Effect of sodium naphthalenide, a key SET reagent, on trifluoroacetyl derivatives

Article abstract of DOI:10.1016/j.tetlet.2005.08.052

Aromatic trifluoroacetyl derivatives on treatment with single electron transfer (SET) reagent, sodium naphthalenide, yield symmetrical defluorinated dimers, whereas for aliphatic trifluoroacetyl compounds the reaction usually fails. Investigations have been made for different substituents as well as for similar types of chloro and bromo compounds to establish the scope of the reaction.

Full text of DOI:10.1016/j.tetlet.2005.08.052

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 7033–7035
Effect of sodium naphthalenide, a key SET reagent,
on trifluoroacetyl derivatives
a,
a
a
b
*
Avijit Banerji, Debasish Bandyopadhyay, Bidyut Basak, Kumar R. Sur,
c
a
a
Jyoti N. Paul, Julie Banerji and Asima Chatterjee
a
Centre of Advanced Studies on Natural Products including Organic Synthesis, Department of Chemistry, Calcutta University,
2, A. P. C. Road, Kolkata 700 009, India
9
Department of Chemistry, R. K. Mission Vivekananda Centenary College, Rahora, 24-Parganas(N), West Bengal, India
b
c
Department of Chemistry, Krishnanagar Govt. College, Nadia 741 101, West Bengal, India
Received 17 June 2005; revised 4 August 2005; accepted 11 August 2005
Abstract—Aromatic trifluoroacetyl derivatives on treatment with single electron transfer (SET) reagent, sodium naphthalenide,
yield symmetrical defluorinated dimers, whereas for aliphatic trifluoroacetyl compounds the reaction usually fails. Investigations
have been made for different substituents as well as for similar types of chloro and bromo compounds to establish the scope of
the reaction.
Ó 2005 Elsevier Ltd. All rights reserved.
Organic reactions through a single electron transfer
SET) mechanism have received increasing interest in
vation, we become interested in studying the effect of
NaNaph on different trifluoroacetyl systems in order
to see whether dimericdefluorinated produ tc s would
be produced in other cases or the action of NaNaph
on 3-trifluoroacetylindole was a special case.
(
recent years. Among several SET reagents, sodium
naphthalenide has attracted special attention due to its
cost effectiveness as well as easy availability. A number
1
–6
of reactions have been reported where sodium naph-
thalenide has been used successfully as a SET reagent.
In this investigation, a solution (deep green in color) of
NaNaph was prepared at 0 °C by treating sodium with
naphthalene in dry THF under nitrogen. A solution of
the substrate in THF was then added dropwise to the
sodium naphthalenide solution with stirring for 2 h at
0–5 °C and the progress of the reaction was monitored
7
–12
As a part of our investigations in this field,
we have
reported the effect of sodium naphthalenide on various
heterocycles. In this connection, we have recently
1
3
reported
the reaction of sodium naphthalenide
(
NaNaph) with 3-trifluoroacetylindole, which yielded a
1
4
symmetrical dimeric compound as the sole product.
The interesting aspect of this reaction is that though
the starting material is a fluorinated compound, the
symmetrical dimer is totally lacking fluorine as con-
by TLC. It was found that, for all the aromatic(both
carbocyclic and heterocyclic) derivatives, the reaction
proceeded well (Scheme 1) whereas aliphatictrifluoro-
acetyl derivatives, for example, ethyl, isopropyl, and n-
butyl trifluoroacetyl compounds did not take part in
1
9
firmed by F NMR spectroscopy. Based on this obser-
O
C
O
C
0
NaNaph, 0-5 C
Ar
COCF3
Ar
CH2
CH2
Ar
THF, 2 h, N2
Scheme 1.
Keywords: Sodium naphthalenide; SET; Trifluoroacetyl; Aromatic heterocycles.
*
Corresponding author. Tel.: +91 33 2350 8386; fax: +91 33 2351 9755; e-mail: ablabcu@yahoo.co.uk
0040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.08.052

