Synthesis of chiral aziridines through decarboxylative generation of sulfur ylides and their reaction with chiral sulfinyl imines

Article abstract of DOI:10.1080/00397910802654898

Reaction of sulfur ylides with a series of aryl substituted chiral nonracemic sulfinyl imines afforded the corresponding aziridines in good yields with good stereoselectivity. The sulfur ylides were generated by the thermally induced decarboxylation of carboxymethylsulfonium betaines. A drop in the diastereomeric ratio was observed when going from electron-deficient to electron-releasing aryl substituted imines. S-Methylene aziridinations involving the decarboxylation of carboxymethylsulfonium betaine functionality complements existing technologies with the advantages of the reaction protocol, levels of conversion, and scope.

Full text of DOI:10.1080/00397910802654898

This article was downloaded by: [Moskow State Univ Bibliote]
On: 29 September 2013, At: 08:37
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954
Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH,
UK
Synthetic Communications: An
International Journal for Rapid
Communication of Synthetic
Organic Chemistry
Publication details, including instructions for
authors and subscription information:
http://www.tandfonline.com/loi/lsyc20
Synthesis of Chiral Aziridines
Through Decarboxylative
Generation of Sulfur Ylides
and Their Reaction with Chiral
Sulfinyl Imines
David C. Forbes a , Sampada V. Bettigeri a , Sejal
R. Amin a , Christie J. Bean a , Amanda M. Law a
Robert A. Stockman b
&
a Department of Chemistry, University of South
Alabama, Mobile, Alabama, USA
b School of Chemistry, University of Nottingham,
University Park, Nottingham, UK
Published online: 01 Jun 2009.
To cite this article: David C. Forbes , Sampada V. Bettigeri , Sejal R. Amin ,
Christie J. Bean , Amanda M. Law & Robert A. Stockman (2009) Synthesis of Chiral
Aziridines Through Decarboxylative Generation of Sulfur Ylides and Their Reaction
with Chiral Sulfinyl Imines, Synthetic Communications: An International Journal
for Rapid Communication of Synthetic Organic Chemistry, 39:13, 2405-2422, DOI:
10.1080/00397910802654898
To link to this article: http://dx.doi.org/10.1080/00397910802654898
PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the
information (the “Content”) contained in the publications on our platform.
However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness,
or suitability for any purpose of the Content. Any opinions and views
expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the
Content should not be relied upon and should be independently verified with
primary sources of information. Taylor and Francis shall not be liable for any
losses, actions, claims, proceedings, demands, costs, expenses, damages,
and other liabilities whatsoever or howsoever caused arising directly or
indirectly in connection with, in relation to or arising out of the use of the
Content.
This article may be used for research, teaching, and private study purposes.
Any substantial or systematic reproduction, redistribution, reselling, loan,
sub-licensing, systematic supply, or distribution in any form to anyone is
expressly forbidden. Terms & Conditions of access and use can be found at
http://www.tandfonline.com/page/terms-and-conditions

Synthetic Communications1, 39: 2405–2422, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910802654898
Synthesis of Chiral Aziridines Through
Decarboxylative Generation of Sulfur Ylides and
Their Reaction with Chiral Sulfinyl Imines
David C. Forbes,1 Sampada V. Bettigeri,1 Sejal R. Amin,1
Christie J. Bean,1 Amanda M. Law,1 and Robert A. Stockman2
1Department of Chemistry, University of South Alabama, Mobile,
Alabama, USA
2School of Chemistry, University of Nottingham, University Park,
Nottingham, UK
Abstract: Reaction of sulfur ylides with a series of aryl substituted chiral non-
racemic sulfinyl imines afforded the corresponding aziridines in good yields
with good stereoselectivity. The sulfur ylides were generated by the thermally
induced decarboxylation of carboxymethylsulfonium betaines. A drop in the
diastereomeric ratio was observed when going from electron-deficient to
electron-releasing aryl substituted imines. S-Methylene aziridinations involving
the decarboxylation of carboxymethylsulfonium betaine functionality comple-
ments existing technologies with the advantages of the reaction protocol,
levels of conversion, and scope.
Keywords: Asymmetry, aziridination, methylene transfer, S-ylide
INTRODUCTION
Nucleophilic alkylidene transfer agents have been shown to be extremely
useful for the introduction of functionality into organic molecules.[1]
Once generated, they can and do react with a large variety of
Received November 17, 2008.
Address correspondence to Robert A. Stockman, School of Chemistry,
University of Nottingham, University Park, Nottingham NG7 2RD, UK. E-mail:
robert.stockman@nottingham.ac.uk
2405

2406
D. C. Forbes et al.
p-acceptors.[2] A representative list of processes involving a p-acceptor
would include formation of oxiranes from aldehydes and ketones,
aziridines from imines, and cyclopropanes from electron-deficient olefins.
The direct and stereospecific assembly of small ring carbo- and heterocyc-
lic building blocks is a very attractive synthetic transformation, especially
when considering the assembly of materials of biological and medicinal
significance.[3,4] Previous communications from our laboratory reported
a novel protocol for the preparation of alkylidene agents. The protocol
had as its key step the decarboxylation of carboxymethyl betaine
functionality, which generated the requisite sulfur ylides in situ
(Scheme 1).[5] Sulfur ylide intermediate ii is best described as a semistabi-
lized ylide when compared to thioacetate scaffolds consisting of not alkyl
aryl substitution but alkyl alkyl substitution on sulfur. Although tradi-
tional points of stabilization would focus on the alkylidene carbon,
attachments onto the sulfur moiety and even solvation of the intermedi-
ate itself have also been shown to improve the half-lives of sulfur ylides.[6]
When ylide ii is used in excess quantities, clean conversion of aldehyde to
oxirane functionality is observed. The ease by which the sulfur ylide is
generated from sulfonium salt 1 is the key advantage of this method over
other existing technologies. That is, the generation of the ylides by decar-
boxylation has distinct advantages over more traditional methods. First,
the process does not require the use of strong and often pyrophoric bases
such as butyl lithium or sodium hydride. Second, the method does not
require expensive metal catalysts. Third, this approach is compatible with
ecologically benign solvent systems. And finally, through fine-tuning
of the electronics of the betaine, a range of activity and lifetime of
methylidene agent can be created.
Although we are very satisfied with the chemistry, the methylene
transfer technology using sulfonium salt 1 has yet to reach its full poten-
tial when considering catalysis, additions to other p-acceptors, and asym-
metry. Efforts to address the latter two, additions to other p-acceptors
and asymmetry, have been made, and reported herein are our findings
in the stereoselective assembly of heterocylic building blocks of aziridine
functionality.
Scheme 1. Methylene transfer of alkyl=aryl aldehydes using S-ylide technologies.

