Synthesis of hyperbranched poly(aryl amine)s via a carbene insertion approach

Article abstract of DOI:10.1039/b804392m

A novel diazirine functionalised aniline derivative, 3-(3-aminophenyl)-3- methyldiazirine 1, was prepared and employed as an AB₂-type monomer in the synthesis of hyperbranched polymers; thus providing the first instance in which polyamines have been prepared via carbene insertion polymerisation. Photolysis of the monomer 1 in bulk and in solution resulted in the formation of hyperbranched poly(aryl amine)s with degrees of polymerisation (DP) varying from 9 to 26 as determined by gel permeation chromatography (GPC). In solution, an increase in the initial monomer concentration was generally found to result in a decrease in the molecular weight characteristics of the resulting poly(aryl amine)s. Subsequent thermal treatment of the poly(aryl amine)s caused a further increase in the DP values up to a maximum of 31. Nuclear magnetic resonance (NMR) spectroscopic analysis revealed that the increase in molecular weight upon thermal treatment resulted from hydroamination of styrenic species formed in the initial photopolymerisation or activation of diazirine moieties.

Full text of DOI:10.1039/b804392m

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PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Synthesis of hyperbranched poly(aryl amine)s via a carbene insertion approach
Anton Blencowe,†a William Fagour,a Chris Blencowe,a Kevin Cosstickb and Wayne Hayes*a
Received 13th March 2008, Accepted 18th March 2008
First published as an Advance Article on the web 22nd April 2008
DOI: 10.1039/b804392m
A novel diazirine functionalised aniline derivative, 3-(3-aminophenyl)-3-methyldiazirine 1, was prepared
and employed as an AB2-type monomer in the synthesis of hyperbranched polymers; thus providing the
first instance in which polyamines have been prepared via carbene insertion polymerisation. Photolysis
of the monomer 1 in bulk and in solution resulted in the formation of hyperbranched poly(aryl amine)s
with degrees of polymerisation (DP) varying from 9 to 26 as determined by gel permeation
chromatography (GPC). In solution, an increase in the initial monomer concentration was generally
found to result in a decrease in the molecular weight characteristics of the resulting poly(aryl amine)s.
Subsequent thermal treatment of the poly(aryl amine)s caused a further increase in the DP values up to
a maximum of 31. Nuclear magnetic resonance (NMR) spectroscopic analysis revealed that the
increase in molecular weight upon thermal treatment resulted from hydroamination of styrenic species
formed in the initial photopolymerisation or activation of diazirine moieties.
process possessed enhanced solubility and processability whilst
Introduction
retaining highly desirable magnetic properties similar to their
Hyperbranched polyamine macromolecules (including den-
linear analogues. Highly conjugated hyperbranched poly(amino
drimers) have received significant attention over the past 20 years
arylene)s prepared from functionalised triphenylamines exhibit
as a result of their wide range of potential biomedical and
a variety of enhanced functional properties, such as polyradical
cations with high-spin states,12 high light-emitting efficiencies and
photoconductivity,10,11 and, therefore, have potential in an array
of technological applications in organic electronics, photonics and
spintronics.
materials applications, including adhesives, printing inks, dyes,
fixative agents, cationic dispersants, chelating agents and scavenger
resins.1 The most widely developed dendritic polyamines are the
poly(propylene imine) (PPI) series developed by Meijer and co-
workers.2 However, PPI dendrimers are prepared via a labour
intensive multi-step divergent strategy involving repetitive Michael
additions and reductions. More recently, Haag and co-workers
have produced hyperbranched analogues3 of PPI dendrimers
by utilising poly(ethylene imine)s (PEI) as branching scaffolds.
