Reactions of bis(silyl-substituted) methyllithium with α-hydrogen- free nitriles into 1,3,5-triazines

Article abstract of DOI:10.3987/COM-05-10357

Bis(silyl-substituted) methyllithium has been found to catalyze a conversion of α-hydrogen-free nitriles directly to yield 2,4,6-trisubsituted s-triazines. The generally high yields and relatively mild reaction conditions of this procedure suggest an alternative to other aromatic nitrile cyclotrimerization reactions. Silicotropic rearrangements from C to N or N to N and an unusual elimination of LiCR₂R (R=SiMe₃, R=SiMe₂NMe₂) were observed.

Full text of DOI:10.3987/COM-05-10357

HETEROCYCLES, Vol. 65, No. 6, 2005
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HETEROCYCLES, Vol. 65, No. 6, 2005, pp. 1425 - 1430
Received, 31st January, 2005, Accepted, 14th April, 2005, Published online, 15th April, 2005
REACTIONS OF BIS(SILYL-SUBSTITUTED) METHYLLITHIUM WITH
α-HYDROGEN-FREE NITRILES INTO 1,3,5-TRIAZINES
Xia Chen, Sheng-Di Bai, Li Wang, and Dian-Sheng Liu*
The School of Chemistry and Chemical Engineering and The Institute of Modern
Chemistry, Shanxi University, Taiyuan 030006, P. R. China
e-mail: chenxia@sxu.edu.cn
Abstract –Bis(silyl-substituted) methyllithium has been found to catalyze a
conversion of α-hydrogen-free nitriles directly to yield 2,4,6-trisubsituted
s-triazines. The generally high yields and relatively mild reaction conditions of
this procedure suggest an alternative to other aromatic nitrile cyclotrimerization
reactions. Silicotropic rearrangements from C to N or N to N and an unusual
elimination of LiCR2R' (R=SiMe3, R'=SiMe2NMe2) were observed.
INTRODUCTION
A series of studies on the reactions of Li[CH3-nRn] (n=1, 2, or 3 and R=SiMe3) with α-hydrogen-free
nitriles showed that different kinds of addition products such as 1-azaallyl-, β-diketiminato- or
1,3-diazaallyllithium compounds could be yielded.1-5 Normally, as a troublesome side reaction, the
N-lithioimine could add further to molecules of nitrile, leading to aggregate or cyclic products such as
pyrimidines and triazines. 6-9 However, the triazines were often in limited amount; the mechanism of their
formation was sometimes obscure. 10-11
In our early investigation it was shown that addition reactions of bis(trimethylsilyl)methyllithium reagent
[LiN(R)C(Bu-t)CHR]2
Li[CHR2] (R = SiMe3) or 1-azaallyllithium
with cyanoamines R''CN (R'' = Me2N,
12
1-piperidyl or p-pyridyl)
led to β-diketiminatolithium and uniformed or mixed 2,4,6-trisubsituted
triazines. However, if other α-hydrogen- free nitriles e.g. PhCN or substituted PhCN were used instead of
the cyanoamines the triazine products were not observed. Treatment of LiCR3(thf)2 (R=SiMe3) with
PhCN afforded the 1-azaallyl [Li{N(R)C(Ph)CR2}(thf)] other than β-diketiminate or triazine 13,14 It is our
interesting to renovate the limit of this type reaction by using other lithium analogous such as
dimethylaminodimethylsilyl-bis(trimethylsilyl)methyllithium LiCR2R' (R=SiMe3, R'=SiMe2NMe2). We

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proved that the reaction routes involve silicotropic rearrangements from C to N or N to N and an unusual
elimination reaction. The paper describes an improved procedure for the preparation of 1,3,5-s-triazine
derivatives under mild reaction conditions in context of α-hydrogen-free nitriles and using LiCR2R' as a
catalyst.
RESULTS AND DISCUSSION
The reaction of various α-hydrogen-free nitriles R1CN (R1 = Me2N or 1-piperidyl) with Li[CHR2]
(R=SiMe3,)
in
hexane
gave
symmetrical
2,4,6-(tri)(dimethylamino)-s-triazine
or
2,4,6-(tri)(1-piperidinyl)-s-triazine in good yield (>90%). However, the different interaction of Li[CHR2]
with aromatic nitriles had been reported to give different kinds of addition products such as 1-azaallyl-
and β-diketiminato-lithium compounds.1-5 But if LiCR2R' , the analogue of Li[CHR2], was been used
instead of Li[CHR2], the 2,4,6-trisubsituted s-triazines (7-12) were also obtained (Scheme 1).
R1
N
N
Li[CR'R2]
R = Me3Si-
R' = Me2NMe2Si-
R1CN
R1
R1
N
1 R1 = Me2N-
2 R1 = 1-Piperidyl
3 R1 = Ph
(7-12)
4 R1 = m - Tolyl
5 R1 = p - Tolyl
6 R1 = o - Tolyl
Ph
N
NMe2
N
N
N
N
N
N
N
Ph
Ph
NMe2
Me2N
N
N
N
N
(7)
(8)
Me
(9)
Me
Me
Me
N
N
N
N
N
N
N
N
N
Me
(12)
Me
Me
(10)
(11)
Me
Me
Scheme 1
In order to investigate the catalyst effect of the lithium reagent, the reaction of LiCR2R' with excessive
α-hydrogen-free nitriles R1CN (1-6) and t-BuCN was studied. High yields of triazine compounds (7-11)