Methylene Transfers onto Chiral Sulfinimines
2407
Scheme 2. Reaction of chiral sulfinyl imines with trimethylsulfonium iodide.
RESULTS AND DISCUSSION
Stockman and coworkers have published several reports on the Corey–
Chaykovsky reaction of chiral sulfinyl imines (Scheme 2).[7] By perform-
ing methylene transfers derived from trimethyl sulfonium iodide, they
prepared a series of aliphatic, aromatic, and heterocyclic tert-butylsulfi-
nyl aziridines.[6d] Reaction times ranged between 3 and 10 h using NaH
as base and dimethyl sulfoxide (DMSO) as solvent at 20ꢀC, and this
led to the greatest levels of conversion and diastereoselectivity.
Intrigued by this report, we embarked upon an aziridination study
using our technology involving the decarboxylation of carboxymethylsul-
fonium betaine functionality to generate a sulfur ylide in situ. One of our
goals was to address the question of whether alternative reagents and sol-
vent systems could be used without significantly compromising the levels
of conversion, while maintaining good levels of stereoselectivity. For
comparative purposes, we chose to test a series of aryl substituted chiral
nonracemic tert-butylsulfinyl imines against our sulfonium salt 1. As we
found in our epoxidation studies,[5] the incorporation of S-aryl function-
ality offers added stability of the sulfur ylide (vide infra), and thus we
hypothesized that this would result as well in good levels of conversion
when subjected to imine functionality. Except for this single modifica-
tion, use of imine as opposed to aldehyde functionality, all other reaction
conditions were kept the same as in our previously optimized work with
aldehyde p-acceptors. A total of seven sulfinimine derivatives were sur-
veyed. The data from the study are presented in Table 1.
Each system, aldehyde to imine and imine to aziridine, afforded the
desired material in excellent overall yield. The yields for aziridine forma-
tion are of isolated and chromatographically pure material. All reactions
reported here were clean as judged by gas chromatography (GC) and
NMR analysis of the crude reaction mixture. The levels of diastereocon-
1
trol were obtained of the crude reaction mixture by H NMR. The ana-
lytical data of the major diastereomer for aziridine 2d is consistent with
that of previous reports.[7] The diagnostic peaks for both the major and
minor aziridines of each system were obtained (data not shown).

2408
D. C. Forbes et al.
Table 1. Sulfonium methylidene aziridinations using sulfonium salt 1
Entry
1, a
Imine
Yield (%)a
97
drb
87:13
2, b
3, c
96
94
78:22
77:23
4, d
5, e
95
85
74:26
84:16
6, f
93
89
80:20
89:34
7, g
aIsolated chromatographically pure material.
1
bDetermined by H NMR (crude reaction mixture).
Although the isolated yields are excellent, Table 1 reveals some inter-
esting trends when looking at the levels of diastereocontrol. The diaster-
eoselectivities observed in this series, which is believed to be under kinetic
control, ranged from a low of 66:34 for electron-releasing aryl imines to a
high of 87:13 with electron-withdrawing imines. Electron-deficient aryl
imines (entries 1–3) resulted in levels of diastereocontrol ranging from
87:13 (entry 1) to 77:23 (entry 3). The levels of diastereocontrol with these
two examples served as bookends when switching to electron-neutral
imines (entry 4) and the two examples representing disubstituted

Methylene Transfers onto Chiral Sulfinimines
2409
electron-releasing aryl functionality (entries 5 and 6). It is unique with the
latter that when going from a disubstituted aryl system consisting of
electron-releasing groups to a monosubstituted electron-releasing group
(entry 7), the level of diastereocontrol drops to 66:34.
Although significantly great levels of diastereocontrol could be
obtained with our technology, it was at the expense of aziridine conversion
(dr ¼ 90:10 at 50% conversion for 2d). Lower levels of diastereocontrol
were observed overall, but we were encouraged by the fact that extremely
high levels of conversion were obtained with a process that does not rely on
DMSO as solvent and strong bases such as NaH or nBuLi.
The trend in diastereocontrol is supported by the model proposed by
Aggarwal et al.[8] and Edwards et al.[9] which has the electrostatic inter-
actions of the sulfur atom and hetereoatom as a key interaction in the
formation of small ring heterocycles. For aziridination reactions,
although less is known about the transition state, there is evidence that
the crucial electrostatic interactions (as is the case of oxirane formation)
can be offset with unfavorable steric interactions when considering the
formation of 1,2,3-trisubstituted aziridines.[10]
With our 1,2-disubstituted systems, a more electron-rich system
would predict that the sp2 hybridization of the carbon of the imine
(or oxirane) is maintained. This downplays the electrostatic interactions
of p-acceptor (nitrogen) and sulfonium salt (sulfur), which in turn,
diminishes the steric effects of the tert-butyl moiety. As a result, a
switch in the transition state is proposed when analyzing the diastereos-
electivities obtained (Fig. 1). That is, a switch from a closed (cisoid) to
an open (transoid) transition state may be operative and would explain
the trend in diastereoselectivities observed when electron-deficient and
Figure 1. Operative transition states in the aziridination reaction of sulfur ylides.

2410
D. C. Forbes et al.
electron-releasing aryl imines are subjected to methylene aziridination
processes using sulfonium salt 1. Figure 1 offers two models—both
result in formation of the same diastereomer. The illustration highlights
the two limiting scenarios for a favorable electrostatic interaction
(closed) and one that does not rely on the two highlighted developing
charges (closed).
As for entries 5 and 6, which have two electron-releasing groups, the
substitution patterns at both the meta- and para- positions do offset one
another when considering the overall electronics of the p-acceptor at the
imine carbon.[11] The highlight of this approach is the extent of conver-
sion when looking at reaction of a series of electronically unique aldi-
mines bearing as a directing group, tert-butyl sulfinyl functionality.
Each system afforded the desired product in excellent yield. This was vali-
dated when we conducted a side-by-side comparison of this approach
with reaction conditions in an earlier study (Table 2).
Differences in conversion were observed when comparing the two
methods using different sulfonium salts [entry 1 (sulfonium salt 1) and
entry 2 (trimethylsulfonium iodide)]. Both ylides are effective methyli-
dene agents. Any differences in mass throughput to the desired product
Table 2. A Comparison of conversion and diastereocontrol
Entry
Sulfonium salt
1
Base
Temperature (ꢀC)
Yield (%)a
drb
1
2
Ca2CO3
NaH
78
78
95
86
74:26
76:24
3c
n-BuLi
ꢁ20
56
84
92:8
93:7
4c,d
NaH
20
aIsolated chromatographically pure material.
1
bDetermined by H NMR (crude reaction mixture).
cReference 7d.
dSolvent is DMSO.

