On the preparation of carbamoylsilanes

Article abstract of DOI:10.1081/SCC-120020211

Various N,N-disubstituted carbamoyltrimethylsilanes can be prepared by the addition of LDA to a mixture of TMSCl and the appropriate formamide in THF at -78°C. Slow (syringe pump) addition of LDA is crucial to obtaining good yields.

Full text of DOI:10.1081/SCC-120020211

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On the Preparation of Carbamoylsilanes
Robert F. Cunico a & Jianxin Chen a b
a Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois,
USA
b Datong Medical College, Datong, China
Published online: 17 Aug 2006.
To cite this article: Robert F. Cunico & Jianxin Chen (2003) On the Preparation of Carbamoylsilanes, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 33:11, 1963-1968, DOI:
10.1081/SCC-120020211
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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 11, pp. 1963–1968, 2003
On the Preparation of Carbamoylsilanes
#
*
Robert F. Cunico and Jianxin Chen
Department of Chemistry and Biochemistry, Northern
Illinois University, DeKalb, Illinois, USA
ABSTRACT
Various N,N-disubstituted carbamoyltrimethylsilanes can be
prepared by the addition of LDA to a mixture of TMSCl and the
appropriate formamide in THF at ꢀ78ꢁC. Slow (syringe pump)
addition of LDA is crucial to obtaining good yields.
Key Words: Carbamoylsilane;
Lithiation; Coupling.
Metalation-silylation;
Amides;
*Correspondence: Robert F. Cunico, Department of Chemistry and Biochemistry,
Northern Illinois University, DeKalb, Illinois, 60115, USA; Fax: 815-753-4802;
E-mail: rfc@marilyn.chem.niu.edu.
#Current address: Datong Medical College, Datong, China.
1963
DOI: 10.1081/SCC-1200201211
Copyright & 2003 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com

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1964
Cunico and Chen
The carbamoylsilane 3a has been shown to exhibit unique reactivity
towards electrophilically-substituted C-H and CꢂC bonds[1] as well as
aldehydic and ketonic C¼O[2] bonds. We previously reported the pre-
paration of 3a from the in situ silylation of the carbamoyllithium 2
derived from formamide 1a, and ascribed this success to the possible
stabilization of this species by chelation.[3] The reaction was carried out
by dropping-funnel addition of LDA to a mixture of 1a and TMSCl over
a 6–7 h period in a dropwise, but stop-and-start fashion. It has now been
found that when the addition is closely monitored such that addition is
continuous at the slowest rate possible under these conditions, addition is
complete after only 4 h at the scale previously reported and results in
significant reductions in the yield of 3a. Upon adopting motorized
syringe addition of LDA over an 8 h period, however, formerly obtained
yields of 3a were reestablished. We then discovered that not only 3a, buta
range of differently N,N-disubstituted carbamoylsilanes, including those
lacking the possibility of chelation (Table 1) could be obtained in
preparatively useful yields by this procedure. This observation signifi-
cantly increases the scope and potential utility of this synthesis.
Several competing reactions may account for the low yields of 3f
and 3g. Nudelman has shown that (at ambient temperatures) the reaction
of lithium dialkylamides with N,N-disubstituted formamides produces a
carbonyl adduct( 4) which collapses to a dialkylamine and a carbamoyl-
lithium 5 (Sch. 1).[4] If this scheme is applicable under present circum-
stances, 4g, obtained by the addition of LDA to 1g, could instead be
expected to preferentially expel the more stable lithium diphenylamide
(Sch. 1, R ¼ Ph). In contrast to the known compatibility of LDA and
TMSCl under the reaction conditions,[5] silylation of the lithium diphenyl-
amide would ensue.[6] Indeed, N,N-diphenylformamide (1g) was found to
afford the silylated derivative N-(trimethylsilyl)diphenylamine instead of
the expected 3g. Alternatively, if 5 (R ¼ Ph) is initially formed, it may be
unstable with respect to expulsion of CO to form lithium diphenylamide.[7]
Parallel behavior may also accountfor the lower yield of 3f observed.

