2944
M. Kitamura et al.
LETTER
(3) For the use of alternative diazo transfer reagents and
Table 1 Diazo Transfer of Azidoimidazolinium Salt 2 to 1,3-Dicar-
bonyl Compoundsa
conditions, see: (a) For imidazole-1-sulfonyl azide, see:
Goddard-Borger, E. D.; Stick, R. V. Org. Lett. 2007, 9,
3797. For trifluorometanesulfonyl azide, see: (b) Wurz,
R. P.; Lin, W.; Charette, A. B. Tetrahedron Lett. 2003, 44,
8845. (c) Cavender, C. J.; Shiner, V. J. Jr. J. Org. Chem.
1972, 37, 3567. (d) For mesyl azide, see: Taber, D. F.;
Ruckle, R. E. Jr.; Hennessy, M. J. J. Org. Chem. 1986, 51,
4077. (e) For p-carboxybenzenesulfonyl azide, see:
Hendrickson, J. B.; Wolf, W. A. J. Org. Chem. 1968, 33,
3610. (f) For 2-azido-3-ethylbenzothiazolium
tetrafluoroborate, see: Balli, H.; Löw, R.; Müller, V.;
Rempfler, H.; Sezen-Gezgin, A. Helv. Chim. Acta 1978, 61,
97. (g) For(azidochloromethylene)dimethylammonium
chloride, see: Kohel, B.; Viehe, H. G. Angew. Chem. Int. Ed.
Engl. 1980, 19, 716. (h) For naphthalene-2-sulfonyl azide
and p-(n-dodecyl)benzenesulfonyl azide, see: Hazen, G. G.;
Weinstock, L. M.; Connell, R.; Bollinger, F. W. Synth.
Commun. 1981, 11, 947. (i) For 2,4,6-triisopropylphenyl-
sulfonyl azide, see: Lombardo, L.; Mander, L. N. Synthesis
1980, 368. (j) For p-nitrophenyl azide, see: Herbranson, D.
E.; Hawley, M. D. J. Electroanal. Chem. 1983, 144, 423.
(k) For azidotris(diethylamino)-phosphonium bromide, see:
McGuiness, M.; Shechter, H. Tetrahedron Lett. 1990, 31,
4987. For polymer-bound sulfonyl azide, see: (l) Harned,
A. M.; Sherrill, W. M.; Flynn, D. L.; Hanson, P. R.
Tetrahedron 2005, 61, 12093. (m) Green, G. M.; Peet, N. P.;
Metz, W. A. J. Org. Chem. 2001, 66, 2509. (n) Roush, W.
R.; Feitler, D.; Rebek, J. Tetrahedron Lett. 1974, 15, 1391.
(o) For reaction in ionic liquid, see: Ramachary, D. B.;
Narayana, V. V.; Ramakumar, K. Tetrahedron Lett. 2008,
49, 2704.
O
O
O
O
R1
R2
NaN3
3
2
R1
R2
MeCN
Et3N, THF
0 °C, time
N2
0 °C, 30 min
Entry
R1
R2
Time
Yield (%)b
1
2
3
4
5
6
7
8
Me
Me
Ph
Ph
10 min
10 min
2 h
98
93
99
82
79
99
94
95
Me
Ph
Me
Me
OEt
OEt
N(Me)2
OEt
2 h
4 h
4 h
–CH2C(CH3)2CH2–
–OC(CH3)2O–
10 min
10 min
a Molar ratio of 3/NaN3/1,3-dicarbonyl compounds/
Et3N = 1.2:1.2:1:2.
b Isolated yield.
Azidoimidazolinium salt 2 was also applicable to the
preparation of Ohira–Bestmann reagent 9,8 which was ob-
tained in 76% by the reaction with diethyl (2-oxopro-
pyl)phosphonate (8; Scheme 4).
(4) (a) Hudlicky, T.; Govindan, S. V.; Frazier, J. O. J. Org.
Chem. 1985, 50, 4166. (b) Doyle, M. P.; Dorow, R. L.;
Terpstra, J. W.; Rodenhouse, R. A. J. Org. Chem. 1985, 50,
1663. (c) Ledon, H. Synthesis 1974, 347.
O
O
(EtO)2P
(5) Kitamura, M.; Chiba, S.; Narasaka, K. Bull. Chem. Soc. Jpn.
O
O
8 (1.0 mmol)
NaN3
2003, 76, 1063.
(1.5 mmol)
(EtO)2P
Et3N (2.0 mmol)
(6) The formation of salt 2 was confirmed by mass spectral
analysis. The FAB(positive) mass spectrum of the mixture of
the chloroimidazorium salt 3 and sodium azide showed a
peak at m/z = 140, which corresponds to the calculated mass
of [2 – Cl–]+.
2
3
MeCN
THF
(1.5 mmol)
N2
9 76%
0 °C, 30 min
0 °C, 1 h
Scheme 4
(7) Typical procedure: [Caution: Although we have never had
any trouble with azidoimidazolinium salt 2, it is potentially
explosive.] To a solution of 2-chloro-1,3-dimethyl-
imidazolinium chloride (3; 1.2 mmol) in acetonitrile (2 mL),
sodium azide (1.2 mmol) was added at 0 °C and the mixture
was stirred for 30 min. 1,3-Dicarbonyl compound (1.0
mmol) and triethylamine (2.0 mmol) in THF (4 mL) was
added to the mixture, which was stirred until the 1,3-
dicarbonyl compound was consumed (reaction monitored by
TLC). The reaction was quenched with water, and organic
materials were extracted three times with CH2Cl2. The
combined extracts were washed with water and brine, and
then dried over anhydrous sodium sulfate. The solvent was
removed in vacuo to afford the crude compound, which was
almost pure. The crude materials were purified by flash
column chromatography (silica gel: hexane–ethyl acetate) to
give pure 2-diazo-1,3-dicarbonyl compound.
In conclusion, we have developed an efficient diazotiza-
tion method for 1,3-dicarbonyl compounds using diazo-
nium salt 2, which is easily prepared from commercially
available compounds in one step. Using this diazotization
approach, 2-diazo-1,3-dicarbonyl compounds were ob-
tained in high yields and were easily isolated.
References and Notes
(1) For reviews, see: (a) Zhang, Z.; Wang, J. Tetrahedron 2008,
64, 6577. (b) Doyle, M. P.; Ye, T.; McKervey, M. A.
Modern Catalytic Methods for Organic Synthesis with Diazo
Compounds; John Wiley & Sons: New York, 1998. (c) Ye,
T.; McKervey, M. A. Chem. Rev. 1994, 94, 1091.
(d) Padwa, A.; Austin, D. J. Angew. Chem. Int. Ed. Engl.
1994, 33, 1797. (e) Doyle, M. P. Chem. Rev. 1986, 86, 919.
(2) For reviews on the synthesis of a-diazo compounds by diazo
transfer using tosyl azide, see: (a) Regitz, M. Synthesis
1972, 351. (b) Regitz, M. Angew. Chem. Int. Ed. Engl. 1967,
6, 733.
(8) (a) Ohira, S. Synth. Commun. 1989, 19, 561. (b) Müller, S.;
Liepold, B.; Roth, G. J.; Bestmann, H. J. Synlett 1996, 521.
Synlett 2009, No. 18, 2943–2944 © Thieme Stuttgart · New York