Chemistry of N-substituted 2,2-difluoro-3,3-bis (trifluoromethyl)aziridines

Article abstract of DOI:10.1016/S0022-1139(00)00295-5

Variety of N-Aryl and N-alkyl-2,2-difluoro-3,3-bis(trifluoromethyl)aziridines are prepared by reaction of the corresponding imines of hexafluoroacetone with difluorocarbene generated by thermolysis of hexafluoropropylene oxide. Results of reaction of N-aryl-2,2-difluoro-3,3-bis(trifluoromethyl)-aziridines with CsF, CF₃SO₃H, HF and thermal rearrangement are presented.

Full text of DOI:10.1016/S0022-1139(00)00295-5

Journal of Fluorine Chemistry 106 (2000) 25±34
Chemistry of N-substituted 2,2-di¯uoro-3,3-bis
(tri¯uoromethyl)aziridines
Viacheslav A. Petrov*
DuPont Central Research and Development, Experimental Station, P.O. Box 80328, Wilmington, DE 19880-0328, USA1
Received 10 March 2000; accepted 21 March 2000
Abstract
Variety of N-Aryl and N-alkyl-2,2-di¯uoro-3,3-bis(tri¯uoromethyl)aziridines are prepared by reaction of the corresponding imines of
hexa¯uoroacetone with di¯uorocarbene generated by thermolysis of hexa¯uoropropylene oxide. Results of reaction of N-aryl-2,2-di¯uoro-
3,3-bis(tri¯uoromethyl)-aziridines with CsF, CF3SO3H, HF and thermal rearrangement are presented. # 2000 Elsevier Science S.A. All
rights reserved.
Keywords: N-Aryl and N-alkyl- 2,2-di¯uoro-3,3-bis(tri¯uoromethyl)aziridines; Preparation; Reactions with acids; CsF; Thermolysis
1. Introduction
[15±16] or alkylamines [17]. N-phenyl-2,2-di¯uoro-3,3-
bis(tri¯uoromethyl)aziridine (2a) has been synthesized in
moderate yield by the reaction of N-phenylimine of hexa-
¯uoroacetone and hexa¯uoropropene oxide (HFPO) as a
source of di¯uorocarbene [1]. Since this synthetic strategy
potentially provided simple route to a variety of substituted
2,2-di¯uoro-3,3-bis(tri¯uoromethyl)-aziridines, in present
work slightly modi®ed procedure was expanded for the
synthesis of new N-aryl- and not previously reported N-
alkyl-2,2-di¯uoro-3,3-bis(tri¯uoromethyl)aziridines.
Compounds 2a±i are prepared by reacting excess of
HFPO with corresponding N-arylimine of hexa¯uoroace-
tone (1a±i) at l80±l908C.
Despite the fact that a number of ¯uorinated aziridines
have been reported [1±10] in the last 30 years, the known
chemistry of poly¯uorinated aziridines is limited to several
examples of electrophilic and cycloaddition reactions
[3,4,6], (with the exception of 1-F-t- butyl-3,3-bis(tri¯uor-
omethyl)aziridin-2-one, the chemistry of which is mostly
governed by reactivity of the carbonyl group [11±14]. Only
three aziridine derivatives of per¯uoroisobutene (namely, N-
phenyl-2,2-di¯uoro-3,3-bis(tri¯uoromethyl)-aziridine [1],
N-benzyl- 2,2-di¯uoro-3,3-bis(tri¯uoromethyl)aziridine [2]
and 2,2-di¯uoro-3,3-bis(tri¯uoromethyl)aziridine [2] have
been reported to date.
In search of new potential ¯uorinated monomers the chem-
istry of 2,2-di¯uoro-3,3-bis(tri¯uoromethyl)-aziridines, car-
rying an aryl or an alkyl substituent at nitrogen is explored.
2. Results
(1)
2.1. Synthesis of aziridines
A large number of imines of hexa¯uoroacetone substi-
tuted at nitrogen are readily available through the reaction
of hexa¯uoroacetone (HFA) with either aryl isocyanates
* Tel.: ‡1-302-695-1958; fax: ‡1-302-695-8281.
E-mail address: viacheslav.a.petrov@usa.dupont.com (V.A. Petrov).
1 Publication No 7975.
Typical conversion of imine is 80±90% and product
formed in the reaction has purity of 80±95%. Aziridines
0022-1139/00/$ ± see front matter # 2000 Elsevier Science S.A. All rights reserved.
PII: S 0 0 2 2 - 1 1 3 9 ( 0 0 ) 0 0 2 9 5 - 5

26
V.A. Petrov / Journal of Fluorine Chemistry 106 (2000) 25±34
2a±i in analytically pure form are isolated by treatment of a
crude reaction mixture with a solution of KOH in ethanol,
followed by distillation (see Section 5). This procedure
affords compounds 2a±i in 23±75% yield. Since N-arylazir-
idines 1a±i have limited lifetime at temperature over 1808C
(see Section 3.3) temperature and reaction time have a
signi®cant effect on the yield of aziridines.
sulfolane portion of the product and following distillation.