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Carbamoylsilanes
Table 1. Preparation of carbamoyl(trimethyl)silanes.
1965
Carbamoylsilane
R1
CH3
R2
Yield (%)
3a
3b
3c
3d
3e
3f
CH2OCH3
CH2OCH3
CH3
70
64
67
81
77
40
0
CH2OCH3
CH3
CH(CH3)2
CH3
CH3
CH(CH3)2
CH(CH3)Ph
Ph
3g
Ph
Ph
Scheme 1.
EXPERIMENTAL
NMR spectra were obtained at 500 MHz in C6D6 unless otherwise
indicated. IR spectra are of neat samples. All reactions and workups
involving carbamoylsilanes were carried out under strictly anhydrous con-
ditions and an argon atmosphere. A manifold was used for evacuations
and argon refills. Brief exposure of the carbamoylsilanes to air during
transfer procedures was acceptable. Distillations employed a vacuum-
jacketed 100 ꢃ 5 mm nickel-chromium wire spiral-packed column unless

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1966
Cunico and Chen
otherwise noted. n-Butyllithium was obtained from ACROS Organics.
THF was distilled from sodium-benzophenone as needed. ‘‘Anhydrous’’
pentane was obtained from Aldrich Chemicals. A KDS syringe pump
driving a 50 mL gas-tight syringe was used for LDA introduction.
N,N-Dimethylcarbamoyl(trimethyl)silane (3c)
Typical Procedure
LDA was prepared by dropwise addition of n-butyllithium (16.5 mL
of a 2.5 N in hexanes solution, 41 mmol) to a stirred solution of diisopro-
pylamine (6.0 mL, 4.3 g, 43 mmol) in 28 mL THF at ꢀ78ꢁC. After warming
ꢁ
t o 25C, the LDA solution was transferred to the syringe of the syringe
pump and slowly introduced over 8 h to a stirred mixture of N,N-dimethyl-
formamide(3.0 g,41 mmol),chlorotrimethylsilane(7.0 mL,6.2 g,57 mmol)
and 60 mL THF held at ꢀ78ꢁC. The reaction mixture was allowed to
slowly warm to room temperature overnight, and volatiles removed at
10 mm Hg. Pentane (15 mL) was added, and the mixture stirred several
hours, during which time a granular precipitate appeared. The mixture
was filtered (‘‘M’’ glass frit filter tube) under argon, solvent removed
under vacuum, and the residue fractionally distilled to give 4.0 g (67%)
of analytically pure 3c, bp 37–41ꢁC (0.9 mm Hg). IR: 1574, 1377, 1250,
1
1115, 918, 845, 763 cmꢀ1. H NMR: ꢀ ¼ 2.76 (3H, s), 2.54 (3H, s), 0.30
(9H, s). 13C NMR: ꢀ ¼ 185.3, 36.1, 32.0, ꢀ1.2. Anal. calcd for C6H15NOSi:
C, 49.61; H, 10.41; N, 9.64. Found: C, 49.45; H, 10.45; N, 9.50.
N,N-bis(Methoxymethyl)carbamoyl(trimethyl)silane (3b)
From N,N-bis(methoxymethyl)formamide.[8] Bp 48–56ꢁC (0.1 mm Hg).
1
IR: 1678, 1560, 1389, 1251, 1185, 1099, 1072, 919, 847 cmꢀ1. H NMR:
ꢀ ¼ 5.02 (2H, s), 4.50 (2H, s), 3.33 (3H, s), 3.03 (3H, s), 0.34 (9H, s).
13C NMR: ꢀ ¼ 190.0, 78.0, 73.2, 55.5, 54.5, ꢀ1.3. Anal. calcd for
C8H19NO2Si: C, 46.79; H, 9.33; N, 6.82. Found: C, 46.70; H, 9.19;
N, 7.30. HRMS calcd for C8H19NO2Si: 205.1135. Found: 205.1130.
N,N-bis(2-Methylethyl)carbamoyl(trimethyl)silane (3d)
Kugelrohr distillation (110ꢁC, 0.02 mm Hg) afforded an analytically
pure softwhiet solid.

