Reactions of nitrilium salts with indole and pyrrole and their derivatives in the synthesis of imines, ketones and secondary amines

Article abstract of DOI:10.1016/j.tet.2015.05.005

Abstract Reactions of N-methyl- and N-ethyl-nitrilium salts with indole and pyrrole and their derivatives yield imines or imine salts in good yields. The related imines are obtained from the salts after careful basification and hydrolysis of the imine salts or the imines by heating with aqueous base give the related ketones in good yields. Alternatively, the imine salts can be reduced using sodium borohydride in methanol to give the related secondary amines.

Full text of DOI:10.1016/j.tet.2015.05.005

Accepted Manuscript
Reactions of nitrilium salts with indole and pyrrole and their derivatives in the
synthesis of imines, ketones and secondary amines
Robert G. Giles, Harry Heaney, M.J. Plater
PII:
S0040-4020(15)00646-8
10.1016/j.tet.2015.05.005
TET 26722
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 12 February 2015
Revised Date: 27 April 2015
Accepted Date: 1 May 2015
Please cite this article as: Giles RG, Heaney H, Plater MJ, Reactions of nitrilium salts with indole and
pyrrole and their derivatives in the synthesis of imines, ketones and secondary amines, Tetrahedron
(2015), doi: 10.1016/j.tet.2015.05.005.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT
Graphical Absract
Reactions of nitrilium salts with indole and pyrrole and their derivatives in the synthesis of imines, ketones and
secondary amines+
Robert G. Giles,a Harry Heaneya*, M. J. Platerb
a Department of Chemistry, Loughborough University, Loughborough, Leicestershire, LE11 3TU, UK
b Department of Chemistry, University of Aberdeen, Aberdeen, AB24 3FX
+Dedicated to the memory of Robert Giles, 1961 - 2005 and Alan Katritzky, 1928 - 2014
Corresponding author, Tel.: + 44 (0)1509 222555; e mail h.heaney@lboro.ac.uk
Abstract
Reactions of N-methyl- and N-ethyl-nitrilium salts with indole and pyrrole and their derivatives yield imines or
imine salts in good yields. The related imines are obtained from the salts after careful basification and hydrolysis of
the imine salts or the imines by heating with aqueous base give the related ketones in good yields. Alternatively, the
imine salts can be reduced using sodium borohydride in methanol to give the related secondary amines.
Key words: indole(s), pyrrole(s), ketones, secondary amines
Introduction
The acylation of indole and pyrrole and their derivatives have been studied over a long period of time, particularly
because many have been found to be important in routes to pharmacologically active substances. However, a major
problem, particularly associated with early work, using for example acyl halides, concerned the ease of the acid
catalysed polymerisation reactions of indoles and pyrroles which resulted from the formation of protic acids as co-
products.1 The well established positional selectivity in electrophilic substitution reactions of indole and pyrrole
that normally results from attack at the 3- and 2-positions respectively has been reviewed.2 The recent report of

ACCEPTED MANUSCRIPT
reactions of 3-methylindole with acetyl chloride in the presence of a number of Lewis acids gave in a number of
cases, mixtures of products, including a product derived by the acetylation of the dimer 1-(3,3’-dimethyl-2,3-
dihydro-1H,1’H-[2,2’]biindolyl.3
A variety of interesting approaches have been reported more recently that demonstrate the continuing importance of
acyl derivatives of indoles and pyrroles: including Vilsmeier reactions using amides other than formamide
derivatives,4 reactions of 1-p-toluenesulfonylpyrrole with carboxylic acids in the presence of trifluoroacetic
anhydride,5 reactions of pyrrylmagnesium chloride with 2-pyridylthiol esters,6 and reactions using acyl chlorides in
the presence of zinc.7 Various catalytic processes have been reported:8-11 including reactions of indole, with Lewis
acid complexes, of for example stannic chloride and aluminium chloride, that were first reported by Schmitz-
Dumont,12 exemplified by a recent report using acyl halides.13 In connection with the acylation of indoles, the
screening of a wide range of metal chlorides showed that zirconium chloride was a particularly effective Friedel-
Crafts catalyst in dichloroethane;14 and dialkylaluminium chlorides have also been shown to be efficient catalysts in
dichloromethane.15 Other recently devised methods include reactions of N-(2-haloacyl)pyridinium salts with indole
that give predominantly the 3-subsituted product;15 electron rich alkenes, for example enol ethers, have been used in
oxidative Heck reactions that result in the formation of N-protected-3-acylindoles after hydrolysis of the initially
formed enol ethers;16 and microwave-assisted acylation reactions of indoles have also been carried out on
alumina18a and in an ionic liquid system.18b
We were interested in the possibility of using N-alkylnitrilium fluoroborates in reactions with indole and pyrrole
and some of their derivatives in order to generate related imines: ketones could thus be accessed by hydrolysis and
secondary amines after the reduction of imine salts. Preliminary results have been reported,19 and we now present a
full account including additional data.20 The first reports of the preparation of nitrilium salts,21 included the
interaction of Meerwein’s salt, triethyloxonium fluoroborate, with acetonitrile.21c A number of other methods have
been reported, for example using methyl fluorosufonate to alkylate acetonitrile,22 and by the reaction ethyl
chloroformate with benzonitrile:23a the reactions of a range of alkyl chloroformates with other nitriles has been
studied in more detail.23b Reactions of N-methylnitrilium salts with ionic azides have been reported previously,23a,24
and nmr spectra of N-alkylnitrilium salts were also presented in an early report.25 Reactions of N-methylnitrilium
triflates with electron-rich carbocyclic aromatic compounds have been studied,26 and alkylbenzonitrilium salts have
been used as acyl-cation equivalents in the synthesis of highly substituted xanthones.27
Results and Discussion
Although trimethyloxonium fluoroborate was available commercially that material had been shown to be
contaminated by ethyl dimethyloxonium fluoroborate and pure material was prepared from dimethyl ether of high
purity together with methyl iodide and silver fluoroborate.28 We prepared trimethyloxonium fluoroborate by
passing dimethyl ether into a solution of high purity dimethoxycarbenium fluoroborate in dichloromethane.29
Trimethyloxonium fluoroborate then gave N-methylacetonitrilium fluoroborate in an almost quantitative yield by
allowing a slight excess of acetonitrile to react with the salt at ambient temperature for 15 – 24 h: in some cases
longer times were employed but with little or no improvement in the yields of the nitrilium salts. The preparation of
N-methylacetonitrilium fluoroborate was achieved more rapidly, but in a slightly lower yield, by gently heating a
suspension of trimethyloxonium fluoroborate in an excess of acetonitrile until the evolution of dimethyl ether had
ceased. Other N-methylnitrilium fluoroborate salts were prepared and are listed in Table 1. We did not observe the
formation of triazinium fluoroborate salts26 in any of our reactions.
Table 1. The Preparation of N-Alkylnitrilium fluoroborates

ACCEPTED MANUSCRIPT
Nitrile
Oxonium Salt
Nitrilium Salt
Yield (%)
95a 75b
58a 57b
96a 59b
80b
Trimethyloxonium
Trimethyloxonium
Trimethyloxonium
Trimethyloxonium
Trimethyloxonium
Trimethyloxonium
Triethyloxonium
N-Methylacetonitrilium
N-Methylpropionitriliuium
N-Methyl-n-butyronitrilium
N-Methyl-i-butyronitrilium
N-Methylpivalonitrilium
N-Methylbenzonitrilium
N-Ethylacetonitrilium
Acetonitrile
Propionitrile
n-Butyronitrile
i-Butyronitrile
Pivalonitrile
Benzonitrile
Acetonitrile
75b
75a 60b
85a
a reaction carried out at ambient temperature for 15-48 h: b reaction carried out by heating at ca. 30 °C for 5
– 10 min.
Reactions with indole and indole derivatives
We began our study of reactions of -excessive heterocycles by investigating reactions of the above nitrilium
salts with indole and substituted indoles. When we added a solution of indole (1) in dichloromethane to a
suspension of N-methylacetonitrilium fluoroborate in dichloromethane at room temperature the reaction mixture
became hot and turned rapidly dark red and, after treatment of the cold product with aqueous sodium hydroxide,
we isolated 3-acetylindole in a modest yield. We therefore investigated the reaction at lower temperatures,
shown in Scheme 1. When we added a cold solution of indole (1) in dichloromethane slowly to N-
methylacetonitrilium fluoroborate in dichloromethane at –70 °C no evidence of a reaction was observed.
However, when the mixing was repeated at –50 °C and the reaction mixture was kept at –20 °C for 24 h a red
salt (2) was isolated, after filtration, in a 95% yield. The colour of the salt is evidently due to delocalisation of
the positive charge. The related imine (3) was isolated in 81% yield after shaking a dichloromethane suspension
of the salt (2) briefly with an aqueous 2M sodium hydroxide solution. A single peak in the 1H NMR spectrum at
H 3.33 ppm indicated that a single product, the E-diastereoisomer, was formed:30 the data do not indicate the
additional presence of the tautomeric 3H-indole derivative in any of the 3-substituted indolylimines.
Scheme 1. The Reaction of Indole with N-Methylacetonitrilium fluoroborate and Base Treatment of the
Resultant Imine Salt.
Our best low temperature conditions, as used in the reaction of indole (1) with N-methylacetonitrilium
fluoroborate, were also used with the substituted indoles (4–8) and using other N-methyl fluoroborate salts that
we prepared from other nitriles: the results are summarised in Table 2. In the majority of the reactions the salts
(9–17) related to the compound (2) were isolated in good to excellent yields. However, in some cases, where the
solubility of the salt was relatively high in dichloromethane, the imine related to the compound (3) was also
isolated after basification of the filtrate. In two cases no attempt was made to isolate the initially formed salt and
the related imines (19 and 20) were obtained by treatment with aqueous 2M sodium hydroxide solution.
Table 2. Reactions of Indole and Substituted Indoles with N-Methylnitrilium fluoroborates

ACCEPTED MANUSCRIPT
Indole
Indole (1)
Indole (1)
Indole (1)
Indole (1)
Indole (1)
Indole (1)
1-Methylindole (4)
2-Methylindole (5)
1,2-Dimethylindole (6)
1-Benzylindole (7)
2-Phenylindole (8)
Nitrilium Fluoroborate Imine Salt yield (%)
Imine yield (%)
Acetonitrilium
Propionitrilium
Butyronitrilium
Iso-Butyronitrilium
Pivalonitrilium
Benzonitrilium
Acetonitrilium
Acetonitrilium
Acetonitrilium
Acetonitrilium
Acetonitrilium
2 R1,R2 =H, R3 = Me (95)
9 R1,R2 =H, R3=Et (63)
10 R1,R2 =H, R3=Pr (77)
11 R1,R2 =H, R3=i-Pr
18 (35%)
19 (36%)
20 (68 %)
12 R1,R2 =H, R3=Ph (91)
13 R1,R3=Me, R2 = H (70)
14 R1 = H,R2,R3=Me, (82)
15 R1,R2,R3 =Me, (70)
21 (8%)
16 R1 = Bn,R2 = H, R3 = Me (81)
17 R1 = H, R2 = Ph, R3 = Me (72)
A reaction was carried out using 3-methylindole (22) together with N-methylacetonitrilium fluoroborate
(Scheme 2) in order to establish whether the N-methylacetonitrilium ion was sufficiently electrophilic to effect
substitution at the 2-position: because of the high solubility of the resulting imine salt we isolated the salt (23) in
33% yield and, after basification of the remaining solution, the imine (24) in 34% yield. We do not have
evidence concerning the initial position of attack in the reaction of 3-methylindole, although by analogy to
earlier results, for example on the acetylation of 3-methylindole,31a and the Vilsmeier formylation of
tetrahydrocarbazole, 31b and methyl 3-indolylacetate,31c it is possible that attack occurs initially at the 3-position
followed by rearrangement to the 2-position and re-aromatisation after loss of a proton. Again, the 1H NMR
spectrum of the compound (24) indicated that the single diastereoisomer had the E-configuration.
Scheme 2. The Reaction of 3-Methylindole with N-Methylacetonitrilium fluoroborate.
In addition to the imines (17 -20 and-23) we also isolated imines from the salts listed in Table 2 by shaking a
suspension of the salt in dichloromethane briefly with aqueous 2M sodium hydroxide. The imines were

ACCEPTED MANUSCRIPT
converted into the related acylindoles by heating them with an aqueous solution of sodium acetate. The yields of
the purified imines and the acylindoles are listed in Table 3. The hydrolysis of the imine salt (23) gave 2-acetyl-
3-methylindole (25) in 95% yield after purification.
Table 3. The Isolation of Imines from Fluoroborate salts and Conversion of the Imines into Ketones
Imine Fluoroborate Imine (yield)a
3-Acylindole (yield)b
3 (81 %)
18 (35%)
26 (68%)
27 (36%)
28 (78%)
29 (80%)
30 (62%)
31 (84%)
32 (61%)
33 (80%)
3-Acetylindole 34 (51%)
2
9
3-Propionylindole 35 (63%)c
3-Butyroylindole 36 (72%)d
3-iso-Butyroylindole 37 (96%)
3-Pivaloylindole 38 (98%)
10
11
12
13
14
15
16
17
3-Benzoylindole 39 (99%)e
3- Acetyl-1-methylindole 40 (71%)
3-Acetyl-1,2-dimethylindole 41 (84%)
3-Acetyl-1-benzylindole 42 (67%)
3-Acetyl-2-phenylindole 43 (67%)e
a) yield of imine after purification, b) yield of 3-acylindole after purification, c) yield in a one-pot reaction
without isolation of the intermediate imine salt or imine, d) yield obtained directly from the imine salt, e)
by hydrolysis of the imine salt by heating under reflux with aqueous sodium acetate solution.
Reactions with pyrrole and pyrrole derivatives
Our investigation of the reactions of N-methylnitrilium fluoroborate salts with pyrrole and substituted pyrroles
was undertaken in the first instance in order to establish that the nitrilium salts were electrophilic enough to give
good yields of products of attack at the 2-position, or at the 3-position when 2,5-dimethylpyrrole was used. We
were also interested to establish whether increasing the size of the alkylnitrilium salt would influence the site of
attack on pyrrole and whether increasing the bulk of a substituent on the pyrrole nitrogen would divert the
substitution towards reaction at the 3-position. As was the case in the reaction of indole, the addition of a
dichloromethane solution of pyrrole at room temperature to a suspension of N-methylacetonitrilium fluoroborate
in dichloromethane was also accompanied by a pronounced exotherm; the addition of water and basification
resulted in our isolation of 2-N-methylacetyliminopyrrole (45) in only 23% yield. A significant amount of the
pyrrole was evidently destroyed in that reaction. We therefore reverted to our low temperature protocol in which
the slow mixing of the reactants was carried out at –30 °C followed by storage at –20 °C for 16 h. From the
latter reaction, Scheme 3, we isolated the anticipated imine salt (44) in 78% yield together with the related E-
imine (45) in 16% yield after the addition of water and careful basification. The temperature at which the
addition is made and the filtration is carried out affects the relative amounts of the two products that are isolated:
in a second reaction where the addition of pyrrole to the suspension of N-methylacetonitrilium fluoroborate in
dichloromethane was carried out at –50 °C, followed by storage at –20 °C for 2 d, and the filtration was carried