The recovery of product soluble in sulfolane is not
attempted, which obviously lowered the yield.
(3)
On the other hand, yields of N-methyl- and N-ethyl-2,2-
di¯uoro-3,3-bis(tri¯uoro-methyl)aziridines (2j and 2k,
respectively) in this reaction are consistently higher (84
and 75%), due to the absence of byproducts, which is
probably a result of signi®cantly higher thermal stability
of N-alkyl-2,2-di¯uoro-3,3-bis(tri¯uoro-methyl) aziridines
(see below).
Aziridine 2h (Arˆm-CF3±C6H4±) is more active towards
CsF. The rearrangement is completed after 12 h at 100±
1108C and according to NMR data of crude reaction mixture
compound 3b is a single product formed in this process.
(4)
No formation of other byproducts, oligomers, or poly-
meric materials is observed in reaction of both 2a and 2h
with CsF.
(2)
3.2. Reaction with strong protic acids
In general, introduction of ¯uorine substituents decreases
the reactivity of aziridine ring towards electrophiles.
Recently it has been reported that the basicity of 1-alkyl-
2-tri¯uoromethyl aziridines is approximately two-orders of
magnitude lower than that of non-¯uorinated aziridines [6].
1-Alkyl-2-tri¯uoromethyl aziridines, unlike hydrocarbon
analogs, do not interact with acetic acid at ambient tem-
perature; however, the reaction with 20% hydrochloric or
50% sulfuric acid rapidly proceeds at room temperature [6].
Further accumulation of ¯uorine substituents in an aziridine
ring leads to signi®cant reduction of reactivity towards
acids. For example, aziridine 2a has been isolated by dis-
tillation from concentrated H2SO4 [1]. Compounds 2d and
2h (Arˆo-F±C6H4± and m-CF3±C6H4± respectively), simi-
lar to 2a, do not interact with concentrated sulfuric and
hydrochloric acids at ambient temperature (258C, 1 day).
However, the reaction between 2h and signi®cantly
stronger than H2SO4-tri¯uoromethanesulfonic acid [20]2
proceeds at 258C to give amine 4a as a single product
(NMR).
All synthesized aziridines are liquids with boiling points
that are 20±308C higher than those of starting imines. The IR
spectra of compounds 2a±k exhibit strong absorption near
1500 and 1450 cm 1, typical of halogenated aziridines [1±
3,5,18]. The EI mass spectra contain the intense peak of a
parent ion for each compound. Similar to reported for
compound 2a [1], 19F NMR spectra of compounds 2b±k
show resonances ±CF2± group at approximately 120 ppm,
and CF3 groups of aziridine ring at 65 ppm and with
expected ratio of intensities and multiplicity of signals. In
the 13C{1H} spectra of compounds 2d and 2i, signals having
resonances around 51 and 102 ppm (see Table 2) based on
corresponding J1±2 and J1±3 coupling constants between
carbon and ¯uorine, are assigned to [±C(CF3)2] and ±
CF2± carbons of aziridine ring.
3. Reactions
3.1. Reaction with cesium fluoride
Poly¯uorinated epoxides, such as octa¯uoroisobutene and
hexa¯uoropropylene oxides are known to rapidly react with
nucleophiles at ambient temperature [19]. N-aryl-2,2-
di¯uoro-3,3-bis(tri¯uoromethyl)-aziridines are much less
sensitive to the action of nucleophiles. For example, azir-
idine 2a has been found to be inert to the action of CsF at
20±808C [1].
Actually, as it is found in the present study compound 2a
(ArˆC6H5) slowly reacts with CsF in sulfolane solvent at
100±1108C. Under these conditions the rearrangement, that
takes about 50 h for completion, leads to the formation of
imidoyl ¯uoride 3a as a single product (NMR). Compound
3a is isolated in moderate yield by separation of insoluble in
(5)
Aziridine 2g (Arˆo-CF3±C6H4±) reacts with CF3SO2OH
producing amine 4b as a major product along with small
amount (10%) of the corresponding benzoic acid 4c, prob-
ably forming as a result of subsequent hydrolysis of the
CF3± group of compound 4b during isolation step.
2 Values of H0ˆ 12 for 100% H2SO4 and 14.1 for CF3SO2OH.
Anhydrous HF (99.5%) is much weaker acid H0ˆ 11, however, acidity of
HF can be significantfly increased by addition of Lewis acids. For
example, 7 mol% solution of BF3 in HF has H0ˆ 16.6.

V.A. Petrov / Journal of Fluorine Chemistry 106 (2000) 25±34
27
isomeric indolinones (either 5c, e or 5d, f) is a major process
in reaction of 2b or 2e (Arˆm-Cl±C6H4± and m-F±C6H4±)
aziridines with HF/BF3, crude reaction mixture in both cases
contains a noticeable amount of the corresponding amines
4e and 4f.