7034
A. Banerji et al. / Tetrahedron Letters 46 (2005) 7033–7035
the reaction at all even after lengthening the reaction
time. The reaction between methyl trifluoroacetyl deriv-
ative viz. 1,1,1-trifluoro acetone with NaNaph yielded a
trace amount of the corresponding dimeric product.
(46%) was obtained. All the products were characterized
by extensive NMR studies. The NMR data of three rep-
resentative compounds are listed.
1
4
Probably, the electron-withdrawing character of the
fluorine atoms decreases the electron density of the
corresponding system to such an extent that the initial
attack by NaNaph to the carbonyl system is facilitated.
But for N-alkyl indoles (Scheme 2), the yields decrease
extensively with increasing +I effect of the alkyl group,
The substrates used and the products obtained from
treatment of various aromaticheter loye cs with
NaNaph are shown in Table 1. Trifluoroacetyl benzene
(
entry 6) gave the best yield of dimer (98%), but for
benzotriazole (entry 4) a comparatively low yield
Table 1. Products isolated from the reactions between sodium naphthalenide and aromatic trifluoroacetyl compounds via Scheme 1
Entry
Substrate
Product
Yield (%)
COCF3
O
C
O
C
13
94
1
CH2
CH2
N
H
N
H
N
H
O
O
2
3
COCF3
82
69
N
H
C
CH2
CH2
C
N
H
N
H
N
O
O
N
N
N
N
N
C
CH2
CH2
C
N
COCF3
O
C
O
C
N
N
N
S
N
N
N
CH2
CH2
N
4
N
46
COCF3
O
O
5
6
95
98
COCF3
S
C
CH2
CH2
C
S
COCF3
O
C
O
C
CH2
CH2
O
C
O
C
COCF3
7
CH
CH
93
2
2
O
O
COCF3
C
CH2
CH
C
2
0
NaNaph, 0-5 C
N
R
N
R
N
R
THF, 2h, N2
1
1
1
1
1
, 2a R=H
, 2b R=Me
, 2c R=Et
, 2d R=n-Pr
, 2e R=n-Bu
2
1
Scheme 2.

