Arylallylic lithium compounds, internally versus externally coordinated: Comparison of their structures and dynamic behavior via X-ray crystallography and NMR

Article abstract of DOI:10.1021/ja0765215

A comparison of externally coordinated arylallyllithiums with internally coordinated arylallyllithiums using a combination of X-ray and NMR studies shows that 2-bis(2-methoxyethyl)aminomethyl-1-phenylallyllithium 7, and 2-bis(2-methoxyethyl)aminomethyl-1,3-diphenylallyllithi um 8, are indeed fully internally coordinated with all phenyls endo, and lithium is close to one terminal allyl carbon. By contrast, among the externally coordinated analogs 1-phenylallyl-lithium.(HMPT)₄ 5, and 1-phenylallyllithium.(THF) 6, both phenyls are exo and the proximity of lithium to anion was only detected in compound 6. Lithium-7 NMR clearly identifies the Li(HMPT)₄ ⁺ complex in 5, whereas a ⁷Li{¹H} HOESY experiment reveals ⁷Li to be coordinated to THF in 6 and close to the PhC terminal allyl carbon. Carbon-13 NMR shows that all of the above compounds are fully delocalized despite differences among the sites of lithium and their separations from the anions. Changes in the ¹³C NMR line shapes show that the diphenyl compound 8 undergoes a very fast 1,3-lithium sigmatropic shift, and all of the phenyls in the above compounds undergo fast rotation around their phenyl C_ipso-C_allyl bonds. Barriers to rotation, ΔH^? from NMR line shapes for 5, 6, 7, and 8 respectively, are 19.8, 14.6, 10.2, and 8.9 kcal·mol^-1. The decrease in barriers is clearly correlated with a decrease in separation of lithium from an allyl terminal carbon and implies that especially among the latter three, 6, 7, and 8, lithium is involved in the mechanism for phenyl rotation. This question is discussed.

Full text of DOI:10.1021/ja0765215

Published on Web 03/06/2008
Arylallylic Lithium Compounds, Internally versus Externally
Coordinated: Comparison of Their Structures and Dynamic
Behavior via X-ray Crystallography and NMR
Gideon Fraenkel,* Xiao Chen, Judith Gallucci, and Yulin Ren
Department of Chemistry, Ohio State UniVersity, Columbus, Ohio 43210
Received August 29, 2007; E-mail: fraenkel@mps.ohio-state.edu
Abstract: A comparison of externally coordinated arylallyllithiums with internally coordinated arylallyllithiums
using a combination of X-ray and NMR studies shows that 2-bis(2-methoxyethyl)aminomethyl-1-phenyla-
llyllithium 7, and 2-bis(2-methoxyethyl)aminomethyl-1,3-diphenylallyllithi um 8, are indeed fully internally
coordinated with all phenyls endo, and lithium is close to one terminal allyl carbon. By contrast, among the
externally coordinated analogs 1-phenylallyl-lithium.(HMPT)4 5, and 1-phenylallyllithium.(THF) 6, both phenyls
are exo and the proximity of lithium to anion was only detected in compound 6. Lithium-7 NMR clearly
identifies the Li(HMPT)4+ complex in 5, whereas a 7Li{1H} HOESY experiment reveals 7Li to be coordinated
to THF in 6 and close to the PhC terminal allyl carbon. Carbon-13 NMR shows that all of the above
compounds are fully delocalized despite differences among the sites of lithium and their separations from
the anions. Changes in the 13C NMR line shapes show that the diphenyl compound 8 undergoes a very
fast 1,3-lithium sigmatropic shift, and all of the phenyls in the above compounds undergo fast rotation
around their phenyl Cipso-Callyl bonds. Barriers to rotation, ∆Hq from NMR line shapes for 5, 6, 7, and 8
respectively, are 19.8, 14.6, 10.2, and 8.9 kcal‚mol-1. The decrease in barriers is clearly correlated with a
decrease in separation of lithium from an allyl terminal carbon and implies that especially among the latter
three, 6, 7, and 8, lithium is involved in the mechanism for phenyl rotation. This question is discussed.
Introduction
allylic lithium compounds with tethered potential ligands for
Li+, see for example 4, shown with terminal allyl 13C shifts.
