J. S. Yadav et al. / Tetrahedron Letters 45 (2004) 2951–2954
2953
SCN
CH3
I2
CH3
NH4SCN
+
N
H
N
H
MeOH, r.t.
1
2
Scheme 1.
I2
MeOH, r.t.
+
NH4SCN
SCN
SCN
NCS
+
N
R
N
R
N
R
1
3
4
Scheme 2.
SCN
I2
MeOH, r.t.
1
R1
NH4SCN
R
+
N
N
R
R
5
1
Scheme 3.
such as aniline, N,N-dimethylaniline, N-ethylaniline,
N-phenylaniline with ammonium thiocyanate in the
presence of molecular iodine resulted in the formation of
aryl thiocyanates in high yields (Table 1, entries 5j–5m,
Scheme 3).
References and notes
1. (a) Wood, J. L. In Organic Reactions; Wiley: New York,
1967; Vol. III, pp 240–266; (b) Kelly, T. R.; Kim, M. H.;
Curtis, A. D. M. J. Org. Chem. 1993, 58, 5855–5857.
2. (a) Wood, J. L. In Organic Reactions; Adams, R., Ed.;
John Wiley & Sons: New York, 1946; Vol. 3, Chapter 6;
(b) Guy, R. G. In The Chemistry of Cyanates and their
Thio Derivatives; Patai, S., Ed.; John Wiley & Sons: New
York, 1977; Part 2, Chapter 18, p 819.
3. (a) Toste, F. D.; Laronde, F.; Still, W. J. Tetrahedron Lett.
1995, 36, 2949–2952; (b) Grant, M. S.; Snyder, H. R.
J. Am. Chem. Soc. 1960, 82, 2742–2744.
4. Kita, Y.; Takeda, T.; Mihara, S.; Whelan, B. A.; Thoma,
H. J. Org. Chem. 1995, 60, 7144–7148.
5. (a) Toste, F. D.; De Stefano, V.; Still, I. W. J. Synthetic
Commun. 1995, 25, 1277–1286; (b) Nair, V.; George, T.
G.; Nair, L. G.; Panicker, S. B. Tetrahedron Lett. 1999, 40,
1195–1196.
6. Chakrabarty, M.; Sarkar, S. Tetrahedron Lett. 2003, 44,
8131–8133.
7. (a) Deka, N.; Kalita, D. J.; Borah, R.; Sharma, J. C.
J. Org. Chem. 1997, 62, 1563; (b) Vaino, A. R.; Szarek, W.
A. Synlett 1995, 1157; (c) Lipshutz, B. H.; Keith, J.
Tetrahedron Lett. 1998, 39, 2495.
8. (a) Yadav, J. S.; Reddy, B. V. S.; Hashim, S. R. J. Chem.
Soc., Perkin Trans. 1 2000, 3082; (b) Yadav, J. S.; Reddy,
B. V. S.; Sabitha, G.; Reddy, G. S. K. K. Synthesis 2000,
1532; (c) Kumar, H. M. S.; Reddy, B. V. S.; Reddy, E. J.;
Yadav, J. S. Chem. Lett. 1999, 857; (d) Yadav, J. S.;
Reddy, B. V. S.; Rao, C. V.; Chand, P. K.; Prasad, A. R.
Synlett 2001, 1638.
In the case of aryl amines, the products were obtained
with high para-selectivity. In all cases, the reactions
proceeded rapidly at room temperature with high regio-
selectivity. As solvent, methanol appeared to give the
best results. The products were characterized by 1H
NMR, IR and mass spectroscopic data and also by
comparison with authentic samples.5;6 This method is
very clean and free from side products. Among the
various oxidants such as DDQ, Mn(OAc)3ꢀ2H2O,
Bi(NO3)3ꢀ5H2O and C6H5I(OAc)2 studied for this
transformation, molecular iodine was found to be the
most effective in terms of conversion and reaction rates.
The scope and generality of this process is illustrated
with respect to various indoles and aryl amines and the
results are presented in Table 1.9
In conclusion, we describe a simple, convenient and
highly efficient protocol for the preparation of aryl and
heteroaryl thiocyanates through the electrophilic thio-
cyanation of aromatic and heteroaromatic compounds
using molecular iodine as promoter.
9. General procedure: To a stirred solution of ammonium
thiocyanate (3 mmol), and iodine (1 mmol) in methanol
(10 mL), the indole, aryl amine (1.0 mmol) or pyrrole
(2 mmol) was added slowly in a dropwise manner and the
mixture was allowed to stir at room temperature for the
appropriate time (Table 1). After complete conversion as
indicated by TLC, the reaction mixture was quenched with
Acknowledgements
B.V.S. thanks CSIR, New Delhi, for the award of a
fellowship.