A. Banerji et al. / Tetrahedron Letters 46 (2005) 7033–7035
7035
Table 2. Products isolated from the reactions between sodium
naphthalenide and 3-trifluoroacetyl (N-alkyl) indoles via Scheme 2
5. Wilberg, K. B.; Williams, V. Z. J. Org. Chem. 1970, 35,
369–373.
6
7
8
9
. Fujita, T.; Suga, K.; Watanaber, S. Chem. Ind. 1973, 231–
32.
. Banerji, A.; Jana, S.; Sur, K. R. J. Ind. Chem. Soc. 1989,
6, 664–672.
. Banerji, A.; Paul, J. N.; Maiti (ne e´ ), S.; Sur, K. R. Ind. J.
Chem. 1994, 33B, 576–578.
Entry
Substrate
Product
Yield (%)
2
1
2
3
4
5
1a
1b
1c
1d
1e
2a
2b
94
53
31
9
6
2c
2d
— (no reaction)
—
. Banerji, A.; Maiti, S. Ind. J. Chem. 1993, 32B, 889–891.
1
1
0. Banerji, A.; Maiti, S. Ind. J. Chem. 1994, 33B, 532–539.
1. Banerji, A.; Maiti, S. Tetrahedron 1994, 50, 9079–9096.
in the order n-Pr > Et > Me. However, for the N-butyl
derivative, the reaction did not take place at all (Table 2).
12. Banerji, A.; Bandyopadhyay, D.; Basak, B.; Prang e´ , T.;
Neuman, A. J. Struct. Chem. 2005, 46, 935–940.
1
1
3. Banerji, A.; Bandyopadhyay, D.; Basak, B. Heterocycles
004, 64, 2371–2377.
4. A deep green dilute solution of sodium naphthalenide was
prepared at 0 °C by treating 1.01 g (0.043 mol) sodium
with 4.08 g (0.032 mol) naphthalene in dry THF (50 ml)
under dry nitrogen. To this, a solution of the substrate
2
An attempt was also made using trichloro- and tri-
bromoacetyl derivatives of indole as substrates. In both
cases, no reaction was observed. Although the electron-
withdrawing capacity of chlorine is high, yet perhaps it
fails to decrease the electron density of the system
enough so that the attack of NaNaph to the carbonyl
group does not take place.
(
0.02 mol) in 20 ml THF was added and the mixture
stirred for 2 h at 0–5 °C. The reaction mixture was then
poured into 100 ml citric acid–sodium acetate buffer
(
pH ꢀ 4.5) and extracted thrice with 25 ml distilled chlo-
roform. The chloroform extract was washed successively
with aqueous sodium bicarbonate solution and distilled
water, dried over sodium sulfate (anhydrous) and finally in
a rotary evaporator under reduced pressure to remove a
trace amount of water. Column chromatography yielded
It was reported earlier that defluorination could be per-
1
5
formed by electrolytic reduction, but the present study
reveals that the aromatictrifluoroa ce tyl derivatives on
treatment with sodium naphthalenide yield symmetrical
defluorinated dimers as the sole products. The reactivity
decreases with increase in electron density of the aro-
maticsystem as well as the ele ct ron-donating nature of
the substituents present in the substrate.
the corresponding defluorinated dimeric product. 1,4-
0
(
3
3,3 -Diindolyl)-1,4-dioxobutane; mp 189 °C: IR (KBr)
ꢁ
1
1
236, 1640, 1432, 749 cm
;
H NMR (500 MHz, pyri-
dine-d ) d 14.22 (2H, s), 10.03 (2H, d, J = 7.8 Hz), 9.83
5
(
(
2H, s), 8.70 (2H, d, J = 8.0 Hz), 8.43–8.55 (4H, m), 4.77
4H, s); C NMR (125 MHz, pyridine-d ) d 196.10,
5
13
1
1
39.23, 134.85, 128.19, 124.01, 123.65, 123.63, 119.22,
Acknowledgements
+
13.78, 35.67; EIMS (70 eV) m/z 318 (M +2, 39%). 1,4-
0
(
(
3,3 -(N-ethyl)diindolyl)-1,4-dioxobutane; mp 216 °C: IR
We are thankful to Dr. Subrata Laskar, Department of
Chemistry, Burdwan University; Dr. Kaushik Ganguly,
Department of Chemical Engineering, Calcutta Univer-
sity; and Dr. Sanjoy Kumar, Department of Physics,
Jadavpur University for skillful assistance.
ꢁ1 1
KBr) 1648, 1437, 748 cm ; H NMR (500 MHz, pyri-
) d 9.63 (2H, d, J = 7.4 Hz), 9.07 (2H, s), 8.59 (2H,
d, J = 7.8 Hz), 8.37–8.43 (4H, m), 4.42 (4H, s), 2.52 (4H,
dine-d
5
13
m), 1.02 (6H, t, J = 2.1 Hz);
pyridine-d ) d 194.16, 136.29, 133.98, 125.15, 123.01,
22.85, 122.63, 120.76, 114.09, 41.90, 34.98, 15.09; EIMS
C NMR (125 MHz,
5
1
+
(
70 eV) m/z 373 (M +1, 54%). 1,4-Diphenyl-1,4-dioxobu-
ꢁ
1 1
References and notes
tane; mp 171 °C: IR (KBr) 1680, 1575, 1480, 775 cm ; H
NMR (300 MHz, CDCl ) d 7.87 (4H, distorted d), 7.30
(2H, m), 7.21 (4H, m), 4.72 (2H, m);
(75.5 MHz, CDCl ) d 195.17, 136.30, 132.08, 127.20,
126.64, 37.85; EIMS (70 eV) m/z 238 (M , 26%).
3
1
3
1
2
3
. Wrobel, Z.; Makosza, M. Synlett 1993, 597–598.
. Makosza, M. Chimia 1994, 48, 499–500.
. Wrobel, Z.; Makosza, M. Tetrahedron 1997, 53, 5501–
C NMR
3
+
5
514.
15. House, H. O. Modern Synthetic Reactions, 2nd ed.;
The Benjamin/Cummings Publishing Company: Califor-
nia, 1972; p 161.
4
. Scouten, C. G.; Barton, F. E.; Burgers, J. R.; Story, P. R.;
Garst, J. F. J. Chem. Soc., Chem. Commun. 1969, 78–79.