ACCEPTED MANUSCRIPT
out on the cold reaction mixture, the compounds (44) and (45) were isolated in 89% and 5% respectively. The
imine (45) was also obtained in an almost quantitative yield by taking an aqueous solution of the imine salt (44)
to pH 10 by the addition of 2M aqueous sodium hydroxide solution followed by extraction into dichloromethane
and distillation. When the imine (45) was heated with aqueous sodium acetate 2-acetylpyrrole (46) was obtained
in 92% yield after purification, as shown in Scheme 4. Only one reaction was carried out using pyrrole together
with N-ethylacetontrilium fluoroborate which gave the anticipated imine in 19% yield: the reaction conditions
used were not further optimised.
Scheme 3. The Reaction of Pyrrole with N-Methylacetonitrilium fluoroborate.
Scheme 4. The Formation of 2-Acetylpyrrole (46) by Hydrolysis of the Imine (45).
Reactions of pyrrole with a series of other nitrilium salts, shown in Table 4, resulted in substitution at the 2-
position. It appears that increasing the bulk at the carbon end of the nitrilium salt does not have any effect on the
position of attack on pyrrole. Whereas the low temperature reaction of N-methylbenzonitrilium fluoroborate
with pyrrole in dichloromethane resulted in the isolation of the imine salt, the greater solubility of the imine salts
derived from the other nitrilium fluoroborates led to the isolation of the products of the reactions as the imines
after careful base treatment. In some cases we were unable to obtain accurate elemental analytical data for
imines because of their very ready hydrolysis to the related ketones. Hydrolysis of the imines was carried out by
heating the imines under reflux briefly with aqueous sodium acetate solution and those reactions gave the
expected ketones in acceptable yields.
Table 4. The Reactions of Pyrrole with Nitrilium fluoroborates and Hydrolysis of the Imines

ACCEPTED MANUSCRIPT
Nitrilium salt
Imine salt yield (%)
R = Me 44 78%
R = Me 44 89%
Imine yield (%)
R = Me 45 16%
R = Me 45 5%
2-Acylpyrrole yield (%)
R = Me 46 92%
Acetonitrilium
Acetonitrilium
Acetonitrilium
Propionitrilium
n-Butyronitrilium
i-Butyronitrilium
Pivalonitrilium
Benzonitrilium
R = Me 46 78%
R = Et 53 66%
R = Pr 54 84%
R = i-Pr 55 95%
R = t-Bu 56 92%
R = Ph 57 58%
R = Et 48 93%
R = Pr 49 83%
R = i-Pr 50 57%
R = t-Bu 51 55%
R = Ph 52 8%
R = Ph 47 78%
A reaction of 2,5-dimethylpyrrole with N-methylacetonitrilium fluoroborate using our low temperature reaction
conditions gave 3-N-methylacetylimino-2,5-dimethylpyrrole hydrofluoroborate (58) in 90% yield. The imine
salt (58) was suspended in dichloromethane and after shaking briefly with aqueous sodium hydroxide solution
the imines (59) were isolated in 70% yield and identified by 1H nmr spectroscopy as a 6:1 mixture of the E- and
Z-isomers. Hydrolysis of the imine mixture gave 3-acetyl-2,5-dimethylpyrrole (60) in 68% yield.
The product of the reaction of 2,5-dimethylpyrrole with N-methylacetonitrilium fluoroborate and the derived
deprotonation product and the hydrolysis product obtained from the imine
The synthesis of 3-substituted pyrrole derivatives is of general interest,32 and whereas some catalytic reactions
on N-substituted pyrroles lead to selective attack at the 3-position, many reactions result in attack at the 2-
position. It is of interest to note that the rearrangement of 2-acylpyrroles to the related 3-isomers occurs in the
presence of a number of strong protic acids, probably following protonation at the carbon atom substituted by
the acyl group.33 Friedel-Crafts acylation reactions of 1-benzenesulfonyl- or 1-p-toluenesulfonyl-pyrrole have
been studied over a long period of time and early results,34 showed that using aluminium chloride together with
acyl chlorides resulted in the formation of the 3-acyl-derivatives: further work showed that reactions other
Lewis acids resulted in lower selectivity and reactions carried out using boron trifluoride-etherate resulted in
substitution predominantly at the 2-position.35 A more recent study using variable mole equivalents of
aluminium chloride in Friedel-Crafts acylation reactions of 1-p-toluenesulfonylpyrrole strongly supports the
suggestion that organoaluminium complexes are involved, leading predominantly to acylation at the 3-position,
particularly when large amounts of catalyst are involved.36 However, Friedel-Crafts alkylation reactions of 1-
benzenesulfonyl-pyrrole showed lower selectivity.37 In our study using 1-benzenesulfonylpyrrole we found that
N-methylacetonitrilium fluoroborate was unreactive using our low temperature reaction conditions; but that
heating a mixture of the reactants under reflux in dichloromethane for 72 h resulted in the formation of the 2-
acetylimine fluoroborate salt (61) in a 75% yield, shown in Scheme 5. Hydrolysis of a portion of the crude
reaction mixture, and comparison with a sample of 3-acetylpyrrole (62) prepared by the published procedure,35
established that 2-acetylpyrrole (46) was the only ketone produced: this result lends further support to the

ACCEPTED MANUSCRIPT
suggestion that organoaluminium complexes are involved when using strongly electrophilic (hard) Lewis
acids.36
Scheme 4. The Reaction of 2-Benzenesulfonylpyrrole with N-Methylacetonitrilium fluoroborate and Hydrolysis
of the Imine salt (61).
A number of studies have shown that bulky substituents on nitrogen, notably N-tri-isopropylsilylpyrrole (TIPS-
pyrrole) (63)38a can lead to significant or exclusive attack by electrophiles at the 3-position in pyrrole, they
include Vilsmeier formylation,38b and trifluoroacetylation.38c More recently, titanium tetrachloride catalysed
reactions of 1-acylbenzotriazoles with TIPS-pyrrole have been shown to give 3-acylpyrroles in excellent yields
after removal of the silyl-residue.39 N-t-Butyldimethylsilylpyrrole was also been used to direct acylation to the
3-position in pyrrole even using aluminium chloride and acyl chlorides.40 In our experiments using N-
methylacetonitrilium fluoroborate and TIPS-pyrrole in dichloromethane at low temperatures we observed low
selectivity. For example, a reaction carried out where the reagents were mixed at –50 °C and then stored at –22
°C for 42 h gave a homogeneous solution from which, after the addition to water, we isolated from the organic
layer 3-N-methylacetyliminopyrrole hydrofluoroborate (64) in a 30% yield and from the aqueous layer, after
basification with aqueous 2M sodium hydroxide and heating, we obtained 2-acetylpyrrole (46) in a 37% yield.
The imine salt (64) was heated under reflux with 2M aqueous sodium hydroxide to give 3-acetylpyrrole (62) in
an 84% yield as shown in Scheme 5. Additional experiments were conducted where the crude reaction mixtures
of products were hydrolysed directly to give mixtures of 2- and 3-acetylpyrroles which were analysed by 1H
NMR spectroscopy and by glc analysis and gave values for the ratios (62) : (46) of 1.14:1 and 1.11:1. Although
the desilylation of N-silylpyrroles using tetrabutylammonium fluoride is known,38a an nmr experiment carried
out at 35 °C where we mixed tetrabutylammonium fluoroborate with TIPS-pyrrole did not show desilylation
over a 24 h period. Although the exact sequence of events in our reactions cannot be determined, we assume that
desilylation by fluoroboric acid was involved and that led to the formation of the product of attack at the 2-
position.
Scheme 5. The Reaction of TIPS-pyrrole with N-Methylacetonitrilium fluoroborate and Hydrolysis of the Imine
salt (64).

ACCEPTED MANUSCRIPT
The Vilsmeier formylation of a number of N-alkylpyrrole derivatives has been shown to give mixtures of 2- and
3-formyl-pyrroles:41 those results can be compared to our results of reactions of nitrilium fluoroborate salts with
a number of other N-substituted pyrrole derivatives that were carried out in order to establish the amounts of
substitution at the 2- versus the 3-position. The N-substituted pyrrole derivatives that we studied were N-methyl-
(65), N-t-butyl- (66), N-benzyl- (67), N-benzhydryl- (68), 5-(pyrrol-1-yl)-10,11-dihydro-5H-
dibenzo[a,d]cycloheptene (69), and N-trityl-pyrrole (70).
N-Substituted pyrrole derivatives used in reactions with nitrilium fluoroborates
All of the N-substituted pyrrole derivatives, with the exception of 5-(pyrrol-1-yl)-10,11-dihydro-5H-
dibenzo[a,d]cycloheptene (69) have been reported previously. We prepared some of the N-substituted pyrrole
derivatives by standard procedures, involving the reaction of the pyrrolyl-anion in dimethylsulfoxide using the
appropriate halide: N-benzhydrylpyrrole was prepared by that method in a 73% yield. It is interesting to note
that the preparation of N-benzhydrylpyrrole has been reported very recently by a decarboxylative reaction of 4-
hydroxyproline in the presence of benzophenone.42 Good yields of N-substituted pyrrole derivatives were also
obtained by the Clauson-Kass method,43 using 2,5-dimethoxytetrahydrofuran and the appropriate bulky amine:
for example, 5-(pyrrol-1-yl)-10,11-dihydro-5H-dibenzo[a,d]cycloheptene (69) was prepared from 5-amino-
10,11-dihydro-5H-dibenzo[a,d]cycloheptene (71)44 by that method in a 79% yield, shown in Scheme 6.
Scheme 6. The Synthesis of 5-(Pyrrol-1-yl)-10,11-dihydro-5H-dibenzo[a,d]cycloheptene (66).
Reactions of N-methylnitrilium fluoroborate salts were carried out with the N-alkyl-substituted derivatives (65)
– (70). The only reaction where we were able to isolate imine salts was that using 1-t-butylpyrrole (66), shown
in Scheme 7, from which we isolated the two salts (72) and (73) in 40% and 52% respectively. The imines (74)
and (75) were also isolated from the salts (72) and (73) in 88% and 71% respectively; and after hydrolysis of the
imine salts 2-acetyl-1-t-butylpyrrole (76) and 3-acetyl-1-t-butylpyrrole (77) were obtained in 79% and 75%
yield respectively. Reactions of a number of 1-acylbenzotriazole derivatives with N-methylpyrrole (65) have
been reported but no 3-acyl derivatives were detected in crude reaction mixtures.39 Similarly, in the case of the
acylation reactions of N-methylpyrrole using 1,5-diazabicyclo[4.3.0]non-5-ene as a catalyst, no products were
reported that resulted from attack at the 3-position.9 We observed that reactions of acetonitrilium fluoroborate

ACCEPTED MANUSCRIPT
with N-methylpyrrole (65) gave, as the major product, that derived from attack at the 2-position: we also
isolated in a small amount the product from attack at the 3-position; hydrolysis of those products gave access to
the related acyl derivatives, in some cases in “one pot” reactions. 1-Methyl-3-acetylpyrrole has been reported
previously by the Friedel-Crafts acetylation of a Vilsmeier intermediate obtained from N-methylpyrrole
followed by hydrolysis to 4-acetyl-2-formyl-1-methylpyrrole and deformylation.45 With the exception of
reactions of N-tritylpyrrole, from which we only isolated a product derived from attack at the 3-position in the
pyrrole ring, all of the reactions using the other N-alkylpyrrole derivatives gave mixtures of products from
which the 2- and 3-acyl -1-alkylpyrrole derivatives were obtained. The results of the reactions of the N-
substuted pyrrole derivatives are shown in Table 5. We believe that we can exclude rearrangement of the first
formed 2-substituted product to the 3-substituted product because when we attempted to acylate the imine
fluoroborate salt (44) using acetyl chloride and aluminium chloride, work up of the reaction mixture gave 2-
acetylpyrrole (46) and no detectable amount of 3-acetylpyrrole (62) or 2,4-diacetylpyrrole. A reaction between
N-methylpyrrole (65) and N-methylpivalonitrilium fluoroborate provided a surprising result: although an imine
salt was not isolated we did isolate 2-N-methylpivaloylimino-1-methylpyrrole in 59% yield after extraction of
the reaction mixture into water followed by basification. Remarkably, when 2-N-methylpivaloylimino-1-
methylpyrrole was heated under reflux for 2 h in aqueous methanolic sodium hydroxide solution, hydrolysis was
not observed and 2-N-methylpivaloylimino-1-methylpyrrole was re-isolated.
Scheme 7. The Reaction of 1-t-Butylpyrrole with with N-Methylacetonitrilium fluoroborate and Formatiom and
Hydrolysis of the Related Imines.
Table 5. Reactions of N-Alkyl- and N-Aralkyl-pyrrole Derivatives with N-Methylnitrilium Fluoroborate Salts
and the Isolation of Imines and Hydrolysis Products.
N-Substityted
Pyrrole
N-Methylnitrilium 2-acylimine 3-acylimine 2-acylpyrrole 3-acylpyrrole
Fluoroborate
derivative
N-Methyl- (65)
N-t-Butyl- (66)
Acetonitrilium
Acetonitriliuma
78 57%
74 88%
79 9%
75 71%
80 86%
76 79%
81 75%
77 75%

ACCEPTED MANUSCRIPT
N-Benzyl- (67)
Acetonitrilium
Acetonitriliumb
82 43%
83 10%
86 64%
91 27%
84 64%
87 52%
89 45%
85 73%
88 25%
90 13%
N-Benzhydryl (68)
5-(pyrrol-1-yl)-10,11- Acetonitriliumc
dihydro-5H-dibenzo
[a,d]cycloheptene (69)
N-Trityl (70)
Acetonitriliumd
92 42%
a) The 2- and 3-substituted imine salts were isolated in the ratio of 4:5 in a combined yield of 92%: b) the 3-
substituted imine was not isolated from the reaction: c) the 2- and 3-substituted imine salts and the related
imines were not isolated from the reaction: d) the 3-acetyl derivative was the only product identified from the
reaction.
Reactions using 1,3-dimethoxybenzene
Although the Friedel-Crafts acylation of carbocyclic aromatic compounds has been much studied and presents
no major difficulties,46 we investigated the reaction of N-methylacetonitrilium fluoroborate with m-
dimethoxybenzene in order to obtain and characterise the imine salt that could be hydrolysed to give 2,4-
dimethoxyacetophenone. In an early experiment we showed that when we heated a mixture of N-
methylacetonitrilium fluoroborate and m-dimethoxybenzene in dichloromethane at 40 °C for 48 h, 2,4-
dimethoxyacetophenone (95) could be isolated in a 60% yield after an aqueous work-up. When a duplicate
reaction was worked up under conditions such that the aqueous solution remained acidic, we were able to isolate
the imine salt, N-(2,4-dimethoxy- -methylbenzylidene)methylammonium fluoroborate (93) in 55% yield.
Deprotonation of the salt (93) proved to be difficult because of the ease of hydrolysis of both the imine salt and
the related imine. However, deprotonation in ethanolic sodium ethoxide gave the imine (94) in 76% yield. The
reactions involving m-dimethoxybenzene, including hydrolysis reactions, are shown in Scheme 8.
Scheme 8. The reaction of m-Dimethoxybenzene with with N-Methylacetonitrilium fluoroborate and Hydrolysis
of the Imine salt (93).
Reduction of imine salts
In our preliminary communication we reported that the iminium salt (44) could be reduced to the related
secondary amine by sodium borohydride in methanol.19 The direct amination of aldehydes and ketones using