(6)
Reaction between 2h and anhydrous HF in the presence of
boron tri¯uoride catalyst is also straightforward selectively
producing only one product, identi®ed as amine 4d
(7)
Since commercial anhydrous HF has lower acidity than
CF3SO2OH or even H2SO4 [20], boron trifluoride catalyst
is used in this reaction to enhance the acidity of HF [20]. No
reactions of 2,2-difluoro-3,3-bis(trifluoromethyl)-aziridines
with HF without catalyst are attempted.
(9)
At the same time, interaction of aziridine 2d (Arˆo-F±
C6H4) and HF/BF3 under similar conditions leads to the
formation of nearly equal amounts of amine 4g and indo-
linone 5g
Both the character and position of a substituent in the
phenyl ring of aziridines has a signi®cant effect on the
course of the reaction with strong acids. In sharp contrast
to compounds 2g and 2h, interaction of aziridines 2c, f
(Arˆp-Cl±C6H4± and p-F±C6H4±, respectively) with HF/
BF3 mixture leads to a different result. Although both
reactions are highly selective, NMR analysis of crude
products (after hydrolysis of reaction mixture to remove
excess of HF) indicates the presence of only one compound
1
in each case. Based on data of H, 13C, 19F NMR and IR
spectroscopy of isolated materials, indolinone structures 5a
and 5b are assigned to these compounds, respectively.
(8)
(10)
Both compounds are isolated and fully characterized. The
structure of compound 5g is confirmed by X-ray diffraction
study.
The structure of compound 5a is established by data of X-ray
crystallography (see Fig. 1). Although the formation of two
3.3. Thermolysis
N-alkylazirldines 2j, k have signi®cantly higher thermal
stability compared to N-arylaziridines 2a±i. For example,
aziridine 2k (RˆMe) is recovered unchanged after 18 h at
2208C. On contrary, N-aryl-2,2-di¯uoro-3,3-bis(tri¯uoro-
methyl)aziridines have limited stability at temperature over
1808C. Compound 2a is completely converted into a mixture
of two new compounds [ratio 1:1; small amount of uni-
denti®ed impurities (ꢀ5%, NMR)] after 24 h at 2208C. 19F
NMR spectrum of crude reaction mixture in dry CDCl3 has
two sets of signals present. Resonances at 55.52 and
67.36 ppm (ratio 1:3) are assigned to aniline 6a, whereas
the second set of signals [ 67.80 (6F, d, 4 Hz)) 70.25 (1F,
1
sept., 4 Hz)] is assigned to imidoyl ¯uoride 6b. H NMR
spectrum along with the resonances of aromatic protons also
contain a septet at 4.63 ppm [±CH(CF3)2]. The IR spectrum
Fig. 1

28
V.A. Petrov / Journal of Fluorine Chemistry 106 (2000) 25±34
of the crude reaction mixture contains a new band at
1
1659 cm (C=N). The high-resolution mass-spectra (GC/
The conversion of compound 6d to indolinone 5a by treat-
ment of the mixture of 6c and 6d with water in acetone
constitutes additional evidence for the correct assignment of
the structure.
MS) of the mixture reveal molecular ions for both com-
pounds with experimentally determined masses in good
agreement with the calculated values for both materials.
Based on combined data structures 6a and 6b are assigned,
respectively, to the products thermolysis of compound 2a.
(13)
4. Discussion
Formation of imines, 3a and 3b, in the reaction of
aziridines 2a and 2h (ArˆC6H5± and m-CF3±C6H4±) with
CsF results from the attack of ¯uoride anion on the carbon of
aziridine ring bearing two CF3 groups. High regioselectivity
of this process is surprising, since, a nucleophilic attack in
hydrocarbon aziridines as a rule occurs on a less sterically
hindered carbon of the ring [21]. Signi®cantly longer time of
the reaction aziridine 2a with CsF (50 h versus 12 h for 2h,
see Table 1) is an indication of higher reactivity of 2h, which
is probably a result of higher positive charge on 3-carbon of
aziridine ring, probably due to higher electronegativity of
aryl substituent at nitrogen (Arˆm-CF3±C6H4±). The
(11)
Aziridine 2c under these conditions behaves similarly,
producing a mixture of aniline 6c and imidoyl ¯uoride 6d.
