Lithiation of diamine ligands to chiral building blocks: Syntheses, selectivities, and lithiated intermediates

Article abstract of DOI:10.1021/om100035g

The direct deprotonation of the chiral nitrogen ligands (R,R)-TECDA (2) and (R,R)-TEMCDA (6) with tert-butyllithium to highly reactive building blocks is reported. The regioselectivity of the lithiation reactions can be explained by the isolated precoordi

Full text of DOI:10.1021/om100035g

1858 Organometallics 2010, 29, 1858–1861
DOI: 10.1021/om100035g
Lithiation of Diamine Ligands to Chiral Building Blocks: Syntheses,
Selectivities, and Lithiated Intermediates
Viktoria H. Gessner and Carsten Strohmann*
€
Anorganische Chemie, Technische Universitat Dortmund, Otto-Hahn-Strasse 6, 44227 Dortmund, Germany
Received January 13, 2010
Summary: The direct deprotonation of the chiral nitrogen
ligands (R,R)-TECDA (2) and (R,R)-TEMCDA (6) with
tert-butyllithium to highly reactive building blocks is reported.
The regioselectivity of the lithiation reactions can be explained
the involved proximity of the relevant groups are necessary
for the viability of the reaction and give way to regioselec-
tive lithiations.4 Thereby, the isolation and structure eluci-
dation of crucial intermediates is a powerful tool to gain
insight into the reaction mechanism. As such, it could be
explained why N,N,N0,N0-tetraethylethylenediamine (TEEDA)
is deprotonated in β-position to the nitrogen, whereas
TMEDA undergoes R-lithiation.5 This selective β-lithiation
attracted our interest, as this methodology provides access to
unsymmetrical lithium amides and their corresponding
amines. Starting from a chiral ethyl-substituted amine even
chiral secondary amines should be accessible, which bear
synthetic potential above all as chiral auxiliaries in organo-
catalysis.6 To evaluate this pathway, the symmetric diamine
(1R,2R)-N,N,N0,N0-tetraethylcyclohexane-1,2-diamine [(R,R)-
TECDA, 2] (Chart 1) seemed to be a suitable starting
system.
by the isolated precoordinated intermediates such as tBuLi
(R,R)-TECDA in combination with computational studies.
3
Introduction
The application of chiral nitrogen ligands in combination
with organolithium compounds is among the most impor-
tant methodologies in asymmetric synthesis, which has been
pioneered by Hoppe and Beak.1 However, recent investiga-
tions have shown that the ligand systems used are not always
inert under the reaction conditions and undergo decom-
position reactions with the lithium base. R-Lithiation and
β-deprotonation reactions of tertiary methyl and ethyl
amines, respectively, have been reported resulting in side
products and the loss of Lewis base.2 Besides this disfavored
decomposition of the ligand, these reactions can also be
employed synthetically such as for the preparation of nitro-
gen ligands or amino-functionalized organometallics. This
was proven by means of chiral R-lithiated (1R,2R)-N,N,N0,
N0-tetramethylcyclohexane-1,2-diamine [(R,R)-TMCDA, 1]
and a series of further di- and triamines (Chart 1).3
Results and Discussion
The diamine (R,R)-TECDA was synthesized by ethylation
of the (1R,2R)-cyclohexane-1,2-diamine with ethyl sulfate.7
The free amine can easily be obtained by racemic resolution
of a mixture of all isomers with L-tartaric acid and sub-
sequent release with KOH.8 To clarify the reactivity of 2
toward deprotonation reactions with alkyllithiums, a solu-
tion of the amine in pentane was treated with an equimolar
amount of tert-butyllithium at -78 °C and warmed to room
temperature. Upon warming, gas formation was observed at
around 0 °C. Subsequent cooling of the reaction mixture to
-78 °C gave crystals of chiral lithium amide 4 in 79% yield as
result of the abstraction of the β-hydrogen atom and follow-
ing elimination of ethene. The same reactivity was observed
with sBuLi and iPrLi.3,4,9
Preliminary studies in our group have proven that these
reactions proceed via precoordinated intermediates of the Lewis
base and the organolithium reagent. This precoordination and
*Corresponding author. E-mail: mail@carsten-strohmann.de.