ACCEPTED MANUSCRIPT
sodium borohydride in the presence of a number of acids has been reported more recently.47
Acyloxyborohydride-derivatives, including sodium triacetoxyborohydride, along with a number of other
reducing agents have been reported in connection with reductive amination reactions.48 We carried out some
reactions in which iminium fluoroborate salts were reduced to the related amines using sodium borohydride in
methanol, in order to establish the generality of the protocol: the results of those reactions are given in Table 6.
The reduction of imine salts using sodium borohydride in methanol
Table 6. The Formation of Secondary Amines by the Reduction of an N-Methylindol-3-yl- and Some Pyrrolyl-
iminium fluroborate Derivatives by Sodium borohydride in Methanol.
Imine fluoroborate R1, R2
Salt
13
44
47
61
72
73
Amine Yield %
R1 = 1-Methylindol-3-yl-, R2 = Me
R1 = Pyrrol-2-yl-, R2 = Me
82
96
65
97
R1 = Pyrrol-2-yl-, R2 = Ph
62
98
R1 = 1-Benzenesulfonylpyrrol-2-yl-, R2 = Me
R1 = 1-t-Butylpyrol-2-yl-, R2 = Me
R1 = 1-t-Butylpyrol-3-yl-, R2 = Me
84
99
77
100
82
101
Conclusions
The results reported in this paper show that the use of N-alkylnitrilium fluoroborate salts allows good yields of
acylated aromatic systems to be obtained after the hydrolysis of the intermediate imine salts or imines,
particularly in the case of indole and pyrrole and their derivatives. Secondary amines can also be accessed easily
by reduction of the intermediate imine salts using sodium borohydride in methanol.
Experimental section
General
Melting points were determined using a Kofler hot-stage apparatus and are uncorrected. 1H NMR spectra were
recorded using Varian EM360A or Perkin-Elmer R32 spectrometers, operating at 60 and 90 MHz respectively,
in CDCl3 unless otherwise specified, with TMS as internal standard. 13C NMR spectra were recorded at 20 MHz
using a Bruker WP80 spectrometer. Chemical shifts ( ) are reported in parts per million and coupling constants
(J) in hertz. Infra-red spectra were recorded as liquid films or Nujol mulls using a Perkin-Elmer 177
spectrometer. Ultra-violet spectra were recorded for solutions in ethanol using a Pye-Unicam SP8-250
spectrometer. High resolution mass spectra (HRMS-EI, 70 eV) were recorded using a Kratos MS80/DS55
spectrometer. Analytical thin layer chromatography was carried out using silica-gel (FG254 according to Stahl)
plates of 0.25 mm thickness. Flash column chromatography was carried out using silica-gel (Merk 230-400

ACCEPTED MANUSCRIPT
mesh). Analytical gas chromatography was carried out using a Pye 104 instrument fitted with a 1.5 m column of
OV17 on Gas-Chrom Q. Elemental analyses were carried out by Fisons plc (Pharmaceuticals Division).
Preparation of nitrilium salts
N-Methylacetonitrilium fluoroborate, method 1.
Acetonitrile (4.10 g, 100 mmol) was added to trimethyloxonium fluoroborate29 (14.8 g, 100 mmol) and allowed
to stand at room temperature for 1-2 days. After the evolution of dimethyl ether had ceased a transparent oil
remained and crystallised to leave a pale green solid which was heated at 50 °C for 30 min at 0.1 mm to give N-
methylacetonitrilium fluoroborate (11.4 – 13.6 g, 80 – 95%): IR (nujol) νmax 2420 cm–1, δH (90 MHz, – 40 °C,
SO2/CD2Cl2) 2.78 Me), 3.71 (Me) ppm; δC (20 MHz, – 40 °C, SO2/CD2Cl2) 2.2, 29.9, 107.9 ppm, (RT, CD3CN)
2.0, 29.7, 108.0ppm, (RT CD3NO2) 1.7, 29.8, 108.3 ppm.
N-Methylacetonitrilium fluoroborate, method 2.
Acetonitrile (10 mL, 230 mmol) was added to trimethyloxonium fluoroborate (8.00 g, 56 mmol) and heated
gently until the evolution of dimethyl ether ceased (ca. 5 min). Excess acetonitrile was removed in vacuo and the
residue suspended in anhydrous dichloromethane (50 mL) to give a white solid, which was filtered and dried to
give N-methylacetonitrilium fluoroborate (5.0 – 5.8 g, 65 – 75%).
N-Methylpropionitrilium fluoroborate, method 2.
Propionitrile gave N-methylpropionitrilium fluoroborate (57%) νmax 2400 cm–1, δH (90 MHz, CD3CN) 1.47 (m,
CH2) 3.17 m, CH2), 3.80 (m, Me) ppm; δC (20 MHz, – 40 °C, SO2/CD2Cl2) 7.2 (Me), 11.2 (CH2), 29.7 (Me),
107.7 (C, t, J 13C–14 N 48.3 Hz) ppm.
N-Methylbutyronitrilium fluoroborate, method 2.
Butyronitrile gave N-methylbutyronitrilium fluoroborate (95%) νmax 2405 cm–1, δH (90 MHz, CD3CN) 1.09 (t, J
7 Hz, Me) 1.95 (m, CH2) 3.25 (m, CH2), 3.73 (Me), 3.8 (m, Me) ppm; δC (20 MHz, – 40 °C, SO2/CD2Cl2) 8.9
(Me), 13.3 (CH2), 14.7 (CH2), 26.5 (t, Me J 13C–14 N 6.6 Hz), 105.7 (q, 48 Hz) ppm.
Experiments with isobutyronitrile and pivalonitrile were carried out by M. J. Plater.
N-Methylisobutyronitrilium fluoroborate and N-methylpivalonitrilium fluoroborate were prepared using method
2 in 80% and 75% respectively.
N-Methylbenzonitrilium fluoroborate, method 2.
Benzonitrile gave N-methylbenzonitrilium fluoroborate (74%) νmax 2380 cm–1, δH (90 MHz, CD3CN) 3.93 (br,
Me), 7.6 (m, 5H) ppm: δC (20 MHz, – 40 °C, SO2/CD2Cl2) 31.7 (Me), 102.4, 130.1, 135.3, 138.7 ppm
N-Ethylacetonitrilium fluoroborate24c
A mixture of acetonitrile (4.1 g, 100 mmol) and triethyloxonium fluoroborate (19 g, 100 mmol) was allowed to
stand at room temperature for 2 d and then heated to expel diethyl ether before evacuation to remove excess
acetonitrile. The N-ethylacetonitrilum fluoroborate was obtained as a red oil (13.4 g, 85%) νmax 2420 cm–1, δH

ACCEPTED MANUSCRIPT
(90 MHz, CD3CN) 1.46 (m, Me), 2.78 (m, Me), 4.02 (m, CH2) ppm: δC (20 MHz, CD3CN) 1.9 (Me), 11.3 (Me),
41.0 (CH2, t, J 13C–14 N 5 Hz), 108.2 (C, t, J 13C–14 N 45 Hz) ppm.
The majority of the substituted indole and pyrrole derivatives were prepared by established methods.
Preparation of substituted pyrrole derivatives
1-Benzyhydrylpyrrole (68)49
Sodium hydride (2.60 g, 108 mmol) and pyrrole (10.0 g, 149 mmol) were stirred in DMSO (100 mL) at 50 °C
under nitrogen until the evolution of hydrogen ceased (ca. 2 h). Benzhydryl chloride (16.2.g, 80 mmol) was
added to the cold (10 °C) reaction mixture at a rate to keep the temperature below 35 °C. After a further 2 h
water (200 mL) was added and the precipitate was collected and gave, after recystallisation from ethanol, 1-
benzhydrylpyrrole (68) (13.6 g, 73%), colourless needles, mp 72-73 °C (lit.42 mp 70-74 °C): λmax 198 (log10
4.59) nm: δH (90 MHz, CDCl3) 6.25-6.35 (m, 2H), 6.50-6.60 (m, 1H), 6.65-6.75 (m, 2H), 7.1-7.5 (m, 10 H)
ppm: δC (20 MHz, CDCl3) 66.7 (CH), 108.3 (2 x CH), 121.0 (2xCH), 127,8 (2xCH), 128.2 (4XCH), 128.5
(4xCH), 140.7 (2xC) ppm; HRMS 233.1211, C17H15N requires 233.1204; Found C, 87.90, H, 6.70, N, 5.90%,
Calc. for C17H15N C, 87.50, H, 6.50, N, 6.00%.
1-Dibenzosuberylpyrrole (69) from dibenzosubarone oxime
Dibenzosubarone oxime44 (10.2 g, 46 mmol) in ethanol (500 mL) was heated under reflux while sodium (60 g,
2.6 mol) was added in small portions over 90 min. and gave dibenzosuberylamine (71) (8.8 g, 92%), mp 88-91
°C (lit.44 mp 91-92 °C). The amine (71) (7.4 g, 35 mmol), 2,5-dimethoxytetrahydrofuran (5.6 g, 43 mmol),
glacial acetic acid (30 mL), and benzene (90 mL) were stirred and heated under reflux for 16 h and then
concentrated in vacuo. The resulting solid was rcrystallised (treatment with charcoal) from ethanol to give 5-
(pyrrol-1-yl)-10,11-dihydro-5H-dibenzo[a,d]cycloheptane (69) [dibenzosuberylpyrrole], mp 123-125 °C, (7.3 g,
79%); λmax 198 (log10 4.61) nm: δH (90 MHz, CDCl3) 2.53-3.20 (m, 4H), 5.98 (s, 1H), 6.15 (t, 2H, J = 2 Hz),
6.35 (t, 2H, J = 2 Hz), 7.07-7.48 (m, 8H) ppm: δC (20 MHz, CDCl3) 31.7 (2x CH2), 69.5 (CH), 108.0, 120.4 ,
126.4, 128.9, 131.1, 131.3, 136.8, 140.6 ppm: HRMS 259.1362, C19H17N requires 259.1361; Found: C, 88.20,
H, 6.70, N, 5.35%, C19H17N requires C, 88.00, H, 6.60, N, 5.40%.
Reactions of indole and its derivatives with N-alkylnitrilium fluoroborates and deprotonation and
hydrolysis of the products
3-N-Methylacetyliminoindole fluoroborate (2), 3-N-Methylacetyliminoindole (3), and 3-acetylindole (34)
A solution of indole (4.00 g, 34 mmol) in dichloromethane (20 mL) was added slowly to a stirred suspension of
N-methylacetonitrilium fluoroborate (4.90 g, 34 mmol) in dichloromethane (30 mL) at – 50 °C, keeping the
temperature below – 45 °C during the addition. The reaction mixture was then kept at – 22 °C for 24 h which
then gave 3-N-methylactyliminoindole hydrofluoroborate (2) as a red solid (8.40 g, 95%) (from EtOH), mp 205-
207 °C: λmax 249 (log10 4.24), 264 (4.24), and 328 (4.45) nm, νmax 3315, 1623, 1150-960 cm–1, δH (90 MHz,
CD3CO CD3) 2.98 (s,3H), 3.60 (d, 3H, J = 6 Hz), 7.30-7.52 (m, 2H), 7.71-8.00 (m, 2H), 8.62 (d, 1H, J = 4 Hz),
8.62 (br s, 1H) 11.78 (br s, 1H) ppm, δC (20 MHz, CD3CO CD3) 25.8, 36.6, 108.4, 114.5, 124.4, 125.3 (2xC),
126.7, 137.9, 138.1, 175.7 ppm; Found: C 50.45, H 5.0, N 10.45%, C11H13BF4N2 requires C 50.80, H 5.05, N
10.75 %.
The iminium salt (2) (2.34 g, 9 mmol) was suspended in dichloromethane (30 mL) and shaken with aqueous
sodium hydroxide solution (30 mL, 2 M) until dissolution was complete. The organic layer was washed with

ACCEPTED MANUSCRIPT
water and gave, after recrystallization from light petroleum (40-60 °C) 3-N-methylacetyliminoindole (3), (1.25
g, 81%), mp 114-116 °C: λmax 254 (log10 4.46), 269 (4.45), 286 (4.42), and 332 (4.16) nm, νmax 1607 cm–1, δH
(CDCl3) 2.11 (s, 3H), 3.33 (s, 3H), 6.82-7.22 (m, 4H), 8.27-8.45 (m, 1H), 9.43 (br s, 1H) ppm, δC (CDCl3) 16.4,
38.2, 111.4, 111.8, 120.8, 122.1, 122.5, 125.6, 127.6, 137.5, 165.3 ppm, : HRMS 172.006, C11H12N2 requires
172.1000.
3-N-Methylacetyliminoindole hydrofluoroborate (2) (2.20 g, 8.9 mmol) and sodium acetate (5 g, 61 mmol) in
water (30 mL) were heated under reflux for 10 min and gave, after recrystallization from toluene/light petroleum
(40-60 °C), 3-acetylindole (34) mp 190-191 °C (lit.50 mp 191 °C).
3-N-Methylpropionyliminoindole hydrofluoroborate (9), 3-N-methylpropionyliminoidole (18) and 3-
propionylindole (35)
Indole (2.1 g, 18 mmol) and N-methylpropionitrilium fluoroborate (2.8 g, 17.8 mmol) in dichloromethane (45
mL), initially at – 50 °C and then at –22 °C for 24 h gave 3-N-methylpropionyliminoindole hydrofluoroborate
(9) as a red solid, (3.1 g, 63%) mp 99-100 °C (from EtOH): λmax 253 (log10 4.45), 266 (4.47), 287 (4.26), 333
(4.44) nm, νmax 3340, 1622m 1150-950 cm–1, δH (CD3CN) 1.28 (t, 3H, J = 7 Hz), 3.12 (q, 2H, J = 7 Hz), 3.35 (d,
3H, s after D2O exchange), 7.07-7.24 (m, 2H), 7.40-7.62 (m, 2H), 8.03 (m, 1H), 9.15 (br s, 1H) 12.00 (br s, 1H)
ppm, δC (CD3CN) 11.7, 32.7, 36.9, 107.5, 114.7, 122.1, 124.7, 125.1, 125.7, 137.9, 139.6, 181.4 ppm: Found: C
52.60, H 5.55, N 10.00%, C12H15BF4N2 requires C 52.60, H 5.00, N 10.20 %.
The dichloromethane layer was added to water the aqueous layer was taken to pH 10 with aqueous sodium
hydroxide solution (2 M) and extracted with dichloromethane (3 x 30 mL). Concentration of the combined
organic layers gave an oil (1.4 g) which crystallised and, after recrystallization from chloroform/light petroleum
(40-60 °C), gave 3-N-methylpropionyliminoidole (18) (1.16 g, 35%), a white powder mp 82-83 °C, λmax 259
(log10 4.22), 269 (4.22), 283 (4.18), 334 (3.88) nm, νmax 1618 cm–1, δH (90 MHz, CDCl3) 1.13 (t, 3H, J = 7
Hz), 2.65 (q, 2H, J = 7 Hz), 3.45 (s, 3H), 7.15-7.35 (m, 4H), 8.37-8.53 (m, 1H), 9.20 (br s, 1H), δC (20 MHz,
CDCl3) 11.8, 23.1, 37.3, 111.8, 116.9, 120.9, 122.3, 122.5, 126.0, 127.6, 137.7, 170.1 ppm: HRMS 186.1153,
C12H14N2 requires 186.1156.
Indole (4.9 g, 42 mmol) and N-methylpropionitrilium fluoroborate (6.30 g, 40 mmol) in dichloromethane (65
mL), initially at – 50 °C and then at –22 °C for 24 h was allowed to come to room temperature and the solvent
evaporated to leave an oil which was heated under reflux with aqueous sodium hydroxide (50 mL) for 1 h. The
cold reaction mixture was then extracted with dichloromethane (3 x 30 mL) and the combined organic solutions
were then washed with water (50 mL), dried (MgSO4) and concentrated in vacuo. The residual solid was
recrystallized from toluene/light petroleum (40-60 °C), and gave 3-propionylindole (35) (4.6 g, 63 %), mp 168-
171 °C (lit4a mp 171-173 °C), λmax 291 (log10 4.36), 252 (4.28), 237 (4.39) nm, νmax 1620 cm–1, δH (CDCl3/
CD3SO CD3) 1.18 (t, 3H, J = 7 Hz), 2.81 (q, 2H, J = 7 Hz), 7.00-7.43 (m, 3H), 7.77 (s, 1H), 8.04-8.28 (m, 1H),
9.60 (br s, 1H) ppm, δC (CD3SO CD3) 13.3, 32.0, 112.1, 117.0, 121.5, 121.7, 122.7, 125.8, 133.4, 136.9, 196.1
ppm: HRMS 173.0844, calc for C11H11NO 173.0841.
3-N-Methylbutyryliminoindole hydrofluoroborate (10), 3-N-methylbutyryliminoidole (26) and 3-
butyrylindole (36)
Indole (5.00 g, 43 mmol) and N-methylbutyronitrilium fluoroborate (7.30 g, 42 mmol) in dichloromethane (35
mL), initially at – 50 °C and then at –22 °C for 24 h gave 3-N-methylbutyryliminoindole hydrofluoroborate (10)
as a red solid, (9.2 g, 77%) mp 103-104 °C (from EtOH): λmax 253 (log10 4.36), 266 (4.37), 287 (4.16) 334
(4.33) nm, νmax 3300, 1622, and 1150-950 cm–1, δH (90 MHz, CD3CN) 0.99 (t, 3H, J = 7 Hz), 2.81 (sextet, 2H, J
= 7 Hz), 3.15 (t, 2H, J = 7 Hz), 3.46 (d, 3H, J = 7 Hz, s after D2O). 7.32-7.50 (m, 2H), 7.65-7.83 (m, 2H), 8.30