As shown via NMR and X-ray crystallography, externally
coordinated allylithium, 1, with selected 13C shifts, is delocalized
with coordinated lithium normal to the center of the allyl
plane.1,2
NMR and X-ray crystallography confirmed internal coordina-
tion of Li+ and partial delocalization of the allyl moiety. We
proposed that the ligand tether is too short to site lithium normal
to the center of the allyl plane as in 1. Instead, it places lithium
near normal to the allyl plane at one of the allyl termini. From
this aberant site, lithium polarizes the allyl anion to be partly
delocalized.4 It would appear that the electronic structure of a
nominally delocalized carbanion may be influenced by the
relatiVe orientation of the carbanion with respect to counterion,
which is Li+ in this case. We call this effect Site Specific
Electrostatic Perturbation Of Conjugation, SSEPOC. We have
shown how this effect depends on the length of the ligand tether
and the ligand structure.4 One can imagine that alkyl substitution
By contrast unsolVated allylic lithium compounds such as 2
a 3 may be considered to be largely localized because their
NMR spectra so closely resemble those of alkenes.3 Until not
long ago, there were no reports of species whose degrees of
delocalization lie between those of 1 and the system 2 a 3.
However, we have since uncovered such species. They are
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78, C1. (d) Boche, G.; Etzrodt, H.; Marsch, M.; Massa, H.; Baum, G.;
Dietrich, H.; Mahdi, W. Angew. Chem. 1986, 98, 84. (e) Boche, G.;
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Chem. 1985, 50, 4563-4565. (b) Glaze, W. H.; Jones. P. C. J. Chem. Soc.
1969, 1434. (c) Glaze, W. H.; Hanicac, J. E.; Moore, M. L.; Chandpuri, J.
J. Organometal. Chem. 1972, 44, 39. (d) Glaze, W. H.; Hanicac, J. E.;
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51, 13.
9
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J. AM. CHEM. SOC. 2008, 130, 4140-4145
10.1021/ja0765215 CCC: $40.75 © 2008 American Chemical Society

Arylallylic Lithium Compounds
A R T I C L E S
might enhance localization, while conjugating substituents would
stabilize delocalized carbanionic species. In this work, we report
the extent of SSEPOC in the case of internally coordinated
arylallyl lithium compounds. Two examples are considered.
Results for each will be compared to those for its corresponding
externally coordinated analog.
It will be shown that while the externally and internally
solvated arylallyllithiums may be regarded as essentially delo-
calized, internal solvation determines the stereochemistry of
phenyl and has profound effects on dynamic behavior of these
compounds.
δ as endo with phenyl also endo as in the X-ray structure. To
compare the influence of internal coordination in 7 to that of
external coordination on the structure of 1-phenyl-allyllithium,
we have reinvestigated externally solvated 5 and 6.
The 13C shifts we obtained for 5 and 6 are closely similar to
those reported by Ahlbrecht6 and Schlosser.7 Lithium-7 NMR
at 140 K of 1-phenylallyllithium, prepared with four equiv of
HMPT8 in THF solution, consists of an equally spaced 1:4:6:
4:1 quintet. With increasing temperature, this multiplet progres-
sively averages to a single line by 170 K. These observations
establish that lithium is complexed to four HMPTs8 with 2J (7-
Li, 31P) ) 7.7 Hz and that the system undergoes a fast
intermolecular Li+, HMPT coordination exchange by 170 K.9
The two previous reports on NMR of 5 and 6 describe these
preparations as incorporating exo-phenyl,6,7 without supporting
evidence. Our measurement of the C2H, C3H vicinal coupling
constant of 12 Hz puts it half way between the cis and trans
vicinal coupling constants connecting the allyl methylene
hydrogens with the central C2H hydrogen of respectively 9 and
15 Hz. Neither of our preparations of 5 and 6 exhibited NOESY
interactions between either of the allyl methylene protons and
aromatic protons. By contrast, as noted above, the allylic
methylene proton in 7 at 3.776 δ shows a strong NOESY
interaction with aromatic protons. The latter allyl proton is
significantly deshielded compared to the allyl methylene
proton shifts in 5 and 6, due to its proximity to the endo-phenyl
in 7. Taken together, these observations place phenyl exo in 5
and 6.