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Carbamoylsilanes
1967
IR: 1671, 1569, 1435, 1369, 1302, 1253, 1208, 1107, 1042, 844 cmꢀ1
.
1H NMR: ꢀ ¼ 3.90 (1H, septet, J ¼ 7 Hz), 3.07 (1H, septet, J ¼ 7 Hz), 1.65
(6H, d, J ¼ 7 Hz), 0.91 (6H, d, J ¼ 7 Hz), 0.33 (9H, s). 13C NMR: ꢀ ¼ 186.0,
48.9, 45.8, 20.83, 20.79, ꢀ1.3. Anal. calcd for C10H23NOSi: C, 59.64;
H, 11.51; N, 6.95. Found: C, 59.41; H, 11.66; N, 6.95.
N-Methyl-N-(1-phenylethyl)carbamoyl(trimethyl)silane (3e)
From N-methyl-N-(1-phenylethyl)formamide.[9] Bp 88–90ꢁC
.
(0.05 mm Hg). IR: 1567, 1384, 1250, 842 cmꢀ1 1H NMR (CD2Cl2):
ꢀ ¼ 7.3–7.5 (5H, m), 6.17 (1H, q, J ¼ 7 Hz), 2.79 (3H, s), 1.52 (3H, d,
J ¼ 7 Hz), 0.376 (9H, s) and 7.3–7.5 (5H, m), 5.22 (1H, q, J ¼ 7 Hz),
2.61 (3H, s), 1.70 (3H, d, J ¼ 7 Hz), 0.379 (9H, s). 13C NMR (CD2Cl2):
ꢀ ¼ 186.2, 141.1, 128.3, 127.3, 126.9, 47.6, 29.7, 15.3, ꢀ1.3 and 186.7, 140.4,
128.6, 127.2, 126.7, 54.8, 25.7, 17.7, ꢀ1.0. Anal. calcd for C13H21NOSi:
C, 66.33; H, 8.99; N, 5.95. Found: C, 66.62; H, 9.08; N, 6.11.
N-Methyl-N-phenylcarbamoyl(trimethyl)silane (3f )
Short path distillation afforded analytically pure material, bp
74–78ꢁC (0.1 mm Hg). 1H NMR: ꢀ ¼ 7.04 (3H, m), 6.90 (2H, d,
J ¼ 6.5 Hz), 3.21 (3H, s), 0.09 (9H, s). 13C NMR (CD2Cl2): ꢀ ¼ 187.2,
144.0, 129.4, 128.4, 127.8, 35.1, ꢀ1.3. Anal. calcd for C11H17NOSi: C,
63.72; H, 8.26; N, 6.76. Found: C, 63.78; H, 8.33; N, 6.71.
ACKNOWLEDGMENT
The authors acknowledge the donors of the Petroleum Research
Fund, administered by the American Chemical Society, for support of
this research.
REFERENCES
1. Cunico, R.F. Tetrahedron Lett. 2001, 42, 2931.
2. Cunico, R.F. Tetrahedron Lett. 2002, 43, 355.
3. Cunico, R.F. Tetrahedron Lett. 2001, 42, 1423.
4. Nudelman, N.S.; Linares, G.E.G. J. Org. Chem. 2000, 65, 1629.
5. Corey, E.J.; Gross, A.W. Tetrahedron Lett. 1984, 25, 495.

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1968
Cunico and Chen
6. Wannagat, U.; Kruger, C.; Niederprum, H.Z. Anorg. Allgem. Chem.
1962, 314, 80.
7. Kambe, N.; Inoue, T.; Sonoda, N. Organic Syntheses; Coffen, D.L.,
Ed., 1993; Vol. 72, 154–161.
8. Schollkopf, U.; Beckhaus, H. Angew. Chem. Int. Ed. Engl. 1976,
15, 293.
9. Berry, M.B.; Blagg, J.; Craig, D.; Willis, M.C. Synlett 1992, 659.
Received in the USA October 20, 2002