, NMR (400 MHz, CDCl , ppm): d 2.40 (s, 3H), 2.55 (s, 3H), 7.23
3
1
3
CDCl
3
, ppm): d 6.62 (dd, J ¼ 3.54, 1.64 Hz, 1H) 7.26 (d, J ¼ (m, J ¼ 7.93 Hz, 2H), 7.83 (m, J ¼ 7.93 Hz, 2H); C NMR (101
13
6
3.54 Hz, 1H), 7.61–7.79 (m, 1H), 9.67 (s, 1H); C NMR (50 MHz, MHz, DMSO-d , ppm): d 21.6, 26.4, 128.4, 129.2, 134.8, 143.6,
+
CDCl
for C H O
5 4 2
5
3
, ppm): d 112.5, 120.7, 147.9, 153, 177.6; GC MS (ESI) calcd 197.3; HRMS (ESI) calcd for C
[M]+ 97; found 97. 135.0807.
-Bromo-2-thiophenecarboxaldehyde (2j). 15 mg, 85%; colour-
9
H
10O [M + H] 135.0804; found
30
1
Cyclopentanone (2t). 100 mg, 85%; colourless oil; H NMR
1
less oil; H NMR (200 MHz, CDCl , ppm) d 7.18–7.23 (m, 1H), (400 MHz, CDCl , ppm) d 1.84–2.02 (m, 4H), 2.12 (t, J ¼ 7.32 Hz,
3
3
1
3
13
7.53–7.57 (m, 2H), 9.78–9.80 (m, 1H); C NMR (50 MHz, CDCl3, 4H); C NMR (101 MHz, CDCl , ppm) d 23.2, 38.3, 220.7; GC-MS
3
ppm): d 125.0, 131.5, 136.7, 145.2, 181.81; HRMS (ESI) calcd for (ESI) calcd for C H O [M] 85.0; found 85.0.
5
8
+
26
1
C
5
H
3
3
BrOS [M + H] 190.9161; found 190.9162.
Cyclohexanone (2u). 200 mg, 86%; colourless oil; H NMR
-Pyridinecarboxaldehyde (2k). 200 mg, 88%; colourless oil; (200 MHz, CDCl , ppm) d 1.67–1.79 (m, 2H), 1.80–1.97 (m, 4H),
H NMR (200 MHz, CDCl
, ppm): d 7.51 (dd, J ¼ 7.71, 4.93 Hz, 2.27–2.39 (m, 4H); C NMR (50 MHz, CDCl
H), 8.20 (d, J ¼ 7.83 Hz, 1H), 8.87 (dd, J ¼ 4.61, 1.07 Hz, 1H), 41.91, 211.39; GC-MS (ESI) calcd for C
25
3
1
13
3
3
, ppm) d 25.1, 27.0,
1
9
6
H
10O [M] 98.0; found
1
3
.03–9.15 (m, 1H), 10.14 (s, 1H); C NMR (50 MHz, CDCl, ppm) 98.0.
30
1
d 124.1, 131.4, 135.8, 152.1, 154.7, 190.8; HRMS (ESI) calcd for
C H NO [M + H] 108.0444; found 108.0446.
Cycloheptanone (2v). 45 mg, 85%; colourless oil; H NMR
+
(200 MHz, CDCl , ppm): d 1.56–1.87 (m, 8H), 2.38–2.63 (m, 4H);
6
5
3
26
1
13
3-Phenyl propan-1-al (2l). 40 mg, 86%; colourless oil;
H
C NMR (50 MHz, CDCl , ppm): d 24.36, 30.46, 43.80, 214.64;
3
+
NMR (200 MHz, CDCl3, ppm): d 2.70–2.81 (m, 2H), 2.89–2.99 (m, HRMS (ESI) calcd for C
7
H
12O [M + H] 113.0961; found
1
3
2
H), 7.14–7.25 (m, 5H), 9.79 (t, J ¼ 1.26 Hz, 1H); C NMR (50 113.0965.
MHz, CDCl , ppm): d 28.2, 45.3, 126.3, 128.3, 128.4, 128.5, 128.6,
40.3, 201.1; HRMS (ESI) calcd for C
found 157.0648.
31
1
3
2-Adamantanone (2w). 90 mg, 80%; white solid; H NMR
+
1
9
H
10O [M + Na] 157.0624; (400 MHz, CDCl
3
, ppm): d 1.9 (br. s, 2H), 2.0 (m, 5H), 2.1 (m,
1
3
5H), 2.6 (br. s, 2H); C NMR (50 MHz, CDCl
3
, ppm): d 27.5, 36.3,
+
Propionaldehyde (2m). 100 mg, 80% {isolated by distillation}; 39.3, 47.0, 218.5; HRMS (ESI) calcd for C H O [M + H]
1
0
14
1
colourless oil; H NMR (200 MHz, CDCl , ppm) d 1.11 (t, J ¼ 173.0937; found173.0123.