Results and Discussion
Results of our NMR studies of externally coordinated
phenylallyllithiums 5 and 6 and internally coordinated species
6 and 7 are conveniently summarized in Table 1.
Compounds 5 and 6 were prepared by metalation of allyl
benzene, see 9 f 6 f 5. Compound 12, the immediate precursor
of 7, came from the interconversions 10 f 11 f 12. Compound
16, the precursor of 8, was produced by the sequence 13 f 14
f 15 f 16. Finally, metalation of 12 and 16 produced 7 and
8, respectively.
Below, we first describe the results of structural studies
followed by a comparison of the dynamic rotation behavior
among all compounds studied.
The X-ray crystallography of 7 (see the ORTEP plot in Figure
1) establishes that phenyl is endo and lithium is localized near
C3 of allyl and is also fully coordinated to both methoxy
oxygens and nitrogen of the pendant ligand as well as to oxygen
of one THF molecule, see Figure 1 for numbering. Lithium is
nearly centered and coplanar with respect to the two methoxy
oxygens and C3. The oxygen of THF and nitrogen lie on
opposite sides of the latter plane and are nearly colinear with
lithium, Figure 2.
The allyl bonds of 7 are of different lengths with C2-C3 at
1.432(2) Å, being significantly longer than that of C2-C4 at
1.357(3) Å, which implies a greater π contribution to the C2-
C4 bond versus theC2-C3 bond due to the proximity of Li to
C3.
Given the clear differences in solvation of Li+ in 5, 6, and 7,
it is interesting that all three species exhibit similar allyl 13C
shifts, see the structures with shifts in Table 1. From the
magnitude of these shifts, it would appear that all three
compounds incorporate delocalized anions despite the proximity
of Li+ to C3 in 7 and the clear separation of lithium in Li-
+
(HMPT)4 from the allylic anion in 5. By contrast, while
externally coordinated 17 is clearly fully delocalized9 its
internally coordinated analog 4 was shown to be partly localized
due to the abberant site of Li+ in 4 compared to that in 17.
Lithium lies off the axis normal to the allyl plane at C3 with
a torsional angle C1-C2-C3-Li of 55.64(16)°. Interestingly,
the phenyl plane is twisted anticlockwise with respect to the
allyl plane, see arrow on 7, with the torsional angle C2-C3-
C5-C6 being -17.8(3)°.
Thus, while SSEPOC is significant in 4, aryl-allyl conjuga-
tion renders the effect relatively unimportant in 7.
The X-ray crystal structure of 8 reveals that lithium is fully
coordinated to the tethered ligand, one terminal allyl carbon,
and to oxygen of one THF, see the Ortep plot in Figure 3. Both
methoxy oxygens and one terminal allyl carbon are near
coplanar with centered lithium. Nitrogen lies nearly normal to
the latter plane with oxygen of THF on the opposite side.
Interestingly, structures 7 and 8 are very similar.
The solution NMR data for 7 are consistent with its X-ray
structure. Thus, a 7Li {1H} HOESY5 experiment shows a strong
7
interaction between Li and C3H, as well as with protons on
the methoxy methyls. A NOESY experiment reveals proximity
of the allyl methylene proton at 3.776 δ to the phenyl ortho
and meta protons at, respectively, 6.170 δ and 6.092 δ. This
result assigns the allyl methylene proton of 7 in solution at 3.776
(6) Ahlbrecht, H.; Zimmerman, K.; Boche, G.; Decker, G. J. Organmetal.
Chem. 1984, 262, 1-10.
(4) (a) Fraenkel, G.; Qiu, F. J. Am. Chem. Soc. 1997, 119, 3571-3579. (b)
Fraenkel, G.; Qiu, F. J. Am. Chem. Soc. 1996, 118, 5828-5829. (c)
Fraenkel, G.; Duncan, J. H.; Wang, J. J. Am. Chem. Soc. 1999, 121, 432-
443. (d) Fraenkel, G.; Martin, K. J. Am. Chem. Soc. 1995, 117, 10336-
10344. (e) Fraenkel, G.; Chow, A.; Fleischer, R.; Liu, H. J. Am. Chem.