Modified PEI/PPI hyperbranched polymers and PPI dendrimers
are currently being investigated for a number of biochemical
applications, including non-viral gene transfer vector design,3,4
drug delivery5,6 and as antimicrobial agents.7 Hyperbranched ally-
lamines have been prepared via palladium catalysed decarboxyla-
tive multi-branching ring-opening polymerisation of cyclic carba-
mates, such as 5,5-dimethyl-6-ethenylperhydro-1,3-oxazin-2-one,
using primary or secondary amines as initiators.8 Although the
monomers do not contain branch points, branching units are gen-
erated through propagation reactions leading to the formation of
hyperbranched polyamines with a degree of polymerisation (DP)
between 16 and 47, and a degree of branching (DB) between 44 and
81%. Hyperbranched polyanilines9 and poly(amino arylene)s10,11
have also been investigated thoroughly for their potential ap-
plication to conducting and magnetic polymeric materials—
hyperbranched m-polyanilines prepared via a palladium catalysed
After successfully developing a carbene insertion polymeri-
sation approach to hyperbranched polyethers,13 we decided to
investigate the preparation of hyperbranched polyamines via a
similar strategy. Herein, we present the foremost preparation of
hyperbranched polyamines using a diazirine functionalised aniline
derivative, 3-(3-aminophenyl)-3-methyldiazirine 1, as an AB2-type
monomer. The polymerisation proceeds by way of photochemical
activation of the diazirine moieties yielding highly reactive car-
benes that are capable of inserting into N–H bonds to afford
secondary (linear units) and tertiary (branched units) amines.
The polymerisation process was examined at various monomer
concentrations and in a variety of inert fluorinated solvents and
the resulting hyperbranched polyamines were analysed via GPC,
and NMR, UV-vis and IR spectroscopies.
Results and discussion
The aminodiazirine
1 was prepared in 4 steps from 3-
aminoacetophenone 2 (Scheme 1) using a similar procedure to that
reported by Liu et al.14 The acetophenone derivative 2 was firstly
converted to its corresponding benzylimine 3 through reaction
with benzylamine in the presence of zinc(II) chloride. The crude
imine 3 was subsequently reacted with hydroxylamine-O-sulfonic
acid (HOSA) in liquid ammonia to afford the diaziridine 4, which
was then oxidised to the aminodiazirine 1 using chromic acid.15
Polymerisation of the aminodiazirine monomer 1 (Scheme 2)
was conducted in bulk, as suspensions in perfluorinated solvents
and in solution. Initially, the monomer 1 and solvent were added
aDepartment of Chemistry, The University of Reading, Whiteknights,
Reading, UK RG6 6AD. E-mail: w.c.hayes@reading.ac.uk.; Tel: +44 (0)118
378 6491
bInvista (UK), P.O. Box 401, Wilton Site, Middlesbrough, Cleveland, UK
TS6 8JJ
† Current address: Polymer Science Group, Department of Chemical
and Biomolecular Engineering, The University of Melbourne, Parkville,
Melbourne, Victoria 3010, Australia.
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Scheme
1 Synthesis of 3-(3-aminophenyl)-3-methyldiazirine 1: (a)
BnNH2, ZnCl2, ꢀ; (b) NH3, HOSA, −78 ◦C; (c) NaCr2O7, H2SO4.
Fig. 1 GPC RI traces of poly(aryl amines)s prepared: (a) from photolysis
of monomer 1 in bulk (P1c), hexafluorobenzene (P1d) and perfluoropy-
ridine (P1e); (b) from photolysis and thermolysis of monomer 1 in bulk
(P2c) and hexafluorobenzene (P2d); (c) at monomer concentrations of
0.08, 0.17, 0.34, 0.68 and 1.35 M (P3a–e, respectively).
been well established17 that conventional calibration with linear
polymers underestimates the molecular weight characteristics of
hyperbranched macromolecules, it enabled comparison of the
polyamines prepared via different conditions without providing
absolute molecular weights.
The polyamines P1a–c prepared via photolysis in bulk or as
suspensions had comparable molecular weights corresponding to
a DP of 9 (Table 1). Solution phase polymerisations conducted
in hexafluorobenzene (C6F6) and perfluoropyridine (C5F5N) af-
forded polyamines P1d–e, which possessed DPs of 13 and 14,
respectively. The difference in molecular weight of polyamines
prepared in solution and those in bulk is believed to arise from
the close proximity of the monomers in bulk and suspension
photopolymerisations, which results in the formation of azines18
that compete with the desired carbene insertion mechanism.
