Regio- and Stereoselective Lithiation of 2,3-Diphenylaziridines: A
Multinuclear NMR Investigation
Vito Capriati,† Saverio Florio,*,† Renzo Luisi,*,† Andrea Mazzanti,‡ and Biagia Musio†
Dipartimento Farmaco-Chimico, UniVersità di Bari, Consorzio InteruniVersitario Nazionale Metodologie e
Processi InnoVatiVi di Sintesi C.I.N.M.P.I.S., Via E. Orabona 4, I-70125 - Bari, Italy, and Dipartimento
di Chimica Organica “A. Mangini”, UniVersità di Bologna, Viale Risorgimento 4,
I-40136 - Bologna, Italy
florio@farmchim.uniba.it; luisi@farmchim.uniba.it
ReceiVed January 11, 2008
The R-lithiation-trapping sequence of trans-N-alkyl-2,3-diphenylaziridines (s-BuLi or s-BuLi/TMEDA),
taking place with a stereochemistry which dramatically depends on the solvent coordinating ability
(inversion of configuration in THF and retention in toluene), has been carefully investigated. 1H,13C, and
7
Li multinuclear NMR investigations at low temperature suggest that two differently configured lithiated
aziridines (monomeric cis-1-Li in THF and dimeric trans-1-Li in toluene) are involved.
Introduction
In a recent paper from our lab, we reported that trans-Nalkyl-2,3-diphenylaziridines undergo exclusively R-lithiation
with a stereochemistry that proved to be solvent-dependent1
(retention of configuration in toluene and inversion in THF).
To explain this solvent-dependent stereochemistry, we assumed
that two differently configured organolithiums could be involved, likely a cis- in THF and a trans-aziridinyllithium in
toluene, although starting from the same diphenylaziridine
(Scheme 1).
To prove the validity of such an assumption, a detailed
multinuclear NMR investigation of the neutral and lithiated
N-propyl-2,3-diphenylaziridine trans-1 (Figure 1) has been
carried out in both THF-d8 and toluene-d8.
Results and Discussion
Lithiation of trans-N-Propyl-2,3-diphenylaziridine 1 in
THF-d8 in an NMR Tube. Aziridine trans-1 in THF-d8 at 195
†
Università di Bari.
‡ Università di Bologna.
(1) Luisi, R.; Capriati, V.; Florio, S.; Musio, B. Org. Lett. 2007, 9, 12631266.
K shows two slowly equilibrating topomers (Figure 1a).2 Upon
treatment of trans-1 with s-Bu7Li, a fast deprotonation occurs,
giving the corresponding R-lithiated intermediate (Figure 1b).
Comparing the 1H NMR spectra of the neutral and lithiated
aziridine, a strong shielding of all the aromatic protons of the
phenyl ring directly bonded to the lithiated carbon atom (CR)
testifies that a change in its electronic distribution has occurred.
A complete assignment of the above protons has been made
possible by a DQF-gCOSY analysis (see the Supporting
Information), disclosing that the two Ho of the lithiated
intermediate have completely different chemical shifts (5.80 and
7.10 ppm) and the Hp proton is less shielded than expected (6.20
ppm).3 The different chemical shifts of the two ortho protons
of the phenyl ring bonded to the CR carbon may be ascribed to
a reduced mobility of this phenyl ring which rotates slowly
around the CR-Ci bond.4
(2) For a definition of topomer, see Binsch, G.; Eliel, E. L.; Kessler, H.
Angew. Chem., Int. Ed. 1978, 10, 570-572.
(3) (a) Peoples, P. R.; Grutzner, J. B. J. Am. Chem. Soc. 1980, 102,
4709-4715. (b) Hogan, A.-M. L.; O’Shea, D. F. J. Org. Chem. 2007, 72,
9557-9571.
10.1021/jo800069k CCC: $40.75 © 2008 American Chemical Society
Published on Web 03/22/2008
J. Org. Chem. 2008, 73, 3197-3204
3197
Capriati et al.
FIGURE 1. 1H NMR (599.944 MHz) spectra of the neutral trans-2,3-diphenylaziridine 1 (a) and the R-lithiated intermediate (b) obtained upon
treatment of trans-1 with s-Bu7Li in THF-d8 at 195 K (• ) unreacted starting material).