Methylene Transfers onto Chiral Sulfinimines
2411
are most likely due to competing side reactions when going from an
unstabilized to a semistabilized sulfur ylide.
Substantial differences were noted when looking at changes in reac-
tion temperature (entry 3) and solvent (entry 4). An inverse relationship
between temperature and diastereocontrol is not surprising. To address
these differences using our method, we conducted a temperature survey
using DMSO as solvent. Presented in Table 3 are our results using
DMSO as base as a function of reaction temperature.
For comparative purposes, entry 5 lists the extent of conversion using
tetrahydrofuran (THF) as solvent. For this study, we elected to use an
electron-deficient aryl imine so that a rapid screen could be conducted.
The longer reaction times presented in Table 1 assure completion of
the reactions. Perhaps most striking with this survey is that in refluxing
THF, the level of diastereoselectivity is high (entry 4 versus entry 5).
Furthermore, the level of diastereocontrol at room temperature using
DMSO (entry 1) is on par with that of refluxing THF (entry 5). As stated
previously, while levels of conversion dropped, significantly great levels
of diastereocontrol could be obtained with our technology in THF when
operating closer to room temperature. The key, however, is the process.
High levels of conversion can be obtained without the need to use DMSO
as solvent and strong bases such as NaH or nBuLi.
The results for our decarboxylation approach show extremely high
levels of conversions while operating at a much warmer reaction condi-
tions than aziridination protocols found in the literature. It is interesting
that a comparison of reaction of sulfonium salt 1 with trimethylsulfonium
Table 3. Temperature survey using DMSO
Entry
Temperature (ꢀC)
Solvent
Ratioa (aziridine=imine)
dra
1
2
3
4
5
21
40
60
80
80
DMSO
DMSO
DMSO
DMSO
THF
13:87
42:58
56:44
92:8
86:14
83:17
79:21
70:30
87:13
>95:5
1
aDetermined by H NMR (crude reaction mixture).

2412
D. C. Forbes et al.
iodide resulted in nearly identical levels of diastereocontrol. To explain
these results, we propose that at high temperatures, the decarboxylation
rate is fast providing relatively high levels of ylide that can be trapped
by suitably modified p-acceptors. Attempts to react sulfonium salt 1 with
unactivated imines resulted in recovery of the starting imine. As we noted
in prior reports, as the electrophilicity of the carbonyl compound
decreases, the forward rate of reaction slows down and fails to compete
effectively with ylide fragmentation and other side reactions. These obser-
vations and the data presented herein document the clear relationship
between electronic control and diastereoselectivity. Research in our group
continues in the areas of (1) understanding the electrostatic relationships
of this process, (2) increasing the scope of substrate using modified sulfo-
nium salts, and (3) preparation and use of a chiral, nonracemic sulfide pro-
moter. The results from these studies will be reported in due course.
CONCLUSION
Methylene transfer to imine functionality activated and directed with a
tert-butyl sulfinyl moiety using decarboxylation of arylcarboxymethylsul-
fonium betaines has been achieved. Although extremely high levels of
imine conversion were observed, the levels of diastereocontrol are at best
considered to be moderate. The levels of conversion were significant espe-
cially when working with electron-releasing aryl imine functionality.
Although greater levels of diastereocontrol could be achieved when oper-
ating at cooler reaction temperatures, cooler temperatures resulted in
lower levels of conversion, given that the protocol has as its key step
the thermal decarboxylation of carboxymethyl betaine functionality.
Notwithstanding the levels of diastereocontrol nor the thermal
requirements when considering conversion, the ease by which the sulfur
ylide is generated and both the scope and levels of conversion obtained
are, together, the key advantages of this method over other existing
technologies.
EXPERIMENTAL
Representative Procedure for the Preparation of N-Sulfinyl Imines
Aldehyde (1.5 equiv), anhydrous copper sulfate (2.0 equiv), anhydrous
dichloromethane (3.0 mL), and (S)-(ꢁ)-2-methyl-2-propane sulfinamide
(1.0 equiv, 2.0 mmol) was added to a 50-ml, round-bottomed flask
equipped with a stir bar and septum. The reaction mixture was allowed

Methylene Transfers onto Chiral Sulfinimines
2413
to stir under an argon atmosphere for a period of 24 h, at which time the
reaction was monitored by thin-layer chromatography (TLC) analysis
until complete. When complete as judged by TLC analysis, the reaction
mixture was filtered. After concentration of the filtrate in vacuo, the
crude reaction mixture was immediately purified by silica-gel chromato-
graphy (radial chromatography) using a gradient eluent system of
hexanes and EtOAc (9:1) to afford analytically pure N-sulfinyl imine.
[S(S),N(E)]-2-Methyl-N-[(phenyl)methylene]-2-propanesulfinamide
From the combination of 0.242 g (2 mmol), (S)-(ꢁ)-2-methyl-2-propane
sulfonamide, 0.318 g (3 mmol) benzaldehyde, and 0.640 g (4 mmol) CuSO4,
0.470 g (95%) of the title compound was isolated as an oil after silica gel
25
chromatography. Analytical data: ½aꢂD þ 109 (c 1.0, CHCl3). [(R)-(ꢁ) lit.
20
½aꢂD ꢁ 104 (c 1.0, CHCl3)].[12] IR (cmꢁ1) 2960, 2924, 1605, 1572, 1449,
1
1082; H NMR (300 MHz, CDCl3) d 7.85 (d, J ¼ 7.8, 2H), 7.52–7.45 (m,
3H), 1.23 (s, 9H);13C NMR (75MHz, CDCl3) d 162.8, 134.1, 132.5,
129.4, 129.0, 57.8, 22.7; TLC Rf 0.41 (EtOAc=hexane, 1=9). HRMS (ESI)
calcd. for C11H15NOS (M þ H) 210.0953; found 210.0946.
[S(S),N(E)]-2-Methyl-N-[(4-nitrophenyl)methylene]-2-propanesulfinamide
From the combination of 0.242 g (2 mmol) (S)-(ꢁ)-2-methyl-2-propane
sulfonamide, 0.453 g (3 mmol) 4-nitrobenzaldehyde, and 0.640 g (4 mmol)
CuSO4, 0.401 g (96%) of the title compound was isolated as a yellow solid
25
after silica-gel chromatography. Analytical data: ½aꢂD þ57 (c 1.0, CHCl3),
22
mp 131–132ꢀC; [(R)-(ꢁ) lit. ½aꢂD ꢁ55 (c 1.0, CHCl3), mp 138–140ꢀC].[13]
IR (cmꢁ1) 3113, 2950, 1615, 1585, 1530, 1473, 1313, 1178, 1007; 1H NMR
(300 MHz, CDCl3) d 8.66 (s, 1H), 8.32 (d, J ¼ 8.7, 2H), 8.01 (d, J ¼ 7.8,
2H), 1.25 (s, 9H); 13C NMR (75 MHz, CDCl3) d 160.7, 149.9, 138.9,
130.1, 124.3, 58.5, 22.7; TLC Rf 0.38 (EtOAc=hexane, 1=9). HRMS
(ESI) calcd. for C11H14N2O3S (M þ H) 255.0810; found: 255.0808.
[S(S),N(E)]-2-Methyl-N-[(4-chlorophenyl)methylene]-2-
propanesulfinamide
From the combination of 0.242 g (2 mmol) (S)-(ꢁ)-2-methyl-2-propane
sulfonamide, 0.423 g (3 mmol) 4-chlorobenzaldehyde, and 0.640 g
(4 mmol) CuSO4, 0.447 g (92%) of the title compound was isolated as a
25
white solid after silica-gel chromatography. Analytical data: ½aꢂD þ76
(c 1.0, CHCl3), mp 41–42ꢀC [lit. mp ((R)-(ꢁ)) 41–42ꢀC].15 IR (cmꢁ1
)