(1) For asymmetric synthesis with chiral organolithium bases, see:
(a) Hoppe, D.; Hintze, F.; Tebben, P. Angew. Chem., Int. Ed. Engl. 1990,
29, 1422. (b) Kerrick, S. T.; Beak, P. J. Am. Chem. Soc. 1991, 113, 9708.
(c) Whisler, M. C.; Beak, P. J. Org. Chem. 2003, 68, 1207. (d) Coldham, I.;
Copley, R. C. B.; Haxell, T. F. N.; Howard, S. Org. Biomol. Chem. 2003, 1,
1532. (e) Metallinos, C.; Szillat, H.; Taylor, N. J.; Snieckus, V. Adv. Synth.
Catal. 2003, 345, 370. (f) W€urthwein, E.-U.; Behrens, K.; Hoppe, D.
Chem.;Eur. J. 1999, 5, 3459.
Lithium amide 43 crystallizes in the trigonal crystal system,
space group R3 (Figure 1). The highly symmetric molecule
€
€
(2) (a) Kohler, F. H.; Hertkorn, N.; Blumel, J. Chem. Ber. 1987, 120,
2081. (b) Harder, S.; Lutz, M. Organometallics 1994, 13, 5173.
(5) Gessner, V. H.; Strohmann, C. J. Am. Chem. Soc. 2008, 130,
14412.
(3) (a) Schakel, M.; Aarnts, M. P.; Klumpp, G. W. Recl. Trav. Chim.
Pays-Bas 1990, 109, 305. (b) Strohmann, C.; Gessner, V. H. Angew. Chem.,
Int. Ed. 2007, 46, 8281. (c) Karsch, H. H. Chem. Ber. 1996, 129, 483.
(6) For review on proline catalysis, see: (a) List, B. Tetrahedron 2002,
58, 5573. (b) Jarvo, E. R.; Miller, S. J. Tetrahedron 2002, 58, 2481. (c) Notz, W.;
Tanaka, F.; Barbas, C. F.III. Acc. Chem. Res. 2004, 37, 580. (d) Mukherjee, S.;
Yang, J. W.; Hoffmann, S.; List, B. Chem. Rev. 2007, 107, 5471.
(7) Cole, A. P.; Mahadevan, V.; Mirica, L. M.; Ottenwaelder, X.;
Stack, T. D. P. Inorg. Chem. 2005, 44, 7345.
(8) (a) Larrox, J. F.; Jacobsen, E. N. J. Org. Chem. 1994, 59, 1939.
(b) Kizirian, J.-C.; Cabello, N.; Pinchard, L.; Caille, J.-C.; Alexakis, A.
Tetrahedron 2005, 61, 8939.
(9) The formation of 4 via R-lithiation is very unlikely, as no
carbenoid behavior has ever been observed for analogous R-lithiated
compounds: (a) Boche, G.; Marsch, M.; Harbach, J.; Harms, K.; Ledig,
B.; Schubert, F.; Lohrenz, J. C. W.; Ahlbrecht, H. Chem. Ber. 1993, 126,
1887. (b) Strohmann, C.; Abele, B. C. Angew. Chem., Int. Ed. Engl. 1996,
35, 2378.
€
€
(d) Kohn, R. D.; Seifert, G.; Kociok-Kohn, G. Chem. Ber. 1996, 129, 1327.
(e) Bruhn, C.; Becke, F.; Steinborn, D. Organometallics 1998, 17, 2124.
(f) Arnold, J.; Knapp, V.; Schmidt, J. A. R.; Shafir, A. J. Chem. Soc., Dalton
Trans. 2002, 3273. (g) Kamps, I.; Mix, A.; Berger, R. J. F.; Neumann, B.;
StammLer, H.-G.; Mitzel, N. W. Chem. Commun. 2009, 5558. (h) Kamps, I.;
Langlitz, I.; Mix, A.; Neumann, B.; StammLer, H.-G.; Mitzel, N. W. Dalton.
