Synthesis and reactivity of 1-substituted 2-fluoro- and 2,2-difluoroaziridines

Article abstract of DOI:10.1021/jo071253e

(Chemical Equation Presented) A straightforward synthesis toward 2-fluorinated aziridines was developed via ring closure of β-fluorinated β-chloroamines, which were obtained via reduction of the corresponding α-fluorinated amides by borane. When 1-benzyl-2-fluoroaziridine was treated with methanol, reaction occurred at the 2-position, giving rise to N-benzyl-2,2-dimethoxyethylamine, while in the case of 1-benzyl-2,2- difluoroaziridine the 3-position was attacked, giving rise to N-benzyl-2-methoxyacetamide. These reactions point to the divergent reactive behavior of monofluoro- and difluoroaziridines.

Full text of DOI:10.1021/jo071253e

ab initio calculations, where it was found that a nucleophilic
induced ring opening of the aziridine ring was predicted to occur
much faster as compared to nonfluorinated analogues.6 In
contrast to 2-chlorinated aziridines, only very few literature data
are available concerning 2-fluoroaziridines, most of which have
been synthesized via carbene or nitrene additions to suitable
imines or olefins.7-11 Moreover, almost no 2,2-difluoroaziridines
are known.12-17 Surprisingly, 2,2-difluoroaziridines could not
be synthesized via difluorocarbene additions to imines, while
analogous reactions using dichloro- or chlorofluorocarbenes gave
rise to the corresponding 2,2-dihalogenated aziridines.18 Very
recently, we developed an efficient pathway for the synthesis
of 3-substituted 2-fluoro- and 2,2-difluoroaziridines via ring
closure of suitable â-halogenated amines.19 However, this
methodology can only be applied for the synthesis of fluorinated
aziridines with substitution at the 3-position. We herein describe
an alternative synthetic method toward â-chloro-â-fluoroamines
and the application of the latter compounds in the synthesis of
new 3-unsubstituted fluorinated aziridines, which can be used
as building blocks for further organic transformations and which
provide experimental proof related to recently reported theoreti-
cal predictions.6 It should be noted that the latter fluorinated
aziridines cannot be synthesized via currently known methods
such as fluorocarbene additions to CdN-bonds or starting from
R-fluorinated imines, as this would imply the use of imines
derived from formaldehyde or fluoroacetaldehyde, respectively,
which cannot be handled readily.
To enable the synthesis of 3-unsubstituted 2-fluoroaziridines
5, suitable â-chloro-â-fluoroamines 3 were required as starting
compounds for ring-closure reactions (Scheme 1). Therefore,
commercially available ethyl chlorofluoroacetate 1 was treated
with primary amines in dichloromethane at room temperature
for 16 h resulting in the corresponding R-chloro-R-fluorocar-
boxylic amides 2. 2-Chloro-2-fluorocarboxylic amides 220,21
were treated with a variety of reducing agents to obtain new
chlorofluoroamines 3. While the use of LiAlH4 or chloroalane
(AlClH2) in THF or diethyl ether at room temperature gave no
reaction or resulted in tarry reaction mixtures when reflux
Synthesis and Reactivity of 1-Substituted
2-Fluoro- and 2,2-Difluoroaziridines
Guido Verniest,† Filip Colpaert, Eva Van Hende, and
Norbert De Kimpe*
Department of Organic Chemistry, Faculty of Bioscience
Engineering, Ghent UniVersity, Coupure Links 653,
B-9000 Ghent, Belgium
norbert.dekimpe@ugent.be
ReceiVed June 15, 2007
A straightforward synthesis toward 2-fluorinated aziridines
was developed via ring closure of â-fluorinated â-chloro-
amines, which were obtained via reduction of the corre-
sponding R-fluorinated amides by borane. When 1-benzyl-
2-fluoroaziridine was treated with methanol, reaction occurred
at the 2-position, giving rise to N-benzyl-2,2-dimethoxy-
ethylamine, while in the case of 1-benzyl-2,2-difluoroaziri-
dine the 3-position was attacked, giving rise to N-benzyl-
2-methoxyacetamide. These reactions point to the divergent
reactive behavior of monofluoro- and difluoroaziridines.