SCHEME 1
The other phenyl ring bonded to the Cβ carbon in the lithiated
aziridine displays a less marked shielding of all the aromatic
protons in the range 6.65-6.85 ppm, likely as a result of an
anisotropic effect (Figure 1b).5
1D- and 2D-NOESY experiments, performed on the lithiated
species, provided hints on the relationship between spatially
close protons. In particular, a selective preirradiation of the
proton Hβ (2.32 ppm), within a double pulsed field gradient
spin-echo (DPFGSE-NOE) sequence,6 showed an enhancement
of the NCH2 and the ortho protons (H′o) of the phenyl ring
linked to Cβ (Figure 2). Moreover, NOESY experiments
confirmed that the lone pair on the aziridine nitrogen is probably
in a trans relationship with respect to the CR-Li bond.7 Such
spatial correlations and the upfield shift of the aromatic protons
seem to suggest a cis configuration of the lithiated intermediate,
namely, cis-1-Li. It was also interesting to find, in the
2D-NOESY experiment, that the two pairs of protons Ho and
(4) Kuhen, M.; Gunther, H.; Amoureux, J.-P.; Fernandez, C. Magn.
Reson. Chem. 2002, 40, 24-30.
(5) Hoell, D.; Lex, J.; Mullen, K. J. Am. Chem. Soc. 1986, 108, 59835991.
(6) Neuhaus, D.; Williamson, M. The nuclear OVerhauser effect in
structural and conformational analysis; VCH: New York, 1989; p 264.
3198 J. Org. Chem., Vol. 73, No. 8, 2008
Hm gave exchange peaks, confirming that this phenyl ring rotates
slowly, with respect to the NMR time scale, around the CR-Ci
bond likely due to an increased double bond character (Figure
2).4
Additional information on the nature of the lithiated aziridine
and its aggregation state can be obtained from 13C NMR
analysis.8 The 13C NMR spectrum of the lithiated aziridine in
THF-d8 at 195 K shows sharp and well-resolved signals (Figure
3): the ipso (Ci) and para (Cp) carbons of the phenyl ring,
directly bonded to the CR, are upfield (116.0 ppm) and downfield
(160.7 ppm) shifted, respectively, according to an enhanced π
charge density in this phenyl ring, as found for other benzylic
anions.9
(7) Analogous conclusions have been reported for other lithiated aziridines; see (a) Haner, R.; Olano, B.; Seebach, D. HelV. Chim. Acta 1987,
70, 1676-1693. (b) Hine, J.; Hahn, S. J. Org. Chem. 1982, 47, 17381741. (c) Boche, G.; Lohrenz, J. C. W.; Opel, A. In Lithium Chemistry;
Sapse, A.-M., Schleyer, P. von R., Eds.; Wiley: New York, 1995; p 195.
(d) Bordwell, N. R.; Vanler, R.; Zhang, X. J. Am. Chem. Soc. 1991, 113,
9856.
(8) Bauer, W. In Lithium Chemistry - A Theoretical and Experimental
OVerView; Saspe, A. M., Schleyer, P. von R., Eds.; Wiley: New York,
1995; p 125.
NMR InVestigation on R-Lithiated Aziridines
FIGURE 2. 2D- and 1D-NOESY on R-lithiated aziridine cis-1-Li in THF-d8 at 195 K.
FIGURE 3.
13
C NMR (150.856 MHz) spectra of neutral trans-1 and lithiated aziridine cis-1-Li in THF-d8 at 195 K.
SCHEME 2
C-7Li coupling and 7Li (233.161 MHz) NMR spectrum
of the lithiated aziridine cis-1-Li in THF-d8 at 195 K.
FIGURE 4.
13
Phase-sensitive heterocorrelation experiments (gHSQCDEPT) allow also a complete assignment of each carbon atom
to the corresponding directly bonded proton (see the Supporting
Information). The aziridine carbon atoms are both shifted downfield, but the CR-Li is the most shifted one (78.2 ppm), exhibiting
a quartet with a relative intensity of approximately 1:1:1:1,
consistent with one lithium coupled to a single 13C, and a coupling constant of 1J13C-7Li ) 31.0 Hz (Figure 4).8 Such multiplicity
and the value of this coupling constant suggest that the lithiated
J. Org. Chem, Vol. 73, No. 8, 2008 3199
Capriati et al.
