Mendeleev Commun., 2006, 16(5), 258–259
1,4-diazadiene condensation with chloromethyl ether or ester.4,5
However, we found the condensation of diazadienes 3 and 4
with ClCH2OEt or BrCH2OMe to produce the corresponding
DAIS in unsatisfactory yields of 20–25% at best.
Therefore, we turned our attention to electrophilic dimethyl-
methyleneammonium salts 5a,b. To our satisfaction, these salts
proved to be the reagents of choice for imidazolium ring
formation starting with diazadienes 3 and 4. The reaction is fast
(10–15 min), mildly exothermic and easily controllable thus
lending itself for scaling up. The isolation of formed products
1a,b, 2a consists in the evaporation of the reaction mixture and
crystallization of the product.†
Although the proposed method consists of two steps (iminium
salts are generated in situ), both of these steps are experimentally
simple and short-timed and could be easily performed during a
working day on a several-gram level. Therefore, the method is
deemed to be a viable alternative to the existing one-pot method
for the preparative synthesis of DAISs.
References
3 W. A. Herrmann, C. Kocher, L. J. Goossen and G. R. J. Artus, Chem.
Eur. J., 1996, 2, 1627.
5 F. Glorius, G. Altenhoff, R. Goddard and C. Lehmann, Chem. Commun.,
2002, 2704.
†
1,4-Diazadienes 3 and 4. Glyoxal (25 ml of 40% aqueous solution,
0.22 mol) was gradually mixed (5 min) with a solution of ButNH2 (46 ml,
0.44 mol) in CH2Cl2 (60 ml). Anhydrous CaCl2 (20 g, 0.18 mol) was
added to this solution with stirring and cooling (ice bath). After 30 min,
the mixture was warmed close to boiling and an organic layer was
separated by decantation. The layer was rotary evaporated in a vacuum
and the crystallization of an oily residue was induced by moistening with
diethyl ether with the subsequent vacuum drying. The yield of
crystalline diazadiene 3 was 34.1 g (92%), mp 55 °C.6 The same proce-
dure in (CH2Cl)2 was applied to synthesise diazadiene 4, yield 80%,
mp 146–147 °C.6 Both diazadienes are used in the next step without
additional purification.
6 H. Dieck and I. W. Renk, Chem. Ber., 1971, 104, 92.
Received: 3rd March 2006; Com. 06/2693
1,3-Di-tert-butylimidazolium chloride 1a. Acetyl chloride (3.14 ml,
44 mmol) was added with stirring and cooling below 15 °C to a solution
of CH2(NMe)2 (6 ml, 44 mmol) in (CH2Cl)2 (20 ml). A white suspen-
sion of salt 5a was formed. The solution of diazadiene 3 (6.7 g, 40 mmol)
in (CH2Cl)2 (10 ml) was added in one portion to this suspension. Cooling
was removed and after a spontaneous exothermal stage (ca. 15 min) the
solution was rotary evaporated at 75 °C in a vacuum leaving the oily
mixture of the product with AcNMe2 (formed during salt 5a generation).
This mixture after dilution with (CH2Cl)2 (5 ml) and EtOAc (10 ml) and
cooling separated the crystals of DAIS 1a. Filtration, washing with EtOAc
and drying afforded 6.7 g (79%) of 1a. 1H NMR (200 MHz, [2H6]DMSO)
d: 1.62 (s, 18H, 2But), 8.17 (s, 2H, NCHCHN), 9.42 (s, 1H, NCHN).2
When crystallization is performed from CH2Cl2–EtOAc, 1a forms a solvate
with one molecule of CH2Cl2.
1,3-Di-tert-butylimidazolium bromide 1b. Mixed salt 5b and NMe4Br
was prepared by a reaction of CH2(NMe2)2 with MeBr in MeCN. Diaza-
diene 3 (7.8 g, 0.046 mol) in CH2Cl2 (30 ml) was added to this salt
mixture (14.6 g, 0.05 mol of 5b) producing almost immediate exo-
thermal reaction. After 30 min, the reaction mixture was filtered, the
filtrate was concentrated in a vacuum, and the residue was crystallised
from MeCN–(CH2Cl)2, giving 4.23 g (49%) of DAIS 1b. 1H NMR
(200 MHz, [2H6]DMSO) d: 1.62 (s, 18H, 2But), 8.10 (s, 2H, NCHCHN),
9.10 (s, 1H, NCHN).
1,3-Dicyclohexylimidazolium chloride 2a was prepared analogously to
1
1a starting from diazadiene 4 (13.4 g), yield 16.2 g (81.5%). H NMR
(200 MHz, [2H6]DMSO) d: 1.2–2.2 (m, 20H, 10CH2), 4.40 (t, 2H, 2CH),
8.00 (s, 2H, NCHCHN), 9.80 (s, 1H, NCHN).
Mendeleev Commun. 2006 259
Mistryukov, Electron A.