ACCEPTED MANUSCRIPT
(m, 1H), 9.50 (br s, 1H), 11.0 (br s, 1H) ppm, δC (20 MHz, CD3CN) 13.7, 21.9, 37.0, 40.8, 107.5, 116.0, 124.4,
126.0, 126.9, 127.3, 139.5 (2 x C), 180.5 ppm: Found: C 54.60, H 6.20, N 9.60%, C13H17BF4N2 requires C
54.20, H 5.95, N 9.70 %.
The imine salt (10) (2.02 g, 7 mmol) was suspended in dichloromethane (30 mL) and shaken with aqueous
sodium hydroxide solution (30 mL, 2 M) until dissolution was complete. The organic layer was washed with
water and gave, after recrystallization from chloroform/light petroleum (40-60 °C) 3-N-
methylbutyryliminoindole (26), (948 mg, 68%), mp 98-99 °C: λmax 256 (log10 4.32), 269 (4.32), 283 (4.29),
334 (3.91) nm, νmax 1610 cm–1, δH (90 MHz, CDCl3) 0.98 (t, 3H, J = 7 Hz), 1.3-1.85 (m, 2H), 2.65 (t, 2H, J = 7
Hz), 3.45 (s, 3H), 7.10–7.33 (m, 4H), 8.48 (m, 1H), 8.77 (br s, 1H) ppm, δC (20 MHz, CDCl3) 14.3, 20.9, 32.0,
37.7, 111.8, 117.4, 120.8, 122.3, 122.4, 126.0, 127.7, 137.7, 169.1 ppm: HRMS Found 200.1317 C13H16N2
requires 200.1313.
3-N-methylbutyryliminoindole hydrofluoroborate (10) 2.11 g, 7.33 mmol and sodium acetate (3 g, 37 mmol) in
water (30 mL) were heated under reflux for 10 min and gave, after recrystallization from toluene, 3-
butyroylindole (36) 0.98 g 72%, mp 179-180 °C (lit.51 mp 181-183 °C): λmax 239 (log10 4.38), 253 (4.26), 294
(4.39) nm, νmax 1620 cm–1, δH (CD3SO CD3) 0.99 (t, 3H, J = 7 Hz), 1.80 (sxt, 2H, J = 7 Hz), 2.82 (t, 3H, J = 7
Hz), 7.12–7.58 (m, 3H), 7.92 (s, 1H) 8.30–8.50 (m, 1H), 10.50 (br s, 1H) ppm, δC (20 MHz, CDCl3) 13.9, 18.4,
39.8, 112.0, 116.9, 121.8, 122.8, 127.8, 132.9, 137.0, 195.7 ppm: HRMS Found 187.1002 C12H13NO requires
187.0997.
3-N-Methyl-iso-butyryliminoindole (19 ) and 3-iso-Butyrylindole (37)
Experiments carried out by M. J. Plater.
Indole (1.60 g, 14 mmol) and N-methyl-iso-butyronitrilium fluoroborate (2.40 g, 14 mmol) in dichloromethane
(10 mL), initially at – 50 °C and then at –22 °C for 18 h was allowed to come to room temperature and the
solvent evaporated to leave an oil which was basified with aqueous sodium hydroxide (50 mL) for followed by
extraction with dichloromethane (3 x 20 mL). The combined organic layers were dried (MgSO4) and evaporated
to leave 3-N-methyl-iso-butyryliminoindole (19) after recrystallization from toluene (1.00 g, 36%), mp 138-139
°C: λmax 214 (log10 4.12), 273 (4.15), 334 (4.40) nm, νmax 1630 cm–1, δH (60 MHz, CDCl3) 1.14 (d, 6H, J = 7
Hz), 2.94 (m, 1H), 3.14 (s, 3H), 7.10-7.50 (m, 3H), 7.88 (s, 1H), 8.40-8.80 (br s, 1H) ppm, δC (20 MHz, CDCl3)
20.3, 40.0, 41.0, 111.9, 112.3, 120 -123 (3 x C), 126.4), 131.9, 135.8, 174.2 ppm: HRMS Found 200.1315
C13H16N2 requires 200.1313.
3-N-Methyl-iso-butyryliminoindole (19) (0.5 g, 2.5 mmol) and sodium acetate (3 g, 37 mmol) in water
(30 mL) were heated under reflux for 15 min and gave, after recrystallization from toluene, 3-iso-
butyrylindole (37) 0.45 g 96%, mp 130-132 °C (lit.52 mp 127-129 °C): νmax 1610 cm–1, δH (60 MHz,
CDCl3) 1.16 (d, 6H, J = 7 Hz), 3.38 (m, 1H), 7.25-7.43 (m, 3H), 7.89 (m, 1H), 8.43(m, 1H), 9.65 (br s,
1H) ppm, δC (20 MHz, CDCl3) 21.5, 37.3, 112.2, 116.0, 122.0, 122.1, 123.1, 125.0, 132.0, 136.5, 200.0
ppm: HRMS Found 187.0996 calc for C12H13NO 187.0997.
3-N-Methylpivaloyliminoindole (20) and 3-pivaloylindole (38)
Experiments carried out by M. J. Plater.
Indole (1.10 g, 9.5 mmol) and N-methylpivalonitrilium fluoroborate (1.60 g, 9.5 mmol) in
dichloromethane (10 mL), initially at – 50 °C and then at –20 °C for 18 h was allowed to come to room
temperature and the solvent evaporated to leave an oil which was dissolved in water (60 mL), basified

ACCEPTED MANUSCRIPT
with aqueous sodium hydroxide (50 mL) followed by extraction with dichloromethane (3 x 15 mL). The
combined organic layers were dried (MgSO4) and evaporated to leave crystalline 3-N-
methylpivaloyliminoindole (20) (1.60 g, 78%), after recrystallization from toluene (1.4 g, 69%), mp 141-
142 °C: λmax 275 (log10 4.22), 341 (4.21) nm, νmax 1620 cm–1, δH (60 MHz, CDCl3) 1.3 (s, 9H), 3.05 (s,
3H), 6.95-7.52 (m, 5H), 8.44-8.7 (br s, 1H) ppm, δC (20 MHz, CDCl3) 32.1, 48.3, 114.5, 123-126, 137.2,
163.0 ppm: HRMS 214.1470 C14H18N2 requires 214.1469.
3-N-Methylpivaloyliminoindole (20) (1.30 g, 6.1 mmol) and sodium acetate (3.00 g, 37 mmol) in
water/methanol (30 mL, 1:1) were heated under reflux for 15 min. Removal of the majority of the
methanol gave 3-pivaloylindole (1.20 g, 98%), mp 135-136 °C (lit.53 mp 139-140 °C, lit.14 mp 160-162
°C): νmax 1605 cm–1, δH (60 MHz, CDCl3) 1.51 (s, 9H), 7.2-7.91 (m, 4H), 8.4-8.61 (m, 1H), 9.1 (br s, 1H)
ppm, δC (20 MHz, CDCl3) 32.0, 48.3, 112.2, 117.0, 124.5, 125.1, 126.0, 129.5, 132.5, 138.0, 208.0 ppm:
HRMS 201.1156 calc for C13H15NO 201.1154.
3-N-Methylbenzoyliminoindole hydrofluoroborate (12) 3-N-Methylbenzoyliminoindole (29)and 3-
benzoylindole (39)
Indole (2.30 g, 20 mmol) and N-methylbenzonitrilium fluoroborate (4.00 g, 20 mmol) in dichloromethane (10
mL), initially at – 50 °C and then at –22 °C for 5 d gave a pale yellow solid of 3-N-methylbenzoyliminoindole
hydrofluoroborate (12 ) 5.7 g, 91%, mp 182-183 °C (from ethanol): λmax 270 (log10 4.43), 290 (4.34), and 346
(3.85) nm; νmax 3300, 1630, 1150 -950 cm–1, δH (90 MHz, CD3CN) 3.31 3.64 (3H ratio 2.2 : 1), 7.40–7.85 (m,
10 H), d 11.50 (br s, 1H) ppm; δC (20 MHz, CD3CN) 36.1, 34.6, 106.1, 110.5, 113.0, 113.5, 120.2, 120.6, 122.8,
123.4, 124.0, 124.5, 126.7, 128.8, 129.1, 129.3, 130.3, 133.7, 137.2, 138.0, 138.3, 139.7, 172.5 ppm: Found: C
60.00, H 4.80, N 8.60%, C16H15BF4N2 requires C 59.65, H 4.70, N 8.70 %.
The imine salt (12) (1.01 g, 3.1 mmol) was suspended in dichloromethane (30 mL) and shaken with
aqueous sodium hydroxide solution (30 mL, 2 M) until dissolution was complete. The organic layer was
washed with water and gave, after recrystallization from chloroform/light petroleum (40-60 °C) and gave
3-N-methylbenzoyliminoindole (29), (583 mg, 80%), mp 149-150 °C: λmax 279 (log10 4.40) nm; νmax
1598 cm–1, δH (90 MHz, CDCl3) 3.27, 3.44 (ratio 2 : 1), 7.00–7.80 (m, 9H), 8.25–8.45 (m, 1H), 10.30 (br
s, 1H) ppm; δC (20 MHz, CDCl3) 40.4, 41.9, 115.7, 116.3, 117.2, 121.2, 122.5, 122.9, 125.3, 126.2,
127.8, 128.3, 129.8, 135.6, 136.3, 165.6 ppm: HRMS Found 234.1163 C16H14N2 requires 234.1157.
The imine salt (12) (935 mg, 2.9 mmol) and sodium acetate (3 g, 37 mmol) in water (30 mL) were heated
under reflux for 10 min and gave, after recrystallization 3-benzoylindole (39) 635 mg, 99%, mp 244-246
°C (from ethanol) lit.54 mp 242-245 °C: λmax 245 (log10 4.56), 264 (4.43), 311 (4.50) nm; νmax 1598 cm–
1, δH (CDCl3) 7.20 – 7.40 (m, 3H), 7.42 – 7.62 (m, 3H), 7.73 – 7.90 (m, 3H), 8.07 (s 1H) 8.80 (br s, 1H)
ppm ; δC (CDCl3) 112.2, 115.6, 121.8, 122.0, 123.2, 126.5, 128.3, 128.4, 130.9, 135.3, 137.0, 141.0, 190.5
ppm: HRMS Found 221.0840 C15H11NO requires 221.0841.
3-N-Methylacetylimino-1-methylindole hydrofluoroborate (13), 3-N-Methylacetylimino-1-methylindole
(29), and 3-acetyl-1-methylindole (39)
1-Methylindole (4) (6.70 g, 51 mmol) in dichloromethane (10 mL) was added slowly to a stirred
suspension of N-methylacetonitrilium fluoroborate (7.4 g, 51 mmol) in dichloromethane (25 mL) at – 50
°C, keeping the temperature below – 45 °C during the addition. The reaction mixture was then kept at –
22 °C for 15 h which then gave 3-N-methylactylimino-1-methylindole hydrofluoroborate (13) as a pink
solid (9.80 g, 70%), mp 231-231 °C (from ethanol): λmax 252 (log10 4.13), 265 (4.03), 333 (4.32) nm;
νmax 3315, 1612, 1150-950 cm–1, δH (90 MHz, CD3CN) 2.79 (s, 3H), 3.45 (d, 3H J = 7 Hz, singlet after

ACCEPTED MANUSCRIPT
D2O exchange), 3.93 (s, 3H), 7.32 – 7.66 (m, 3H), 7.70 – 7.88 (m 1H), 8.31 (s, 1H), 9.35 (br s, 1H) ppm,
δC (20 MHz, CD3CN) 25.9, 34.7, 36.6, 207.0, 112.8, 122.4, 124.9, 125.5, 127.4, 138.7, 141.5, 174.3 ppm.
Found C 52.55, H 5.50, N 10.20%, C12H15BF4N2 requires C 52.60, H 5.50, N 10.20 %.
The iminium salt (13) (1.87 g, 6.82 mmol) was suspended in dichloromethane (30 mL) and shaken with
aqueous sodium hydroxide solution (30 mL, 2 M) until dissolution was complete. The organic layer was
washed with water and gave, after recrystallization from ethanol 3-N-methylacetylimino-1-methylindole
(29), (795 mg, 62%), mp 95-96 °C: λmax 253 (log10 4.82), 297 (4.72), 332 (4.70) nm: IR νmax 1609 cm–1,
δH (90 MHz, CDCl3) 2.12 (s, 3H), 3.34 (s, 3H), 3.55 (s, 3H), 7.15-7.28 (m, 4H), 8.42-8.60 (m, 1H) ppm,
δC (20 MHz, CDCl3) 15.5, 32.6, 38.7, 109.0, 117.9, 120.8, 122.4, 123.3, 126.2, 130.4, 137.7, 163.0 ppm.
Found C 77.15, H 7.50, N 15.10%, C12H14N2 requires C 77.40, H 7.60, N 15.05%.
The imine salt (13) (1.94 g, 7 mmol) and sodium acetate (5 g, 61 mmol) in water (30 mL) were heated
under reflux for 10 min and gave, after recrystallization from ethanol, 3-acetyl-1-methylindole (39) 790
mg, 71%, mp 109-110 °C (lit.13 mp 106-107 °C): : λmax 241 (log10 4.15) 298 (4.19) nm; νmax 1635 cm–1,
δH (90 MHz, CDCl3) 2.34 (s, 3H), 3.51 (s, 3H), 7.10-7.32 (m, 3H), 7.41 (s, 1H), 8.31-8.45 (m, 1H), δC (20
MHz, CDCl3) 27.3, 33.1, 109.7, 116.5, 122.3, 123.1, 126.1, 136.1, 137.4, 192.8 ppm. Found C 75.90, H
6.45, N 8.05%, Calc. for C11 H11 NO, C 76.25, H 6.40, N 8.10 %: HRMS Found 173.0843 C11H11NO
requires 173.0841.
3-N-Methylacetylimino-1-benzylindole hydrofluoroborate (16), 3-N-Methylacetylimino-1-benzylindole
(32), and 3-acetyl-1-benzylindole (42)
1-Benzylindole (6.60 g, 32 mmol) in dichloromethane (25 mL) was added slowly to a stirred suspension
of N-methylacetonitrilium fluoroborate (4.60 g, 32 mmol) in dichloromethane (25 mL) at – 50 °C,
keeping the temperature below – 45 °C during the addition. The reaction mixture was then kept at – 22 °C
for 48 h which then gave 3-N-methylacetylimino-1-benzylindole hydrofluoroborate (16) as a pink solid
(9.00 g, 81%), mp 199-200 °C (from ethanol): λmax 251 (log10 4.13), 264.5 (4.04), 333 (4.33) nm: νmax
3360, 1612, 1150-950 cm–1, δH (90 MHz, CD3CN) 2.86 (s, 3H), 3.50 (d, 3H J = 7 Hz, singlet after D2O
exchange), 5.57 (s, 2H), 7.25-7.65 (m, 8H), 7.79-7.91 (m, 1H), 8.54 (s, 1H), 9.50 (br s, 1H) ppm, δC (20
MHz, CD3CN) 26.2, 36.9, 52.5, 107.9, 113.5, 122.8, 125.1, 125.7, 127.9, 128.5, 129.5, 136.8, 138.0,
140.8, 175.5 ppm. Found C 61.70, H 5.50, N 7.95%, C18H19BF4N2 requires C 61.75, H 5.45, N 8.00 %.
The iminium salt (16) (2.15 g, 6.14 mmol) was suspended in dichloromethane (30 mL) and shaken with
aqueous sodium hydroxide solution (30 mL, 2 M) until dissolution was complete. The organic layer was
washed with water and gave, after recrystallization from ethanol, 3-N-methylacetylimino-1-benzylindole
(32), (980 mg, 61%), mp 94-95 °C: λmax 250 (log10 4.16), 294 (4.22), 332 (3.41) nm: νmax 1609, cm–1,
δH (90 MHz, CDCl3) 2.13 (s, 3H), 3.37 (s, 3H), 5.13 (s, 2H), 6.94-7.19 (m, 8H), 7.32 (s, 1H), 8.52-8.70
(m. 1H) ppm, δC (20 MHz, CDCl3) 15.7, 38.8, 50.0, 109.7, 118.7, 121.1, 122.6, 123.4, 126.5, 126.7,
127.7, 128.8, 129.7, 137.2, 137.5, 163.5 ppm. Found C 82.10, H 6.85, N 10.65%, C18H18N2 requires C
82.40, H 6.90, N 10.70 %.
The imine salt (16) (2.11 g, 6 mmol) and sodium acetate (5.00 g, 61 mmol) in water (50 mL) were heated
under reflux for 10 min and gave 3-acetyl-1-benzylindole (42) (95%), after recrystallization from ethanol,
1.00 g, 67%, mp 104-105 °C (lit.55 mp 102-103 °C): : λmax 240 (log10 4.04) 298 (4.10) nm;
νmax 1640 cm–1, δH (90 MHz, CDCl3) 2.44 (s, 3H), 5.22 (s, 2H), 7.04-7.30 (m, 8H), 7.72 (s, 1H), 8.40-
8.57 (m, 1H) ppm, δC (20 MHz, CDCl3) 27.6, 50.6, 110.3, 117.4, 122.7, 123.5, 126.6, 127.1, 128.2, 129.0,
135.3, 136.0, 137.2, 193.1 ppm. HRMS Found 249.1147, C17H15NO requires 249.1154.