FIGURE 5. 1H NMR spectra of the neutral trans-2,3-diphenylaziridine 1 and the R-lithiated intermediate obtained upon treatment with s-BuLi/
TMEDA in toluene-d8 at 195 K (( ) signals of bonded TMEDA).
aziridine may be monomeric in THF solution with the lithium
ion, likely, tightly bonded to the carbanionic carbon.10
Accordingly, only one signal was observed in the 7Li NMR
spectrum as expected for a single aggregation state. A change
in concentration has no effect, and the above results are
reproducible. Attempts to perform dynamic experiments failed
because, in THF, the lithiated aziridine is unstable above 213
K, undergoing ring opening to give deoxybenzoin 3 presumably
from lithiated enamine 2 (Scheme 2).11
To summarize, all the data above seem to suggest a cis
configuration for the lithiated aziridine in THF and a monomeric
structure. Therefore, excluding that neutral aziridine trans-1
isomerizes to the cis-isomer,1 we must conclude that it is the
trans-1-Li isomer that, as soon as it is generated, isomerizes to
the cis-1-Li counterpart.
Lithiation of trans-N-Propyl-2,3-diphenylaziridine 1 in
Toluene-d8 at 195 K in an NMR Tube. A similar investigation
(9) (a) O’Brien, D. H.; Russell, C. R.; Hart, A. J. J. Am. Chem. Soc.
1976, 98, 7427-7429. (b) Oakes, F. T.; Sebastian, J. F. J. Organomet. Chem.
1978, 159, 363-371. (c) Ahlbrecht, H.; Harbach, J.; Hauck, T.; Kalinowski,
H. O. Chem. Ber. 1992, 125, 1753-1762. (d) Ahlbrecht, H.; Harbach, J.;
Hoffmann, R.; Ruhland, T. Liebigs Ann. 1995, 211-216. (e) Ahlbrecht,
H.; Harbach, J.; Kalinowski, H.-O.; Lang, A.; Maier, G. Chem. Ber./Recl.
1997, 130, 683-686.
(10) Attempts to perform 1H-7Li HOESY experiments [as reported in
(a) Bauer, W. Magn. Reson. Chem. 1996, 34, 532-537; (b) Alam, T. M.;
Pedrotty, D. M.; Boyle, T. J. Magn. Reson. Chem. 2002, 40, 361-365]
failed, likely because of a too short relaxation time of the 7Li nuclei under
the experimental conditions.
(11) (a) Luisi, R.; Capriati, V.; Florio, S.; Ranaldo, R. Tetrahedron Lett.
2003, 44, 2677-2681. (b) Troisi, L.; Granito, C.; Carlucci, C.; Bona, F.;
Florio, S. Eur. J. Org. Chem. 2006, 775-781. (c) O’Brien, P.; Rosser, C.
M.; Caine, D. Tetrahedron 2003, 59, 9779-9791.
3200 J. Org. Chem., Vol. 73, No. 8, 2008
like that just described for neutral and lithiated aziridine trans-1
in THF, has been performed in toluene-d8 at 195 K. Lithiated
aziridine has been generated in an NMR tube by treating a
solution of aziridine trans-1 in toluene (∼0.1 M) with s-BuLi
in the presence of TMEDA, which proved to be crucial for the
deprotonation to occur.
1H NMR spectra of the neutral and lithiated aziridine in this
solvent are reported in Figure 5. Contrary to what was observed
in THF, no strong upfield shift for the aromatic protons of the
phenyl ring directly bonded to the CR has been observed, with
the exception of Hp at 6.95 ppm which was slightly shifted
upfield, as expected.3
The chemical shifts of the aromatic protons in the neutral
and lithiated aziridine (7.0-7.5 vs 6.9-7.5 ppm) suggest that,
in this case, probably there is no deep change in the arrangement
of the phenyl rings. In the upfield part of the 1H NMR spectrum,
four new signals have been detected: gHSQC-DEPT experiments (see the Supporting Information) suggest that the two
broad multiplets at 0.75 and 1.6 ppm are due to the CH2 groups,
whereas the two large singlets at 0.94 and 1.53 ppm are due to
the CH3 groups of TMEDA. The above signals are present in
the spectrum together with the free TMEDA signals at 2.1 ppm
(CH3) and 2.4 ppm (CH2) and do not change their chemical
shifts upon changing the equivalents of TMEDA for the
deprotonation. At 195 K, it seems as though the exchange
between bonded and free TMEDA may occur slowly with
respect to the NMR time scale; raising the temperature up to
225 K, the signals become broader, thus testifying that a
faster exchange is now underway (see the Supporting Information).