Trans. 2009, 8363. (i) Kamps, I.; Bojer, D.; Hayes, S. A.; Berger, R. J. F.;
Neumann, B; Mitzel, N. W. Chem.;Eur. J. 2009, 15, 11123.
(4) (a) Strohmann, C.; Gessner, V. H. Chem. Asian J. 2008, 3, 1929.
€
(b) Bojer, D.; Kamps, I.; Tian, X.; Hepp, A.; Pape, T.; Frohlich, R.; Mitzel,
N. W. Angew. Chem., Int. Ed. 2007, 46, 3002. (c) Strohmann, C.; Gessner,
V. H. Angew. Chem., Int. Ed. 2007, 46, 4566.
r
pubs.acs.org/Organometallics
Published on Web 03/02/2010
2010 American Chemical Society

Note
Organometallics, Vol. 29, No. 7, 2010 1859
Chart 1
forms a trimeric structure with a central Li-N six-membered
ring, which adopts a chair conformation. The Li-N dis-
tances vary between 1.972(7) and 2.146(7) A and are thus
˚
comparable to those of known lithium amides.10 Due to the
high symmetry of the molecule (C3), the lithium atoms form a
˚
equilateral Li3-triangle with lateral lengths of 3.013(12) A.
The β-lithiation can be employed synthetically (Scheme 1)
such as for the preparation of unsymmetrical chiral ligands.
Lithium amide 4 can be hydrolyzed to amine 5 in 84%
isolated yield, which can afterward be transferred via
Eschweiler-Clarke methylation in 91% yield to (1R,2R)-
N0,N0,N00-triethyl-N00-methylcyclohexane-1,2-diamine [(R,R)-
TEMCDA (6)] (Scheme 1). Contrary to (R,R)-TMCDA
(1), which undergoes selective R-lithiation of its methyl
group, 2 is a rare example of a tertiary amine, which shows
direct β-deprotonation.5
Figure 1. Molecular structure of chiral lithium amide 43. Se-
˚
lected bond lengths [A] and angles [deg]: Li-N(2) 1.972(7),
Li-N(2)00 2.022(7), Li-N(1) 2.146(7), Li-Li0 3.013(12); N-
(2)-Li-N(2)00 131.7(4), N(2)-Li-N(1) 88.6(3), N(2)00-Li-N-
(1) 139.6(4), Li-N(2)-Li0 97.9(4), Li00-Li-Li0 60.0. Symmetry
operations: 0: -xþy, -xþ1, z; 00: -yþ1, x-yþ1, z.
To clarify this reactivity, the intermediate tert-butyl-
lithium adduct was isolated at -78 °C without previous
warming to prevent the decomposition to the lithium amide 4.
Scheme 1
tBuLi (R,R)-TECDA (3) crystallizes out of pentane as
3
monomeric alkyllithium species in the orthorhombic crystal
system, space group P212121, with two molecules in the
asymmetric unit (one of them depicted in Figure 2). Both
˚
molecules show shortened Li-C [2.138(4) and 2.140(4) A]
˚
and Li-N distances [2.087(4) to 2.124(4) A] typical for
monomeric alkyllithiums.11 Such a monomer has also been
observed with isopropyllithium as lithium reagent.11c Both,
iPrLi (R,R)-TECDA and tBuLi (R,R)-TECDA represent
3
3
possible intermediates of the deprotonation reaction of 2.
In these adducts, the ethyl groups are arranged toward the
alkyllithium, bringing the β-hydrogen atoms proximate to
the carbanionic center. This precoordination according to
(10) For lithium amide structures, see: (a) Sun, C.; Williard, P. G.
J. Am. Chem. Soc. 2000, 122, 7829. (b) Neculai, D.; Roesky, H. W.; Neculai,
A. M.; Magull, J.; Herbst-Irmer, R.; Walfort, B.; Stalke, D. Organometallics
2003, 22, 2279. (c) Arnold, P. L.; Mungur, S. A.; Blake, A. J.; Wilson, C.