Upon thermal treatment all the polymers increased in molecular
weight to afford polyamines P2a–d with DPs of 12–31. This
increase was most prominent for polymer P2d, for which the
DP more than doubled. This increase in Mw can clearly be
observed in the GPC RI trace of polymer P2d (Fig. 1, (b)), which
shows the disappearance of a low molecular weight shoulder
present at ca. 0.6 kDa in the trace of polymer P1d (Fig. 1, (a))
and a significant increase in the upper molecular weight range
from ca. 10 to 50 kDa. The observed increase in molecular
weight was postulated to occur as result of: (i) the formation of
reactive carbenes from the activation of diazirine or diazoalkane
moieties present after the initial photopolymerisation, and/or
(ii) hydroamination of styrenic species formed from 1,2-hydrogen
migration of photogenerated carbenes.19,20
Scheme 2 Synthesis of hyperbranched polyamines from the aminodi-
azirine 1.
to a glass vial fitted with a stirrer bar, which was argon flushed and
sealed. The vial was placed 2 cm away from a 125 watt high-power
mercury vapour lamp and irradiated for 24 h. Suspension phase
reactions were vortexed at 1200 rpm prior to irradiation to produce
a fine suspension of the monomer in the solvent, which was
maintained during the reaction with rapid stirring. Perfluorinated
solvents were employed to eliminate any unwanted reaction of
the photogenerated carbenes with the reaction medium, as the
inherent strength of C–F bonds (DHbond ≈ 488 kJ mol−1) deters
carbene insertion. The solvent was removed in vacuo and the
residue dried to afford polyamines P1a–e (94–99%) as yellow to
brown solids. To ensure complete decomposition of the diazirine
moieties and any diazoalkanes (formed via isomerisation of the
diazirines16) the polymers were heated at 150 ◦C in vacuo for
12 h to afford polyamines P2a–e, respectively, as glassy brown
solids with a reduction in weight of 0–4%. All of the polymers
with the exception of P2e were soluble in methanol, N,N-
dimethylformamide (DMF) and dimethylsulfoxide (DMSO). The
insolubility of P2e was attributed to extensive intermolecular
cross-linking upon thermal treatment.
In order to investigate the effect of monomer concentration on
the photopolymerisation a series of reactions were conducted. As
the monomer concentration was increased from 0.08 to 0.68 M the
molecular weight and polydispersity of the resulting polyamines
The polymers were analysed by GPC coupled with RI detection
(Fig. 1) using linear polystyrene calibrants. Although it has
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Table 1 Reaction conditions employed for the synthesis of polyamines P1a-P3e and their molecular weight characteristics
Polyamine
Conditions
Solventa
Conc.a/M
Mwb/kDa
Mnb/kDa
PDIb
DP
P1a
P1b
P1c
P1d
P1e
P2a
P2b
P2c
P2d
P2e
P3a
P3b
P3c
P3d
P3e
hm
FC-72ꢀR c
C6F15Nd
Neat
N/Ae
N/A
N/A
0.67
0.67
N/A
N/A
N/A
0.67
0.67
0.08
0.17
0.34
0.68
1.35
1.1
1.1
1.1
1.6
1.7
1.8
1.6
1.4
0.9
0.9
0.8
1.0
1.2
1.2
1.2
1.1
1.6
1.2
1.2
1.4
1.6
1.4
1.5
1.4
1.3
2.3
9
9
9
13
14
15
13
12
31
hm
hm
hm
C6F6
hm
C5F5N
FC-72ꢀR
C6F15N
Neat
C6F6
C5F5N
C6F6
C6F6
C6F6
C6F6
C6F6
hm/D
hm/D
hm/D
hm/D
hm/D
hm
3.7
Insolublef
3.1
1.4
1.3
1.3
1.3
1.4
2.2
1.9
1.8
1.6
1.7
26
21
19
17
20
hm
2.5
2.3
2.1
2.4
hm
hm
hm
a Solvent and concentration used in photochemical polymerisation stage. b GPC analysis was conducted in DMF containing 0.05 M LiBr at 60 ◦C
and using polystyrene calibrants. c Perfluoro-n-hexane. d Perfluorotriethylamine. e N/A = not applicable. f Polymer is insoluble in solvent used for GPC
analysis.