NMR InVestigation on R-Lithiated Aziridines
FIGURE 6. 1D NOESY on R-lithiated aziridine trans-1-Li in toluene-d8 at 195 K (( ) bonded TMEDA).
A 1D-NOESY experiment was performed by selective
preirradiation of the benzylic proton Hβ: the corresponding
NOEs interactions are depicted in Figure 6. The enhancement
of the ortho protons (Ho and H′o) of both phenyl rings is a clear
evidence of a trans relationship between them. The above
evidence suggests that, in toluene, the lithiated aziridine exists
as trans-1-Li.
All the above considerations have been confirmed by 13C
NMR and HSQC-DEPT experiments (see the Supporting
Information). In the 13C NMR spectrum (Figure 7), the Ci and
Cp of the phenyl ring directly bonded to the lithiated carbon
atom are downfield (154.3 ppm) and upfield shifted (120.3
ppm), respectively. Signals of the free TMEDA and those of
the bonded TMEDA (two singlets at 56.2 and 56.9 ppm for the
CH2 and two singlets at 43.7 and 46.9 ppm for the CH3) are
also in the range 40-60 ppm.
Lithiated carbon at 73.5 ppm is a poorly resolved septet
(Figure 8b) (1J13C-7Li ) 19 Hz) reminiscent of a dimeric
structure.12,13 The 7Li NMR spectrum shows only one signal
likely due to two equivalent lithium ions linked to a single 13C.
The question that rises at this point is about the structure of
the dimeric lithiated intermediate in toluene (homochiral or
heterochiral) and its “architecture” with reference to how the
TMEDA should strongly solvate such a dimer.
To demonstrate the stereochemistry of trans-1-Li into the
dimeric structure, lithiation of the chiral nonracemic aziridine
(S,S)-trans-1, simply prepared from the commercially available
(R,R)-2 (Scheme 3),14 has been examined.
Lithiation in toluene-d8 of (S,S)-trans-1 gives a species which
shows spectra (1H, 13C, and 7Li NMR) identical to those obtained
from racemic aziridine trans-1, thus supporting the homochiral
hypothesis (see the Supporting Information). Concerning the
structure of the dimer, 1H NMR analysis reveals a 2:1 ratio
between trans-1-Li and bonded TMEDA. Assuming that a slow
exchange between free and bonded TMEDA takes place, the
structure of the lithiated aziridine in toluene-d8 may be the one
depicted in Figure 9A, that is, an endless polymer of homochiral
dimeric units with TMEDA acting as a bridging ligand, as
proposed for other lithiated TMEDA-solvated intermediates.15
However, at present, a dimeric structure with two solvating
molecules of TMEDA cannot be ruled out (Figure 9B).16
Regardless of the solution structure A or B, it can be stated
that in toluene aziridine trans-1-Li should be a trans-configured
homochiral dimer.
The proposed model that accounts for the trans-1-Li to cis1-Li isomerization mentioned above (in THF) could be the one
depicted in Scheme 4. THF should solvate the lithium ion of
trans-1-Li as soon as it is formed, thus promoting a quick
(12) Dynamic reasons or fast quadrupolar-induced relaxation of
the 7Li nucleus could account for the low resolution of the septet-like signal
of CR which, however, is similar enough to the signal simulated (Figure 10) using WINDNMR (Reich, H. J. J. Chem. Educ.
Software 1996, 3D, 2; http://www.chem.wisc.edu/areas/reich/plt/windnmr.
htm).
(13) By using s-Bu6Li (prepared as analogously described for n-Bu6Li;
see Hilmersson, G.; Davidsson, Ö. Organometallics 1995, 14, 912)
to accomplish the deprotonation, no improvement in the resolution of the
CR-6Li signal was observed obtaining a featureless lump (see the Supporting
Information).
