Studies on enamides. VI. An improvised methodology for orton rearrangement under neutral condition

Article abstract of DOI:10.1081/SCC-100105326

A highly efficient methodology in neutral medium has been developed for the synthesis of bromoanilides from the corresponding anilides using N-bromosuccinimide in carbon tetrachloride under irradiation with visible light. The products are obtained in highly pure crystalline state with an excellent yield.

Full text of DOI:10.1081/SCC-100105326

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1
STUDIES ON ENAMIDES. VI. AN IMPROVISED
METHODOLOGY FOR ORTON REARRANGEMENT UNDER
NEUTRAL CONDITION
a
a
Somnath Ghosh & Susmita Baul
a
Department of Chemistry, Jadavpur University, Calcutta, 700 032, India
Version of record first published: 15 Aug 2006.
1
To cite this article: Somnath Ghosh & Susmita Baul (2001): STUDIES ON ENAMIDES. VI. AN IMPROVISED METHODOLOGY
FOR ORTON REARRANGEMENT UNDER NEUTRAL CONDITION, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 31:18, 2783-2786
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SYNTHETIC COMMUNICATIONS, 31(18), 2783–2786 (2001)
1
STUDIES ON ENAMIDES. VI.
AN IMPROVISED METHODOLOGY
FOR ORTON REARRANGEMENT
UNDER NEUTRAL CONDITION
Somnath Ghosh* and Susmita Baul
Department of Chemistry, Jadavpur University,
Calcutta 700 032, India
ABSTRACT
A highly efficient methodology in neutral medium has been
developed for the synthesis of bromoanilides from the corre-
sponding anilides using N-bromosuccinimide in carbon tetra-
chloride under irradiation with visible light. The products are
obtained in highly pure crystalline state with an excellent
yield.
The rearrangement of N-chloro- or N-bromoanilides in the pre-
2
sence of acid, as first observed by Orton in 1901, is classically known as
3
Orton rearrangement. Afterwards, it has been shown that use of chlorine or
4
bromine in conjunction with the corresponding mineral acids or other
5
acid such as trifluoroacetic acid or ultraviolet light as well as radical
6,7
8
initiator such as benzoyl peroxide in carbon tetrachloride or tertiary-
8
,9
butyl hydroperoxide
in chlorobenzene also furnishes Orton product.
*
Corresponding author.
2
783
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

ORDER
REPRINTS
2
784
GHOSH AND BAUL
Almost all of these deal with the mechanistic aspects of this rearrangement
5
based on kinetic and crossover experiments.
In connection with some other works, we needed 2-bromoethyl
benzanilide (2), which we envisaged to prepare by allylic bromination of
1
-methylbenzanilide (1) with N-bromosuccinimide in dry carbon tetra-
0
2
chloride in the presence of visible light (Scheme 1).
Scheme 1.
However, we could isolate only 4-bromo-2-methylbenzanilide (3) in
1
1–14
almost quantitative yield. A systematic study of the literature
1
showed
in 1944 wherein he reported the
5
there is a single report by Bui-Hoı
¨
preparation of 4-bromoacetanilide from acetanilide by the reaction of
NBS in refluxing carbon tetrachloride. We undertook this study further
and wish to report herein the present methodology which necessitates
neither the prior preparation of N-bromoanilides nor the use of hazardous
chlorine or bromine in acidic condition; and the overall process is thus an
environment friendly reaction in neutral medium.
In a typical experimental procedure, exactly equimolar quantities
(
10 mmol) of anilide and freshly crystallized dry NBS are subjected to irra-
diation in dry carbon tetrachloride (50 mL) with visible light (150 W or
00 W tungsten lamp, Philips India Ltd.) for 40–45 min. Initially, a pale
2
yellow color develops (usually within 5 min) which gradually changes to
canary yellow, then to orange or crimson red. The products are crystallized
out from orange colored solution or in some cases; the crimson red color
slowly vanishes to afford the crystalline product from the hot solution. This
is filtered, washed liberally with water to free it from adhering succinimide,
dried and the melting points are recorded after a second crystallization from
suitable solvents. The yields are nearly quantitative (Table).
The mechanism of this reaction has also been settled by performing
the reaction of N-methylacetanilide with NBS under the aforementioned