Angew. Chem., Int. Ed. 2003, 42, 4981. (d) Lappert, M. F.; Slade, M. J.;
Singh, A.; Atwood, J. L.; Rogers, R. D.; Shakir, R. J. Am. Chem. Soc. 1983,
105, 302. (e) Wanat, R. A.; Collum, D. B.; Van Duyne, G.; Clardy, J.; DePue,
R. T. J. Am. Chem. Soc. 1986, 108, 3416. (f) Bernstein, M. P.; Romesberg, F.
E.; Fuller, D. J.; Harrison, A. T.; Collum, D. B.; Liu, Q. Y.; Williard, P. G.
J. Am. Chem. Soc. 1992, 114, 5100. (g) Sakuma, K.; Gilchrist, J. H.;
Romesberg, F. E.; CajthamL, C. E.; Collum, D. B. Tetrahedron Lett. 1993,
34, 5213.
(11) For organolithium structures, see: (a) Nichols, M. A., Williard,
P. G. J. Am. Chem. Soc. 1993, 115, 1568. (b) Strohmann, C.; Strohfeldt, K.;
Schildbach, D. J. Am. Chem. Soc. 2003, 125, 13672. (c) Strohmann, C.;
Strohfeldt, K.; Schildbach, D.; McGrath, M. J.; O'Brien, P. Organometallics
2004, 23, 5389. (d) Strohmann, C.; Dilsky, S.; Strohfeldt, K. Organometal-
lics 2006, 25, 41. (e) Strohmann, C.; Gessner, V. H. J. Am. Chem. Soc. 2007,
the complex-induced proximity effect (CIPE) results in the
selective abstraction of the β-hydrogen atom to
4
(Scheme 1).12
To evaluate the energetic difference between the observed
selective β-lithiation and a potential competing R-deproto-
nation of 2, DFT studies at the B3LYP/6-31þG(d) level were
performed. Starting from tBuLi (R,R)-TECDA (3) the re-
3
action barriers for all possible transition states were calcu-
lated. Due to the chirality of the molecule, two transition
states for the β-lithiation of the ethyl group and two for the
R-lithiaton of the methylene units are possible (Figure 3).
The β-lithiation possesses the lowest reaction barrier, being
€
129, 5982. (f) Gessner, V. H.; Daschlein, C.; Strohmann, C. Chem.;Eur. J.
2009, 15, 3320. (g) Kottke, T.; Stalke, D. Angew. Chem., Int. Ed. Engl.
1993, 32, 580. (h) Strohmann, C.; Gessner, V. H.; Damme, A. Chem.
Commun. 2008, 3381. (i) Strohmann, C.; Seibel, T.; Strohfeldt, K. Angew.
Chem., Int. Ed. 2003, 42, 4531.
(12) (a) Whisler, C. M.; MacNeil, S.; Snieckus, V.; Beak, P. Angew.
Chem., Int. Ed. 2004, 43, 2206. (b) Hartung, C. G.; Snieckus, V. In Modern
Arene Chemistry; Astruc, D., Ed.; Wiley-VCH: Weinheim, Germany, 2002;
pp 330-367. (c) Beak, P.; Meyers, A. I. Acc. Chem. Res. 1986, 19, 356.
preferred by 9 kJ mol-1 compared to the R-deprotonation.
3
The most favored transition state shows a barrier of only
92 kJ mol-1, which confirms the viability of the reaction at
3
temperatures below room temperature. Interestingly, the
trimerization of the product via this transition state would

1860 Organometallics, Vol. 29, No. 7, 2010
Gessner and Strohmann
Scheme 2
R-stannylated amine 11 (Scheme 2). Only traces of the un-
lithiated amine 6 and the secondary amine resulting from
lithiation/elimination of the N(Me)Et group could be detected
(see Supporting Information (SI)). This suggests the formation
of the lithiated intermediates 8 and 9 during the reaction seq-
uence. For insight into this reaction step the intermediate tert-
Figure 2. Molecular structure of tBuLi (R,R)-TECDA (3).