(P3a–d) decreased, however, when the monomer concentration
was further increased to 1.35 M (P3e) a slight increase in
molecular weight was observed. The decrease in molecular weight
with increasing monomer concentration can be accounted for by
consideration of carbene N–H insertion versus azine formation.
At high monomer concentration interaction between carbenes
and diazirines or diazoalkanes is more probable, thus azine
formation is favoured.20,21 At low monomer concentrations the
relative proportion of carbenes is higher resulting in a higher
yield of insertion products and as result, higher molecular weight
polyamines.
UV-visible spectroscopic analysis of the aminodiazirine 1
Fig. 3 IR spectrum of poly(aryl amine) P1d.
(Fig. 2) revealed an absorption centred at k = 378 nm correspond-
ing to a p–p* transition of the diazirine moiety. In comparison,
would have been expected if the intermediate carbenes had reacted
the absence of this absorption band in the spectra of polyamines
P1d and P2d indicated that the majority of the diazirine moieties
had decomposed under the conditions employed. IR spectro-
scopic analysis of the polyamine P1d (representative of all the
with oxygen.22 Furthermore, the absence of absorption bands at
ca. 2050 cm−1 implied20 that diazoalkane moieties were not present
after the initial photochemical polymerisation.
1H and 13C NMR spectroscopic analysis of the polyamine P1d
polyamines—see Fig. 3) revealed several strong absorptions at ca.
3355, 1604 and 1320 cm−1 corresponding to N–H, aromatic C–
C and C–N bonds, respectively. The absence of an absorption
band at ca. 1700 cm−1 implied that the polymer end groups were
not terminated by acetophenone type moieties (Scheme 2), which
was dominated by resonances consistent with the desired amine
linkages formed through the insertion of carbenes into N–H
1
bonds. For example, the H NMR spectrum of P1d (Fig. 4, (a))
consisted of resonances at ca. dH 1.3 and 4.2 ppm, corresponding
to methyl and methine protons, b and a to amine groups,
respectively.23 Minor resonances at ca. dH 2.15 and 5.2/5.6 ppm,
corresponding to methyl protons adjacent to azine linkages
and geminal vinylic protons present in styrenic end groups
(Scheme 2), respectively, could also be observed. Furthermore,
13C NMR spectroscopic analysis revealed resonances between dC
54.9–55.4 ppm, corresponding to methine carbons adjacent to
aromatic and amine functionalities.23 Upon thermal treatment
1
the H NMR spectrum of the resulting polyamine P2d (Fig. 4,
(b)) remained similar to that of P1d, with the exception that
the resonances resulting from the styrenic protons were now
absent. Therefore, it can be deduced that the observed increase
in molecular weight upon thermal treatment originates from
thermally driven hydroamination of styrenic moieties with amine
functionalities or activation of trace amounts of diazirine moieties.
1H NMR spectroscopic analysis of the polyamine P1c prepared
Fig. 2 UV-visible spectra of aminodiazirine 1 and poly(aryl amine)s P1d
and P2d.
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Scheme 3 Proposed reaction pathways operating during photopolymeri-
sation of the aminodiazirine 1.
Fig. 4 1H NMR spectra of poly(aryl amine) P1d (a) and its thermally
cured derivative P2d (b).
conversion.26 In general, these singlet-state carbenes undergo rapid
relaxation and inter-system crossing (ISC) to the ground triplet
state (5T)27 or intramolecular 1,2-hydrogen migration to form
styrenic species (6) (Scheme 3).28 Although there is a significant
energy barrier to 1,2-hydrogen migration in the singlet state,
polar solvents such as acetonitrile dramatically accelerate the
intramolecular rearrangement.29 Alternatively, as is observed for
diarylcarbenes, the excited singlet-state carbenes could undergo
ISC to afford excited triplet-state carbenes (5T*), which then relax
to the ground triplet state (5T).30 In addition, the triplet carbenes
can interact with other species present in the reaction mixture
leading to ISC back to the low-lying singlet state.26
from photolysis of neat aminodiazirine 1 revealed a significant
increase in resonances at dH 2.15 ppm (relative to other methyl
proton resonances) corresponding to methyl protons adjacent to
azine linkages. This observation accounts for the difference in
molecular weight between the polyamines prepared in solution
(P1d–e) and those prepared in neat (P1c) or suspension phase
reactions (P1a–b), as the formation of azine leads to retardation
of the growing polymer chain.