Fluorinated amines have been the subject of considerable
research because these compounds are highly interesting build-
ing blocks for pharmaceutical and agrochemical purposes.1,2 This
increasing interest is a consequence of the special properties of
fluorine to drug design.3 Next to â-fluorinated and perfluorinated
amines, R-fluorinated amines have also been synthesized
previously.4,5 However, R-fluoroamines generally require an
electron-withdrawing group at nitrogen for reasons of stability.
In the case of saturated azaheterocyclic R-fluoroamines, C-
fluorinated aziridines occupy a special place because of the
intriguing combination of a strained ring system with an
R-fluoroamine moiety. Only recently, the profound effect of
fluorine on the reactivity of aziridines was studied by means of
(6) Banks, H. D. J. Org. Chem. 2006, 71, 8089.
(7) Khlebnikov, A. F.; Novikov, M. S.; Shinkevich, E. Y.; Vidovic, D.
Org. Biomol. Chem. 2005, 3, 4040.
(8) Konev, A. S.; Novikov, M. S.; Khlebnikov, A. F. Tetrahedron Lett.
2005, 46, 8337.
(9) Usuki, Y.; Fukuda, Y.; Ilo, H. ITE Lett. Batteries New Technol. Med.
2001, 2, 237.
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(11) Yamanaka, H.; Kikui, J.; Teramura, K.; Ando, T. J. Org. Chem.
1976, 41, 3794.
(12) Zeifman, Y. V.; Ter-Gabrielyan, E. G.; Gambaryan, N. P.; Knun-
yants, I. L. Russ. Chem. ReV. 1984, 53, 256.
(13) Lork, A.; Gard, G.; Hare, M.; Mews, R.; Stohrer, W. D.; Winter,
R. J. Chem. Soc., Chem. Commun. 1992, 12, 898.
(14) Krespan, C. G. J. Org. Chem. 1986, 51, 332.
(15) Petrov, V. A. J. Fluorine Chem. 2000, 106, 25.
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31, 789.
* To whom correspondence should be addressed. Tel: ++32 (0)9 264 59
51. Fax: ++32 (0)9 264 62 43.
† Postdoctoral Fellow of the Research Foundation
Vlaanderen).
- Flanders (FWO-
(1) Welch, J. T.; Eswarakrishnan, S. Fluorine in Bioorganic Chemistry;
John Wiley & Sons: New York, 1991.
(2) Baasner, B.; Hageman, H.; Tatlow, J. C. Organo-Fluorine Com-
pounds. In Houben-Weyl Methods of Organic Chemistry, E10a-c, additional
and supplementary volume to the 4th ed.; Georg Thieme-Verlag: Stuttgart,
1999; Vol. E10a-c.
(3) (a) Kirk, K. L. J. Fluorine Chem. 2006, 127, 1013. (b) Dolbier, W.
R. J. Fluorine Chem. 2005, 126, 157.
(18) Khlebnikov, A. F.; Novikov, M. S.; Kostikov, R. R. MendeleeV
Commun. 1997, 145.
(19) Van Hende, E.; Verniest, G.; Surmont, R.; De Kimpe, N. Org. Lett.
2007, 9, 2935.
(20) Bailey, P. D.; Baker, S. R.; Boa, A. N.; Clayson, J.; Rosair, G. M.
Tetrahedron Lett. 1998, 42, 7755.
(4) Percy, J. M. Sci. Synth. 2006, 34, 379.
(5) Li, Y.; Hu, J. Angew. Chem., Int. Ed. 2005, 44, 5882.
(21) Halpert, J.; Jaw, J. Y.; Balfour, C.; Kaminsky, L. S. Drug Metab.
Dispos. 1990, 18, 168.