Soc. 2005, 126, 14995. (f) Fraenkel, G.; Gallucci, J.; Liu, H. J. Am. Chem.
Soc. 2006, 128, 8211.
(5) Bauer, W. NMR of Organolithium Compounds: General Aspects and
Application of Two Dimensional, Hetero-nuclear Overhauser Effect
Spectroscopy (HOESY). In Lithium Chemistry A Theoretical and Experi-
mental OVerView; Sapse, A.-M., Schelyer P.v.R., Eds.; John Wiley and
Sons: Chichester, 1995; Chapter 5, pp 125-172.
(7) Schlosser, M.; Lehmann, R.; Jenny, T. J. Organometal. Chem. 1990, 389,
149-157.
(8) (a) Reich, H. J.; Green, D. P.; Medina, M. A.; Goldenberg, W. S.;
Gundmundsson, B. O.; Dykstra, R. R.; Phillips, N. H. J. Am. Chem. Soc.
1998, 120, 7201. (b) Reich, H. J.; Green, D. P. J. Am. Chem. Soc. 1989,
111, 8729. (c) Reich, H. J.; Borst, J. P. J. Am. Chem. Soc. 1991, 113, 1835.
(d) Reich, H. J.; Borst, J. P.; Dykstra, R. R.; Green, D. P. J. Am. Chem.
Soc. 1993, 115, 8728. (e) Reich, H. J.; Dykstra, R. R. J. Am. Chem. Soc.
1993, 115, 7041.
(9) Kaplan, J. I.; Fraenkel, G. NMR in Chemically Exchanging Systems;
Academic Press: New York, 1980; Chapters 5 and 6.
9
J. AM. CHEM. SOC. VOL. 130, NO. 12, 2008 4141

A R T I C L E S
Fraenkel et al.
Table 1. Compounds 5, 6, 7 and 8. Proposed Structures with 13C
and (1H) Chemical Shifts, δ Scale, J in Hz
Figure 1. ORTEP diagram of compound 7. Selected bond distances, Å
and angles °: C2-C3 1.432(2), C2-C4 1.357(3), C3-Li 2.359(4), C4-
C2-C3 130.69(17), C1-C2-C3-Li 55.64(16), C2-C3-C5-C6-17.8-
(3).
Figure 2. Coordination arrangement around lithium in 7.
Figure 3. ORTEP diagram of compound 8. Most hydrogen atoms have
been removed for clarity; selected bond distances, Å and angles °: C1-
C2 1.382(2), C2-C3 1.416(2), Li-C3 2.370(3), C1-C2-C3 130.92(12),
C4-C2-C3-Li 54.92(12), C2-C3-C17-C18-15.3(2), C2-C1-C11-
C16-14.8(2).
Both phenyls in 8 are endo with each phenyl rotated with
respect to the allyl plane by -15.3(2)° (C2-C3-C17-C18)
and -14.8(2)° (C2-C1-C11-C16) at C3 and C1, respectively.
See arrows on the structure in Table 1. Lithium is closest to
one allyl terminus, C3 with the C4-C2-C3-Li torsional angle
of 54.92(12)° (Ortep numbering). Due to the proximity of Li+
to one terminal allyl carbon C3, the C2-C3 bond of 1.416-
(2)Å is slightly longer than the C1-C2 bond of 1.382(2)Å.
The solution NMR data for 8 are consistent with the X-ray
crystallographic structure and also reveal some interesting
dynamic effects. Thus, the single narrow resonance at 90.4 δ,
observed at 290 K and assigned to both terminal allyl carbons,
a n-BuLi, hexanes, THF, -10 °C. b HMPT. c (CH3OCH2CH2)2NH. d NaH,
DMSO, 24h vV. e Ph3P+CH2Ph Cl- 0 °C. f n-BuLi, Et2O, hexanes.
g PhCh2MgCl, THF, -10 °C. h NaH, DMSO, 80 °C. i Ph3P+CH2Ph Cl-,
RT. j n-BuLi, Et2O.
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4142 J. AM. CHEM. SOC. VOL. 130, NO. 12, 2008

Arylallylic Lithium Compounds
A R T I C L E S
Table 2. Activation Parameters for Phenyl Rotation
broadens with decreasing temperature and disappears into the
baseline by 180 K. This is most likely the result of a fast lithium
1,3 sigmatropic shift which effectively inverts the configuration,
see eq 1.