3
1
3
28
1
7
.39 Hz, 3H), 2.39–2.56 (m, 2H), 9.80 (s, 1H); C NMR (50 MHz,
o-Tolualdehyde (2x). 50 mg, 87%; colourless oil; H NMR
CDCl3, ppm): d 6, 37.2, 203; GC-MS (ESI) calcd for C
8.04; found 58.0.
Heptaldehyde (2n). 143 mg, 90%; colourless oil; H NMR ppm): d 19.6, 126.3, 131.8, 132.1, 133.7, 134.2, 140.6, 192.9;
3
H
6
O [M] (200 MHz, CDCl
3
, ppm): d 2.70 (s, 3H), 7.23–7.56 (m, 3H), 7.83
1
3
5
(d, J ¼ 7.33 Hz, 1H), 10.30 (s, 1H); C NMR (50 MHz, CDCl
3
,
23
1
+
(
500 MHz, CDCl
3
, ppm): d 0.90 (t, J ¼ 6.48 Hz, 3H), 1.29–1.37 (m, HRMS (ESI) calcd for C
8 8
H O [M + H] 121.0648; found 121.648.
29
6
1
3
1
H), 1.57–1.69 (m, 2H), 2.42 (td, J ¼ 7.25, 1.53 Hz, 2H), 9.77 (s,
4-(Methylthio)benzaldehyde (2y). 30 mg, 85%; colourless oil;
1
3
1
H); C NMR (126 MHz, CDCl , ppm): d 14, 22.1, 22.4, 28.8,
H NMR (200 MHz, CDCl , ppm): d 2.50 (s, 3H), 7.26–7.32 (m,
3
3
+
13
1.5, 43.9, 202.3; HRMS (ESI) calcd for C H O [M + H]
15.1117; found 115.0868.
2H), 7.71–7.78 (m, 2H), 9.89 (s, 1H); C NMR (50 MHz, CDCl3,
7
14
ppm): d 14.7, 125.2, 130, 133, 147.9, 191.2; HRMS (ESI) calcd for
27
1
+
Isobutyraldehyde (2o). 150 mg, 89%; colourless oil; H NMR
500 MHz, CDCl
, ppm): d 1.09–1.11 (m, 6H), 2.40 (dtd, J ¼
C
8
H
8
OS [M + H] 153.0369; found 153.367.
(
1
3
1
3
4.11, 7.06, 7.06, 1.14 Hz, 1H), 9.57–9.80 (m, 1H); C NMR (126
, ppm): d 15.4, 40.9, 204.5; GC-MS (ESI) calcd for
O [M] 73.0; found 73.0.
MHz, CDCl
C H
4 8
3
23
1
Benzophenone (2p). 150 mg, 83%; white solid; H NMR (200
MHz, CDCl , ppm): d ppm 7.41–7.60 (m, 6H), 7.75–7.84 (m, 4H);
3
1
3
C NMR (50 MHz, CDCl , ppm): d 128.2, 130.1, 132.3, 137.7,
3
+
1
96.4; HRMS (ESI) calcd for C13
H
11O [M + H] 183.0804; found
1
83.0803.
30
1
Tetralone (2q). 75 mg, 87%; colourless oil; H NMR (200
MHz, CDCl
3
,ppm): d 2.04–2.25 (m, 2H), 2.56–2.72 (m, 2H), 2.97
(
(
t, J ¼ 6.06 Hz, 2H), 7.16–7.35 (m, 2H), 7.38–7.51 (m, 1H), 8.02
1
3
dd, J ¼ 7.77, 1.20 Hz, 1H); C NMR (50 MHz, CDCl , ppm):
3
d 23.32, 29.77, 39.13, 126.65, 127.28, 128.68, 132.68, 133.30,
1
+
23
44.30, 197.88; HRMS (ESI) calcd for C H O [M + H]
2-Benzylisoindoline-1,3-dione (p). Phthalimide (1 g, 6.79
1
0
10
1
47.0804; found 147.0806.
mmol) was taken in round bottom ask equipped with
Acetophenone (2r). 112 mg, 90%; colourless oil; H NMR (200 magnetic stirrer and dissolved in dry DMF (25 mL).