ACCEPTED MANUSCRIPT
3-N-Methylacetylimino-2-methylindole hydrofluoroborate (14), 3-N-Methylacetylimino-2-methylindole
(30), and 3-acetyl-2-methylindole (40)
2-Methylindole (4) (3.70 g, 28 mmol) in dichloromethane (20 mL) was added slowly to a stirred
suspension of N-methylacetonitrilium fluoroborate (4.10 g, 28 mmol) in dichloromethane (30 mL) at – 50
°C, keeping the temperature below – 45 °C during the addition. The reaction mixture was then kept at –
22 °C for 5 d which then gave 3-N-methylacetylimino-2-methylindole hydrofluoroborate (14) as a white
solid (6.3 g, 82%), mp 200-201 °C (from ethanol): λmax 272 (log10 4.38) 338 (4.08) nm, νmax 3320,
1642, 1150-950 cm–1, δH (90 MHz, CD3CN) 2.71 (s, 3H), 2.76 (s, 3H), 3.45 (d, 3H J = 7 Hz, singlet after
D2O exchange), 7.25 -7.60 (m, 3H), 7.70-7.84 (m, 1H), 9.95 (br s, 1H), 10.75 (br s, 1H) ppm, δC (20
MHz, CD3CN) 15.8, 20.9, 33.7, 108.4, 112.1, 120.2, 123.5, 125.9, 126.3, 136.8, 248.6, 178.4 ppm. Found
C 52.95, H 5.40, N 10.20%, C12H15N2 requires C 52.60, H 5.50, N 10.20 %.
The imine salt (14) (2.33 g, 8.5 mmol) was suspended in dichloromethane (30 mL) and shaken with
aqueous sodium hydroxide solution (30 mL, 2 M) until dissolution was complete. The organic layer was
washed with water and gave, after recrystallization from ethanol, 3-N-methylacetylimino-2-methylindole
(32) as a mixture of diastereoisomers, (1.30 g, 82%), mp 119-123 °C: λmax 274 (log10 4.47) 339 (3.59)
nm, νmax 1618 cm–1, δH (90 MHz, CDCl3) 2.30 (s, 3H), 3.10 (d, J = 1.5 Hz, Z-isomer), 3.33 (s, E-isomer),
6.93-7.18 (m, 3H), 7.61-7.76 (m, 1H), 10.04 (br s, 1H) ppm, δC (20 MHz, CDCl3) 12.4, 19.0 (E-isomer),
28.6 (Z-isomer), 38.1 (E-isomer), 40.8 (Z-isomer), 111.0, 115.3, 119.1, 119.7, 120.9, 126.6 (Z-isomer),
127.1, 132.4, 135.5 (E-isomer), 136.1, 167.2 ppm. HRMS Found 186.1162 C12H14N2 requires 186.1157.
The imines (32) (523 mg, 2.8 mmol) and sodium acetate (2.50 g, 30 mmol) in water (20 mL) were heated
under reflux for 10 min and gave, after recrystallization from ethanol, 3-acetyl-2-methylindole (40) 419
mg, 71%, mp 203-204 °C (lit.56 mp 200 °C): λmax 239 (log10 4.47), 265 (4.37), 299 (4.41) nm, νmax 1610
cm–1, δH (90 MHz, CD3SOCD3) 2.55 (s, 3H), 2.72 (s, 3H), 7.12-7.32 (m, 2H), 7.40-7.55 (m, 1H), 8.01-
8.20 (m, 1H), 9.80 (br s, 1H), δC (20 MHz, CD3SOCD3) 14.8, 30.6, 11.1, 113.6, 120.6, 121.2, 121.6,
127.0, 134.8, 144.0, 193.0 ppm. HRMS Found 173.0840 C11H11NO requires 173.0841.
2-N-Methylacetylimino-3-methylindole hydrofluoroborate (23), 2-N-Methylacetylimino-3-methylindole
(24), and 2-acetyl-3-methylindole (25)
3-Methylindole (22) (2.30 g, 16 mmol) in dichloromethane (20 mL) was added slowly to a stirred
suspension of N-methylacetonitrilium fluoroborate (2.30 g, 16 mmol) in dichloromethane (20 mL) at – 50
°C, keeping the temperature below – 45 °C during the addition. The reaction mixture was then kept at –
22 °C for 2 h which then gave, after recrystallization from ethanol, 2-N-methylacetylimino-3-methylindole
hydrofluoroborate (23) 1.45 g, 33%, mp 198-200 °C: λmax 228 (log10 4.21), 312 (4.26) 338 (4.31) nm,
νmax 3360, 1624, 1150-950 cm–1, δH (90 MHz, CD3CN) 2.55 (s, 3H), 2.69 (s, 3H), 3.43 (s, 3H), 7.10-7.55
(m, 3H), 7.74 (d, J = 8 Hz, 1H), 9.85 (br s, 1H) 10.50 (br s, 1H), δC (20 MHz, CD3CN) 11.8, 19.4, 34.5,
111.6, 113.8, 122.6, 127.3, 127.7, 130.1, 140.5, 174.5 ppm. Found C 52.50, H 5.60, N 9.80%,
C12H15N2BF4 requires C 52.60, H 5.50, N 10.20 %.
The dichloromethane filtrate was basified to pH 10 with aqueous sodium hydroxide solution (2M) and
gave 2-N-methylacetylimino-3-methylindole (24) 1.15 g, 34 % after recrystallization from ethanol, mp
134-135 °C): λmax 221 (log10 4.52), 304 (4.56) nm, νmax 1604 cm–1, δH (90 MHz, CDCl3) 2.30 (s, 3H),
2.53 (s, 3H), 3.32 (s, 3H), 6.97-7.30 (m, 3H), 7.52-7.67 (m, 1H), 9.30 (br s, 1H) ppm, δC (20 MHz,
CDCl3) 10.1, 16.1, 38.1, 111.0, 111.8, 119.0, 119.6, 123.8, 130.0, 134.3, 135.5, 161.4 ppm. Found C
77.45, H 7.70, N 14.70 C12H14N2 requires C 77.40, H 7.60, N 15.05% HRMS 186.1155 C12H14N2 requires
186.1157.

ACCEPTED MANUSCRIPT
The imine salt (23) (776 mg, 2.8 mmol) and sodium acetate (3.00 g, 36 mmol) in water (20 mL) were
heated under reflux for 10 min and gave 2-acetyl-3-methylindole (25) (95%), after recrystallization from
ethanol, 202 mg, 41%, mp 149-150 °C (lit.57 mp 144-145 °C): λmax 233 (log10 4.56) 309 (4.69) nm, νmax
3315, 1632 cm–1, δH (90 MHz, CDCl3) 2.65 (6 H), 7.09-7.50 (m, 3H), 7.75 (d, J = 8 Hz, 1H), 9.35 (br s,
1H) ppm δC (20 MHz, CDCl3) 10.8, 28.8, 111.9, 118.5, 119.9, 121.1, 126.4, 128.8, 132.7, 136.1, 190.5
ppm. Found HRMS 173.0842 C11H11NO requires 173.0841.
3-N-Methylacetylimino-1,2-dimethylindole hydrofluoroborate (15), 3-N-Methylacetylimino-1,2-
methylindole (31), and 3-acetyl-1,2-methylindole (41)
1,2-Dimethylindole (22) (6.20 g, 42 mmol) in dichloromethane (20 mL) was added slowly to a stirred
suspension of N-methylacetonitrilium fluoroborate (6.20 g, 43 mmol) in dichloromethane (20 mL) at – 50
°C, keeping the temperature below – 45 °C during the addition. The reaction mixture was then kept at –
22 °C for 1 d which then gave 3-N-methylacetylimino-1,2-dimethylindole hydrofluoroborate (15) in 87%
yield, after recrystallization from ethanol, 8.50 g, 70%, mp 198.5-199 °C: : λmax 275 (log10 4.30), 344
(3.85) nm, νmax 3340, 1625, 1150-950 cm–1, δH (90 MHz, CD3CN) 2.54 (s, 3H), 2.78 (s, 3H), 3.44 (s, 3H),
3.70 (s, 3H), 7.28-7.58 (m, 3H), 7.73-7.88 (m, 1H), 10.40 (br s, 1H) ppm, ), δC (20 MHz,CD3CN) 13.7,
21.3, 31.4, 34.0, 109.9, 112.3, 120.4, 124.5, 125.0, 126.0, 139.0, 148.6, 178.9 ppm. Found C 54.30, H
6.05, N 9.50%, C13H17N2BF4 requires C 54.20, H 5.95, N 9.70 %.
The imine salt (15) (1.67 g, 5.8 mmol) was suspended in dichloromethane (30 mL) and shaken with
aqueous sodium hydroxide solution (30 mL, 2 M) until dissolution was complete. The organic layer was
washed with water and gave, after recrystallization from chloroform/light petroleum (40-60 °C), 3-N-
methylacetylimino-1,2-dimethylindole (31) as a mixture of diastereoisomers, (1.30 g, 82%), mp 81-82 °C:
λ
max 279 (log10 4.42) 344 (3.47) nm, νmax 1614 cm–1, δH (90 MHz, CDCl3) 2.20 (s, 3H), 2.29 (s, 3H, E-
isomer), 2.33 (d, J = 1 Hz, Z-isomer), 2.50 (s, E-isomer), 3.09 (d, J = 1 Hz, Z-isomer), 3.34 (s, E-isomer),
3.50 (s, E-isomer), 3.55 (s, Z-isomer), 7.00-7.42 (m, 3H), 7.62-7.80 (m, 1H) ppm, δC (20 MHz, CDCl3)
11.5 (Z), 116.0 (E), 29.4 (E), 38.9 (Z), 41.2, 108.9, 109.1, 116.4, 119.0. 119.8, 120.0, 121.0, 121.3, 126.6,
133.0, 136.4, 136.5, 136.8, 165.4, 166.2 ppm. Found C 77.65, H 8.10, N 13.95%, C13H16N2 requires C
77.95, H 8.05, N 14.00 %. Found HRMS 200.1320 C13H16N2 requires 200.1313.
The imine salt (15) (2.29 g, 8 mmol) and sodium acetate (9.00 g, 110 mmol) in water (50 mL) were
heated under reflux for 10 min and gave 3-acetyl-1,2-dimethylindole (41) 1.25 g, 84%), after
recrystallization from ethanol, mp 113-114 °C (lit.58 mp 110 °C): λmax 242 (log10 4.48) 263 (4.30), 302
(4.43) nm, νmax 1640 cm–1, δH (90 MHz, CDCl3) 2.69 (s, 3H), 2.80 (s, 3H), 3.72 (s, 3H), 7.27-7.40 (m,
3H), 7.92-8.10 (m, 1H) ppm, δC (20 MHz, CDCl3) 10.6, 27.4, 29.7, 107.7, 112.2, 119.0, 120.1, 124.6,
134.8, 143.2, 192.4 ppm. HRMS Found 187.0998 C12H13NO requires 187.0997.
3-N-Methylacetylimino-2-phenylindole hydrofluoroborate (17), 3-N-Methylacetylimino-2-phenylindole
(33), and 3-acetyl-2-phenylindole (43)
2-Phenylindole (8) (4.70 g, 24.3 mmol) in dichloromethane (60 mL) was added slowly to a stirred
suspension of N-methylacetonitrilium fluoroborate (3.60 g, 25 mmol) in dichloromethane (25 mL) at – 50
°C, keeping the temperature below – 45 °C during the addition. The reaction mixture was then kept at –
22 °C for 5 d which then gave 3-N-methylacetylimino-2-phenylindole hydrofluoroborate (17) in 87%
yield, after recrystallization from ethanol, 5.9 g, 72%, mp 212-213 °C: : λmax 237 (log10 4.68) 306 (4.70)
nm, νmax 3320, 1650, and 1150-950 cm–1, δH (90 MHz, CDCl3) 2.44 (s, 3H), 3.39 (s, 3H), 7.35-7.74 (m,
8H), 7.84-7.96 (m, 1H), 8.10 (br s, 1H), 10.50 (br s, 1H); signals of lower intensity were observed at 2.75