HETEROCYCLES, Vol. 65, No. 6, 2005
1427
were obtained. Minor product (12) was formed and there were no triazine products produced from the
reaction of LiCR2R' and t-BuCN. We supposed that the steric effect was the main reason. A proposed
mechanism is given in Scheme 2 as steps i-v: (i) C-C coupling, (ii) silyl migration, (iii) the first time of
N-C coupling and silyl group migration, (iv) the second time of N-C coupling and silyl group
migration, (v) the third time of N-C coupling and silyl migration finally an LiCR2R' elimination to give
triazines.
R1
C
R1
C
R1
C
R1
C
R1CN
i
R
N
R
N
Li
R'R2C
R'RC
Li
R'RC
LiCR2R'
R
N
Li
N
R'RC
iii
ii
Li
R=SiMe3, R'=SiMe2NMe2
R1CN
R1
Li
R'RC
R'RC
R
R1
C
R1
R1
C
R
C
N
N
R'RC
Li
N
R1CN
iv
N
N
N
N
N
LiCR2R'
+
R1
C R1
C
CR1
R1
C
R1
C
v
R1
RN
Li
R1
N
N
(7-12)
Scheme 2 Schematic process of formation of triazine (7-12)
In conclusion, the reaction of organic lithium reagents with various sterically less-hindered
α-hydrogen-free nitriles provides a simple and convenient one-pot process from the readily available
materials to uniformed and mixed 2,4,6-trisubsituted s-triazines in the mild conditions. A new and simple
direct synthetic method for s-triazines was supplied from the reaction catalyzed by lithium complex.
EXPERIMENTAL
All manipulations were carried out under argon, using standard Schlenk technique. Solvents (hexane,
1
13
ether) were distilled from drying agents and degassed with argon prior to use. H-NMR and C-NMR
spectra were recorded on Bruker DKX300 apparatus. Elemental analyses were performed by Vario-III
analyzer.
2,4,6-Tri(dimethylamino)-1,3,5-triazine (7).
Dimethyl cyanamide (0.50 mL, 6.00 mmol) was added by syringe to a stirred solution of
[(SiMe3)2CSiMe2NMe2]Li(TMEDA) (1.10 g, 2.89 mmol) in hexane (ca. 20 mL) at 0 °C. The mixture was
warmed to rt, stirred for 12 h, concentrated and the residue was crystallized from hexane at –30 °C to give
white crystalline pure complex (7) (0.38 g, 91%): mp 170-173 °C; 1H NMR (300 MHz, C6D6): δ =3.09 (s,
13
18H, NMe2); C NMR (75 MHz, C6D6): δ 36.54 (s, NMe2), 167.26 (s, ipso-C of ring). Anal. Calcd for
C9H18N6: C, 51.41; H, 8.63; N, 39.97. Found: C, 51.25; H, 8.75; N, 39.14.