(12)
Table 1
Conditions for preparation and reactions of aziridines 2a±k
Entry
Reactants (g)
Molar ratio
Time (h)
Temperature (8C)
Product (yield %)
1
1a (65), HFPO (226)
1b (55), HFPO (166)
1c (75), HFPO (225)
1d (70), HFPO (224)
1e (72), HFPO (230)
1f (80), HFPQ (257)
1g (59), HFPO (158)
1h (95), HFPO (225)
1i (80), HFPO (240)
1j (20), HFPO (90)
1k (30), HFPO (70)
2a (16), CsF (O.5)a
2h (8) CsF (1.5)b
1:5
16
16
16
16
16
16
16
16
16
16
16
50
12
16
4
185
180
185
180
180
180
180
180
180
200
200
100±110
100±110
25
2a, 75
2b, 54
2
1:5
1:4.1
3
2c, 63
2d, 35
4
1:5
5
1:5
1:5
2e, 38
2f, 23
6
7
1:5
2g, 37
2h, 64
8
1:5
9
1:4.7
1:5
2i, 28
2j, 84
10
11
12
13
14
15
16
17
18
19
20
21
22
23
1:5
2k, 75
3a, 50
1:17
1:22
0.15:1
3b, 56
4a, 71
4b, cc 67
4d, 95
5a, 80
2h (6), HOSO2CF3 (15)
2g (2), HOSO2CF3 (8)
2h (20), BF3 (5) HF (100)
2c (20), BF3 (5) HF (100)
2f (18), BF3 (5) HF (100)
2b (20), BF3 (5) HF (100)
2c (20) BF3 (5) HF (100)
2d (20) BF3 (5) HF (100)
2a (20)
0.1:1
25
0.056:0.073:5
0.06:0.073:5
0.058:0.073:5
0.06:0.073:5
0.06:0.073:5
0.06:0.073:5
±
12
12
12
12
12
12
20
24
50
50
50
5b, 88
50
4e, 5c, e, 95d
4f, 5d, f, 90e
4g, 5g 75f
6a, b 95g
6c, d 91h
50
50
220
220
2c (18)
±
a In sulfolane as a solvent (20 ml).
b In sulfolane as a solvent (10 ml).
c Ratio 9:1.
d Ratio 6:56:38.
e Ratio 6:72:22.
f Ratio 42:58.
g Ratio 1:1.
h Ratio 63:37.

V.A. Petrov / Journal of Fluorine Chemistry 106 (2000) 25±34
29
Scheme 1.
absence of oligomers or polymeric materials in both reac-
tions is a re¯ection of low nucleophilicity and high steric
hindrance of azaanion 7a, which is not able to attack another
molecule of aziridine under reaction conditions (see
Scheme 1).
Reduced reactivity of poly¯uorinated azaanions is usually
a result of accumulation of bulky ¯uoroalkyl groups at
nitrogen and it has been previously observed for bis(pef-
¯uoroalkyl)azaanions (Rf)2N [22]. In general, their reac-
tivity is signi®cantly lower than that of either RfN(F) [23]
or (CF3)2N [22].
Electronic properties of aryl substituent also have a
pronounced effect on the reactivity of N-aryl-2,2-di¯uoro-
3,3-bis(tri¯uoromethyl)aziridines with electrophiles. Selec-
tive formation of amines 4a, b, d in reaction of aziridines 2g,
h (Arˆo-CF3±C6H4± and m-CF3±C6H4±) with tri¯ic acid
and anhydrous HF is probably the result of reaction that
starts with protonation of the nitrogen of the aziridine ring
and is followed by ring opening with formation of amine 4
Scheme 3.
with acids involves selective heterolysis of the N±CF2 bond
of the aziridine ring.
through a,a-di¯uorocarbocation
(Scheme 2).
(7b)
intermediate
On the other hand, the result of similar reaction of
aziridines 2c and 2f (Arˆp-Cl±C6H4± and p-F±C6H4±,
respectively) with HF is surprising. This time, the replace-
ment of electron withdrawing CF3 group by substituent
carrying unshared electron pair alters the course of reaction
and instead of formation expected (CF3)3C±N(H)±Ar, this
process leads to formation of indolinones 5 as a solo product
in each case. Scheme 3 presents possible mechanism
explaining this result.
It is worthy of note, that the regioselectivity of this process
does not depend on the position of a tri¯uoromethyl group in
the phenyl ring, and the reaction of both isomers 2g and 2h
The process starts with protonation of ¯uorine at C-2 of
the heterocycle resulting in the formation of cyclic iminium
cation 8 (Scheme 3, route `A'), which is converted into 9. It
undergoes intermolecular cyclization producing intermedi-
‡
ate 10. Aromatization of 10 by the elimination of H
produces imidoyl ¯uoride (11). Compound 11 is hydrolyzed
to the ®nal product Ð indolinone 5 Ð during isolation step,
when the reaction mixture is treated with water.
However, the conversion of 2 into 11 may be also
described as a concerted electrocyclic two-step process
(Scheme 3, route `B'), where the ®rst step Ð heterolysis
of C±F bond of heterocycle Ð proceeds simultaneously with
Scheme 2.