˚
3
Selected bond lengths [A]: C(33)-Li(2) 2.140(4), C(15)-Li(1)
butyllithium adduct, tBuLi (R,R)-TEMCDA (7), was isolated.
3
2.138(4), Li(1)-N(2) 2.096(4), Li(1)-N(1) 2.124(4), Li(2)-N(3)
2.087(4), Li(2)-N(4) 2.0963(4).
This monomer is isomorphous to the presented TECDA adduct 3
due to disorder of the methyl group in the molecule. Yet, this
disorder prevented the formation of crystals of sufficient quality
(see SI). It has to be noted that upon precoordination of the
alkyllithium to the diamine, the nitrogen atom with the methyl
substituent becomes stereogenic. The disorder indicates no specific
preference of one configuration at the stereogenic nitrogen atom.
Computational studies [B3LYP/6-31þG(d)] of the two diastereo-
mers show an energetic difference of only 4 kJ mol-1
.
3
To obtain further information about the observed selecti-
vities of the deprotonation, calculations of the possible transi-
tion states of the R- and the β-deprotonation were performed
with tBuLi (R,R)-TEMCDA (7) as starting point. Due to the
3
unsymmetrical substitution pattern and the chirality of the
molecule, a total of eight R- and six β-lithiations as well as
several conformers have to be considered (see SI).13 Contrary
to (R,R)-TECDA, four of these transition states are in the
range of only 8 kJ mol-1. Thereby, in contradiction to experi-
3
ment the most favored transition state is that of the β-deproto-
nation of the N(Me)Et moiety, which has been observed only in
traces. However, the experimentally observed main product 8
exhibits two transition states of suitable energies disfavored by
only 1 and 8 kJ mol-1. The competing R-lithiation of the
3
methyl group to 9 possesses an 8 kJ mol-1 higher reaction
Figure 3. Optimized transition states and reaction barriers of
the R- and β-deprotonation of 2; [B3LYP/6-31þG(d)].
3
barrier. Overall, considering the statistical favoritism of the
β-lithiation of the NEt2 over the N(Me)Et moiety, the calcula-
tions reflect the formation of the product mixture. Comparable
yield the configuration at the lithiated nitrogen observed in
the molecular structure of lithium amide 43.
to the deprotonation of (R,R)-TECDA, the barrier of 97 kJ mol-1
3
confirms the viability of the reaction.
In conclusion we have described a simple synthetic procedure
to an unsymmetrical chiral amine by direct deprotonations of
tertiary amines. While (1R,2R)-N,N,N0,N0-tetraethylcyclohexane-
1,2-diamine [(R,R)-TECDA, 2] shows selective β-lithiation to
the corresponding lithium amide 4, (1R,2R)-N0,N0,N00-triethyl-
N00-methylcyclohexane-1,2-diamine [(R,R)-TEMCDA (6)] un-
dergoes β-lithiation but also R-lithiation of its methyl group.
We are currently investigating the control of regioselectivity by
variation of the employed deprotonation reagent and the
substitution pattern of the diamine.
Regarding amine 6, R- and β-deprotonation of a methyl
group are possible. Again we mainly observed β-deprotonation
of the diethyl-substituted amino function (NEt2), however,
with the R-lithiation of the methyl group as a side-reaction.
Lithiation of the (R,R)-TEMCDA (7) ligand (same reaction
conditions as for 2) and subsequent trapping with tributyltin
chloride resulted in a 3:1 mixture of amine 10 (formed by
aqueous workup of the interim formed stannazane) and the
(13) Additional calculations were performed on the MP2/6-31G
level, giving the same results as the DFT studies with a barrier of
98 kJ/mol (for further information, see the Supporting Information).