(14) Lohray, B. B.; Gao, Y.; Sharpless, K. B. Tetrahedron Lett. 1989,
30, 2623-2626.
(15) Examples of polyamine solvation and TMEDA effects have been
investigated; see (a) Schade, S.; Boche, G. J. Organomet. Chem. 1998, 550,
359-379. (b) Schade, S.; Boche, G. J. Organomet. Chem. 1998, 550, 381395. (c) Collum, D. Acc. Chem. Res. 1992, 25, 448-454. (d) Harder, S.;
Boersma, J.; Brandsma, L.; Kanters, J. A.; Bauer, W.; Pi, R.; Schleyer, P.
v. R.; Schollhorn, H.; Thewalt, U. Organometallics 1989, 8, 1688-1696.
(16) The reaction is extremely slow without TMEDA. All attempts to
generate the lithiated intermediate without TMEDA by transmetalation from
the corresponding tributyltin aziridine were unsuccessful.
J. Org. Chem, Vol. 73, No. 8, 2008 3201
Capriati et al.
FIGURE 7.
13
C NMR spectra of the neutral and lithiated aziridine trans-1 in toluene-d8 at 195 K.
FIGURE 8. Simulated (a) and real (b) 13C-7Li coupling and 7Li NMR
spectrum (c) for the lithiated aziridine trans-1-Li in toluene-d8 at 195 K.
FIGURE 9.
SCHEME 4
SCHEME 3
isomerization17,18 to the thermodynamically more stable cis-1Li that exists as a contact ion pair as suggested by the 13C-7Li
coupling constant found.19,3a
That the solvating property of the medium could promote
such isomerization has been proved with the following experi(17) Assuming a cis relationship between the nitrogen lone pair and the
CR-Li bond, the solvent separated ion pair should suffer destabilizing
interactions which should favor the isomerization (see ref 7).
(18) For examples of interconversion between the contact ion pair and
solvent ion pair, see (a) Reich, H. J.; Sikorski, H.; Thompson, J. L.; Sanders,
A. W.; Jones, A. C. Org. Lett. 2006, 8, 4003-4006; (b) Ruhland, T.;
Hoffmann, R. W.; Schade, S.; Boche, G. Chem. Ber. 1995, 128, 551-556.
3202 J. Org. Chem., Vol. 73, No. 8, 2008
ment performed in an NMR tube. To a solution of trans-1-Li
in toluene-d8, 10 equiv of THF-d8 was added, and the resulting
mixture was spectroscopically monitored: the 13C NMR spectra
before and after the addition of THF are shown in Figure 10.
As can be noted, the Ci and Cp of the phenyl ring directly bonded
to the lithiated carbon (CR) after the addition of THF-d8 show
the same chemical shifts observed for cis-1-Li in THF-d8. After
(19) (a) Hoell, D.; Schnieders, C.; Mullen, K. Angew. Chem., Int. Ed.
Engl. 1983, 22, 243-245. (b) McKeever, D.; Waack, R. J. Organomet.
Chem. 1971, 28, 145-151.
(20) It has been reported that a crown-ether could also promote, in the
flask, the same trans-1-Li to cis-1-Li isomerization (see ref 1).
NMR InVestigation on R-Lithiated Aziridines
FIGURE 10. THF-promoted isomerization of trans-1-Li to cis-1-Li in an NMR tube.
mm autoswitchable broadband gradient (Z) probe and on a customquenching with a proton source, the cis-configured neutral
built triple resonance 5 mm gradient (Z) probe working at the
aziridine has been recovered.20
following frequencies: 599.944 MHz (1H), 150.856 MHz (13C),
and 233.161 MHz (7Li).