1
cpd
∆
Hq kcal
‚
mol-
∆
Sq eu
5
6
7
8
19.8 ( 1.5
14.6 ( 1.0
10.2 ( 0.8
8.9 ( 0.7
+22.7 ( 4
+11.7 ( 2
-2.5 ( 0.5
-8.4 ( 1.5
averages the individual ortho and meta carbon shifts of the two
phenyls. With increasing temperature, the two latter doublets
average to single lines at their respective centers. Activation
parameters for overall rotation of both phenyls are listed in
Table 2.
Similar effects have been observed among other internally
coordinated allylic lithium compounds that are symmetrically
substituted as well as unsubstituted.4
Inspection of Table 2 reveals that decrease of the ∆Hq values
for phenyl rotation follows increasing proximity of Li+ to the
carbanion in the order 5, 6, 7, and 8, where in the last two
structures, the Li-C3(-Ph) separations are similar. This implies
that lithium participates in the mechanism of phenyl rotation at
least for 6, 7, and 8. Such an effect would be minimal in the
A 7Li {1H} HOESY experiment at 300 K of 8 shows strong
7
interactions of Li with both terminal allyl CH’s and to the
hydrogens of both methoxyl methyls. This confirms that the
X-ray structure also prevails in solution.
+
The structure and behavior of internally coordinated 1,3-
diphenylallyllithium 8, is entirely different from its externally
solvated analogs. Thus, in Hoppe’s X-ray structure of 1,3-
diphenylallyllithium‚sparteine, both phenyls are exo and are
coplanar with the allyl framework, and the C-C allyl bond
lengths, at 1.380 Å and 1.392 Å, are almost the same.10 This
implies that the latter structure is slightly more delocalized
than 8.
In addition, Boche’s solution NMR studies of 1,3-dipheny-
lallyllithium show it to consist of an equilibrium mixture of
interconverting isomers 1,3-endo, exo-18, and 1,3-exo, exo-19,
see eq 2, with the latter predominating at lower temperatures.11
case of 5 due to the large separation of lithium in Li(HMPT)4
from the carbanion. Thus, the barrier to phenyl rotation in 5
should be regarded as that of a carbanion that is well-separated
from and unperturbed by lithium. By contrast, in the case of 6,
7, and 8, the proximity of Li+ to phenyl bound allyl carbon
may well facilitate phenyl rotation. Thus, we propose that
developing increase in the Li....CR covalency would promote
tetrahedral stereochemistry at CR, thus decoupling the conjuga-
tion between phenyl and allyl. This would provide a lower
energy path to phenyl rotation in 6, 7 and 8 compared to the
“free” anion in 5. In this model phenyl rotation in 6, 7, and 8
is chemically driven. An illustration depicting the proposed
transition state for phenyl rotation in 7 is shown as 20.
Analysis of changes among the proton NMR line shapes
provided the thermodynamic and activation parameters for the
18 a 19 interconversion. These are listed below (eq 2).
The aromatic 13C NMR line shapes of compounds 5, 6, 7,
and 8 undergo changes with temperature reflective of the
dynamics of rotation of phenyls with respect to the allyl planes.
Thus, at low temperature, the 13C NMR of the ortho and meta
carbons of 5, 6, and 7 each give rise to a 1:1 doublet, whereas
resonances for the ipso and para carbons consist of a single
sharp line each. With increasing temperature above 200 K, the
latter doublets progressively average to single lines at their
respective centers, the ipso and para resonances remaining
unchanged. Line shape analysis provides the activation param-
eters for phenyl rotation listed in Table 2.
Transition states for phenyl rotation such as 20 should also
apply to 8 and, to a lesser extent, to externally coordinated 6.
The latter also showed proximity of Li+ to carbon bound phenyl.