Note
Organometallics, Vol. 29, No. 7, 2010 1861
Experimental Section
6H; N(CH2CH3)2], 1.03-1.18 (m, 4H; CH2), 1.61-1.65 (m, 2H;
CH2), 1.70-1.77 (m, 2H; CH2), 2.23 (s, 3H; NCH3), 2.31-3.64
(m, 8H; CHN þ NCH2CH3). 13C{1H} NMR (100.6 MHz,
CDCl3): δ 14.0 (NCH2CH3), 14.4 [(N(CH2CH3)2], 25.9 þ
26.0 þ 26.8 þ 27.1 (CH2), 36.5 (NCH3), 43.4 [N(CH2CH3)2],
47.8 [(CH3)NCH2CH3], 60.2 [CHN(H)CH2CH3], 62.9
[(CHN(CH2CH3)2]. GC-MS: tR = 4.734 min [80 °C (2 min)-
General Methods. All experiments were carried out under a
dry, oxygen-free argon atmosphere using standard Schlenk
techniques. Involved solvents were dried over sodium and
distilled prior to use. tert-Butyllithium was titrated against
diphenylacetic acid before use. 1H, 13C, and 119Sn NMR spectra
were recorded on Bruker Avance-500 or Avance-400 spectro-
meters at 22 °C if not stated otherwise. Assignment of the signals
was supported by additional DEPT-135 and C,H COSY experi-
ments. All values of the chemical shift are in ppm regarding the
δ-scale. GC/MS analysis were performed on a ThermoQuest
TRIO-1000 (EI = 70 eV); Zebron capillary GC column ZB-1.
10 °C min-1-280 °C (5 min)]; m/z (%): 212 (90) (Mþ), 183 (25)
3
[(M - Me)þ], 112 (100) {[(C6H8(NH2)2]þ}, 86 (83) {[N(C2H5)2-
CH2]þ}.
Synthesis of tBuLi (R,R)-TEMCDA (7). TEMCDA (100 mg,
3
0.47 mmol) was dissolved in 3 mL of n-pentane and cooled
to -50 °C. At this temperaure 0.4 mL (0.53 mmol) of tBuLi
(1.32 M solution in n-pentane) was added and cooled to -78 °C,
giving colorless crystals of the monomeric compound. NMR
Synthesis of tBuLi (R,R)-TECDA (3). (R,R)-TECDA (2)
3
(180 mg, 0.80 mmol) was dissolved in 3 mL of n-pentane and the
reaction mixture cooled to -65 °C. At this temperature 0.6 mL
(1.02 mmol) of tBuLi (1.69 M in n-pentane) was added and cooled
to -78 °C, giving colorless needles of the monomeric compound.
studies of tBuLi (R,R)-TECDA were not possible due to the
3
decomposition of the ligand and the solvent as well as the low
solubility of the compound at low temperatures. For X-ray
crystallography, see SI.
NMR studies of tBuLi (R,R)-TECDA were not possible due to
3
the decomposition of the ligand and the solvent as well as the low
solubility of the compound at low temperatures.
Lithiation and Trapping to 10 and 11. TEMCDA (100 mg,
0.47 mmol) was dissolved in 3 mL of n-pentane, and at -78 °C
0.4 mL (0.53 mmol) of tBuLi (1.32 M solution in n-pentane) was
added, resulting in the formation of the tBuLi adduct. The
reaction mixture was warmed to room temperature, upon which
the formed solid dissolved. After 3 days stirring at rt the mixture
was trapped with 195 mg (0.60 mmol) of tributyltin chloride at
-20 °C and stirred for 1 h at rt. After addition of 20 mL of 2.5 M
HClaq and 20 mL of diethyl ether the mixture was extracted
three times with 2.5 M HClaq. The combined aqueous layers
were afterward set to pH = 11 and extracted with diethyl ether
(3 ꢀ 30 mL). The combined organic layers were dried over
Na2SO4, and the solvent was removed under reduced pressure.