1
From the H NMR spectroscopic evidence presented it was
possible to estimate the relative percentages of each functional
group present in the polyamines, presuming that all resonances
between dH 0.7 and 2.2 ppm originated from methyl protons
and the resonances corresponding to styrenic geminal protons
originated from 1,2-hydrogen migration of carbenes adjacent to
methyl groups. Polyamine P1d was found to possess amine, azine
and styrenic groups in relative percentages of 69, 9 and 8%,
with the remainder originating from unidentified functionalities,
hypothesised to be stilbene and cyclopropane derivatives, which
are common in arylalkylcarbene reactions. The thermally cured
derivative P2d was found to possess amine and azine groups in
relative percentages of 76 and 10%, further confirming that the
styrenic species present after photopolymerisation had undergone
reaction to afford secondary or tertiary amines. Similar yields of
N–H insertion products have also been observed in studies with
diphenylcarbene21,24 and fluorenylidene.25
Given the high reactivity of carbenes it is not surprising that
a diverse range of functional groups and polymeric linkages are
formed in the photopolymerisation of the aminodiazirine 1. The
mechanism of formation of these functional groups is complex, but
can be accounted for by interpretation of previous chemical and
kinetic studies. Photolysis of substituted 3-aryl-3-methyldiazirines
leads to nitrogen extrusion and the generation of carbenes in
singlet electronic states (5S) (Scheme 3) as a result of spin
As observed in previous studies involving reaction of aryl-
carbenes with pyridine29,31 and alkylamines21,24,32 it is reasonable
to assume that ylide 7 (Scheme 3) or tight ion pair formation,
with rate constants that approach a diffusion-limited rate,33 are
dominant in the initial stage of the photopolymerisation. The
resulting ylide 7 ultimately undergoes N–H insertion to afford
secondary 8 or tertiary amines,21,24 which accounts for the majority
of polymeric linkages in the polyamines. Whereas the singlet-
state carbene 5S is predominately responsible for the formation
of ylide 7, it is not exclusively the only reaction pathway by which
secondary or tertiary amines can be formed in the polymerisation.
Theoretically, an excited triplet-state carbene 5T* (which, like its
singlet-state counterpart, possesses an empty low-lying orbital)
might also be involved in the formation of the secondary amine
8, as it has been proposed that reaction of excited triplet-state
carbenes with amines initially forms a triplet charge transfer
intermediate that can decay by ISC into the singlet manifold
producing either a singlet charged transfer complex or an ion
pair/ylide.32 These species are then capable of dissociation to
afford a singlet-state carbene and amine, or undergoing N–H
insertion to afford the amine 8. In comparison, the formation of
the amine 8 via a ground-state triplet carbene 5T would be expected
to follow a radical abstraction–recombination type mechanistic
pathway,21 although potentially carbene 5T and an amine could
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form a complex which undergoes ISC to give the N–H insertion
product.34 Predominantly, reaction of carbene 5T with a primary
or secondary amine would lead to hydrogen abstraction and the
formation of free radical 9 and an aminyl radical (Scheme 3),
which can potentially combine to afford the amine 8, participate
in further abstraction events or undergo radical combination to
yield derivatives such as 2,3-diarybutane 10.
polyamines with higher molecular weights. In addition, an increase
in the concentration of the monomer led to a decrease in the
molecular weight of the resulting polyamine. As a result of the
structural diversity of the polyamines determination of the degree
of branching proved to be unattainable. It is quite clear that this
carbene insertion polymerisation approach can produce highly
functional polyamines in a manner similar to that used to afford
less reactive polyethers. Indeed, this approach may prove amenable
to the production of functional polyamines suitable for use in
molecular electronics or in solid supported scavengers.