MHz, CDCl , ppm): d 2.60 (s, 3H) 7.37–7.58 (m, 3H), 7.89–8.00 K CO (1.87 g, 13.59 mmol) and benzyl bromide (1.162 g, 6.79
24
1
3
2
3
1
3
(m, 2H); C NMR (50 MHz, CDCl
3
, ppm): d 26.50, 128.30, mmol) was added to above reaction mixture. Then the reaction
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mixture was stirred for 12 h at room temperature. Reaction was
Acknowledgements
quenched with H O (12 mL) and extracted with ethyl acetate (3
2
ꢁ
15 mL). The combined organic layer wash with brine and A. H. B. thanks, UGC, New Delhi, India for the award of research
dried over Na SO . The crude product was then puried by fellowship. The authors are thankful to Mr Pramod Mali (Centre
2
4
column chromatography using silica (100–200 mesh) and 20% for NMR Facility, CSIR-NCL) for assistance with NMR Study.
ethyl acetate/pet. ether as eluent gave 90% yield of benzyl pro-
1
tected phthalimide as white solid. 30 mg; H NMR (200 MHz,
Notes and references
CDCl3, ppm): d 4.82 (s, 2H), 7.35 (m, 5H), 7.67 (m, 2H), 7.82 (m,
1
3
2
1
H); C NMR (50 MHz, CDCl
3
, ppm): d 41.63, 123.3, 127.8,
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28.6, 128.7, 132.2, 134.0, 136.4, 168.0; HRMS (ESI) calcd for
C H OS [M + H] 238.0863; found 238.0862.
+
8
8
23
(
1,3-Dioxoisoindolin2-yl) (phenyl)methyl acetate (q).
2-
Benzylisoindoline-1,3-dione (1.5 g, 6.3 mol) was dissolved in
5 mL of chlorobenzene. N-Bromosuccinamide (1.68 g, 9.4
mol), sodium acetate (0.77 g, 9.4 mol) and acetic acid (0.54 mL,
.4 mol) was added to above reaction mixture. Then reaction
mixture was reuxed with constant stirring for 12 h. Aer
completion of reaction, reaction mixture evaporated on reduced
pressure then extracted with ethyl acetate (3 ꢁ 15 mL).
Combined organic layer wash with brine and dried over Na SO .
2
9
2
4
Crude product was puried by column chromatography using
silica gel (100–200 mesh) and 10% ethyl acetate/pet. ether as
eluent. Desired product as a white solid in 75% yield. (30 mg);
1
3
H NMR (200 MHz, CDCl , ppm): d 2.2 (s, 3H), 7.4 (m, 3H), 7.6
1
3
(
d, J ¼ 7.25 Hz, 2H), 7.7 (s, 1H), 7.8 (m, 2H), 7.9 (m, 2H);
C
NMR (50 MHz, CDCl , ppm): d 20.8, 74.2, 123.8, 126.4, 128.5,
3
1
29.0, 131.6, 134.5, 135.1, 166.3, 169.3; HRMS (ESI) calcd for
C H OS [M + Na] 318.0737; found 318.0733.
Amino(phenyl)methyl acetate (r). (1,3-dioxoisoindolin2-yl)-
phenyl)methyl acetate (1 g, 3.38 mol) was taken in two neck
round bottom asks and 20 mL of ethanol was added. To above
solution hydrazine hydrate (0.17 g, 3.38 mol) was added and
reuxed for 20 minutes. Aer 20 minutes acetic acid (0.58 mL, 5.1
mol) was added and further reuxed for 2 h. Then EtOH was
evaporated on reduced pressure and extracted with ethyl acetate (3
+
8
8
23
(
ꢁ
15 mL). Combined organic layer wash with brine and dried over
Na SO . Crude product was puried using silica gel (100–200
2
4
mesh) and 10% ethyl acetate/pet. ether as eluent. Desired product
was obtained as white solid in 60% yield (30 mg). H NMR (200
1
MHz, CDCl
3
, ppm): d 2.4 (s, 3H), 7.4 (m, 3H), 7.7 (dd, J ¼ 7.06,
8 N. Iqbal and E. J. Cho, Adv. Synth. Catal., 2015, 357, 2187–
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13
2.48 Hz, 2H), 7.9 (s, 1H), 10.2 (s, 1H); C NMR (50 MHz, CDCl ,
3
ppm): d 20.3, 127.1, 128.7, 130.0, 133.9, 143.7, 174.0; HRMS (ESI)
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calcd for C H OS [M + Na] 188.0682; found 188.2123.
8
8
1
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32062 | RSC Adv., 2018, 8, 32055–32062
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