The crude product was investigated by NMR spectroscopy,
showing a 3:1 mixture of amine 10 and the stannylated com-
Synthesis of Lithium Amide 43. (R,R)-TECDA (2) (180 mg,
0.80 mmol) was dissolved in 3 mL of n-pentane and the reaction
mixture cooled to -65 °C. At this temperature 0.6 mL (1.02 mmol)
of t-BuLi (1.69 M in n-pentane) was added, and the mixture warmed
to room temperature and stirred for 4 h. Subsequent cooling to
-78 °C gave colorless plates of the lithium amide after 12 h.
Removal of the remaining solution and washing the crystals with
cooled pentane gave lithium amide 53 in 79% yield. The lithiation
was also achieved with sec-butyllithium and isopropyllithium.
Synthesis of 5. (R,R)-TECDA (3.80 g, 16.8 mmol) was dissolved
in 15 mL of n-pentane, and at -30 °C 20.0 mL (34.0 mmol) of
tBuLi (1.69 M in n-pentane) was added. Upon warming to room
temperature, the formed precipitate of adduct 3 dissolved with gas
evolution at around 0 °C. After stirring for 4 days at room temp-
erature the reaction mixture was trapped with H2O and subseq-
uently extracted with diethyl ether (3 ꢀ 20 mL). The combined
organic layers were dried over Na2SO4, the solvent was removed,
and the residue was purified by Kugelrohr distillation (oven
temperature: 80 °C, 9 ꢀ 10-2 mbar), giving amine 5 as a color-
1
pound 11. Amine 10: H NMR (400.1 MHz, CDCl3): δ 0.98
[t, 3JHH = 7.15 Hz, 3H; N(CH2CH3)2], 1.08 [t, 3JHH = 7.10 Hz,
3H; N(CH2CH3)2], 1.03-1.18 (m, 4H; CH2), 1.68-1.87 (m, 3H;
CH2), 2.03-2.08 (m, 1H; CH2), 2.15 (s, 3H; NCH3), 2.21-2.23
(m, 3H; CHN þ NCH2CH3), 2.40-2.46 (m, 2H; NCH2CH3),
2.69-2.75 (m, 1H; CHNH), 3.15 (bs, 1H; NH). 13C{1H} NMR
(100.6 MHz, CDCl3): δ 13.6 þ 15.3 (NCH2CH3), 21.6 þ 24.6 þ
25.5 þ 31.8 (CH2), 36.1 (NCH3), 41.4 þ 46.9 [N(CH2CH3)], 58.2
þ 66.0 (CHN). GC-MS: tR = 4.329 min [80 °C (2 min)-
1
less oil (yield: 2.79 g, 14.1 mmol; 84%). H NMR (500.1 MHz,
3
CDCl3): δ 0.97 [t, JHH = 7.10 Hz, 6H; N(CH2CH3)2], 1.09
(t, 3JHH = 7.12 Hz, 3H; HNCH2CH3), 1.01-1.23 (m, 4H; CH2),
1.62-1.65 (m, 1H; CH2), 1.70-1.76 (m, 2H; CH2), 2.02-2.06 (m,
1H; CH2), 2.22-2.33 [m, 4H; N(CH2CH3)2 þ CHN], 2.40 þ 2.42
[dq, 3JHH = 7.08 Hz, 2JHH = 11.20 Hz, 1H; N(H)CH2CH3], 2.52
þ 2.55 [dq, 3JHH = 7.34 Hz, 2JHH = 12.90 Hz, 2H; N(CH2CH3)2],
10 °C min-1-280 °C (5 min)]; m/z (%): 184 (45) (Mþ), 155 (13)
3
[(M - C2H5)þ], 126 (55) [(M - 2 C2H5)þ], 112 (22) {[(C6H8-
(NH2)2]þ}, 98 (72) [NC6H12)þ], 72 (100) [C4H10N)þ]. R-Stanny-
1
lated amine (11): H NMR (400.1 MHz, CDCl3): δ 0.80-0.91
(m, 6H; SnCH2), 0.84 (t, JHH = 7.30 Hz, 9H; SnCH2-
2.42-2.65 (br, 1H; NH), 2.71þ 2.73 [dq, 3JHH = 7.23 Hz, 2JHH
=
3
11.27 Hz, 1H; N(H)CH2CH3]. 13C{1H} NMR (125.8 MHz,
CDCl3): δ 15.0 [(N(CH2CH3)2], 15.4 [(H)NCH2CH3], 23.1 þ 24.8
þ 25.9 þ 32.2 (CH2), 41.7 [(H)NCH2CH3], 43.3 [N(CH2CH3)2],
3
CH2CH2CH3), 0.87 [t, JHH = 7.45 Hz, 3H; N(CH2CH3)],
3
0.99 [t, JHH = 7.10 Hz, 6H; N(CH2CH3)2], 1.03-1.18 (m,
4H; CH2), 1.22-1.29 (m, 6H; CH2), 1.40-1.47 (m, 6H; CH2),
1.59-1.82 (m, 4H; CH2), 2.26-3.61 (m, 10H; CHN þ NCH2).