A distinguishing feature of singlet-state aryl, diaryl and ary-
lalkylcarbenes is the ability of these species to form azines via
reaction with their diazirine or diazoalkane precursors, which
in the absence of other reactants is generally the dominant
reaction.18 Therefore, the formation of azine linkages in the pho-
topolymerisation of aminodiazirine 1 was unsurprising. Whereas
the azine moieties formed in the polymerisation are unlikely to
participate in secondary reactions, the styrenic species formed can
potentially react with carbenes to afford cyclopropane derivatives
11 (Scheme 3).35 Thus, the relative percentage of styrenic end
Experimental
General
Reagents were purchased from either Fluorochem, Apollo, Acros
Chimica or the Aldrich Chemical Company and were used
1
R
without further purification, unless stated otherwise. FC-72ꢀ,
groups calculated from integration of the H NMR spectrum of
the polyamine P1d may underestimate the extent to which 1,2-
hydrogen migration occurs in the polymerisation. Given that there
is a significant energy barrier to 1,2-hydrogen migration and that
ylide formation is a near diffusion-limited rate process one would
expect that photopolymerisations conducted in electron donating
solvents such as perfluoropyridine and perfluorotriethylamine
(C6F15N) would yield polymers with different molecular weight
characteristics. However, the application of perfluoropyridine and
perfluorotriethylamine as reaction solvents appears to play no dis-
tinguishable part in ylide formation as the polyamines synthesised
in these solvents are analogous to those prepared in non-electron
donating solvents. The apparent lack of ylide formation in these
solvents can be accounted for by consideration of their electron
deficient nature, which results from the electron withdrawing
properties of the fluorine groups. In common with studies of other
hyperbranched polymers reported in the literature,36 the degree of
branching of these polymers proved difficult to ascertain given the
structural diversity of the linear and branching units within the
polyamine architecture.
perfluorotriethylamine, hexafluorobenzene and perfluoropyridine
˚
were distilled from CaH2 and stored over 4 A molecular sieves.
Thin-layer chromatography (TLC) was performed on aluminium
sheets coated with Merck silica gel 60 F254. Developed TLC
plates were stained with potassium permanganate solution or
scrutinized under 254 nm UV light. Column chromatography
was performed using SI60 Sorbent silica (40–63 lm) supplied
from VWR International. 1H Nuclear magnetic resonance (NMR)
spectroscopy was performed on either a Bruker DPX250 (250
MHz) or a Bruker AMX400 (400 MHz) spectrometer (using TMS
and the deuterated solvent as lock and residual solvent). 13C NMR
spectroscopy was performed on Bruker AC250 (62.5 MHz) or
Bruker AMX400 (100 MHz) spectrometers. Infrared spectroscopy
was performed using a Perkin Elmer 1720-X spectrometer with
the samples analysed as thin films. UV-visible analysis was
performed on a Perkin Elmer Lambda 25 UV/VIS spectrometer
using methanol as the solvent. Mass spectra (MS) were obtained
using either a Fisons VG Autospec instrument or a Finnigan
MAT 95 instrument operating in chemical ionization mode, using
ammonia as the impact gas. Gel permeation chromatography
(GPC) was performed on a Polymer Laboratories PL-GPC 220
high temperature chromatograph using PL Mixed Gel columns at
60 ◦C, GPC grade DMF containing 0.05 M LiBr as eluent and PL
Easy-Cal polystyrene calibrants. Samples were dissolved in GPC
grade DMF containing 0.05 M LiBr (2–4 mg mL−1).
Conclusion
Hyperbranched polyamines with DP ranging from 9–31 were
prepared successfully via carbene insertion polymerisation of
carbenes generated from an AB2-type aminodiazirine monomer—
carbene insertion reactions can occur twice at the amine group.
Although the architecture of the polyamines consisted predom-
inantly of amine linkages, structural analysis also indicated the
presence of other moieties, such as azines, which are observed
commonly in the reactions of arylalkylcarbenes. The initial pho-
topolymerisation of the monomer clearly results in the formation
of polyamines with styrenic end groups that are accessible for
further reaction upon thermal treatment, as evidenced by the
observed increase in molecular weight of the polymers. Although
the exact mechanism of formation of the amine linkages is
undetermined, it is evident that such groups could originate from
reaction of both singlet- and triplet-state carbenes with amines.