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2,4,6-Tri(1-piperidinyl)-1,3,5-triazine (8).
[(SiMe3)2CSiMe2NMe2]Li(TMEDA) (0.12 g, 0.31 mmol) was added to a stirred solution of
1-piperidinecarbonnitrile (0.55 mL, 4.75 mmol) in hexane (ca. 15 mL) at the rt. After stirring for 6 h, the
solvent was removed in vacuo. The residue was dissolved in ether (ca. 10 mL) and filtered. The filtrate
was concentrated and stored at –30 °C to give colorless crystals (from ether) of compound (8) (0.47 g,
1
89%): mp 215-216 °C; H NMR (300 MHz, CDCl3): δ 4.43 (s, 12H, NCH2), 2.25 (m, 18H,CH2); 13C
NMR (75 MHz, CDCl3): δ=165.98 (ipso-C of triazine ring), 44.59(o-CH2), 26.37, 25.64 (m-CH2 and
p-CH2). Anal. Calcd for C18H30N6: C, 65.42; H, 9.15; N, 25.43. Found: C, 65.40; H, 9.00; N, 25.17.
2,4,6-Tri(phenyl)-1,3,5-triazine (9).
[(SiMe3)2CSiMe2NMe2]Li(TMEDA) (0.50 g, 1.31 mmol) was dissolved in hexane (ca. 20 mL). PhCN
(1.07 g, 10.4 mmol) was injected into the solution at 0 °C and the solution changed into yellow
immediately. The mixture was warmed to rt. After overnight reaction, it gave some white or light yellow
precipitate. The solvent was removed in vacuo. The remained solid was dissolved in ether (ca. 10 mL)
and filtered. The filtrate was concentrated and stored at –30 °C to give pure colorless crystalline (from
ether) triphenyltriazine (9) (0.97 g, 91%): mp 234-235 °C; 1H NMR (300 MHz, CDCl3): δ 8.86 (d, J=6.9
13
Hz, 6H, o-CH), 7.67 (m, 9H, m- and p-CH); C NMR (75 MHz, CDCl3): δ 172.63 (ipso-C of triazine
ring), 137.23 (ipso-C of phenyl), 133.46 (o-CH), 129.93, 129.60 (m-CH and p-CH). Anal. Calcd for
C21H15N3: C, 81.55; H, 4.85; N 13.59. Found: C, 81.52; H, 4.83; N, 13.69.
2,4,6-Tri(m-tolyl)-1,3,5-triazine (10).
[(SiMe3)2CSiMe2NMe2]Li(TMEDA) (0.23 g, 0.6 mmol) was dissolved in hexane (ca. 20 mL).
m-Tolunitrile (0.70 g, 6.0 mmol) was injected into the solution at 0 °C. The mixture was warmed to rt. for
further reaction. After overnight reaction, some light yellow precipitate were formed. The solvent was
then removed in vacuo. The remaining solid was dissolved in ether (ca. 10 mL) and filtered. The filtrate
was concentrated and stored at –30 °C to give light yellow product (from ether) (10) (0.69 g, 98%): mp
1
146-147 °C; H NMR (300 MHz, CDCl3): δ 8.60 (s, 6H, phenyl), 7.49 (m, 6H, phenyl), 2.56 (s, 9H;
m-CH3); 13C NMR (75 MHz, CDCl3): δ 172.64 (ipso-C of triazine ring), 139.25, 137.23 (ipso-C of
phenyl), 134.24, 130.37, 129.50, 127.19 (CH of phenyl), 22.57 (CH3). Anal. Calcd for C21H21N3: C,
82.05; H, 5.98; N 11.96. Found: C, 81.83; H, 6.19; N, 11.81.
2,4,6-Tri(p-tolyl)-1,3,5-triazine (11).

HETEROCYCLES, Vol. 65, No. 6, 2005
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p-Tolunitrile (0.86 g, 7.31 mmol) was injected into the solution of [(SiMe3)2CSiMe2NMe2]Li(TMEDA)
(0.36 g, 0.94 mmol) in hexane (ca. 20 mL). Some light yellow precipitate were formed. The solvent was
removed in vacuo. The remained solid was dissolved in ether (ca. 10 mL) and filtered. The filtrate was
concentrated and stored at –30 °C to give pure light yellow product (from ether) (11) (0.82 g, 96%): mp
283-285 °C; 1H NMR (300 MHz, CDCl3): δ 7.55 (d, J=9.0 Hz, 6H; o-CH of phenyl), 7.25 (t, J=9.0 Hz,
6H; m-CH of pheny), 2.42 (s, 9H; p-CH3); 13C NMR (75 MHz, CDCl3): δ 172.65 (ipso-C of triazine ring),
143.71, 139.30 (ipso-C of phenyl), 132.05, 129.84 (CH of phenyl), 21.85 (CH3). Anal. Calcd for
C21H21N3: C, 82.05; H, 5.98; N 11.96. Found: C, 82.04; H, 6.02; N, 11.94.
2,4,6-Tri(o-tolyl)- 1,3,5-triazine (12).
[(SiMe3)2CSiMe2NMe2]Li(TMEDA) (0.44 g, 1.15 mmol) was dissolved in hexane (ca. 20 mL).
o-Tolunitrile (1.20 g, 10.24 mmol) was injected into the solution at 0 °C. The mixture was warmed to rt
and reacted overnight. Some light yellow precipitate were formed. The solvent was then removed in
vacuo. The remaining solid was dissolved in ether (ca. 10 mL) and filtered. The filtrate was concentrated
and stored at –30 °C to give pure light yellow product (from ether) (12) (0.23 g, 19%): mp 110-111°C;
1H NMR (300 MHz, CDCl3): δ 7.90-7.32 (m, 12H; phenyl), 2.61-2.45 (m, 9H; o-Me); 13C NMR (75 MHz,
CDCl3): δ 175.50 (ipso-C of triazine ring), 142.90, 138.81 (ipso-C of phenyl), 133.59,
131.57,130.98,129.76,128.76 (CH of phenyl), 21.42 (CH3). Anal. Calcd for C21H21N3: C, 82.05; H, 5.98;
N 11.96. Found: C, 81.95; H, 5.89; N, 12.05.
ACKNOWLEDGEMENTS
This work was supported by Natural Science Foundation of China (20472046, D-S.L.) and Science
Foundation of Shanxi Province (20051011, Xia Chen).
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