Similar transition states to 20 have been proposed in studies
of rotation of allyllithium12 and of benzylic lithium com-
pounds.13
Concluding Remarks
NMR and crystallographic studies of a variety of arylallyl-
lithiums, both internally coordinated 7 and 8, and externally
coordinated 5 and 6, and of the published equilibrium system
18 and 19 show all to be substantially delocalized despite wide
variations in the separations of lithium from the anions. All
phenyls within internally coordinated 7 and 8 are endo, whereas
external coordination of 5 and 6 largely favors the exo phenyl
structure. Endo stereochemistry minimizes repulsion between
the pendant ligand and the substituent phenyl, whereas allyl
delocalization is common among 5, 6, 7, and 8, their dynamic
In the case of 8 at 200 K, both phenyls together give rise to
two 1:1 13C NMR doublets, one for the ortho carbons and a
second one for the meta carbons, the result of slow rotation of
phenyls under conditions of the fast 1,3-sigmatropic shift which
(10) Marr, F.; Fro¨hlich, R.; Hoppe, D. Tetrahedron Asym. 2003 2002, 13, 2587-
2592.
(11) (a) Boche, G.; Schneider, R. Tetrahedron Lett. 1976, 40, 3657-3660. (b)
Boche, G.; Buckl, K.; Martens, D.; Schneider, D. R. Liebigs Ann. 1980,
1135-1171.
(12) Clark, T.; Ronde, C.; Schleyer, P.v.R. Organometallics 1983, 2, 1344-
1351.
(13) Fraenkel, G.; Geckle, M. J. J. Am. Chem. Soc. 1980, 102, 2869.
9
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A R T I C L E S
Fraenkel et al.
Bis(2-methoxyethyl)aminoacetone, 11. A mixture of chloroacetone
(18.5 g, 0.2 mol) bis(2-methoxyethyl)amine (26.7 g, -0.2 mol)
triethylamine (40.4 g, 0.4 mol) and 100 mL acetone was refluxed for
4 h. The solvent was removed in vacuum, and the residue was treated
with 200 mL water which was extracted with chloroform three times
(150 mL × 3). The combined organic phase was dried with MgSO4.
The solvent was removed in vacuum and the residue was distilled bp
65 °C- 68 °C/10 Torr, to give 32 g of the title compound in 85.7%
yield. 1H NMR, CDCl3: 3.332 (t, 4H, (OCH2)2), 3.184 (s, 6H, (OCH3)2),
2.720 (t, 4H, (NCH2CH2O)2), 1.98 (s, CH3CdO). 13C NMR: 208.91,
71.92, 66.11, 58.92, 54.03, 27.43.
behavior varies substantially. Thus, their barriers to phenyl
rotation in 5, 6, 7, and 8 around their Cipso-Callyl bonds decrease
substantially with decreasing separation of lithium from the
C-phenyl carbon, see Table 2. It is concluded that at least for
6, 7, and 8, which may be regarded as contact ion pairs, lithium
is involved in the mechanism for phenyl rotation. The barrier
+
in 5 is ascribed as that of the anion since the Li(HMPT)4
complex keeps the Li+ and the anion well-separated.
Compound 8 is also subject to an unusually rapid 1,3-lithium
sigmatropic shift, which averages the 13C shifts of the terminal
allyl carbons, even at low temperature.
3-(Bis(2-methoxyethyl)amino)-2-methyl-1-phenylpropene, 12. So-
dium hydride (1.8 g (60% in mineral oil), 0.05 mol) was introduced
into 50 mL DMSO and the mixture was heated to 80 °C for 1 h. After
cooling, the resulting solution with an ice bath, a suspension of
triphenylbenzylphosphonium chloride (17.5 g, 0.045 mol) in 120 mL
THF was added, and the mixture was stirred for 1.5 h at rt. Then, under
an argon atmosphere, to this mixture was added bis(2-methoxyethyl)-
amionacetone and the mixture was refluxed for 24 h. The THF was
removed under vacuum, and 40 mL of water was added. This mixture
was extracted three times with 50 mL ether. The combined organic
phases were washed once with brine and dried with MgSO4. After
removal of solvent, the residue was distilled bp (117-121 °C/0.6 Torr),
giving 6.3 g of the title compound with Z/E ) 1/4 as determined with
proton NMR. Proton NMR CDCl3: 7.22-7.05 (m, 5H, Ph), 6.358 (s,
1H, CdC-H), 3.411 (t, 4H, (OCH2)2, E), 3.307 (t, 4H, (OCH2)2 Z),
3.260 (s, OCH3), 2.670 (t, 4H, NCH2CH2, E), 2.525 (t, 4H, NCH2-
CH2, Z), 1.859 (s, CH3, Z), 1.818 (s, CH3, E).