ACCEPTED MANUSCRIPT
and 2.99 ppm giving a ratio of diastereoisomers of 7:1, other minor peaks of low intensity are omitted, δC
(20 MHz, CD3CN) 21.8, 26.7 (minor isomer), 34.1, 37.2 (minor isomer), 109.2, 114.0, 120.4, 124.5,
125.8, 126.3, 131.6, 130.5, 131.9, 137.6, 148.9, 180.0 ppm. Found C 60.90, H 5.20, N 8.20%,
C17H17N2BF4 requires C 60.75, H 5.10, N 8.35%.
The imine salts (17) (1.88 g, 5.3 mmol) was suspended in dichloromethane (30 mL) and shaken with
aqueous sodium hydroxide solution (30 mL, 2 M) until dissolution was complete. The organic layer was
washed with water and gave, after recrystallization from ethanol, 3-N-methylacetylimino-2-phenylindole
(33) as a mixture of diastereoisomers, (1.10 g, 80%), mp 210-212 °C; λmax 237 (log10 4.59) 306 (4.61)
nm, νmax 1650 cm–1, δH (90 MHz, CDCl3) 1.99 (s, E), 2.28 (d, J = 1 Hz, Z), 3.06 (d, J = 1 Hz, Z), 3.34 (s,
E), 7.00-7.70 (m, 8H), 7.89-8.00 (m, 1H), 9.50 (br s, 1H) ratio E:Z ca 1:2, Found HRMS 248.1319
C17H16N2 requires 248.1313.
The imine salt (17) (1.44 g, 4.3 mmol) and sodium acetate (4.5 g, 55 mmol) in water (40 mL) were heated
under reflux for 1 d and gave, after recrystallization 3-acetyl-2-phenylindole (43) 676 mg, 67%, mp 227-
229 °C (from ethanol) lit.59 mp 219-221 °C: λmax 248 (log10 4.78), 264 (4.43), 302 (4.60) nm; νmax 3170,
1618 cm–1, δH (90 MHz, CDCl3) 2.17 (s, 3H), 7.20-7.75 (m, 8H), 8.29-8.45 (m, 1H), 9.80 (br s, 1H) ppm,
δC (20 MHz, CDCl3) 30.0, 111.5, 114.5, 121.7, 128.3, 129.2, 129.9, 132.8, 135.5, 148.8, 193.6 ppm.
HRMS Found 235.0999 C16H13NO requires 235.0997.
Reactions of pyrrole and its derivatives with N-alkylnitrilium fluoroborates and deprotonation and
hydrolysis of the products
2-N-Methylacetyliminopyrrole hydrofluoroborate (44), 2-N-methylacetyliminopyrrole (45), and 2-
acetylpyrrole (46)
Pyrrole (2.80 g, 42 mmol) in dichloromethane (5 mL) was added slowly to a stirred suspension of N-
methylacetonitrilium fluoroborate (6.10 g, 43 mmol) in dichloromethane (30 mL) at – 30 °C, keeping the
temperature below – 25 °C during the addition. The reaction mixture was then kept at – 22 °C for 2 d
which then gave 2-N-methylacetyliminopyrrole hydrofluoroborate (44) 6.90g, 78%, mp 77-78 °C after
recrystallization from dichloromethane; λmax 281 (log10 4.37) 319 (4.02) nm, νmax 3300, 1630, 1150-950
cm–1, δH (90 MHz, CD3CN) 2.85 (s, 3H), 3.58 (d, 3H J = 7 Hz, singlet after D2O exchange), 6.70-6.80
(m, 1H), 7.58-6.80 (m, 2H), 10.10 (br s, 1H), 11.45 (br s, 1H), δC (20 MHz, CD3CN) 22.8, 36.1, 115.7,
126.5, 133.6, 134.1, 167.0 ppm. Found C 39.80, H 5.20, N 13.30%, C7H11N2BF4 requires C 40.05, H
5.30, N 13.35%.
The dichloromethane filtrate extracted into water, basified to pH 10 with aqueous sodium hydroxide solution (2
M) and re-extracted into dichloromethane, dried (MgSO4), concentrated and distilled (Kugelrohr) at 56-58 °C to
give 2-N-methylacetyliminopyrrole (45) 820 mg, 16%, mp 58-59 °C after recrystallization from light petroleum
(40-60 °C); λmax 278 (log10 3.98) nm, νmax 1620 cm–1, δH (90 MHz, CDCl3) 2.13 (s, 3H), 3.24 (s, 3H), 6.17-
6.27 (m, 1H), 6.52-6.62 (m, 1H), 6.80 (t, 1H J = 2 Hz), 11.12 (br s, 1H) ppm, δC (20 MHz, CDCl3) 14.7, 37.8,
108.9,
110.0, 121.5, 133.4, 160.5 ppm. Found C 68.85, H 8.00, N 22.50%, C7H10N2 requires C 68.80, H 8.25, N
22.90%. HRMS Found 122.0849 C7H10N2 requires 122.0844.
A reaction in which pyrrole (1.90 g, 28 mmol) in dichloromethane (5 mL) was added slowly to a stirred
suspension of N-methylacetonitrilium fluoroborate (4.00 g, 28 mmol) in dichloromethane (25 mL) at – 50
°C, keeping the temperature below – 45 °C during the addition. The reaction mixture was then kept at –
22 °C for 2 d which then gave the imine salt (44) and the imine (45) in 85 and 5% yields respectively,

ACCEPTED MANUSCRIPT
The imine (45) (2.18 g, 18 mmol) and sodium acetate (5.00 g, 61 mmol) in water (30 mL) were heated
under reflux for 10 min and gave 2-acetylpyrrole (46) 1.25 g, 84%), after recrystallization from light
petroleum (40-60 °C), mp 91-92 °C (lit.4a mp 91-92 °C); λmax 250 (log10 3.83) 285 (4.38) nm, νmax 1648
cm–1, δH (90 MHz, CDCl3) 2.45 (s, 3H), 6.27-6.38 (m, 1H), 6.92-7.04 (m, 1H), 7.08-7.18 (m, 1H), 9.50
(br s, 1H) ppm, δC (20 MHz, CDCl3) 25.2, 110.3, 117.3, 125.4, 132.0, 188.3 ppm. HRMS Found
109.0520 C6H7N requires 109.0528.
A reaction in which pyrrole (1.90 g, 28 mmol) in dichloromethane (5 mL) was added slowly to a stirred
suspension of N-methylacetonitrilium fluoroborate (4.00 g, 28 mmol) in dichloromethane (30 mL) at – 50
°C, keeping the temperature below – 45 °C during the addition. The reaction mixture was then kept at –
22 °C for 2 d and, after allowing the reaction mixture to come to room temperature, the solvent was
removed in vacuo and a solution of sodium acetate (10.0 g, 122 mmol) in water (40 mL) was added the
residual material. After heating the aqueous solution under reflux for 30 min the cold reaction mixture
was extracted with dichloromethane (2 x 40 mL) and the combined extracts were dried and concentrated
and gave 2-acetylpyrrole (46) 2.4 g, 78%), after recrystallization from light petroleum (40-60 °C), mp
91-92 °C.
2-N-Ethylacetyliminopyrrole
Acetonitrile (1.80 g, 43 mmol) and triethyloxonium fluoroborate (8.00 g, 42 mmol) in dichloromethane
(10 mL) were stirred at room temperature for 2 d before pyrrole (2.80 g, 42 mmol) was added at below –
5 °C. the reaction mixture was stirred at – 10 °C for 15 min and then added to ice/water (50 mL). The
aqueous phase was basified to pH14 with aqueous sodium hydroxide solution (2 M) and extracted into
dichloromethane (3 times 20 mL). The combined extracts were washed with water (30 mL), dried
(MgSO4) and concentrated to leave a liquid which after distillation (Kugelrohr, 65-66 °C at 1.1 mm/Hg)
gave 2-N-ethylacetyliminopyrrole (1.10 g, 19%), λmax 281 (log10 4.68) nm, νmax 1615 cm–1, δH (90
MHz, CDCl3) 1.20 (t, 3H, J = 7 Hz), 2.12 (s, 3H), 3.49 (q, 2H, J = 7 Hz), 6.11-6.21 (m, 1H), 6.48-6.57
(m, 1H), 6.68-6.78 (m, 1H), 9.80 (br s, 1H) ppm, δC (20 MHz CDCl3) 14.4, 15.9, 45.0, 108.9, 110.6,
121.0, 133.6, 157.8 ppm. HRMS Found 136.0995 C5H12N2 requires 136.1000.
2-N-methylpropionyliminopyrrole (48) and 2-propionylpyrrole (53)
Pyrrole (1.20 g, 18 mmol) in dichloromethane (5 mL) was added slowly to a stirred suspension of N-
methylpropionitrilium fluoroborate (2.80 g, 18 mmol) in dichloromethane (15 mL) at – 50 °C, keeping
the temperature below – 45 °C during the addition. The reaction mixture was then kept at – 22 °C for 1 d
to give a homogeneous solution which was allowed to come to room temperature, extracted into water (3
x 30 mL) and basified to pH14 with aqueous sodium hydroxide solution (2 M) and extracted into
dichloromethane (3 times 20 mL). The combined extracts were washed with water (30 mL), dried
(MgSO4) and concentrated to leave a liquid (2.36 g, 93%) which after distillation (Kugelrohr, 90 °C at 1.1
mm) gave 2-N-methylpropionyliminopyrrole (48), (2.07 g, 86%), mp 51-52 °C, λmax 280 (log10 4.59)
nm, νmax 3140, 1617 cm–1, δH (90 MHz, CDCl3) 1.16 (t, 3H, J = 7 Hz), 2.62 (q, 2H, J = 7 Hz), 3.30 (s,
3H), 6.15-6.28 (m, 1H), 6.49-6.58 (m, 1H), 6.75-6.86 (m, 1H), 9.00 (br s, 1H) ppm, δC (20 MHz, CDCl3)
11.9, 21.7, 37.1, 109.0, 110.3, 121.2, 132.5, 164.9 ppm. HRMS Found 136.1008 C5H12N2 requires
136.1000.
The imine (48) (1.03 g, 7.6 mmol) and sodium acetate (5.00 g, 61 mmol) in water (20 mL) were heated
under reflux for 30 min to give 2-propionylpyrrole (53) as a white solid (862 mg, 93%), mp 51-52 °C
after recrystallization from water, mp 51-52 °C, (lit.60 mp 50-52 °C); λmax 284 (log10 4.63) nm, νmax

ACCEPTED MANUSCRIPT
3280, 1642 cm–1, δH (90 MHz, CDCl3) 1.23 (t, 3H, J = 7 Hz), 2.83 (q, 2H, J = 7 Hz), 6.24-6.35 (m, 1H),
6.93-7.03 (m, 1H), 7.05-7.15 (m, 1H), 9.25 (br s, 1H) ppm, δC (20 MHz, CDCl3) 8.8, 30.7, 110.0, 116.2,
125.0, 131.4, 191.8 ppm. HRMS Found 123.0685 C7H9NO requires 123.0684.
2-N-Methylbutyryliminopyrrole (49) and 2-butyrylpyrrole (54)
Pyrrole (2.70 g, 40 mmol) in dichloromethane (5 mL) was added slowly to a stirred suspension of N-
methylbutyronitrilium fluoroborate (6.90 g, 40 mmol) in dichloromethane (30 mL) at – 50 °C, keeping
the temperature below – 45 °C during the addition. The reaction mixture was then kept at – 22 °C for 4 d
to give an homogeneous solution which, after coming to room temperature was added to added to
ice/water (50 mL). The aqueous phase was basified to pH14 with aqueous sodium hydroxide solution (2
M) and extracted into dichloromethane (3 times 20 mL). The combined extracts were washed with water
(30 mL), dried (MgSO4) and concentrated to leave a liquid which, after distillation (Kugelrohr, 120 °C at
6 mm), gave 2-N-methylbutyryliminopyrrole (49), (5.0 g, 83%), mp 46-47 °C, λmax 281 (log10 4.56) nm,
νmax 1614 cm–1, δH (90 MHz, CDCl3) 1.00 (t, 3H, J = 8 Hz), 1.49-1.80 (m, 2H), 2.60 (t, 2H, J = 8.5 Hz),
3.30 (s, 3H), 6.15-6.25 (m, 1H), 6.48-6.57 (m, 1H), 6.72-6.81 (m, 1H), 10.90 (br s, 1H) ppm, δC (20 MHz,
CDCl3) 14.4, 21.1, 30.5, 37.4, 108.9, 110.6, 121.2, 133.0, 163.9 ppm. HRMS Found 150.1148 C9H14N2
requires 150.1157.
The imine (49) (1.54 g, 10.3 mmol) and sodium acetate (6.0 g, 73 mmol) in water (25 mL) were heated
under reflux for 30 min to give 2-butyrylpyrrole (54) as a white solid after recrystallization from water
(1.18 g, 84%), mp 47-48 °C, (lit.61 mp 43-45 °C); λmax 285 (log10 4.54) nm, νmax 3280, 1635 cm–1, δH
(90 MHz, CDCl3) 1.00 (t, 3H, J = 8 Hz), 1.56-2.03 (m, 2H), 2.81 (t, 2H, J = 7 Hz), 6.30-6.41 (m, 1H),
6.95-7.06 (m, 1H), 7.10-7.20 (m, 1H), 10.80 (br s, 1H) ppm, δC (20 MHz, CDCl3) 14.0, 18.9, 40.0, 110.4,
116.3, 125.5, 132.3, 191.7 ppm. HRMS Found 137.0838 C8H11NO requires 137.0841.
N-Methyl-isobutyryliminopyrrole (50) and 2-isobutyrylpyrrole (55)
Experiments carried out by M. J. Plater
Pyrrole (0.80 g, 12 mmol) in dichloromethane (5 mL) was added slowly to a stirred suspension of N-
methyl-iso-butyronitrilium fluoroborate (2.05 g, 12 mmol) in dichloromethane (10 mL) at – 50 °C,
keeping the temperature below – 45 °C during the addition. The reaction mixture was then kept at – 22 °C
for 20 h to give an homogeneous solution which, after coming to room temperature was added to added to
ice/water (45 mL). The aqueous phase was basified to pH14 with aqueous sodium hydroxide solution (2
M) and extracted into dichloromethane (3 times 10 mL). The combined extracts were dried (MgSO4) and
concentrated to leave a liquid (1.03 g, 57%) which, after distillation (Kugelrohr, 80 °C at 2 mm/Hg), gave
2-N-methyl-isobutyryliminopyrrole (50), (900 mg, 38%) as a low melting solid, νmax 1630 cm–1, δH (60
MHz, CDCl3) 1.30 (d, 6H, J = 7 Hz), 2.60 (h, 1H J = 7 Hz), 3.30 (s, 3H), 6.0-7.0 (m, 3H), 8.1 (br s, 1H).
HRMS Found 150.1154 C9H14N2 requires 150.1157.
The imine (50) (400 mg, 2.7 mmol) and sodium acetate (0.22 g, 2.7 mmol) in water/methanol 1:1 (7.5
mL) were heated under reflux for 10 min to give, after evaporation of the solvents 2-isobutyrylpyrrole
(55) as a white solid after recrystallization from water (350 mg, 95%), mp 88-89 °C, νmax 1635 cm–1, δC
(20 MHz, CDCl3) 17.0,32.2, 106.7, 111.3, 120.5, 126.1, 189.2 ppm. HRMS Found 137.0843 C8H11NO
requires 137.0841.
2-N-Methylpivaloyliminopyrrole (51) and 2-pivaloylpyrrole (56)