2414
D. C. Forbes et al.
2982, 2955, 1608, 1589, 1466, 1213, 1083, 674; 1H NMR (300 MHz,
CDCl3) d 8.52 (s, 1H), 7.76 (d, J ¼ 8.5, 2H), 7.43 (d, J ¼ 8.2, 2H), 1.24
(s, 9H);13C NMR (75 MHz, CDCl3) d 161.5, 138.7, 132.5, 130.6, 129.4,
58.0, 22.6; TLC Rf 0.40 (EtOAc=hexane, 1=9). HRMS (ESI) calcd. for
C11H14ClNOS (M þ H) 244.0567; found 244.0563.
[S(S),N(E)]-2-Methyl-N-[(2,6-dichlorophenyl)methylene]-2-
propanesulfinamide
From the combination of 0.242 g (2 mmol) of (S)-(ꢁ)-2-methyl-2-propane
sulfonamide, 0.525 g (3 mmol) 2,6-dichlorobenzaldehyde, and 0.640 g
(4 mmol) CuSO4, 0.371 g (67%) of the title compound was isolated as
25
an oil after silica-gel chromatography. Analytical data: ½aꢂD þ86 (c 1.0,
CHCl3). IR (cmꢁ1) 2982, 2955, 1608, 1589, 1565, 1486, 1213, 1083,
674; 1H NMR (300 MHz, CDCl3) d 8.90(s, 1H), 7.39–7.37 (m, 3H),
1.30 (s, 9H);13C NMR (75 MHz, CDCl3) d 159.4, 135.8, 131.7, 130.4,
129.3, 58.0, 22.6; TLC Rf 0.39 (EtOAc=hexane, 1=9). HRMS (ESI) calcd.
for C11H13Cl2NOS (M þ H) 278.0168; found 278.0173.
[S(S),N(E)]-2-Methyl-N-[(4-methoxyphenyl)methylene]-2-
propanesulfinamide
From the combination of 0.242 g (2 mmol) (S)-(ꢁ)-2-methyl-2-propane
sulfonamide, 0.408 g (3 mmol) 4-methoxybenzaldehyde, and 0.640 g
(4 mmol) CuSO4, 0.458 g (96%) of the title compound was isolated as a
25
white solid after silica-gel chromatography. Analytical data: ½aꢂD þ65
23
(c 1.0, CHCl3), mp 91–92ꢀC, [(R)-(ꢁ)- lit. ½aꢂD ꢁ70 (c 1.0, CHCl3), mp
91–93ꢀC].14 IR (cmꢁ1) 2982, 2959, 1588, 1567, 1508, 1456, 1305, 1256,
1
1078; H NMR (75 MHz, CDCl3) d 8.50 (s, 1H), 7.79 (d, J ¼ 8.5, 2H),
6.96 (d, J ¼ 8.4, 2H), 3.86 (s, 3H), 1.19 (s, 9H); 13C NMR (300 MHz,
CDCl3) d 163.1, 161.8, 131.3, 127.3, 114.4, 57.6, 55.5, 22.6; TLC Rf
0.33 (EtOAc=hexane, 1=9). HRMS (ESI) calcd. for C12H17NO2S
(M þ H) 240.1058; found: 240.1051.
[S(S),N(E)]-2-Methyl-N-[(3,4-methylenedioxyphenyl)methylene]-2-
propanesulfinamide
From the combination of 0.242 g (2 mmol) (S)-(ꢁ)-2-methyl-2-
propane sulfonamide, 0.450 g (3 mmol) 3,4-methylenedioxybenzaldehyde
(piperonaldehyde), and 0.640 g (4mmol) CuSO4, 0.445 g (88%) of the title
compound was isolated as a white solid after silica gel chromatography.