10.1021/jo071253e CCC: $37.00 © 2007 American Chemical Society
Published on Web 10/04/2007
J. Org. Chem. 2007, 72, 8569-8572
8569

SCHEME 1. Synthesis of 2-Fluoroaziridines 5
SCHEME 2. Synthesis of 2,2-Difluoroaziridines 9
temperature and for months at -20 °C. Indeed, from the few
available data it could be concluded that fluorinated aziridines
are more stable as compared to the chlorinated or brominated
analogues.23
To extend this synthetic pathway toward the elusive class of
2,2-difluoroaziridines, 2-chloro-2,2-difluoroamides 7 were re-
duced toward â,â,â-trihalogenated amines 8 using borane
dimethyl sulfide (Scheme 2). 2-Chloro-2,2-difluoroamides 7
were prepared by reaction of ethyl chlorodifluoroacetate 6 with
primary amines. Indeed, when the trihaloamines 8 were treated
with LiHMDS in THF, novel 2,2-difluoroaziridines were
isolated after chromatography or distillation. Remarkably, no
sharp signal could be detected in the 19F NMR spectrum of the
2,2-difluoroaziridines 9a-d, although other spectral data (13C
NMR and MS) clearly revealed that the two fluorine atoms were
present. When the 19F NMR spectrum of difluoroaziridine 9d
was recorded at room temperature, a very broad singlet (from
-114.0 to -134.0 ppm, relative to CFCl3) was observed. In
addition, when the 19F NMR spectrum was recorded at elevated
temperatures (60 °C in DMSO-d6), no clear NMR signal
appeared. However, recording the spectrum at -40 °C gave
rise to a splitting of the broad singlet to two doublets at -110.1
and -136.6 ppm, with a coupling constant J ) 83.2 Hz. The
latter chemical shift is in good agreement with spectral data of
3-substituted 2,2-difluoroaziridines, which we described re-
cently.19 The above-described magnetic resonance characteristics
of the fluorine atoms at the 2-position of compounds 9a-d are
caused by the fact that the rate of inversion at the nitrogen atom
(at 25 °C) is comparable to the time scale at which the NMR
spectrum is recorded, while at -40 °C, this inversion rate is
slowed down resulting in two different 19F NMR signals for
both fluorine atoms.16,24 In addition, elemental analysis data of
the crystalline compound 9d (Anal. Calcd for C13H11F2N: C,
71.22; H, 5.06; N, 6.39. Found: C, 71.27; H, 5.06; N, 6.44)
further supported the correct structure assignment.
temperatures were used, the reduction of the amide using an
excess of borane dimethyl sulfide complex in dichloromethane
yielded the desired amines 3a-d after treatment with Pd/C in
methanol. The latter procedure is required to convert the formed
stable amine-borane complex to the free amine,22 which is not
possible by standard treatments with aqueous 2 M HCl or 2 M
NaOH. Analogous reactions using borane in THF or catechol
borane in refluxing toluene did not improve the yield. The
present method provides useful chlorinated â-fluoroamines.
The resulting new amines 3 were treated with various bases
to induce an intramolecular substitution of chlorine. Although
previous results indicated that heating of R-substituted â-halo-
genated amines with K2CO3 in DMSO could be used to
synthesize 3-substituted 2-fluoroaziridines,19 the reaction of
N-benzyl-N-(2-chloro-2-fluoroethyl)amine 3a with K2CO3 at 100
°C yielded the corresponding fluorinated oxazolidinone 4
instead. Probably, the formation of compound 4 is initiated by
a nucleophilic attack of amine 3a across the carbonyl moiety
of CO2 (from K2CO3), followed by ring closure. Experiments
in which 2-fluoroaziridine 5a was heated in DMSO to 100 °C,
in the presence of an excess of K2CO3, mainly yielded starting
material 5a along with decomposition products. This experiment
suggests that the formation of 4 probably does not proceed via
a CO2 insertion into aziridine 5a.
After an evaluation of different bases (KOH in aqueous THF,
LDA, or LiHMDS in THF) to synthesize aziridine 5a, it was
concluded that optimal yields were obtained when LiHMDS
was used in THF at -10 °C. These reaction conditions resulted
in new 1-substituted-2-fluoroaziridines 5a-d which were puri-
fied by column chromatography on silica gel or via distillation.
2-Fluoroaziridines 5 were stable for several days at room
Having in hand this new method for the synthesis of
fluorinated aziridines, a preliminary reactivity study was
(23) Singh, G. S.; D’hooghe, M.; De Kimpe, N. Chem. ReV. 2007, 107,
2080.
(22) Couturier, M.; Tucker, J. L.; Andresen, B. M.; Dube´, P.; Negri, J.
T. Org. Lett. 2001, 3, 465.
(24) Davies, M. W.; Shipman, M.; Tucker, J. H. R.; Walsh, T. R. J. Am.
Chem. Soc. 2006, 128, 14260.