30
V.A. Petrov / Journal of Fluorine Chemistry 106 (2000) 25±34
electrocyclic ring opening of aziridine ring. The second step
involves concerted 1,5-cyclization of `azapentadienyl'
cation 9 with formation of cation 10, which is converted
further into 11. Mechanistically the ®rst step of transforma-
tion of 2±11 is similar to thermal isomerization of 3,3-
dichloro- and 3,3-dibromo 1,2-diphenylaziridines which
involves heterolysis of the C±halogen bond and electrocyc-
lic ring opening reaction leading to the formation of imidoyl
chloride or bromide [18] or Lewis acid catalyzed isomer-
ization of poly¯uorinated cyclopropanes into ¯uoroole®nes
[24]. Mechanism of the second step of transformation 2±11
is analogous to thermal isomerization of poly¯uorinated
vinyl cyclopropanes [25,26] or 1,5 cyclization of hydro-
carbon [27] polyenes or poly¯uorinated [28,29] dienes
under the action of electrophilic reagents, postulated to
proceed as electrocyclic processes. Absence of type 4
products in the reaction of aziridines 2c, f with HF/BF3
indicates that protonation of nitrogen is either completely
reversible or the rate of a ring opening reaction resulting in
the formation of intermediate 7b (Scheme 2) is signi®cantly
lower than the rate of a ring expansion process leading to
intermediate 11 (Scheme 3).
In sharp contrast to of aziridines 2g and 2h (Arˆo-CF3±
C6H4± and m-CF3±C6H4±) where the regioselectivity of the
reaction with HF is not sensitive to the position of CF3 group
in phenyl ring, the result of ring opening of aziridines 2b±f
(ArˆX±C6H4, XˆCl or F) by acids strongly depends on the
substitutional pattern of the phenyl ring. For example, the
ratio of products 4:5, changes from 40:60 for 2d (Arˆo-F-
C6H4) to 6:94 for 2b and 2e (Arˆm-Cl±C6H4 and m-F±
C6H4) to selective formation of products 5 only in reaction of
2c or 2f (Arˆp-Cl±C6H4± and p-F±C6H4±, respectively) in
reaction with HF. Both mechanisms represented by
Scheme 3 provide a reasonable explanation of observed
experimental facts. Since the reaction involves either
charged intermediates or highly polarized transition state,
p-donor in para-position of phenyl ring is able to effectively
participate in stabilization of electron-de®cient center
through donation of unshared electron pair. This type of
stabilization is still quite effective for chlorine or ¯uorine
substituent in meta-position of phenyl ring, which in reac-
tion of 2b and 2e ensures formation of isomeric indolinones
5c, e and 5d, f as major products. However, ¯uorine, in
ortho-position of phenyl ring cannot participate in stabiliza-
tion of polarized intermediates through `back-donation'
mechanism as effectively as in para- or meta- and actually
starts to destabilize the system through I mechanism.
Probably, for this reason 2d reacts with HF producing almost
equal amounts of compounds 4g and 5g. They are formed as
a result of two competitive reactions: protonation of nitrogen
following by ring opening and addition of counter anion
(process represented by Scheme 2) or protonation of ¯uorine
in ±CF2± group of aziridine ring, leading to compound 11
(Scheme 3). The position of halogen substituent in phenyl
ring affect the ®ne balance between these two processes,
shifting point of the balance towards either formation of
Scheme 4.
compound 4 or 5 with extremes being selective formation of
5 for aziridines carrying Cl or F in para-position of phenyl
group or selective formation of compound 4 in reaction of
aziridines 2g and 2h. In the last case position of substituent
in phenyl ring does not have such signi®cant effect on the
regioselectivity of the reaction as in case of halogen sub-
stituents, since CF3± group possessing only strong I effect
cannot participate in stabilization through `back-donation'
mechanism.
In thermal reactions of N-aryl -2,2-di¯uoro-3,3-bis(tri-
¯uoromethyl)aziridines the formation of mixture of two
compounds is probably the result of two different processes.
The ®rst one is a concerted ring opening of aziridine yielding
azomethine ylide 12. This process may be reversible under
the reaction conditions (Scheme 4)
Ylide 12 having high af®nity towards ¯uoride anion
probably is able to abstract F from the CF2 group of the
aziridine ring. It triggers one of the processes (`A' or `B')
represented by Scheme 3, leading to formation of cation 10
‡
and intermediate 13. The transfer of H from 10 to 13
produces two ®nal products 11 and 14. The whole process
involves addition of 1 mole of HF generated during conver-
sion of 2±11 by ylide 12. Despite the fact, that attempt to trap
azomethine ylide 12 carried out in this work by heating
aziridine 2a with dimethyl acetylene dicarboxylate was
unsuccessful (which may be attributable to the steric hin-
drance of 12) the existence of hydrocarbon and polyhalo-
genated azomethine ylides is well documented in current
literature. Formation of the corresponding cycloadduct in
the thermal reaction of N-aryl-3,3-bis(tri¯uormethyl)aziri-
dine with DMAD has been reported by Burger [3]. Reaction
of di¯uorocarbene generated from ClCHF2 with
(Ph)2C=NCH2C(O)OEt is also believed to proceed through
formation of the corresponding ylide [4] along with cycload-
dition reaction of hydrocarbon aziridines to ¯uoroole®ns

V.A. Petrov / Journal of Fluorine Chemistry 106 (2000) 25±34
31
6. General procedure for preparation of aziridines
The corresponding imine (20±l00 g) and hexa¯uoropro-
pylene oxide (HFPO, 80±250 g) are loaded in a 400 ml
Hastelloy shaker tube, and the reaction mixture is main-
tained at 180±185 (1a±i) or 2008C (1k, j) for 16±18 h. The
reactor is cooled down to room temperature, vented, the
crude reaction mixture is reacted with a 10% NaOH solution
in ethanol to destroy starting material and byproducts,
diluted with water, the organic (lower) layer is separated,
dried over MgSO4 and distilled.