Methylene Transfers onto Chiral Sulfinimines
2415
25
Analytical data: ½aꢂD þ2.6 (c 1.0, CHCl3), mp 64–65ꢀC; IR (cmꢁ1) 2965,
1
2927, 2893, 1622, 1578, 1498, 1253, 1071; H NMR (300 MHz, CDCl3) d
8.37 (s, 1H), 7.17 (d, J¼ 7.9, 2H), 6.76 (d, J¼ 7.9, 2H), 5.93 (s, 2H), 1.07
(s, 9H);13C NMR (75MHz, CDCl3) d 161.6, 151.4, 148.5, 129.0, 126.9,
108.3, 107.1, 101.8, 57.6, 22.5; TLC Rf 0.34 (EtOAc=hexane, 1=9). HRMS
(ESI) calcd. for C12H15NO3S (M þ H) 254.0851; found: 254.0847.
[S(S),N(E)]-2-Methyl-N-[(4-hydroxy-3-methoxyphenyl)methylene]-2-
propanesulfinamide
From the combination of 0.242 g (2 mmol) (S)-(ꢁ)-2-methyl-2-propane
sulfonamide, 0.456 g (3 mmol) 4-hydroxy-3-methoxybenzaldehyde, and
0.640 g (4 mmol) CuSO4, 0.357 g (70%) of the title compound was isolated
25
as a white solid after silica gel chromatography. Analytical data: ½aꢂD
þ24 (c 1.0, CHCl3), mp 109–110ꢀC; IR (cmꢁ1) 3203, 2957, 1573, 1509,
1
1455, 1287, 1029, 865, 821; H NMR (75 MHz, CDCl3) d 8.46 (s, 1H),
7.41–7.32 (m, 2H), 6.98 (d, J ¼ 7.9, 1H), 6.21 (s, 1H), 3.94 (s, 3H), 1.25
(s, 9H); 13C NMR (300 MHz, CDCl3) d 162.1, 150.0, 147.0, 127.1,
125.5, 114.6, 109.8, 57.7, 56.1, 22.6; TLC Rf 0.30 (EtOAc=hexane, 2=8).
HRMS (ESI) calcd. for C12H17NO3S (M þ H) 256.1007; found: 256.0998.
Representative Procedure for the Aziridination of N-Sulfinyl Imines
An oven-dried, 25-mL, round-bottomed flask was equipped with a stir
bar, septum, and condenser. To this system was added (S)-N-sulfinyl
imine (1.0 equiv, 1.0 mmol), cesium carbonate (8.0 equiv), THF
(3.0 mL) and (as a solution), sulfonium salt (6.0 equiv) in THF
(2.0 mL). The solution of sulfonium salt was added in two equal portions
at an interval of 6 h via syringe. The system was externally heated to 80ꢀC
(sand bath). The reaction mixture was allowed to stir for a period of 12 h
to assure completion of reaction. After cooling to room temperature, the
reaction mixture was concentrated in vacuo and immediately purified by
chromatography using neutral alumina and a gradient eluent system of
hexanes and EtOAc (9:1) to afford analytically pure aziridine.
1-[(1,1-Dimethylethyl)sulfinyl]-2-phenylaziridine
From the combination of N-[t-butyl-(S)-sulfinyl]-2-(phenyl)imine
(0.209 g, 1.00 mmol), cesium carbonate (2.584 g, 8.00 mmol), and
carboxymethylmethylphenylsulfonium trifluoromethanesulfonate (1.992g,
6.00mmol) in 2.0 mL of THF, a 74:26 mixture of diastereomers was
measured as determined by 1H NMR of the crude reaction mixture. After

2416
D. C. Forbes et al.
purification by column chromatography using neutral alumina, 0.211 g
(95% yield) of the title compound was obtained. Analytical data of
mixture: IR (cmꢁ1), 3067, 2982, 2868, 1605, 1497, 1073; 1H NMR
(300 MHz, CDCl3) d 7.31–6.91 (m, 5H), 3.61 [t, J ¼ 4.1, 1H (major)],
3.11 [t, J ¼ 3.8, 1H (minor)], 2.91 [d, J ¼ 6.8, 1H (minor)], 2.44 [d,
J ¼ 7.0, 1H (major)], 2.16 [d, J ¼ 3.8, 1H (major)], 2.01 [d, J ¼ 3.8, 1H
(minor)], 1.26 [s, 9H (minor)], 1.17 [s, 9H (major)]; 13C NMR (75 MHz,
CDCl3) d 138.2, 137.5, 129.4, 129.1, 129.0, 128.3, 127.2, 126.9, 57.9,
57.4, 35.3, 32.4, 32.0, 29.2, 23.3; TLC Rf 0.39 (EtOAc=hexane, 1=4).
HRMS (ESI) calcd. for C12H17NOS (M þ H): 224.1109; found:
224.1108. Diagnostic analytical data of major isomer (1H NMR): d
3.61 (t, J ¼ 4.1, 1H), 2.44 (d, J ¼ 7.0, 1H), 2.16 (d, J ¼ 3.8, 1H), 1.17
(s, 9H). Diagnostic analytical data of minor isomer (1H NMR): d 3.11
(t, J ¼ 3.8, 1H), 2.91 (d, J ¼ 6.8, 1H), 2.01 (d, J ¼ 3.8, 1H), 1.26 (s, 9H).
1-[(1,1-Dimethylethyl)sulfinyl]-2-(4-nitrophenyl)aziridine
From the combination of N-[t-butyl-(S)-sulfinyl]-2-(4-nitrophenyl)imine
(0.254 g, 1.00mmol), cesium carbonate (2.584g, 8.00mmol), and carboxy-
methylmethylphenylsulfonium trifluoromethanesulfonate (1.992 g, 6.00 mmol)
in 2.0 mL of THF, an 87:13 mixture of diastereomers was measured as
determined by 1H NMR of the crude reaction mixture. After purification
by column chromatography using neutral alumina, 0.260 g (97% yield) of
the title compound was obtained. Analytical data of mixture: IR (cmꢁ1
)
1
2982, 2867, 1601, 1518, 1474, 1315, 1079; H NMR (300 MHz, CDCl3)
d 8.21 (d, J ¼ 7.0, 2H), 7.44 (d, J ¼ 7.0, 2H), 3.68 (t, J ¼ 3.8, 1H (major)),
3.17 [t, J ¼ 3.5, 1H (minor)], 3.00 [d, J ¼ 7.0, 1H (minor)], 2.50 [d, J ¼ 7.0,
1H (major)], 2.20 [d, J ¼ 3.8, 1H (major)], 2.01 [d, J ¼ 3.8, 1H (minor)],
1.30 [s, 9H (minor)], 1.16 [s, 9H (major)]; 13C NMR (75 MHz, CDCl3) d
148.0, 145.8, 145.2, 128.0, 124.5, 124.2, 58.2, 57.6, 34.5, 33.0, 31.2, 29.7,
23.2, 23.1; TLC Rf 0.32 (EtOAc=hexane, 2=8). HRMS (ESI) calcd. for
C12H16N2O3S (M þ H) 269.0960; found: 269.0949. Diagnostic analytical
data of major isomer (1H NMR): d 3.68 (t, J ¼ 3.8, 1H), 2.50 (d, J ¼ 7.0,
1H), 2.20 (d, J ¼ 3.8, 1H), 1.16 (s, 9H). Diagnostic analytical data of minor
isomer (1H NMR): d 3.17 (t, J ¼ 3.5, 1H), 3.00 (d, J ¼ 7.0, 1H), 2.01
(d, J ¼ 3.8, 1H), 1.30 (s, 9H).
1-[(1,1-Dimethylethyl)sulfinyl]-2-(4-chlorophenyl)aziridine
From the combination of N-[t-butyl-(S)-sulfinyl]-2-(4-chlorophenyl)imine
(0.243 g, 1.00 mmol), cesium carbonate (2.584 g, 8.00 mmol), and