Conclusion
Typical Procedure22 for the Preparation of Lithiated AziriIn conclusion, this work reports, for the first time, a detailed
dine 1. In a 5 mm NMR tube equipped with an Omni-Fit valve,
multinuclear NMR investigation of R-lithiated 2,3-diphenyunder Ar, a filtered (celite) solution of commercial s-BuLi (0.06
laziridines. Strong spectroscopic evidence has been produced
mmol) was added, and the solvent was removed under Vacuum.
to prove that R-lithiated-2,3-diphenylaziridines have different
The resulting oil was then precooled to -78 °C and dissolved in
configurations and aggregation states in different solvents (i.e.,
350 µL of solvent (THF-d8 or toluene-d8). In a separate vial, under
a monomeric cis-1-Li in a coordinating solvent such as THF
Ar, 10 mg (0.04 mmol) of the aziridine 1 (with 0.06 mmol TMEDA
for the experiment performed in toluene) was dissolved in 350 µL
and a TMEDA-solvated dimeric trans-1-Li in toluene), giving
of dry solvent (THF-d8 or toluene-d8). This solution was added to
an explanation for the opposite stereochemical course observed
a precooled (-78 °C) 5 mm NMR tube containing the s-BuLi
in the reactions with electrophiles. Moreover, it has been
solution, and the resulting deep yellow mixture was quickly
demonstrated that the solvent polarity determines the nature and
transferred into the NMR probe precooled to -78 °C. All the
configuration of the lithiated intermediates, disclosing that a
experiments were run without spinning.
switch between two differently configured lithiated aziridines
Spectroscopic Data of trans-N-Propyl-2,3-diphenylaziridine
is possible. The knowledge of the structure of these lithiated
1 in THF-d8. Two slowly equilibrating invertomers, dr: 50/50. 1H
intermediates can have an important repercussion on the
NMR (600 MHz, THF-d8, 195 K) δ 0.80 (t, J ) 6.7 Hz, 3 H),
synthetic applications of lithiated aziridines derived from parent
1.30-1.45 (m, 2 H), 2.09-2.16 (m, 1 H), 2.25-2.32 (m, 1 H),
enantiopure aziridines.21 These studies are at present under
3.08 (d, J ) 2.8 Hz, 1 H), 3.28 (d, J ) 2.8 Hz, 1 H), 7.20 (t, J )
investigation.
7.7 Hz, 1 H), 7.27-7.34 (m, 3 H), 7.35-7.40 (m, 4 H), 7.49 (d, J
) 7.2 Hz, 2 H). 13C NMR (150 MHz, THF-d8, 195 K, assignment
Experimental Section
on the basis of HSQC-DEPT experiment) δ 12.5 (CH3), 24.1 (CH2),
45.0 (CH), 52.2 (CH), 54.4 (NCH2), 126.7, 127.4, 128.4, 128.8,
NMR Spectroscopy. All low-temperature multinuclear NMR
128.9,
130.8, 135.2 (Ci), 142.1 (Ci).
experiments were conducted on a spectrometer equipped with a 5
Spectroscopic Data of Aziridine cis-1-Li in THF-d8. 1H NMR
(600 MHz, THF-d8, 195 K) δ 1.00 (t, J ) 7.4 Hz, 3 H), 1.50-1.60
(21) (a) For a special issue on aziridinyl anions, see Oxiranyl and
Aziridinyl Anions as ReactiVe Intermediates in Synthetic Organic Chemistry,
(m, 1 H), 1.61-1.71 (m, 1 H), 1.98-2.05 (m, 1 H), 2.30 (s, 1 H),
Tetrahedron Symposia-in-Print; Florio, S., Ed.; Tetrahedron 2003, 59,
2.68-2.75 (m, 1 H), 5.85 (d, J ) 8.0 Hz, 1 H), 6.20 (t, J ) 7.3
9693-9864. (b) Hodgson, D. M.; Bray, C. D. In Aziridines and Epoxides
in Organic Synthesis; Yudin, A. K., Ed.; Wiley-VCH: Weinheim, Germany,
2006; pp 145-184. (c) Hodgson, D. M.; Bray, C. D.; Humphreys, P. G.
Synlett 2006, 1-22. (d) Luisi, R.; Capriati, V.; Di Cunto, P.; Florio, S.;
Mansueto, R. Org. Lett. 2007, 9, 3295-3298.
(22) The procedure for an experiment with an aziridine/s-BuLi/TMEDA
ratio of 1/1.5/1.5 and a sample concentration of 0.06 M is reported. Ratios
and concentrations can be changed (0.05-0.2 M).
J. Org. Chem, Vol. 73, No. 8, 2008 3203
Capriati et al.