7. Reaction of aziridines with CsF
A mixture of aziridine, dry CsF and 10±20 ml of dry
sulfolane is maintained at 1008C for 12±50 h. The reaction is
monitored by GC and NMR. Once all starting material is
consumed, the lower layer of reaction mixture is separated
and distilled.
Scheme 5.
being a subject of several publications [30±32]. Recently,
ylides obtained from the reaction of a Schiff base with
di¯uorocarbene have been trapped using electron de®cient
ole®ns [33] and DMAD [34]. Strong evidence for the inter-
mediate formation of corresponding azomethine ylide in
thermal reaction of alkyl 2,2-diphenyl-3-(trichloromethyl)-
aziridine-1-carboxylate has been obtained recently [35].
Alternative mechanism of formation of compounds 11
and 14 involves also dissociation of the C±N bond of the
aziridine ring, but this time with formation of biradical 15
followed by intramolecular cyclization ®nally leading to
amine 16, which is converted under reaction conditions to 11
by transfer of 1 mole HF to ylide 12 (Scheme 5).
8. Reactions of aziridines with protic acids
In a typical experiment, a mixture of 15±20 g of aziridine,
5 g of BF3 and 100 g of anhydrous HF is kept at 508C for
12 h in a 400 ml Hastelloy shaker tube. Water (150 ml) is
injected into reactor. Crude reaction mixture is separated
(solid products are dissolved in ether), dried over MgSO4
and either distilled or recrystallized from CHCl3.
Reaction of 2g, h and HOSO2CF3 is carried out by
dropwise addition of aziridine to excess of acid (Caution:
may be exothermic!), stirring the reaction mixture at 258C
for 16 h and subsequent quenching it with ice. The lower
layer is separated, dried over P2O5 and distilled.
Although mechanism represented by Scheme 4 is prefer-
able one, at this point there are not enough experimental
data, which would allow choosing between these two
mechanisms.
9. Hydrolysis of 6d
5. Experimental section
A mixture of 6c, d (4 g) is dissolved in 10 ml of acetone,
1.5 g of water is added and the reaction mixture is stirred at
258C for 4d. According to NMR and Gd data, conversion of
6d at this point is 100% and the 6c to 5a ratio is 1:1.
Compound 5a is identi®ed in the mixture by 19F NMR and
GC against an authentic sample.
19F and 1H and 13C NMR spectra are recorded on a
Brucker DRX-400 instrument using CFCl3 as an internal
standard and either d-chloroform or d-acetone as a lock
solvent. The IR spectra are recorded with a Perkin-Elmer
1600FT spectrometer. Compounds 1a±i [15,16,36], and 1j,
k [17] are prepared by reported procedures. Cesium ¯uoride
is dried in vacuum (2 h, 1008C) and used immediately after
drying. All other compounds are purchased from commer-
cial sources and used as received. Reaction conditions and
yields are given in Table 1. Data of elemental analysis and
IR, NMR, MS spectroscopy for new materials can be found
in Table 2.
10. Thermolysis of aziridines
A sample of aziridine (5±25 g) is kept in a sealed glass
reactor at 2208C for 18±24 h. The reactor is cooled down,
opened, and the crude reaction mixture (typically containing
more than 95% of two products along with small amount of
unidenti®ed byproducts) is analyzed by NMR, IR and GC/
MS.
Caution! Both hexa¯uoroacetone and anhydrous HF
are toxic and hazardous materials that should be handled
properly by trained personnel only.

Table 2
Properties of new compounds
1
‡
Compounds
bp/8C (mmHg)
1H NMR, d/ppm (J/Hz)
19F NMR ppm, J(Hz)
IR (cm
)
Anal. or MS (M ) found (calc.)