Methylene Transfers onto Chiral Sulfinimines
2417
carboxymethylmethylphenylsulfonium trifluoromethanesulfonate (1.992 g,
6.00 mmol) in 2.0 mL of THF, a 78:22 mixture of diastereomers was
1
measured as determined by H NMR of the crude reaction mixture. After
purification by column chromatography using neutral alumina, 0.246 g
(96% yield) of the title compound was obtained. Analytical data of mixture:
1
IR (cmꢁ1) 2981, 2903, 2871, 1493, 1455, 1080, 663; H NMR (300MHz,
CDCl3) d 7.31–7.18 (m, 4H), 3.56 [t, J ¼ 3.8, 1H (major)], 3.05 [t, J¼ 3.8,
1H (minor)], 2.98 [d, J¼ 6.8, 1H (minor)], 2.45 [d, J ¼ 6.8, 1H (major)],
2.12 [d, J¼ 3.8, 1H (major)], 1.95 [d, J ¼ 3.8, 1H (minor)], 1.28 [s, 9H
(minor)], 1.16 [s, 9H (major)]; 13C NMR (75 MHz, CDCl3) d 135.7, 128.9,
128.7, 128.1, 127.8, 57.5, 57.0, 34.2, 32.0, 30.9, 28.7, 22.8; TLC Rf 0.38
(EtOAc=hexane, 2=8). HRMS (ESI) calcd. for C12H16NClOS (M þ H)
258.0719; found: 258.0717. Diagnostic analytical data of major isomer (1H
NMR): d 3.56 (t, J ¼ 3.8, 1H), 2.45 (d, J ¼ 6.8, 1H), 2.12 (d, J¼ 3.8, 1H),
1.16 (s, 9H). Diagnostic analytical data of minor isomer (1H NMR): d 3.05
(t, J ¼ 3.8, 1H), 2.98 (d, J ¼ 6.8, 1H), 1.95 (d, J ¼ 3.8, 1H), 1.28 (s, 9H).
1-[(1,1-Dimethylethyl)sulfinyl]-2-(2,6-dichlorophenyl)aziridine
From the combination of N-[t-butyl-(S)-sulfinyl]-2-(2,6-dichlorophenyl)
imine (0.277 g, 1.00 mmol), cesium carbonate (2.584 g, 8.00 mmol), and
carboxymethylmethylphenylsulfonium trifluoromethanesulfonate (1.992g,
6.00mmol) in 2.0 mL of THF, a 77:23 mixture of diastereomers was
measured as determined by 1H NMR of the crude reaction mixture. After
purification by column chromatography using neutral alumina, 0.274 g
(94% yield) of the title compound was obtained. Analytical data of mixture:
1
IR (cmꢁ1) 2983, 2921, 2864, 1560, 1455, 1205, 1082, 837, 729; H NMR
(300 MHz, CDCl3) d 7.29–7.07 (m, 3H), 4.18 (s, 1H), 3.14–3.07 (m, 2H),
2.35 [d, J ¼ 7.1, 1H (major)], 2.25 [d, J ¼ 3.8, 1H (minor)], 1.25 [s, 9H
(minor)], 1.18 [s, 9H (major)]; 13C NMR (75 MHz, CDCl3) d 137.3,
136.7, 133.4, 130.5, 130.0, 129.9, 129.5, 129.0, 57.8, 57.4, 33.5, 30.6, 30.2,
27.9, 23.2, 23.0; TLC Rf 0.37 (EtOAc=hexane, 2=8). HRMS (ESI) calcd.
for C12H15Cl2NOS (Mþ H) 292.0327; found: 292.0330. Diagnostic analy-
tical data of major isomer (1H NMR): d 2.35 (d, J ¼ 7.1, 1H), 1.18
(s, 9H). Diagnostic analytical data of minor isomer (1H NMR): d 2.25
(d, J ¼ 3.8, 1H), 1.25 (s, 9H).
1-[(1,1-Dimethylethyl)sulfinyl]-2-(4-methoxyphenyl)aziridine
From the combination of N-[t-butyl-(S)-sulfinyl]-2-(4-methoxyphenyl)imine
(0.239 g, 1.00 mmol), cesium carbonate (2.584 g, 8.00 mmol), and

2418
D. C. Forbes et al.
carboxymethylmethylphenylsulfonium trifluoromethanesulfonate (1.992 g,
6.00mmol) in 2.0 mL of THF, a 66:24 mixture of diastereomers was mea-
sured as determined by 1H NMR of the crude reaction mixture. After pur-
ification by column chromatography using neutral alumina, 0.225 g (89%
yield) of the title compound was obtained. Analytical data of mixture: IR
1
(cmꢁ1) 3053, 2907, 1608, 1504, 1445, 1262, 1037; H NMR (300MHz,
CDCl3) d 7.19 (d, J¼ 8.5, 2H), 6.86 (d, J ¼ 8.5, 2H), 3.86 (s, 3H), 3.79 [s,
3H (major)], 3.55 [t, J¼ 3.8, 1H (major)], 3.05 [t, J¼ 3.8, 1H (minor)],
2.94 [d, J¼ 6.8, 1H (minor)], 2.41 [d, J ¼ 6.8, 1H (major)], 2.13 [d, J ¼ 4.0,
1H (major)], 1.96 [d, J¼ 3.8, 1H (minor)], 1.24 [s, 9H (minor)], 1.16 [s, 9H
(major)]; 13C NMR (75 MHz, CDCl3) d 159.8, 129.4, 129.3, 128.3, 128.0,
114.5, 114.4, 57.9, 57.4, 55.85, 55.82, 35.0, 32.2, 31.7, 30.2, 23.39, 23.36;
TLC Rf 0.34 (EtOAc=hexane, 1=9). HRMS (ESI) calcd. for C13H19NO2S
(M þ H) 254.1215; found: 254.1215. Diagnostic analytical data of major iso-
mer (1H NMR): d 3.79 (s, 3H), 3.55 (t, J¼ 3.8, 1H), 2.41 (d, J ¼ 6.8, 1H),
2.13 (d, J ¼ 4.0, 1H), 1.16 (s, 9H). Diagnostic analytical data of minor isomer
(1H NMR): d 3.86 (s, 3H), 3.05 (t, J ¼ 3.8, 1H), 2.94 (d, J ¼ 6.8, 1H), 1.96
(d, J ¼ 3.8, 1H), 1.24 (s, 9H).
1-[(1,1-Dimethylethyl)sulfinyl]-2-(3,4-methylenedioxyphenyl)aziridine
From the combination of N-[t-butyl-(S)-sulfinyl]-2-(4-nitrophenyl)imine
(0.253 g, 1.00mmol), cesium carbonate (2.584g, 8.00mmol), and carboxy-
methylmethylphenylsulfonium trifluoromethanesulfonate (1.992 g, 6.00 mmol)
in 2.0 mL of THF, a 84:16 mixture of diastereomers was measured as
determined by 1H NMR of the crude reaction mixture. After purification
by column chromatography using neutral alumina, 0.225 g (85% yield) of
the title compound was obtained. Analytical data of mixture: IR (cmꢁ1
)
2962, 2934, 1605, 1562, 1439, 1062; 1H NMR (300 MHz, CDCl3)
d 6.85–6.66 (m, 3H), 5.91 (t, J ¼ 1.6, 2H), 3.49 (t, J ¼ 3.8, 1H (major)),
3.01 [t, J ¼ 3.8, 1H (minor)], 2.90 [d, J ¼ 6.8, 1H (minor)], 2.36 [d,
J ¼ 6.8, 1H (major)], 2.06 [d, J ¼ 3.8, 1H (major)], 1.90 [d, J ¼ 3.8, 1H
(minor)], 1.24 [s, 9H (minor)], 1.14 [s, 9H (major)]; 13C NMR (75 MHz,
CDCl3) d 148.5, 148.4, 147.8, 147.7, 132.1 131.4, 121.1, 120.7, 108.8,
108.7, 106.9, 106.8, 101.6, 57.9, 57.4, 35.2, 32.3, 32.0, 29.0, 23.3; TLC
Rf 0.34 (EtOAc=hexane, 2=8). HRMS (ESI) calcd. for C13H17NO3S
(M þ H) 268.1007; found: 268.1006. Diagnostic analytical data of major
isomer (1H NMR): d 3.49 (t, J ¼ 3.8, 1H), 2.36 (d, J ¼ 6.8, 1H), 2.06
(d, J ¼ 3.8, 1H), 1.14 (s, 9H). Diagnostic analytical data of minor isomer
(1H NMR): d 3.01 (t, J ¼ 3.8, 1H), 2.90 (d, J ¼ 6.8, 1H), 1.90 (d, J ¼ 3.8,
1H), 1.24 (s, 9H).