Experimental Section
1-Phenylallyllithium‚(HMPT)4, 5. An NMR tube was flame-dried
under vacuum and then charged with 1-phenylallyllithium THF complex
(40 mg) under argon. After that, the NMR tube was cooled to -100
°C. Then, HMPT (107.52 mg) was added before it was transferred to
a high vacuum line (10-6 Torr) trapped with liquid nitrogen. Volatile
impurities were pumped out into a liquid nitrogen trap. After 3 h, THF-
d8 (0.5 mL) was vacuum transferred into the NMR tube cooled by a
liquid nitrogen bath. Under high vacuum, the NMR tube was sealed
with a small hot flame. The ratio of allyl‚Li/HMPT was 1/5.5. NMR
data are summarized in Table 1.
1-Phenylallyllithium‚(THF)8, 6. To a solution of 1-phenylpropene
(709 mg, 6.0 mmol) in 6 mL of THF was added a solution of
n-butyllithium in hexanes (4.06 mL, 1.6 M, 6.5 mmol) at -10 °C. The
mixture was stirred at room temperature for 24 h and was then cooled
to -78 °C. Then solvent was removed in vacuum to give a gel-like
material. Pentane (7 mL) was added, and the mixture was stirred for 2
h. The mixture was then cooled to -78 °C, and the solvent was removed
with a syringe. After that, a 7-mL portion of pentane was added with
stirring until a yellow solid formed. The solvent was removed, and the
yellow solid was washed three times with 6 mL pentane. An NMR
tube was flame-dried under vacuum and then charged with 40 mg
product before it was transferred to a high vacuum line (10-6 Torr)
trapped with liquid nitrogen. Volatile impurities were pumped out into
a liquid nitrogen trap. After 3 h, THF-d8 (0.5 mL) was vacuum
transferred into the NMR tube cooled by a liquid nitrogen bath. Under
high vacuum, the NMR tube was sealed with a small hot flame. NMR
data are summarized in Table 1.
2-(Bis(2-methoxyethyl))aminomethyl)-1-phenylallyllithium, 7. A
25-mL Schlenk tube was charged with 3 mL dry diethyl ether and
compound 12 (394.5 mg, 1.5 mmol). After cooling to -78 °C
n-butyllithium (0.94 mL, 1.6 M in hexanes, 1.5 mmol) was added by
syringe. A red solid formed immediately. After warming the mixture
to rt, 3 mL THF was added. The solution was stirred at rt for 2 h.
Solvent was removed under vacuum, and the residue was recrystallized
from ether/THF to give a red solid. An NMR tube was flamed out
under argon and loaded with 54 mg of the title compound. Volatile
components were removed under high vacuum. After pumping for 3
h, 0.5 mL THF-d8 was vacuum transferred into the NMR tube, and the
latter was sealed off with a small hot flame while frozen and under
vacuum. NMR data are summarized in Table 1.
Ethyl-bis(2-methoxyethyl)aminoacetate, 14. A mixture of bis(2-
methoxyethyl)amine (24.5 g, 0.2 mol), ethyl chloracetate (40.4 g, 0.4
mol), triethylamine (40.4 g, 0.4 mol) and 100 mL of ethanol was
refluxed for 12 h. Solvent was removed in vacuum and 150 mL water
was added. The aqueous phase was extracted with chloroform, 3 ×
150 mL, and the combined organic phase was dried with MgSO4.
Distillation at bp 70 °/0.05 Torr gave 36.7 g of the title compound in
83.8% yield: 1H NMR, CDCl3: 3.981 (g, 2H, CH2CH3), 3.324 (s, 2H,
NCH2CdO), 3.352 (t, 4H, (OCH2CH2)2), 3.161 (s, 6H, (OCH3)2), 2.823
(t, 4H, (CH2CH2N)2, 1.121 (t, 3H, CCH3). 13C NMR: 172.04, 71.86,
60.50, 59.09, 56.36, 54.43, 14.66.