58.6 [CHN(H)CH2CH3], 63.2 [(CHN(CH2CH3)2]. [R]20
=
D
13C{1H} NMR (100.6 MHz, CDCl3): δ 6.6 (SnCH2, 1J117Sn-C
145.2 Hz, J119Sn-C = 152.7 Hz), 13.5 [(NCH2CH3)2], 14.0
=
-140.2 (cyclohexane, 0.375 g/100 mL). Anal. Obsd: C 73.68, H
13.22, N 12.56. Calcd: C 72.66, H 13.21, N 14.12. GC-MS: tR =
1
6.918 min [80 °C (2 min)-10 °C min-1-280 °C (5 min)]; m/z (%):
3
(SnCH2CH2CH2CH3), 14.7 (NCH2CH3), 24.8 þ 26.24 þ 26.9 þ
198 (9) (Mþ), 126 (25) {[(C6H8(NH2)NHCH3]þ}, 112 (44)
{[(C6H8(NH2)2]þ}, 86 (100) {[N(C2H5)2CH2]þ}.
27.8 (CH2), 27.4 (SnCH2CH2, 2J117Sn-C = 26.4 Hz, 2J119Sn-C
=
27.6 Hz), 29.2 (SnCH2CH2CH2, 3JSnC = 9.85 Hz), 36.7 (NCH2Sn),
43.6 [N(CH2CH3)2], 47.9 [N(CH2CH3)], 60.3 þ 61.7 (CHN).
119Sn NMR (111.9 MHz, CDCl3, CDCl3): δ -29.3.
Synthesis of 6. (1R,2R)-N,N,N0-Triethylcyclohexane-1,2-dia-
mine [(R,R)-5] (2.97 g, 15.0 mmol) was suspended in 6 mL of
formic acid, and in portions 7 mL of formaldehyde (40% aquous
solution) was added. Subsequently the reacction mixture was
refluxed for 6 h and stirred for an additional 3 h at rt. After
addition of 2 M NaOHaq to pH 11 the mixture was extracted
with diethyl ether (3 ꢀ 150 mL), and the combined organic
layers were washed with water (2 ꢀ 200 mL) and dried over
Na2SO4. After removal of the solvent the residue was purified
by Kugelrohr distillation (oven temperature: 55-60 °C, 6 ꢀ
10-3 mbar), giving product (R,R)-6 as a colorless oil (2.89 g,
13.6 mmol; 91%). 1H NMR (500.1 MHz, CDCl3): δ 0.98
[t, 3JHH = 7.10 Hz, 3H; N(CH2CH3)2], 0.99 [t, 3JHH = 7.10 Hz,
Acknowledgment. Financial support from the Deutsche
Forschungsgemeinschaft and the Fonds der Chemischen
Industrie(FCI) is highlyacknowledged. V.H.G. thanks the
FCI for a doctoral scholarship.
Supporting Information Available: Crystallographic data as a
CIF file, ORTEP plots, and crystallographic, computational,
and experimental details. This material is available free of
charge via the Internet at http://pubs.acs.org.