Methylene Transfers onto Chiral Sulfinimines
2419
1-[(1,1-Dimethylethyl)sulfinyl]-2-(4-hydroxy-3-methoxyphenyl)
aziridine
From the combination of N-[t-butyl-(S)-sulfinyl]-2-(4-hydroxy-3-methoxy-
phenyl)imine (0.127 g, 0.50 mmol), cesium carbonate (1.292 g, 4.00 mmol),
and carboxymethylmethylphenylsulfonium trifluoromethanesulfonate
(0.996 g, 3.00 mmol) in 2.0 mL of THF, a 80:20 mixture of diastereomers
1
was measured as determined by H NMR of the crude reaction mixture.
After purification by column chromatography using neutral alumina,
0.125 g (93% yield) of the title compound was obtained. Analytical data
1
of mixture: IR (cmꢁ1) 3201, 2953, 2853, 1574, 1462, 1267, 1236, 1078; H
NMR (300 MHz, CDCl3) d 6.97–6.77 (m, 3H), 3.90 [s, 3H (minor)], 3.89
[s, 3H (major)], 3.57 [t, J ¼ 4.0, 1H (major)], 3.09 [t, J ¼ 3.8, 1H (minor)],
2.98 [d, J ¼ 6.8, 1H (minor)], 2.45 [d, J¼ 6.8, 1H (major)], 2.15 [d,
J¼ 3.8, 1H (major)], 2.01 [d, J ¼ 3.8, 1H (minor)], 1.30 [s, 9H (minor)],
1.20 [s, 9H (major)]; 13C NMR (75MHz, CDCl3) d 148.2, 148.0, 147.7,
129.1, 128.4, 118.3, 117.7, 110.1, 109.3, 108.2, 108.1, 56.4, 55.9, 54.8,
33.7, 30.7, 30.4, 27.5, 21.8, 21.5; TLC Rf 0.29 (EtOAc=hexane, 2=8).
HRMS calcd. for C13H19NO3S (M þ H) 270.1170; found: 270.1170.
Diagnostic analytical data of major isomer (1H NMR): d 3.89 (s, 3H), 3.57
(t, J ¼ 4.0, 1H), 2.45 (d, J ¼ 6.8, 1H), 2.15 (d, J ¼ 3.8, 1H), 1.20 (s, 9H). Diag-
nostic analytical data of minor isomer (1H NMR): d 3.90 (s, 3H), 3.09
(t, J ¼ 3.8, 1H), 2.98 (d, J ¼ 6.8, 1H), 2.01 (d, J ¼ 3.8, 1H), 1.30 (s, 9H).
Control Reaction: Reaction of N-Sulfinyl Imine with
Trimethylsulfonium Iodide
Trimethylsulfonium iodide (3 equiv) was added to a suspension of NaH (3
equiv of pentane washed 60% in mineral oil) in THF (2 mL). After 10 min
atroom temperature, the cloudyreaction mixture turned clear, at which point
in time a solution of N-sulfinyl imine (1 equiv) in THF (2 mL) was added
dropwise to the mixture. The reaction mixture was externally warmed to
80ꢀC. After stirring at this temperature for a period of 12 h, the reaction mix-
ture was allowed to cool to room temperature. Analysis of the crude reaction
mixture revealed a dr of 76:24. The crude reaction mixture was isolated and
purified as described previously to afford the desired material in 86% yield.
Control Reaction: Reaction of N-Sulfinyl Aziridine with Thioanisole
Thioanisole (0.25 mmol, 0.031 g, 1 equiv), THF (5 ml), 1-[(1,1-
dimethylethyl)sulfinyl]-2-(4-methoxyphenyl)aziridine (0.25 mmol, 0.063 g,

2420
D. C. Forbes et al.
1 equiv), and triethylamine (1 mmol, 0.10 g, 4 equiv) were added to a
25-ml, round-bottomed flask. The reaction mixture was externally
warmed to reflux (80ꢀC) while under an argon atmosphere and allowed
to react for a period of 10 h. When cooled to room temperature, the reac-
tion mixture was analyzed by 1H NMR, which revealed no change in the
initial aziridine-to-thioanisole ratio, indicating no reversion of the
aziridine to betaine intermediate under these reaction conditions.
Control Reaction: Reaction of N-Sulfinyl Aziridine with Thioanisole
in the Presence of N-Sulfinyl Imine
Thioanisole
(0.25 mmol,
0.031 g,
1
equiv),
THF
(5 ml),
1-[(1,1-dimethylethyl)sulfinyl]-2-(4-methoxyphenyl)aziridine (0.25 mmol,
0.063 g, 1 equiv), [S(S), N(E)]-2-methyl-N-[(4-nitrophenyl)methylene]-2-
propanesulfinamide (0.25 mmol, 0.063 g, 1 equiv), and triethylamine
(1 mmol, 0.10 g, 4 equiv) were added to a 25-ml, round-bottomed flask.
The reaction mixture was externally warmed to reflux (80ꢀC) while under
an argon atmosphere and allowed to react for a period of 10 h. When
1
cooled to room temperature, the reaction mixture was analyzed by H
NMR, which revealed no change in the initial ratio of aziridine to thio-
anisole to imine, indicating no reversion of the aziridine to betaine inter-
mediate under these reaction conditions. If reversion was to occur,
trapping the ylide with the more reactive imine was anticipated, and
having no evidence of this derivative in solution, reversion under these
reactions conditions is not proposed.
ACKNOWLEDGMENTS
D. C. F. thanks National Science Foundation (NSF) (CHE 0514004)
and the Camille and Henry Dreyfus Foundation (TH-06-008) for par-
tial funding of this research. S. R. A., C. J. B., and A. M. L. acknowl-
edge financial support through NSF (OISE 0405210), the Alabama
Space Grant Scholars Program, and the University of South Alabama
(University Committee on Undergraduate Research and the University
Honor Program).
REFERENCES
1. (a) Yudin, A. (Ed.), Aziridines and Epoxides in Organic Synthesis; Wiley:
New York, 2006; (b) Trost, B. M.; Melvin, L. S. Jr. In Sulfur Ylides Emerging
Synthetic Intermediates; Academic Press: New York, 1975; vol. 31;