1-Bis(2-methoxyethyl)amino-3-phenylpropanone, 15. Benzylmag-
nesium chloride prepared from benzyl chloride (10.1 g, 0.08 mol) and
magnesium (2.1 g, 0.037 g/atom) in 80 mL THF was added dropwise
at -10 °C to 14 (8.1 g, 0.037 mol) in 80 mL diethyl ether. After the
reaction mixture was stirred for 2 h at rt, it was cooled with an ice
bath and carefully treated with 100 mL of water. After acidification to
pH 6 using 15% HCl the aqueous phase was extracted three times with
50 mL ether. The combined organic phase was washed with 100 mL
water and then dried with MgSO4. Removal of solvent followed by
vacuum distillation bp 125-127 °C/0.1 Torr gave 8.3 g of the title
1
compound in 83.8% yield. H NMR, CDCl3: 7.0-7.2 (m, 5H, Ph),
3.63 (s, 2H, CH2Ph), 3.423 (s, 2H, CH2CdO), 3.294 (t, 4H, (OCH2)2),
3.167 (s, 6H, (OCH3)2), 2.686 (t, 4H, N(CH2CH2)2. 13C NMR: 208.34,
137.13, 135.80, 129.93, 129.04, 127.32, 71.94, 64.43, 58.81, 55.11,
47.60.
2-(Bis(2-methoxyethyl)aminomethyl)-1,3-diphenylallyllithium, 8.
Butyllithium (1.01 mL, 1.6 M, 1.62 mmol) in hexane was syringed
into a 20-mL Schlenk tube previously charged with 3 mL diethyl ether
and 16 (0.55 g, 1.62 mmol) cooled to -78 °C, all under an atmosphere
of argon. The solution was stirred at rt for 2 h. Solvent was removed
in vacuo to yield a red solid, the title compound, which was then
recrystallized from diethyl ether/THF. An NMR tube loaded with 69
mg of 8 was transferred to a high vacuum line and volatile impurities
were pumped at 10-6 Torr, over 3 h, into a trap cooled with liquid
nitrogen. Then, THF-d8 was vacuum transferred into the NMR tube,
which was then sealed off under high vacuum. NMR data are
summarized in Table 1.
Z- and E-1,3-Diphenyl-2-bis(2-methoxyethyl)aminomethylpro-
pene, 16. Sodium hydride (1.2 g, (60% in mineral oil), 0.033 mol)
was introduced into 20 mL of redistilled DMSO, and the mixture was
heated at 80 °C for 1 h and then cooled to room temperature. A
suspension of triphenylbenzylphosphonium chloride (11.66 g, 0.033
mol) in 120 mL of THF was then added to the DMSO solution, and
the mixture was stirred for 1.5 h at rt. Then, ketone 15 (7 g, 0.26 mol)
was added under argon, and the mixture was refluxed for 24 h. The
THF was removed under vacuum, 30 mL of water was added and the
mixture was extracted three times with ether, 50 mL each. The
combined organic phase was washed with brine once and then dried
with MgSO4. After purification by column chromatography 6.8 g of
9
4144 J. AM. CHEM. SOC. VOL. 130, NO. 12, 2008

Arylallylic Lithium Compounds
A R T I C L E S
the title product mixture mixture (Z∼30E) was obtained in 76.9% yield.
1H NMR, CDCl3: 7.09-7.3 (m, 10H, Ph), 6.484 (s, 1H, -C-H), 3.665
(s, 2H, CH2Ph), 3.151 (s, 6H, (OCH3)2), 3.117 (s, 2H, -C-CH2N),
2.534 (t, 4H, NCH2CH2O)2, Z∼30E by NMR. 13C NMR: 141.91,
140.42, 137.70, 129.93, 129.39, 129.17, 128.24, 126.41, 126.01, 71.19,
58.71, 53.77, 53.32, 41.86.
Newman Chair of Chemistry. We thank Dr. Charles Cottrell,
Central Campus Instrumentation Center, for untiring technical
assistance.
Supporting Information Available: NMR and crystallo-
graphic data (CIF format). This material is available free of
charge via the Internet at http://pubs.acs.org.
Acknowledgment. This research was generously supported
by the National Science Foundation and in part by the M. S.
JA0765215
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J. AM. CHEM. SOC. VOL. 130, NO. 12, 2008 4145