ACCEPTED MANUSCRIPT
Experiments carried out by M. J. Plater
Pyrrole (1.40 g, 21 mmol) in dichloromethane (5 mL) was added slowly to a stirred suspension of N-
methylpivalonitrilium fluoroborate (3.50 g, 20 mmol) in dichloromethane (10 mL) at – 50 °C, keeping the
temperature below – 45 °C during the addition. The reaction mixture was then kept at – 22 °C for 18 h to
give an homogeneous solution which, after coming to room temperature was added to added to ice/water
(60 mL). The aqueous phase was basified to pH14 with aqueous sodium hydroxide solution (5 M) and
extracted into dichloromethane (4 times 15 mL). The combined extracts were dried (MgSO4) and
concentrated to leave a liquid (1.8 g, 55%) which, after distillation (Kugelrohr, 90 °C at 2 mm/Hg), gave
2-N-methylpivaloyliminopyrrole (51), (900 mg, 38%) as a viscous oil, νmax 1630 cm–1, δH (CDCl3) 1.18
(s, 9H), 3.01 (s, 3H), 5.90-5.97 (m, 1H), 6.10-6.20 (m, 1H), 6.65-6.75 (m, 1H), 8.95 (br s, 1H) ppm, , δC
(CDCl3) 25.4, 37.1, 39.0, 103.4, 104.5, 113.0, 120.9, 169.2 ppm. HRMS Found 164.1318 C10H16N2
requires 164.1313.
The imine (51) (1.00 mg, 6 mmol) and sodium acetate (0.6 g, 7.3 mmol) in water/methanol 1:1 (25 mL)
were heated under reflux for 10 min to give, after evaporation of the solvents left an oil (800 mg, 92%)
and which, after distillation (Kugelrohr, 95 °C at 2 mm/Hg), gave 2-pivaloylpyrrole (56), mp 102-103 °C,
(lit.62 mp 98-100 °C); νmax 1632 cm–1, δH (60 MHz, CDCl3) 1.40 (s, 9H), 6.15-6.30 (m, 1H), 6.80-6.85 (m,
1H), 6.96-6.98 (m, 1H), δC (20 MHz, CDCl3) 32.5, 47.0, 112.5, 119.2, 125.7, 131.9, 197.5 ppm.
2-N-Methylbenzoyliminopyrrole hydrofluoroborate(47), 2-N-methylbenzoyliminopyrrole (52) and
2-benzoylpyrrole (57)
Pyrrole (1.90 g, 28 mmol) in dichloromethane (5 mL) was added slowly to a stirred suspension of N-
methylbenzonitrilium fluoroborate (5.80 g, 28.3 mmol) in dichloromethane (25 mL) at – 50 °C, keeping
the temperature below – 45 °C during the addition. The reaction mixture was then kept at – 22 °C for 24 h
to give, as a solid after filtration, 2-N-methylbenzoyliminopyrrole hydrofluoroborate as a mixture of
diastereoisomers (47) (6.00 g, 78%) mp 85-89 °C, decomp. (from ethanol): λmax 228 (log10 4.33), 287
(4.43) 322 (4.15) nm, νmax 3300, 1605, 1130-980 cm–1, δH (90 MHz, CD3CN) 3.25 (d, 3H J = 7 Hz,
singlet after D2O exchange), 3.66 (d, 3H J = 7 Hz, singlet after D2O exchange), 6.75-6.88 (m, 2H), 7.5-
7.95 (m, 6H), 9.45 (br s, 1H), 10.50 (br s, 1H) ppm, δC (20 MHz, CD3CN) (major signals) 35.3, 36.4,
115.6, 115.8, 167.0, 167.8 ppm.
The filtrate was added to ice/water (50 mL) and the aqueous layer taken to pH 10 with aqueous sodium
hydroxide solution (2M), extracted with dichloromethane (3 times 30 mL), dried (MgSO4), and
evaporated to give 2-N-methylbenzoyliminopyrrole (52) (4.15 mg 8%), mp 119-120 °C (from CHCl3/
light petroleum bp 40-60 °C): λmax 230 (log10 4.33) 287 (4.58) nm, νmax 1605 cm–1, δH (90 MHz,
CDCl3) 3.24 (s, 3H), 5.98-6.07 (m, 1H), 6.17-6.27 (m, 1H), 6.91-7.00 (m, 1H), 7.24-7.54 (m, 5H), 10.05
(br s, 1H) ppm, δC (20 MHz, CDCl3) 39.8, 109.2, 114.6, 121.9, 128.0, 128.3, 128.5, 133.2, 136.0, 162.8
ppm. HRMS Found 184.1004 C12H12N2 requires 184.1000.
The imine salts (47) (1.68 g, 6.2 mmol) and sodium acetate (5.00 g, 61 mmol) in water (30 mL) were
heated under reflux for 10 min and gave 2-benzoylpyrrole (57) (58%), after recrystallization from light
petroleum (40-60 °C), 202 mg, 58%, mp 78-79 °C (lit.63 mp 77.5-78 °C): λmax 243 (log10 4.34) and 305
(4.66) nm, νmax 3280, 1620 cm–1, δH (90 MHz, CDCl3) 6.30-6.40 (m, 1H), 6.88-6.99 (m, 1H), 7.16-7.28
(m, 1H), 7.42-7.60 (m, 3H), 7.87-8.02 (m, 2H), 8.48 (br s, 1) ppm, δC (20 MHz, CDCl3) 111.0, 120.3,
126.3, 128.4, 129.1, 130.4, 131.9, 138.7, 185.3 ppm. HRMS Found 171.0685 C11H9NO requires
171.0684.

ACCEPTED MANUSCRIPT
3-N-Methylacetylimino-2,5-dimethylpyrrole hydrofluoroborate (58), 3-N-methylacetylimino-2,5-
dimethylpyrrole (59), and 3-acetyl-2,5-dimethylpyrrole (60)
2,5-Dimethylpyrrole (4.00 g, 42 mmol) in dichloromethane (10 mL) was added slowly to a stirred
suspension of N-methylbenzonitrilium fluoroborate (6.00 g, 42 mmol) in dichloromethane (25 mL) at –
50 °C, keeping the temperature below – 45 °C during the addition. The reaction mixture was then kept at
– 22 °C for 5 d to give, as a solid after filtration, 3-N-methylacetylimino-2,5-dimethylpyrrole
hydrofluoroborate as a mixture of a major diastereoisomer (58) (6.0 g, 78%) mp 186-187 °C, (from
ethanol), together with a very small amount of a minor diastereoisomer: λmax 270 (log10 4.40), 323
(4.24) nm, νmax 3420, 1614, 1155-970 cm–1, δH (90 MHz, CD3CN) 2.22 (s, 3H), 2.49 (s,3H), 2.60 (s,3H),
3.38 (d, 3H J = 7 Hz, singlet after D2O exchange), 6.40 (br s, 1H), 9.9 (br s), 9.99 (br s, 1H), δC (20 MHz,
CD3CN) (major diastereoisomer) 12.1, 15.8, 25.7, 36.3, 109,0, 116.0, 130.9, 142.5, 176.1 ppm, (minor
diastereoisomer) 12.1, 15.1, 18.4, 32.9, 106.3, 116.0, 131.4, 140.7, 176.3 ppm. Found C 45.60, H 6.60, N
11.50%, C9H15 N2BF4 requires C 45.40, H 6.35, N 11.75%.
The imine salt (58) (2.31 g, 9.7 mmol) was suspended in dichloromethane (30 mL) and shaken with
aqueous sodium hydroxide solution (30 mL, 2 M) until dissolution was complete (30 sec). The organic
layer was washed with water, dried (MgSO4) and gave, after recrystallization from diethyl ether/light
petroleum (40-60 °C), the yellow 3-N-methylacetylimino-2,5-dimethylpyrrole (59) (1.01 g, 70%), mp
134-135 °C: λmax 275 (log10 4.26), 322 (4.05) nm, νmax 1618 cm–1, δH (90 MHz, CDCl3) 2.12 (s, 6H),
2.16 (s, 3H), 3.23 (s, 3H), 5.97 (s, 1H), 9.42 (br s, 1H) ppm; a resonance at H 5.72 for C4 of the Z-
isomer gave a ratio E:Z ca 6:1, δC (20 MHz, CDCl3) 12.5, 12.9, 17.2, 38.2, 105.9, 122.0, 125.4, 127.2,
166.5 ppm, resonances for the Z-diastereomer were at H 29.0, 40.6, 124.1, 126.5, 167.5 ppm. HRMS
Found 150.1158 C9H14N2 requires 150.1157.
The imine salt (58) (1.40 g, 4.9 mmol) and sodium acetate (3.00 g, 37 mmol) in water (30 mL) were
heated under reflux for 30 min to give 3-acetyl-2,5-dimethylpyrrole (60) as a buff solid after
recrystallization from diethyl ether (546 mg, 68%), mp 95-96 °C, (lit.64 mp 94.5-95 °C); λmax 285 (log10
4.54) nm, νmax 3280, 1635 cm–1, δH (CDCl3) 2.23 (s, 3H), 2.41 (s, 3H), 2.53 (s, 3H), 6.24 (s, 1H), 9.93 (br
s, 1H) ppm, δC (CDCl3) 12.5, 23.9, 28.4, 107.9, 120.9, 126.4, 135.1, 195.9 ppm. HRMS Found 137.0835
C8H11NO requires 137.0841.
2-N-Methylacetylimino-1-methylpyrrole (78), 3-N-methylacetylimino-1-methylpyrrole (79), 2-
acetyl-1-methylpyrrole (80), and 3-acetyl-1-methylpyrrole (81)
A solution of 1-methylpyrrole (2.5 g, 31 mmol) in dichloromethane (5 mL) was added slowly to a stirred
suspension of N-methylacetonitrilium fluoroborate (4.4 g, 31 mmol) in dichloromethane (30 mL) at – 30
°C, keeping the temperature below – 25 °C during the addition. The reaction mixture was then kept at –
22 °C for 30 h which then gave a red solution which was extracted into water and basified to pH14 with
aqueous sodium hydroxide solution (5 M) and extracted into dichloromethane (3 x 20 mL). The combined
organic extracts were dried (MgSO4) and concentrated to give after distillation (Kugelrohr 55-56 °C 1
mm/Hg) 2-N-methylacetylimino-1-methylpyrrole (78) (2.2 g, 52%) λmax 275 (log10 4.41), nm, νmax 1622
cm–1, δH (90 MHz, CDCl3) 2.17 (s, 3H), 3.30 (s, 3H), 3.92 (s, 3H), 6.08-6.18 (m, 1H), 6.50-6.59 (m, 1H),
6.61–6.70 (m, 1H) ppm, δC (20 MHz, CDCl3) 15.3, 37.5, 38.4, 106.3, 112.4, 127.2, 131.8, 160.5 ppm.
Found 136,1001 C8H12N2 requires 136.1000. The residue from the distillation crystallised and gave, after
recrystallization from light petroleum (40-60 °C), 3-N-methylacetylimino-1-methylpyrrole (79) (171 mg,
4%), mp 71-73 °C; λmax 265 (log10 4.54) 289 (4.07) nm, νmax 1615 cm–1, δH (CDCl3) 2.09 (s, 3H), 3.22
(s, 3H), 3.61 (s, 3H), 6.51-6.60 (m, 2H), 6.93-7.03 (m, 1H), δC (CDCl3) 15.2, 36.1, 38.4, 107.1, 121.9,
122.5, 127.6, 163.2 ppm. HRMS Found 136.1006 C8H12N2 requires 130.1000.

ACCEPTED MANUSCRIPT
A larger scale reaction using 1-methylpyrrole (6.60 g, 82 mmol) and N-methylacetonitrilium fluoroborate
(11.7 g, 82 mmol) in dichloromethane (45 mL) gave a mixture of imines that was added to light
petroleum (40-60 °C) (35 mL) and gave crystals of 3-N-methylacetylimino-1-methylpyrrole (79) (1.06 g,
9%) and, after distillation of the residue gave 2-N-methylacetylimino-1-methylpyrrole (78) (6.3 g, 57%).
The imine (78) (2.09 g, 15.4 mmol) and sodium acetate (7 g, 85 mmol) in water (40 mL) were heated
under reflux for 15 min, cooled and extracted into dichloromethane (3 x 30 mL), dried (MgSO4) and
concentrated to give after distillation, (Kugelrohr, 45-46 °C at 1 mm/Hg), (lit.65 bp 88-91 °C / 22mm/Hg),
2-acetyl-1-methylpyrrole (80), (1.63 g, 86%), λmax 258 (log10 4.04) 283 (4.42) nm, νmax 1642 cm–1, δH
(CDCl3) 2.42 (s, 3H), 3.95 (s, 3H), 6.07-6.20 (m, 1H), 6.75-6.87 (m, 1H), 6.90-7.03 (m, 1H) ppm, δC
(CDCl3) 27.0, 37.5, 108.0, 119.7, 131.0 (2 x C), 188.5 ppm. HRMS Found 123.0685 C7H9N0 requires
123.0684.
The imine (79) (825 mg, 15.4 mmol) and sodium acetate (2 g, 24 mmol) in water (20 mL) were heated
under reflux for 15 min, cooled and extracted into dichloromethane (3 x 30 mL), dried (MgSO4) and
concentrated to give after distillation, (Kugelrohr, 110 °C at 1 mm/Hg), 3-acetyl-1-methylpyrrole (81)
(558 mg, 75%), (lit.65 bp 88-89 °C at 1.5 mm/Hg), λmax 250 (log10 4.11) nm, νmax 1642 cm–1, δH
(CDCl3) 2.30, (s, 3H), 3.60 (s, 3H), 6.34-6.44 (m, 2H), 7.11-7.21 (m, 1H) ppm, δC (CDCl3) 26.9, 36.5,
109.2, 123,6, 126.2, 127.2, 193.2 ppm. HRMS Found 123.0687 C7H9N0 requires 123.0684.
2-N-methylpivaloylimino-1-methylpyrrole
Experiment carried out by M. J. Plater.
A solution of 1-methylpyrrole (3.10 g, 38 mmol) in dichloromethane (5 mL) was added slowly to a stirred
suspension of N-methylpivalonitrilium fluoroborate (6.30 g, 38 mmol) in dichloromethane (10 mL) at –
50 °C, keeping the temperature below – 25 °C during the addition. The reaction mixture was then kept at
– 20 °C for 18 h which then gave a dark solution which was extracted into water (3 x 15 mL) and basified
to pH14 with aqueous sodium hydroxide solution (5 M): extraction into dichloromethane (2 x 30 mL).
The combined organic extracts were dried (MgSO4) and concentrated to give crude 2-N-
methylpivaloylimino-1-methylpyrrole (4.0 g, 59%). The crude product was heated under reflux for 2 h in
a mixture of aqueous sodium hydroxide (10 mL) and methanol (120 mL) and after distillation (Kugelrohr
85 °C 2 mm/Hg) 2-N-methylpivaloylimino-1-methylpyrrole (51) (3.3 g, 50%) as a colourless liquid, λmax
209 (log10 4.96), 291 (4.48), 345 (4.56) nm, νmax 1630 cm–1, δH (60 MHz, CDCl3) 11.17 (s, 9H), 2.91 (s,
3H), 3.38 (s, 3H), 5.85 (m, 1H), 6.10 (m, 1H), 6.59 (m, 1H) ppm, δC (20 MHz, CDCl3) 27.1, 33.4, 36.0,
105.6, 119.1, 125.5, 171.0 ppm. HRMS Found 178.1466 C11H18N2 requires 178.1470.
2-N-Methylacetylimino-1-t-butylpyrrole hydrofluoroborate (72), 3-N-methylacetylimino-1-t-
butylpyrrole hydrofluoroborate (73), 2-N-methylacetylimino-1-t-butylpyrrole (74), 3-N-
methylacetylimino-1-t-butylpyrrole (75), 2-acetyl-1-t-butylpyrrole (76), and 3-acetyl-1-t-
butylpyrrole (77)
A solution of 1-t-butylpyrrole (5.80 g, 47 mmol) in dichloromethane (10 mL) was added slowly to a
stirred suspension of N-methylacetonitrilium fluoroborate (6.70 g, 47 mmol) in dichloromethane (30 mL)
at – 30 °C, keeping the temperature below – 25 °C during the addition. The reaction mixture was then
kept at – 22 °C for 15 h and gave a solid which was collected, washed with cold (10 °C) dichloromethane
(30 mL) and recrystallised from ethanol to give 3-N-methylacetylimino-1-t-butylpyrrole
hydrofluoroborate (73), (6.42 g, 52%), mp 222-224 °C, λmax 272 (log10 4.31) nm, νmax 3310, 1633,