Methylene Transfers onto Chiral Sulfinimines
2421
(c)Nitrogen, Oxygen, and Sulfur Ylides Chemistry: A Practical Approach; J. S.
Clark (Ed.); Oxford University Press: Oxford, 2002.
2. McGarrigle, E. M.; Myers, E. L.; Illa, O.; Shaw, M. A.; Riches, S. L.;
Aggarwal, V. K. Chalcogenides as organocatalysts. Chem. Rev. 2007, 107,
5841.
3. (a) Dalko, P. I.; Moisan, L. In the golden age of organocatalysis. Angew.
Chem., Int. Ed. 2004, 43, 5138; (b) Dai, L.-X.; Hou, X.-L.; Zhou, Y.-G.
Stereoselective synthesis of three-membered ring compounds via ylide routes.
Pure Appl. Chem. 1999, 71, 369.
4. (a) Blot, V.; Brier, J.-F.; Davoust, M.; Miniere, S.; Reboul, V.; Metzner, P.
Developments of asymmetric synthesis mediated by chiral sulfur reagents.
Phosphorus, Sulfur, Silicon Relat. Elem. 2005, 180, 1171; (b) Aggarwal, V.
K. In Comprehensive Asymmetric Catalysis; E. N. Jacobsen, A. Pfaltz, H.
Yamamoto, (Eds.); Springer-Verlag: Heidelberg, 1999; vol. 2, pp. 679–693;
(c) Li, A.-H.; Dai, L.-X.; Aggarwal, V. K. Asymmetric ylide reactions: Epox-
idation, cyclopropanation, aziridination, olefination, and rearrangement.
Chem. Rev. 1997, 97, 2341; (d) Stockman, R. A. Heterocyclic chemistry.
Ann. Rep. Prog. Chem., Sec. B. 2004, 100, 149.
5. (a) Forbes, D. C.; Standen, M. C.; Lewis, D. L. Sulfur ylides via decarboxyla-
tion of carboxymethylsulfonium betaines: A novel and mild protocol for the
preparation of oxiranes. Org. Lett. 2003, 5, 2283; (b) Forbes, D. C.; Amin, S.
R.; Bean, C. J.; Standen, M. C. Aryl-substituted sulfonium betaines: Prepara-
tion and use in the epoxidation of aldehydes. J. Org. Chem. 2006, 71, 8287.
6. (a) Cheng, J.-P.; Liu, B.; Zhang, X.-M. Radical substituent effects of
a-sulfonium groups J. Org. Chem. 1998, 63, 7574; (b) Johnson, A. W.; Amel,
R. T. The chemistry of ylides, XVI: The acidifying effects of onium groups.
Can. J. Chem. 1968, 46, 461.
7. (a) Chigboh, K.; Nadin, A.; Stockman, R. A. Direct synthesis of substituted
vinyl aziridines. Synlett 2007, 18, 2879; (b) Morton, D.; Stockman, R. A.
Chiral non-racemic sulfinimines: Versatile reagents for asymmetric synthesis.
Tetrahedron 2006, 62, 8869; (c) Morton, D.; Pearson, D.; Field, R. A.;
Stockman, R. A. A convenient synthesis of chiral nonracemic vinyl aziridines.
Org. Lett. 2004, 6, 2377; (d) Morton, D.; Pearson, D.; Field, R. A.; Stockman,
R. A. Corey–Chaykovsky reaction of chiral sulfinyl imines: A convenient
procedure for the formation of chiral aziridines. Synlett 2003, 13, 1985.
8. Aggarwal, V. K.; Harvey, J. N.; Richardson, J. Unraveling the mechanism of
epoxide formation from sulfur ylides and aldehydes. J. Am. Chem. Soc. 2002,
124, 5747.
9. Edwards, D. R.; Du, J.; Crudden, C. M. Experimental demonstration of
base-catalyzed interconversion of isomeric betaine intermediates in the
coreyꢁchaykovsky epoxidation. Org. Lett. 2007, 9, 2397.
10. Robiette, R. Mechanism and diastereoselectivity of aziridine formation from
sulfur ylides and imines: A computational study. J. Org. Chem. 2006, 71,
2726.
11. Using the dissociation constants for benzoic acid, the rmeta value for OCH3
is þ 0.12, whereas the rpara value for OCH3 is ꢁ0.27 (ꢁ0.37 for OH). For a

2422
D. C. Forbes et al.
more extended list, see Ritchie, C. D.; Sager, W. F. An examination of
structure–reactivity relationships Prog. Phys. Org. Chem. 1964, 2, 323, and
Hansch, C.; Leo, A.; Unger, S.; Kim, K. H.; Nikaitani, D.; Liem, E.
J. ‘‘Aromatic’’ substituent constants for structure–activity correlations.
J. Med. Chem. 1973, 16, 1207.
12. Ardej-Jakuhisiak, M.; Kawecki, R.; Swietlinska, A. A facile synthesis of
N-sulfinylaldimines. Tetrahedron: Asymmetry 2007, 18, 2507.
13. Morton, D. tert-Butyl-sulfinimines: A convinent synthesis of chiral aziridines
(Ph.D thesis, University of East Anglia, Norwich, June 2005).
14. Plobeck, N.; Powell, D. Asymmetric synthesis of diarylmethylamines by
diastereoselective addition of organometallic reagents to chiral N-tert-butane-
sulfinimines: Switchover of diastereofacial selectivity. Tetrahedron:
Asymmetry 2002, 13, 303.