8570 J. Org. Chem., Vol. 72, No. 22, 2007

SCHEME 3. Reaction of Fluoroaziridines 5a and 9a with
Hydrogen Chloride
methoxide under the same reaction conditions as described
above, yielded a complex reaction mixture in which only a small
amount of 2,2-dimethoxyamine 22 could be detected in the 1H
NMR spectrum. However, when the aziridine 5a was simply
heated in methanol in a sealed vessel to 100 °C, a clean
conversion toward N-benzyl-2,2-dimethoxyethylamine 22,28
which is a result of the nucleophilic attack of methanol at the
2-position, was obtained. Also in this case an alternative reaction
pathway (pathway b) is proposed via initial expulsion of a
fluoride anion and reaction of the intermediate azirinium fluoride
23 with methanol. The resulting 2-methoxyaziridine can also
yield in this case dimethoxyamine 22 via a second-order process
or via a first-order reaction by ring opening of aziridine 24 to
25, followed by reaction with methanol.
In conclusion, the ring closure of â-chloro-â-fluorinated
amines has proven to be an efficient and straightforward method
for the synthesis of the elusive class of 2-fluorinated aziridines.
The latter compounds are remarkably stable for months at -20
°C and can easily be used for various reactions without thermal
degradation. Upon treatment of 2-fluoroaziridines with nucleo-
philes, it was observed that reaction occurred at the 2-position,
which is the most electrophilic carbon atom, while in the case
of 2,2-difluoroaziridines, the nucleophilic attack took place at
the 3-position.
performed to study the reaction of the obtained aziridines with
nucleophiles (with and without N-protonation, Scheme 3 and
4). Apart from a very recent study of 3-fluoro-2,2-diphenyl-
aziridines, which were synthesized via fluorocarbene additions
to benzophenone imines, no data on the chemical properties of
fluorinated aziridines have been published.25 The latter study
revealed that 3-fluoro-2,2-diphenylaziridines undergo a ring
opening when reacted with aqueous HCl resulting in 2-hydroxy-
2,2-diphenylacetaldehyde. In order to evaluate the reactivity of
3-unsubstituted difluoro- and monofluoroaziridines, 1-benzyl-
2,2-difluoroaziridine 9a was treated with aqueous 12 M HCl
(Scheme 3). It is proposed that this reaction resulted in a
protonation of the nitrogen atom, followed by an attack of
chloride at the 3-position. After ring opening, the intermediate
R,R-difluoroamine 11 gives rise to N-benzyl-2-chloroacetamide
1226 via an intermediate R-chloroimidoyl fluoride and hydroly-
sis. The same reaction with monofluoroaziridine 5a resulted in
an attack of chlorine at the 2-position after protonation of the
nitrogen atom. Because the reaction conditions using aqueous
12 M HCl yielded amine 3a in very low yield (<10%), hydrogen
chloride gas was bubbled through a solution of aziridine 5a in
CH3CN. This reaction resulted in amine 3a in a better yield
(58%) after basic workup. The difference in reactivity between
di- and monofluoroaziridines 9a and 5a is related to sterical
hindrance in combination with the specific electronic properties
of fluorinated aziridines.
In a second reaction, both aziridines 9a and 9 were treated
with sodium methoxide in methanol (Scheme 4). In the case of
difluoroaziridine 9a, a ring opening can occur, induced by
nucleophilic attack of methoxide at the 3-position (pathway a).
The resulting intermediate 14 is unstable in methanol and results
in the formation of imidate 15, which was easily converted to
2-methoxyacetamide 1627 by hydrolysis. An alternative reaction
mechanism (pathway b) proceeds via an initial expulsion of
fluoride by nitrogen, followed by a nucleophilic attack at the
2-position of the intermediate azirinium ion 17. A second
expulsion of fluoride results in methoxyazirinium species 19
which can undergo either nucleophilic attack of methoxide at
the 3-position in a second-order process or a ring opening toward
intermediate 20 which is subsequently trapped by methanol.