Hz, 1 H), 6.43 (t, J ) 7.3 Hz, 1 H), 6.68-6.72 (m, 3 H), 6.786.85 (m, 3 H), 7.08 (d, J ) 8.0 Hz, 1 H). 13C NMR (150 MHz,
THF-d8, 195 K, assignment on the basis of HSQC-DEPT experiment) δ 13.3 (CH3), 25.0 (CH2, under the solvent’s signal), 55.1
(CβH), 67.3 (NCH2, under the solvent’s signal), 78.2 (CR, q, JC-Li
) 31 Hz), 115.9 (Cp), 123.0, 123.2, 125.4, 126.5, 126.7, 127.4,
146.9 (Ci), 160.5 (Ci). 7Li NMR (233 MHz, THF-d8, 195 K) δ 0.24.
Spectroscopic Data of trans-N-Propyl-2,3-diphenylaziridine
1 in Toluene-d8. Two slowly equilibrating invertomers, dr: 50/
50. 1H NMR (600 MHz, toluene-d8, 195 K) δ 0.89 (t, J ) 6.9 Hz,
3 H), 1.47-1.63 (m, 2 H), 1.94-2.05 (m, 1 H), 2.28-2.38 (m, 1
H), 2.74 (d, J ) 3.1 Hz, 1 H), 3.14 (d, J ) 3.1 Hz, 1 H), 7.007.06 (m, 2 H), 7.07-7.13 (m, 3 H), 7.15-7.21 (m, 1 H), 7.277.32 (t, J ) 7.1 Hz, 2 H), 7.52 (d, J ) 7.3 Hz, 2 H). 13C NMR
(150 MHz, THF-d8, 195 K, assignment on the basis of HSQCDEPT experiment) δ 12.5 (CH3), 23.7 (CH2), 45.0 (CH), 51.6 (CH),
54.1 (NCH2), 126.5, 127.7, 127.9, 130.2, 134.5 (Ci′), 141.3 (Ci).
Spectroscopic Data of Aziridine trans-1-Li-TMEDA Complex in Toluene-d8. 1H NMR (600 MHz, toluene-d8, 195 K) δ 0.75
(m, 2 H, CH2 bonded TMEDA), 0.93 (t, J ) 6.7 Hz, 3 H), 0.94 (s,
3 H, CH3 bonded TMEDA), 1.53 (s, 3 H, CH3 bonded TMEDA),
1.60 (m, 2 H, CH2 bonded TMEDA), 1.66-1.76 (m, 1 H), 1.791.89 (m, 1 H), 2.04-2.09 (m, 1 H, under free TMEDA’s signal),
3204 J. Org. Chem., Vol. 73, No. 8, 2008
2.12 (CH3 free TMEDA), 2.36 (CH2 free TMEDA), 2.85 (s, 1 H),
3.03-3.11 (m, 1 H), 6.95 (t, J ) 7.3 Hz, 1 H), 7.12-7.16 (m, 1
H), 7.17-7.27 (m, 4 H), 7.42-7.50 (m, 4 H). 13C NMR (150 MHz,
THF-d8, 195 K, assignment on the basis of HSQC-DEPT experiment) δ 12.8 (CH3), 25.0 (CH2), 43.7 (CH3 bonded TMEDA), 46.9
(CH3 bonded TMEDA), 56.2 (CH2 bonded TMEDA), 56.9 (CH2
bonded TMEDA), 57.5 (NCH2), 59.8 (CβH), 73.6 (CR, septet-like,
JC-Li ) 19 Hz), 120.3 (Cp), 126.2, 126.3, 126.8, 127.2, 127.4, 147.7
(Ci′), 154.3 (Ci). 7Li NMR (233 MHz, THF-d8, 195 K) δ 1.30.
Acknowledgment. This work was carried out under the
framework of the National Project “Stereoselezione in Sintesi
Organica. Metodologie ed Applicazioni” and supported by the
University of Bari. We thank Prof. Ludovico Lunazzi of the
Department of Organic Chemistry “A. Mangini” of the University of Bologna for useful suggestions.
Supporting Information Available: Experimental procedures,
spectra for trans-1, trans-1-Li, and cis-1-Li, and copy of 1D and
2D NMR experiments. This material is available free of charge
via the Internet at http://pubs.acs.org.
JO800069K