Photopolymerisations conducted in bulk and as suspensions were
found to yield polyamines consisting of large proportions of
azine moieties relative to polymerisations conducted in solu-
tion. Therefore, polymerisations conducted in solution yielded
Synthetic details
Synthesis of 3-(3-aminophenyl)-3-methyldiazirine 1. 3-Amino-
acetophenone 2 (10.0 g, 74.2 mmol), benzylamine (16.2 mL,
148 mmol) and ZnCl2 (2 mol%, 0.21 g, 1.50 mmol) were
added to toluene (250 mL) and heated under reflux using
azeotropic distillation to remove the water produced. After 16 h
R
the mixture was cooled, filtered through a pad of Celiteꢀ and
the filtrate was concentrated in vacuo to afford crude 3-(1-
(benzylimino)ethyl)benzenimine 3 as a yellow oil. The crude
imine 3 was dissolved in dichloromethane (20 mL) and added
to condensed ammonia (220 mL) at −78 ◦C under an argon
atmosphere over a period of 30 min. The mixture was stirred
vigorously at −78 ◦C for 6 h and then HOSA (16.7 g, 148 mmol)
dissolved in methanol (80 mL) was added over a period of
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40 min. After a further 20 h the mixture was warmed to room
temperatureandwater (200mL)was added. The organic phase was
removed and the aqueous phase extracted with dichloromethane
(4 × 75 mL). The combined organic extracts were concentrated
in vacuo to afford the crude diaziridine 4 as a yellow/orange oil,
which was dissolved in 1 : 1 water–acetone (300 mL) and sodium
dichromate (39.7 g, 148 mmol) and concentrated H2SO4 (2 mL,
40.8 mmol) were added. The mixture was stirred in the dark for
20 h and then added to saturated sodium metabissulfite (1 L) and
stirred rapidly for a further 20 hours in the dark. The resulting
(br s), 1.64–1.79 (m), 1.90–2.03 (m), 2.08–2.22 (m), 3.17 (d), 4.00–
4.36 (m), 4.93 (br s), 5.89–7.38 (m) ppm. dC (62.5 MHz; d6-DMSO)
25.2–25.6 (m), 27.1–27.2 (m), 31.3 (s), 35.8 (s), 37.1 (s), 54.9–55.4
(m), 112.8–113.9 (m), 114.4–114.9 (m), 115.5–115.7 (m), 116.6–
116.8 (m), 117.8–118.2 (m), 118.5 (m), 119.4–120.0 (m), 120.7–
120.9 (m), 121.5 (s), 123.5–123.7 (m), 126.6 (s), 129.8–130.9 (m),
139.1 (s), 140.1–141.0 (m), 147.3–150.2 (m) ppm. GPC (0.05 M
LiBr in DMF) Mw = 3.7 kDa, Mn = 1.6 kDa, PDI = 2.3.
Acknowledgements
R
mixture was filtered through a pad of Celiteꢀ and the insoluble
residues were washed with dichloromethane (600 mL). The organic
phase was removed from the filtrate and the aqueous phase was
extracted with dichloromethane (2 × 200 mL). The combined
organic extracts were dried (MgSO4), filtered and concentrated
in vacuo to afford a brown oil. The oil was purified via repeated
column chromatography on silica (4 : 1 hexane–diethyl ether) in
the dark to afford 3-(3-aminophenyl)-3-methyldiazirine 1 as a
yellow oil, 0.98 g (9% from 3-aminoacetophenone 2). mmax/cm−1
This work was supported by a grant to W.H. from the DuPont
Young Professor Programme (postgraduate studentship for A.B.).
The authors also thank EPSRC (GR/R06441) and Polymer
Laboratories Ltd. for the funding provided for the gel permeation
facilities at the University of Reading.
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=
(thin film) 1238, 1328, 1457, 1503, 1588, 1620 (N N), 3215, 3367,
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