2b
76±77 (18)
6.92 (1H dd), 7.08 (1H t),
7.22 (1H dd), 7.35 (1H t)
65.66 (6F t, 8.5), 118.43 (2F hept, 8.5)
1582, 1489, 1456, 1429
F, 46.87 (46.68), N, 4.32 (4.30)
2c
2d
69 (12)
64.73 (6F t, 8), 117.61 (2F hept, 8)
65.70 (6F t, 7), 117.72 (2F hept, 7),
128.04 (1F s)a
1498, 1462
1507, 1453
m/e, 324.9842 (324.9905)
m/e 309.0175, (309.0200)
63±64 (26)
2e
2f
48 (0.1)
65.91 (6F t, 8.5), 111.19 (1F q, 6),
118.88 (2F hept, 8.5)
1612 (d), 1494 1446 (d)
1511, 1476
C, 39.47 (38.85), H, 1.44 (1.30),
m/e 309.0160 (309.0200)
C, 38.95 (38.85), H, 1.39 (1.30),
F, 54.34 (55.31 m/e) 309.0165
(309.0200)
52±53 (14)
64.74 (6F t, 8), 116.37 (1F m)
117.53 (2F hept, 8)
2g
2h
82±83 (20)
65 (18)
7.18 (1H d, 4.5), 7.36 (1H d,7.5),
7.58 (1H t, 8), 7.73 (1H d, 4.5)
7.24 (1H d), 7.31 (1H s), 7.51 (2H m)
61.03 (3F t, 8.5), 63.61 (6F t, 8.5),
113.94 (2F decet, 8.5)
1611, 1589, 1502, 1475
1620, 1600, 1501, 14068
m/e 359.0203 (359.0168)
63.77 (3F s), 65.19 (6F t, 8),
118.18 (2F hept, 8)
C, 37. 14 (36.79), H, 1.39 (1.12),
F, 57.81 (58.12) m/e 359.0070
(359.0168)
2i
57±58 (15)
6.93 (1H m), 6.95 (1H m), 7.11 (1H m)
64.35 (6F m), 111.53 (1F m),
1609, 1517, 1460, 1440
m/e 327.0074 (327.0106)
116.30 (2F oct, 8.5) 121.53 (2F m)b
64.74 (6F t, 9), 120.51 (2F hept, 9)
65.11 (6F t, 9), 119.57 (2F hept, 9)
2j
2k
55±56
70±71
2.97 (s)
1480, 1407
1490, 1450
m/e 229.0146 (229.0138)
C, 30.10 (29.64) N, 5.25 (5.76)
F, 62.07 (62.52)
1.26 (3H t, 7.5), 3.19 (2H m 7.5; 2)
3a
96.5±96 (120)
7.18 (3H m), 7.30 (2H m)
7.48 (1H m), 7.58 (3H m)
73.81 (6F dd, 7;8), 36.39 (1F, d hept,
24;70), 180.02 (1F d hept, 24;8)
62.20 (3F s), 73.79 (6F t, 7), 34.71
(1F, d hept, 22; 7), 180.31 (1F d hept. 22;7)
62.10 (3F s), 66.53 (8F m),
72.96 (3F t, 10)
1750 (C=N)
C, 41.46 (41.25 H, 1.63 (1.73)
F,52.53 (52.20)
3b
4a
±
±
±
1750, (C=N)
C, 36.90 (36.79), H, 1.11 (1.12)
F, 57.80 (58.19), N, 3.16 (3.90)
C, 28.52 (28.30) H, 1.11 (0.99)
4.15 (1H br. s), 7.30 (1H d),
7.36 (1H m), 7.40 (1H m),
3404 (NH), 1452 (SO2)
3472, (NH), 1455 (SO2)
4bc
4.75 (1H br. s), 7.23 (1H t, 7.5),
7.35 (1H, d, 9), 7.52 (1H t, 7.5),
7.8 (1H, d, 9)
60.05 (3F s), 66.90 (8F m),
73.01 (3F t, 5)
m/e 359.0168 (359.0168,
‡
[M- CF3SO3] )
4cc
4d
±
7.06 (1H t, 10), 7.20 (1H, d,10),
7.56 (1H td, 7.5;1) 8.16 (1H, d,d 8;1)
4.0 (1H br. s) 7.26 (1H m), 7.36 (3H m)
66.12 (6F t, 10), 66.49 (2F m),
73.01 (3F t, 5)
63.45 (3F s), 68.86 (9F s)d
3100, 1688 (C=O)
3456, 3395 (NH)
64.7±64.9 (15)
C, 34.70 (34.85), F, 60.13
(60.48), H, 1.60 (1.33)
4ec
4fc
4g
±
±
±
4.24 (1H br s)
4.10 (1H br s)
68.79 (s)
68.92 (9F s), 112.19 (1F m)
69.57 (9F), 127.75 (lF m)
±
±
4.32 (1H br s), 7.12 (3H, m),
7.28 (1H t, 8.5)
3436, 3395 (NH)
C, 36.46 (36.49), H, 1.58 (1.53),
m/e 329.0269 (329.0262)

5ae
5b
182±183f
168±169f
±
6.95 (1H d, 9), 7.40 (1H dd, 9;3),