Attempts to react 1-benzyl-2-fluoroaziridine 5a with sodium
Experimental Section
N-Benzyl-2-chloro-2-fluoroacetamide 2a.20 This procedure can
be used as a general procedure for the synthesis of amides 2a-d
and 7a-d. To a solution of 1.00 g (7.12 mmol) of ethyl 2-chloro-
2-fluoroacetate in 25 mL of CH2Cl2 was added 0.76 g (1 equiv,
7.12 mmol) of benzylamine at 0 °C. The cooling bath was removed
and the mixture was stirred at room temperature for 16 h. The
solvents were evaporated in vacuo, and the resulting crude amide
2a was recrystallized from a 9:1 mixture of hexane and diethyl
ether. Yield: 61%. Mp: 56.2-56.7 °C (no literature data re-
ported).20 1H NMR (300 MHz, CDCl3): δ 4.47 (1H, dd, J ) 15.2,
5.8 Hz), 4.52 (1H, dd, J ) 15.2, 5.8 Hz), 6.30 (1H, d, J ) 50.3
Hz), 6.70 (1H, s(b)), 7.25-7.39 (5H, m). 13C NMR (75 MHz,
CDCl3): δ 43.6, 94.1 (d, J ) 256.1 Hz), 2 × 127.9, 128.0, 2 ×
128.9, 136.9, 164.3 (d, J ) 21.9 Hz). 19F NMR (282 MHz,
CDCl3): δ -143.8 (1F, d, J ) 50.3 Hz). IR (KBr): νmax 3305,
1671, 1549, 1059 cm-1. MS ES+ (m/z): 202/204 (M + H+, 100).
Copies of 1H NMR and 13C NMR spectra are included in Chapter
III of the Supporting Information. Experimental details for analo-
gous compounds 2b-d and 7a-d are included in the Supporting
Information.
N-Benzyl-2-chloro-2-fluoroethanamine 3a. N-Benzyl-2-chloro-
2-fluoroacetamide 2a (1.01 g; 5.00 mmol) was dissolved in 25 mL
of CH2Cl2, and subsequently 1.42 mL (3 equiv, 15.00 mmol) of
borane dimethyl sulfide complex was added. The resulting mixture
was stirred at room temperature. After 24 h, a second amount of
1.42 mL (3 equiv) of borane dimethyl sulfide was added, and
stirring was continued for another 24 h. The reaction was quenched
by gently adding 50 mL of aqueous methanol (1:1) while the
reaction temperature was maintained at 25 °C by the use of an ice
bath (exothermic reaction: evolution of hydrogen gas), the mixture
was extracted with dichloromethane (5 × 50 mL). After drying
(MgSO4) and evaporation of the solvent, the obtained crude mixture
was dissolved in 50 mL of methanol and 0.20 g of Pd/C (20 wt %)
was added at 0 °C. The mixture was stirred for 15 h at room
temperature. After filtration of the catalyst and evaporation of the
solvent, amine 3a was purified via column chromatography over a
(25) Konev, A. S.; Novikov, M. S.; Khlebnikov, A. F. Russ. J. Org.
Chem. 2007, 43, 292.
(26) Kushner, S.; Cassell, R. I.; Morton, J.; Williams, J. H. J. Org. Chem.
1951, 16, 1283.
(27) Kramer, B.; Franz, T.; Picasso, S.; Pruschek, P.; Jager, V. Synlett
1997, 3, 295.
(28) Boisbrun, M.; Jeannin, L.; Toupet, L.; Laronze, J.-Y. Eur. J. Org.
Chem. 2000, 3051.
J. Org. Chem, Vol. 72, No. 22, 2007 8571

SCHEME 4. Reaction of Fluoroaziridines 5a and 9a with Sodium Methoxide or Methanola
a Compound 15 could not be obtained in pure form due to hydrolysis (purity 89%).
short plug of silica gel (hexane/EtOAc/Et3N 96/3.9/0.1, Rf ) 0.10).
Yield: 82%. 1H NMR (300 MHz, CDCl3): δ 1.70 (1H, s(b)), 3.07
(1H, ddd, J ) 4.2, 13.8, 21.7 Hz), 3.21 (1H, ddd, J ) 6.1, 13.8,
14.3 Hz), 3.87 (2H, s), 6.20 (1H, ddd, J ) 4.2, 6.1, 50.7 Hz), 7.24-
7.38 (5H, m). 13C NMR (75 MHz, CDCl3): δ 53.3, 55.3 (d, J )
21.9 Hz), 101.6 (d, J ) 242.3 Hz), 127.5, 2 × 128.2, 2 × 128.7,
139.7. 19F NMR (282 MHz, CDCl3): δ -137.8 (1F, dt(b), J )
and 9a-d. To a solution of 0.50 g (2.67 mmol) of amine 3a in 25
mL of dry THF was added 4.00 mL (4.00 mmol, 1.5 equiv) of a 1
M solution of LiHMDS in hexane at -10 °C. The reaction mixture
was stirred at the same temperature for 3 h. After addition of ice-
water to the mixture, the solution was poured in 25 mL of water
and extracted with diethyl ether (3 × 50 mL). After drying (MgSO4)
and filtration of the drying agent, the solvent was evaporated in
vacuo yielding crude 1-benzyl-2-fluoroaziridine 5a. The obtained
aziridine was purified via column chromatography (hexane/EtOAc/
50.7, 18.0 Hz). IR (NaCl): νmax 3300, 1603, 1496, 1454 cm-1
.