ACCEPTED MANUSCRIPT
1150-950 cm–1, δH (90 MHz, CD3CN) 1.62 (s, 9H), 2.69 (s, 3H), 3.45 (d, 3H, J = 7 Hz, singlet after D2O
exchange), 6.86-6.95 (m, 1H), 7.29-7.39 (m, 1H), 7.95-8.03 (m, 1H), 11.3 (br s, 1H) ppm, δC (20 MHz,
CD3CN) 24.0, 30.4, 35.9, 59.0, 113.0, 115.3, 124.2, 131.8, 174.5 ppm. Found C 49.20, 7.30, N 10.20%,
C11H19N2BF4 requires C 49.60, H 7.20, N 10.50%.
The filtrate was concentrated to give a further solid which was recrystallised from ethanol to give 2-N-
methylacetylimino-1-t-butylpyrrole hydrofluoroborate (72) as a mixture of diastereoisomers, (4.95 g,
40%), mp 108-109 °C, λmax 283 (log10 4.05), 332 (3.99) nm, νmax 3320, 1648, 1150-950 cm–1, δH (90
MHz, CD3CN) 1.60 (s, 9H), 2.74 (s, 3H), 3.45 (d, 3H, J = 7 Hz, singlet after D2O exchange), 6.30-6.45
(m, 1H), 6.85-6.94 (m, 1), (7.50-7.65 (m 1H) ppm, δC (20 MHz, CD3CN) 30.4 31.7, 24.0; 30.4, 32.1 35.9,
62.0, 110.7 110.8, 124.2, 132.0, 133.3, 170.9 ppm. Found C 49.70, 7.30, N 10.20%, C11H19N2BF4
requires C 49.60, H 7.20, N 10.50%.
The imine salt (72) (1.63 g, 6.1 mmol) was suspended in dichloromethane (30 mL) and shaken with
aqueous sodium hydroxide solution (30 mL, 2 M) until dissolution was complete. The organic layer was
washed with water, dried (MgSO4), evaporated and distilled (Kugelrohr 80 °C 0.7 mm/Hg) to give 2-N-
methylacetylimino-1-t-butylpyrrole (74) (958 mg, 88%) as a mixture of diastereoisomers, max 273
(log10 3.85), nm, max 1630 cm–1, H (90 MHz, CDCl3) 1.52 (s, Z-isomer), 1.63 (s, E-isomer), 2.17 (s,
E-isomer), 2.35 (d, J = 1 Hz, Z-isomer), 3.09 (d, J = 1 Hz, Z-isomer), 3.29 (s, E-isomer), 5.75-5.85 (m,
C4, Z-isomer), 6.00-6.22, (m, C3, Z-isomer), 6.30-6.40 (m, E-isomer), 6.84-7.0 (m, C5, both isomers)
ppm, C (20 MHz, CDCl3) 191, 30.7, 31.1, 38.7, 42.3, 56.9, 57.6, 105.9, 107.4, 107.8, 112..8. 116.8,
119.5, 121.4, 166.4 ppm. HRMS Found 178.1470 C11H18N2 requires 178.1470.
The imine salt (73) (1.32 g, 5 mmol) was suspended in dichloromethane (30 mL) and shaken with
aqueous sodium hydroxide solution (30 mL, 2 M) until dissolution was complete. The organic layer was
washed with water, dried (MgSO4) and evaporated and distilled (Kugelrohr 130 °C 1 mm/Hg) to give 3-
N-methylacetylimino-1-t-butylpyrrole (75) (627 mg, 71%), λmax 271 (log10 4.21), nm, νmax 1621 cm–
1, δH (90 MHz, CDCl3) 1.51 (s, 9H), 2.12 (s, 3H), 3.26 (s, 3H), 5.99-6.08 (m, 1H), 6.75-6.85 (m, 1H),
7.23-7.32 (m, 1H), δC (20 MHz, CDCl3) 15.3, 30.7, 38.5, 55.1, 107.2, 117.7, 118.4, 127.0, 163.5 ppm.
HRMS Found 178.1465 C11H18N2 requires 178.1470.
The imine salt (72) (2.60 g, 9.8 mmol) in aqueous sodium hydroxide solution (40 mL, 2M) was heated
under reflux (monitored by gc, OV17, 1.5 m, 150 °C) for 4 d. The reaction mixture was extracted with
dichloromethane (3 times 30 mL), washed with water, dried (MgSO4), evaporated and distilled
(Kugelrohr 125 °C 1 mm/Hg) to give as a liquid 2-acetyl-1-t-butylpyrrole (76) (1.28 g, 79%) λmax 256
(log10 4.11), 294 (4.44) nm, νmax 1644 cm–1, δH (90 MHz, CDCl3) 1.70 (s, 9H), 2.52 (s, 3H), 6.11-6.22
(m, 1H), 7.19-7.32 (m, 2H) ppm, δC (20 MHz, CDCl3) 28.8, 30.2, 58.4, 106.7, 124.6, 127.8, 132.0, 186.8
ppm. Found C 72.45, H 9.50, N 8.35%, C10H15NO requires C 72.70, H 9.15, N 8.50%.
The imine salt (73) (2.00 g, 7.5 mmol) in aqueous sodium acetate (50 mL, 15%) was heated under reflux
for 15 min. . The reaction mixture was extracted with dichloromethane (3 times 30 mL), washed with
water, dried (MgSO4), evaporated and distilled (Kugelrohr 125 °C 1 mm/Hg) to give as a liquid 3-acetyl-
1-t-butylpyrrole (77) (1.28 g, 79%) (lit.66) λmax 249.5 (log10 4.21) nm, νmax 1638 cm–1, δH (90 MHz,
CDCl3) 1.51 (s, 9H), 2.38 (s, 3H), 6.56-6.66 (m, 1H), 6.80-6.89 (m, 1H), 7.47-7.55 (m, 1H) ppm, δC (20
MHz, CDCl3) 26.9, 30.5, 55.8, 109.2, 119.4, 122.9, 125.5, 193.5 ppm. HRMS Found 165.1157 C10H15NO
requires 165.1154.
2-N-Methylacetylimino-1-benzylpyrrole (82), 3-N-Methylacetylimino-1-benzylpyrrole (83), 2-acetyl-
1-benzylpyrrole (84), and 3-acetyl-1-benzylpyrrole (85),

ACCEPTED MANUSCRIPT
A solution of 1-benzylpyrrole (4.50 g, 28.6 mmol) in dichloromethane (5 mL) was added slowly to a
stirred suspension of N-methylacetonitrilium fluoroborate (5.80 g, 40.5 mmol) in dichloromethane (30
mL) at – 30 °C, keeping the temperature below – 25 °C during the addition. The reaction mixture was
then kept at – 22 °C for 38 h which then gave a dark solution which was extracted into water and basified
to pH14 with aqueous sodium hydroxide solution (5 M) and extracted into dichloromethane (3 x 20 mL).
The combined organic extracts were dried (MgSO4) and concentrated to give a mixture of imines that was
suspended in light petroleum (100 mL, bp 40-60 °C), heated to boiling and filtered hot. The solid
obtained was recystallised from dichloromethane/light petroleum (bp 40-60 °C) to give 3-N-
methylacetylimino-1-benzylpyrrole (83), (577 mg, 10%) mp 99-100 °C, λmax 273.0 (log10 4.21) 289
(3.88) nm, νmax 1620 cm–1, δH (90 MHz, CDCl3) 2.14 (s, 3H), 3.26 (s, 3H), 5.05 (s, 2H), 6.62-6.70 (m,
2H), 7.10-7.38 (m, 6H) ppm, δC (20 MHz, CDCl3) 15.7, 37.8, 53.7, 107.9, 122.6, 126.8. 127.3, 128.0,
128.9, 137.4, 164.3 ppm. Found C 79.20, H 7.80, N 12.90%, C14H16N2 requires C 79.20, H 7.60, N
13.20%. HRMS Found 212.1318 C14H16N2 requires 212.1313.
The filtrate was reduced in volume (to ca 20 mL), cooled and gave, after recrystallization from light
petroleum (bp 40-60 °C), 2-N-methylacetylimino-1-benzylpyrrole (82), (2.57 g, 43%) mp 54-55 °C, λmax
273.0 (log10 4.39) nm, νmax 1619 cm–1, δH (90 MHz, CDCl3) 2.05 (s, 3H), 3.18 (s, 3H), 5.70 (s, 2H),
6.11-6.22 (m, 1H), 6.52-6.62 (m, 1H), 6.66-6.75 (m, 1H), 6.95-7.32 (m, 5H) ppm, δC (20 MHz, CDCl3)
15.6, 38.4, 52.3, 107.3, 113.3, 126.8, 127.0, 128.3, 132.8, 140.1, 160.4 ppm. Found C 79.20, H 7.55, N
13.20%, C14H16N2 requires C 79.20, H 7.60, N 13.20%. HRMS Found 212.1309 C14H16N2 requires
212.1313.
The imine (82) (1.63 g, 7.7 mmol) and sodium acetate (3.2 g, 39 mmol) in water (20 mL) were heated
under reflux for 24 h, cooled and extracted into dichloromethane (3 x 30 mL), dried (MgSO4) and
concentrated to give after distillation, (Kugelrohr, bp 130 °C at 0.5 mm/Hg), 2-acetyl-1-benzylpyrrole
(84) (970 mg, 64%), (lit.65 bp 131/5 °C at 1.5 mm/Hg), λmax 250 (log10 4.11) nm, νmax 1642 cm–1, δH (90
MHz, CDCl3 2.35 (s, 3H), 5.54 (s, 2H), 6.12-6.2239m, 1H), 6.80-6.89 (m, 1H), 6.90-7.00 (m, 1H), 7.02-
7.42 (m, 5H) ppm, δC (20 MHz, CDCl3) 27.1, 52.4, 108.5, 120.4, 127.1, 127.4, 128.5, 130.4, 138.4, 188.2
ppm. HRMS Found 199.0997 C13H13NO requires 199.0997.
The imine (83) (577 mg, 2.7 mmol) and sodium acetate (1.0 g, 12 mmol) in water (20 mL) were heated
under reflux for 24 h, cooled and extracted into dichloromethane (3 x 30 mL), dried (MgSO4) and
concentrated to give after distillation, (Kugelrohr, bp 200 °C at 8 mm/Hg), 3-acetyl-1-benzylpyrrole (85)
(970 mg, 64%), (lit.4d 170 °C at 0.2 mbar), λmax 248 (log10 4.08) nm, νmax 1648 cm–1, δH (90 MHz,
CDCl3 2.33 (s, 3H), 4.93 (s, 2H), 6.44-6.55 (m, 2H), 7.00-7.35 ppm, δC (20 MHz, CDCl3) 27.0, 53.7,
110.1, 122.8, 126.3, 127.4, 128.2, 128.6, 129.0, 136.7, 193.3 ppm. HRMS Found 199.0996 C13H13NO
requires 199.0997.
2-N-Methylacetlimino-1-benzhydrylpyrrole (86), 2-acetyl-1-benzhydrylpyrrole (87), and 3-
acetylbenzhydrylpyrrole (88)
A solution of 1-benzhydrylpyrrole (68), (4.00 g, 17.2 mmol) in dichloromethane (20 mL) was added
slowly to a stirred suspension of N-methylacetonitrilium fluoroborate (2.80 g, 19.6 mmol) in
dichloromethane (20 mL) at – 50 °C, keeping the temperature below – 40 °C during the addition. The
reaction mixture was then kept at – 22 °C for 5 d which then gave a dark solution which was extracted
into water and basified to pH14 with aqueous sodium hydroxide solution (5 M) and extracted into
dichloromethane (2 x 20 mL), The combined organic extracts were dried (MgSO4) and concentrated to

ACCEPTED MANUSCRIPT
give a mixture of products. Separation by flash chromatography [silica gel, diethyl ether/ light petroleum
(bp 40-60 °C), 1:4] gave:
(i) 2-Acetyl-1-benzhydrylpyrrole (87), (2.42 g, 52%), mp 120-121 °C (from ethanol), λmax 256 (log10
4.14), 284 (4.44) nm, νmax 1652 cm–1, δH (90 MHz, CDCl3) 2.38 (s, 3H), 6.12-6.22, (1H), 6.67-6.77 (m,
1H), 6.98-7.42 (m, 11H), 7.97 (s, 1H) ppm, δC (20 MHz, CDCl3) 25.9, 62.9, 106.6, 119.3, 126.1, 126.9,
127.6, 131.0, 139.0, 186.8 ppm. Found C 83.30, H 6.50, N 5.00% C19H17NO requires C 82.90, H 6.25, N
5.10%. HRMS Found 275.1305 C19H17NO requires 275.1310:
(ii) 3-Acetyl-1-benzhydrylpyrrole (88), (1.16 g, 25%), mp 107-108 °C (from ethanol), λmax 249 (log10
4.34) nm, νmax 1650 cm–1, δH (90 MHz, CDCl3) 2.35 (s, 3H), 6.52 (s, 1H), 6.58-6.68 (m, 2H), 7.05-7.48
(m, 11H) ppm, δC (20 MHz, CDCl3) 27.1, 67.5, 109.5, 122.9, 126.0, 126.2, 128.3, 128.4, 128.9, 139.5,
193.4 ppm. Found C 82.90, H 6.40, N 4.85% C19H17NO requires C 82.90, H 6.25, N 5.10%. HRMS
Found 275.1313 C19H17NO requires 275.1310.
In a repeat experiment using benzhydrylpyrrole (3.40 g, 14.6 mmol) and N-methylacetonitrilium
fluoroborate (3.20 g, 22.4 mmol), flash chromatography using carefully dried solvents and a freshly
packed column of silca gel, gave two products:
(i) 2-N-methylacetylimino-1-benzhydrylpyrrole (86), (2.70 g, 64%), mp 87-92 °C (from light petroleum,
bp 40-60 °C), λmax 292 (log10 4.52) nm, νmax 1618 cm–1, δH (90 MHz, CDCl3) 2.03 (s, 3H), 3.11 (s,3H),
5.35-5.45 (m, 1H), 5.71-5.81 (m, 1H), 6.38-6.48 (m, 1), 7.05-7.44 (m, 10 H), 9.14 (s, 1H) ppm. HRMS
Found 288.1629 C20H20N2 requires 288.1626
(ii) 3-Acetyl-1-benzhydrylpyrrole (88), (833 mg, 21%),
2-Acetyl-1-dibenzosuberylpyrrole (89), 3-acetyl-1-dibenzosuberylpyrrole (90), and 2-N-
methylacetylimino-1-dibenzosuberylpyrrole (91)
A solution of 1-dibenzosuberylpyrrole (69) 4.00 g, 15.4 mmol) in dichloromethane (25 mL) was added to
a stirred suspension of N-methylacetonitrilium fluoroborate (4.40 g, 30.8 mmol) in dichloromethane (25
mL) at – 50 °C, keeping the temperature below – 40 °C during the addition. The reaction mixture was
then kept at – 22 °C for 7 d which then gave a dark solution which was extracted into water and basified
to pH14 with aqueous sodium hydroxide solution (5 M) and extracted into dichloromethane (2 times 20
mL), The combined organic extracts were dried (MgSO4) and concentrated to give a mixture of products.
Separation by flash chromatography using a new column of silica gel, dry dichloromethane gave:
(i) 2-Acetyl-1-dibenzosuberylpyrrole (89), (2.10 g, 45%), mp 122-123 °C (from ethanol), λmax 254
(log10 3.93), 287 (4.19) nm, νmax 1647 cm–1, δH (90 MHz, CDCl3) 2.28 (s, 3H), 2.68-3.40 (m, 4H), 6.08-
6.18 (m, 1H), 6.90-7.30 (m, 10 H), 7.52 (s, 1H) ppm, δC (20 MHz, CDCl3) 25.9, 30.7, 65.2, 105.6, 1191.8,
124.7, 126.7, 128.8, 129.5, 130.1, 125.8, 138.6, 186.6 ppm. Found C 83.65, H 6.50, N 4.40% C21H19NO
requires C 83.70, H 6.35, N 4.65%. HRMS Found 301.1467 C19H17NO requires 301.1467:
(ii) 3-Acetyl-1-dibenzosuberylpyrrole (90), (0.60 g, 13%), mp 99-100 °C (from chloroform/ light
petroleum (bp 40-60 °C), λmax 254 (log10 3.93), 287 (4.19) nm, νmax 1652 cm–1, δH (90 MHz, CDCl3
2.27 (s, 3H), 2.60-3.18 (m, 4H), 5.96 (s, 1H), 6.26-6.35 (m, 1H), 6.52-6.60 (m, 1H), 6.91-7.00 (m, 1H),
7.10-7.48 (m, 8H) ppm, δC (20 MHz, CDCl3) 27.1, 31.8, 70.0, 109.3, 121.9, 125.1, 125.9, 126.7, 129.5,