7.48 (1H s), 8.33 (1H br. s)
67.47 (s)g
3269 (NH), 1764, 1748, 1460
±
6.98 (1H dd, 13;5), 7.71 (1H td, 9.5 ;3),
7.34 (1H d;8), 7.92 (1H br. s)
5c 7.09 (1H d, 3), 7.21 (1H t, 6),
7.47 (1H d, 6), 8.60 (1H br. s)
5e 6.94 (1H d, 6), 7.21 (1H t, 6),
7.38 (1H d, 9), 8.74 (1H br. s)
5d: 6.83 (1H dd, 8;2), 6.92 (1H t, 9),
7.63 (1H db, 8;5), 8.65 (1H br. s)
5f: 6.83 (1H dd, 8;2), 6.92 (1H t, 9),
7.48 (1H dd, 9;5), 8.78 (1H br. s)
7.23 (2H m), 7.37 (1H d, 9),
7.63 (1H d, 7), 8.68 (1H br. s)
6a: 4.64 (1H hept, 5), 7.42 (2H m),
7.58 (2H m)
67.51 (6F s), 116.31 (1F m)h
67.44 (s)
3280 (NH), 1756, 1727, 1496
±
C, 41.85 (41.83), F, 46.18
(46.32), H, 1.53 (1.40)
±
5c, e
63.47 (s)
5d, fi
152 154f
67.62 (6F, s), 104.328 (1F, m)
66.11 (6F d, 16), 107.97 (1F, m, 16)
68.15 (6F, d;4), 130.39 (1F dd, 5;10)
55.57 (3F, s), 67.36 (6F, dm, 5)
3294, 1759, 1734
3216, 1750, 1720
C, 41.27 (41.83), F, 46.14
(46.32), H, 1.61 (1.40)
5ge
142±142.5f
±
C, 41.37 (41.83), H, 0.87 (1.40)
6a, bc,j
m/e 311.0344 (311.0357)
6b: 7.42 (2H m), 7.58 (2H m)
6c: 4.76 (1H hept, 7), 7.48 (2H m),
7.75 (1H m)
68.80 (6F d, 4), 70.10 (1F hept, 4)
54.76 ) (3F, s), 66.31 (6F, dq, 7;2)
1659 (C=N)
1660 (C=N)
m/e 271.0215 (271.0232)
m/e 344.9974 (344.9967)
6c, dc,k
91±95 (50)
6d: 7.48 (2H m), 7.75 (1H m)
66.53 (6F d, 4), 67.89 (1F hept, 4)
m/e 285.9871, (285.9858,
‡
[M-F] )
a 13C NMR (proton decoupled, d/ppm, J/Hz): 51.28 (m, 27; 34), 101.35 (t, 292), 116.25 (d, 18), 119.52 (s), 119.72 (qt, 282; 3), 124.18 (s), 124.29 (d, 3), 126.21 (d, 9), 153.34 (d, 242).
b 13C NMR (proton decoupled, d/ppm, J/Hz): 51.41 (m, 19; 36), 101.73 (t, 289), 104.60 (dd, 27;23), 111.25 (dd, 23;27), 120.07 (qt, 281; 3), 120.18 (d,10), 120.82 (dd, 20;5), 153.78 (dd, 23; 248), 160.40 (dd,
23;248).
c Is not isolated, identified in crude reaction mixture.
d 13C NMR (proton decoupled, d/ppm, J/Hz): 70.53 (dec., 27), 121.50 (q, 291), 121.86 (dec., 5), 122.13 (s), 124.20 (q, 273), 128.97 (s), 130.64 (s), 131.11 (q,33).
e Structure is determined by X-crystallography.
f Melting point.
g 13C NMR (proton decoupled, d/ppm, J/Hz): 59.93 (sept., 29), 113.61 (s), 119.96 (s), 122.30 (q, 280), 127.31 (s), 128.99 (s), 133.34 (s), 143.11 (s), 164.44 (s).
h 13CNMR (proton decoupled, d/ppm, J/Hz): 58.80 (sept., 30), 112.05 (d, 7), 1 13.83 (d, 24), 118.24 (d, 9), 119.00 (d, 22), 121.01 (q, 285), 139.24 (s), 158.42 (d, 242), 163.38 (s).
i Mixture of 5d and 5f (3:1), crystallized from CHCl3.
j >96% of crude product is mixture of 6a and 6b in ratio 1:1.
k >95% of crude product is mixture of 6c and 6d in ratio 63:37.

34
V.A. Petrov / Journal of Fluorine Chemistry 106 (2000) 25±34
[15] Yu.V. Zeifman, N.P. Gambaryan, I.L. Knunyants, Dokl. Akad. Nauk
Acknowledgements
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