ORDER
REPRINTS
STUDIES ON ENAMIDES. VI
2785
a
Table. Results of NBS Reaction with Anilides
Time
(min)
Yield
(%)
Entry
Substrate
Acetanilide
Benzanilide
3-Chloroacetanilide
2-Methoxyacetanilide
2-Methylacetanilide
Product
1
2
3
4
5
6
30 4-Bromoacetanilide
60 4-Bromobenzanilide
40 4-Bromo-3-chloroacetanilide
60 4-Bromo-2-methoxyacetanilide
45 4-Bromo-2-methylacetanilide
84
94
80
82
87
N-(1-Naphthyl)-acetamide 45 N-(4-Bromo-1-naphthyl)-acetamide 80
a
All the compounds give satisfactory melting points and spectral data (IR, NMR).
condition, whence the starting material is recovered. This clearly shows the
reaction proceeds via Orton rearrangement type pathway and a direct
bromination on aromatic ring is thus excluded.
It is to be noted that allylic bromination does not occur here and also
halogenated anilides undergo bromination, which are otherwise prepared by
a number of steps.
Thus, the extreme efficacy of this methodology in a very short time
offers an excellent improvement over the conventional methods such as use
of bromine and acetic acid etc. The isolation of the product in very high
yield and in pure crystalline state does not involve any clumsy work-up.
Furthermore, the present procedure is devoid of any unwanted side reac-
tions, such as decomposition anilides (Type I cleavage) under the reaction
condition and, it may thus be considered as the easiest and most practical
procedure for the preparation of bromoanilides in a hazardous free environ-
ment friendly reaction condition.
ACKNOWLEDGMENTS
The authors are thankful to Mr. Sumanta Patsa who carried out a
portion of this work for his M.Sc. project and also to DSA, Chemistry and
Jadavpur University for financial assistance.
REFERENCES
1
. Part-5: Ghosh, S.N.; Nandi, B.; Saima, Y. Tetrahedron Lett. 1996,
7, 3169.
. Chattaway, F.D.; Orton, K.J.P. J. Chem. Soc. 1901, 79, 254.
3
2

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786
GHOSH AND BAUL
3. Reviews: Shine, H.J. Aromatic Rearrangements, Elsevier: New York,
1967, pp. 221–230, 362–364; Bieron, J.F.; Dinan, F.J. in Zabicky, J.
The Chemistry of Amides, Wiley: New York, 1973, pp. 263–269.
. For summary, see Orton, K.J.P.; Soper, F.G.; Williams, G. J. Chem.
Soc. 1928, 998.
. Golding, P.D.; Reddy, S.; Scott, J.M.W.; White, V.A.; Winter, G.J.
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5
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7
8
. Hodges, F.W. J. Chem. Soc. 1933, 240.
. Mathews, J.H.; Willamson, R.V. J. Amer. Chem. Soc. 1923, 45, 2574.
. Ayad, K.N.; Beard, C.; Garwood, R.F.; Hickinbottom, W.J. J. Chem.
Soc. 1957, 2981.
9. Coulson, J.; Willams, G.H.; Johnston, K.M. J. Chem. Soc. B 1967, 174.
1
1
0. Waugh, T.D. N-Bromosuccinimide. Its Reactions and Uses, Arapaho
Chemicals Inc.: Boulder, Colo., 1951.
1. Horner, L.; Winkelmann, E.H. Newer Methods of Preparative Organic
Chemistry 1964, 3, 151.
1
1
1
1
2. Djerassi, C. Chem. Rev. 1948, 43, 271.
3. Chapman, N.B.; Willams, J.F.A. J. Chem. Soc. 1952, 5044.
4. Mitchell, R.H.; Lai, Y.-H. J. Org. Chem. 1979, 44, 4733.
7
. Ann. 1944, 556, 1 [Chem. Abstract 1946, 40, 4669 ].
5. Buu-Hoı
¨
Received in the Netherlands November 28, 2000

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