MS ES+ (m/z): 188/190 (M + H+, 100). Copies of 1H NMR and
13C NMR spectra are included in Chapter III of the Supporting
Information. Spectral data for amines 3b-d and 8a-d are included
in the Supporting Information.
1
Et3N 98/1.9/0.1, Rf ) 0.13). Yield: 61%. H NMR (300 MHz,
CDCl3): δ 1.47 (1H, d(b), J ) 4.1 Hz), 2.20 (1H, m), 3.44 (1H,
dd, J ) 13.6, 3.0 Hz), 3.72 (1H, dd, J ) 13.6, 1.9 Hz), 4.68 (1H,
ddd, J ) 71.7, 4.1, 1.1 Hz), 7.24-7.36 (5H, m). 13C NMR (75
MHz, CDCl3): δ 32.7 (d, J ) 12.7 Hz), 59.8, 81.7 (d, J ) 237.7
Hz), 127.5, 2 × 128.1, 2 × 128.6, 137.4. 19F NMR (282 MHz,
CDCl3): δ-174.8 (1F, d(b), J ) 71.7 Hz). IR (NaCl): νmax 1454,
1359, 1124 cm-1. MS ES+ m/z: 152 (M + H+, 100). Anal. Calcd
for C9H10FN: C, 71.50; H, 6.67; N, 9.26. Found: C, 71.84; H,
6.90; N, 9.11. Copies of 1H NMR and 13C NMR spectra are included
in Chapter III of the Supporting Information. Spectral data for
amines 5b-d and 9a-d are included in the Supporting Information.
Synthesis of 5-Fluoro-3-benzyloxazolidin-2-one 4. To a solu-
tion of 0.50 g (2.67 mmol) of amine 3a in 10 mL of DMSO was
added 0.74 g (5.34 mmol, 2 equiv) of K2CO3. The heterogeneous
mixture was placed in a preheated oil bath at 100 °C. Stirring was
continued for 2 h. After the reaction mixture was cooled to room
temperature, 20 mL of water was added and extraction was
performed using CH2Cl2 (3 × 50 mL). The organic layer was
washed three times with brine (3 × 25 mL) and dried over MgSO4.
After filtration, the solvent was evaporated, yielding oxazolidinone
4. The crude compound was purified via column chromatography
(hexane/EtOAc/Et3N 98/1.9/0.1, Rf ) 0.42). Yield: 32%. 1H NMR
(300 MHz, CDCl3): δ 3.46 (1H, ddd, J ) 24.6, 11.3, 0.6 Hz),
3.62 (1H, ddd, J ) 35.1, 11.3, 4.9 Hz), 4.49 (2H, s), 6.08 (1H,
ddd, J ) 64.1, 4.9, 0.6 Hz), 7.25-7.41 (5H, m). 13C NMR (75
MHz, CDCl3): δ 47.8, 50.6 (d, J ) 26.5 Hz), 103.3 (d, J ) 233.1
Hz), 2 × 128.1, 128.4, 2 × 129.1, 134.8, 155.4. 19F NMR (282
Acknowledgment. We are indebted to the Research Foun-
dation - Flanders (FWO - Flanders), Ghent University (GOA,
BOF), and Janssen Pharmaceutica (Johnson & Johnson) for
financial support.
MHz, CDCl3): δ-117 (1F, m). IR (NaCl): νmax 1785, 1763 cm-1
.
Supporting Information Available: General experimental
conditions and spectroscopic data for all new compounds. This
material is available free of charge via the Internet at http://
pubs.acs.org.
MS ES+ m/z: 213 (M + NH4+, 100), 196 (M + H+, 15). Copies
1
of H NMR and 13C NMR spectra are included in Chapter III of
the Supporting Information.
1-Benzyl-2-fluoroaziridine 5a. This procedure can be used as
a general procedure for the synthesis of fluorinated aziridines 5a-d
JO071253E
8572 J. Org. Chem., Vol. 72, No. 22, 2007