Aromatic azapentalenes: 1H- and (mesoionic) 2H-pyrrolotetrazoles. Part 1. Synthesis and spectral characteristics

Article abstract of DOI:10.1039/b007873p

Two separate series of the title systems have been prepared by cyclisation of tetrazolium salts having acylmethyl functions attached to both the ring carbon and the adjacent nitrogen atom (3, 4): (i) working in an acetate buffer led to 7-acyl derivatives (5, 6; Scheme 3), and (ii) treatment with anhydride-base gave 5,7-diacyl compounds by a deviating ring closure mechanism (11, 12; Scheme 4). These materials could be defunctionalised to afford pyrrolotetrazoles (7, 8) which were earlier approached in vain from the respective 5-methyltetrazolium salts (Tschitschibabin reaction). Regarding characterisation data, attention is drawn to the conspicuous spectroscopic differences between the 1H- and the 2H-system. 2H-Pyrrolotetrazoles (6, 8, 12) represent a novel class of Ramsden's 'type C' heteropentalene mesoions.

Full text of DOI:10.1039/b007873p

View Article Online / Journal Homepage / Table of Contents for this issue
Aromatic azapentalenes: 1H- and (mesoionic) 2H-pyrrolo-
tetrazoles. Part 1. Synthesis and spectral characteristics1
Dietrich Moderhack,* Dirk Decker and Bernhard Holtmann
1
Institut für Pharmazeutische Chemie der Technischen Universität, D-38106 Braunschweig,
Germany
Received (in Cambridge, UK) 28th September 2000, Accepted 9th February 2001
First published as an Advance Article on the web 19th March 2001
Two separate series of the title systems have been prepared by cyclisation of tetrazolium salts having acylmethyl
functions attached to both the ring carbon and the adjacent nitrogen atom (3, 4): (i) working in an acetate buffer
led to 7-acyl derivatives (5, 6; Scheme 3), and (ii) treatment with anhydride–base gave 5,7-diacyl compounds
by a deviating ring closure mechanism (11, 12; Scheme 4). These materials could be defunctionalised to afford
pyrrolotetrazoles (7, 8) which were earlier approached in vain from the respective 5-methyltetrazolium salts
(Tschitschibabin reaction). Regarding characterisation data, attention is drawn to the conspicuous spectroscopic
differences between the 1H- and the 2H-system. 2H-Pyrrolotetrazoles (6, 8, 12) represent a novel class of Ramsden’s
‘type C’ heteropentalene mesoions.
group is inactive throughout so as to preclude not only the
Introduction
formation of the (mesoionic) 2H-pyrrolotetrazole VI3b but also
One of the major and most convenient routes to pyrroloazoles
with a bridgehead nitrogen atom (I) consists in base-mediated
cyclisation of N-(acylmethyl)-α-methylazolium ions such as II
(Scheme 1). This approach—an extension of Tschitschibabin’s
that of the analogous 2H-pyrrolo[2,1-c][1,2,4]triazole IV.†4
These shortcomings drew our attention to tetrazolium salts
having an acceptor-substituted methyl group like VIII and IX.
Such species are deprotonated preferably at the C-attached
side-chain7 [in contrast to II and V (a = b = N, c = NRЈ)8] and,
hence, should exhibit an enhanced proclivity for ring closure.
Earlier observations with appropriately substituted imidazo-
liums and benzimidazoliums testify to this effect.9 Since
pyrroloazoles I bearing an additional acyl or ester group at the
pyrrolic half-ring (adjacent to the bridgehead carbon or nitro-
gen atom) can be easily defunctionalised,4a,10 the tetrazolium
salts VIII and IX are promising synthons for III and VI.
Another conceivable route to III and VI constitutes N-alkyl-
ation of the 5H-pyrrolotetrazole VII. However, access to the
starting bicycle is troublesome11a and, as shown by methylation
of the 7-methyl congener,11b the 2H-isomer (type VI) is formed
only sparingly with an overall low yield.
Results and discussion
Synthesis
As candidates for cyclisation we chose the tetrazolium salts 3a–
g and 4a–h (Scheme 2). The derivatives 3e,g and 4a,b,d–h, like
the previously reported 3a,7 were made routinely by treatment
of the tetrazoles 1c,e and 2a–c with the respective α-bromo-
ketone in the presence of silver tetrafluoroborate (cf. ref. 8a).
The salts 3b–d,f resulted smoothly from the reaction of 1f–i
with dimethyl sulfate, which constitutes another method
Scheme 1 Reagents and conditions: i, base, heat.
applied before;8a of the second isomers 4 formed simul-
indolizine synthesis2a—includes the preparation of pyrrolo-
[2,1-b]thiazoles (I; a = b = CH/CR, c = S), 1H-pyrrolo[1,2-a]-
imidazoles (I; a = b = CH/CR, c = NRЈ), 4H-pyrrolo[1,2-a]-
benzimidazoles (I; ab = CC of benzo, c = NRЈ), 1H-pyrrolo-
[2,1-c][1,2,4]triazoles (I; a = CH/CR, b = N, c = NRЈ) and
1H-pyrrolo[1,2-b][1,2,4]triazoles (I; a = N, b = CR, c = NRЈ).2b–f
Surprisingly, application of this method to the correspond-
ing tetrazolium salts (II; a = b = N, c = NRЈ) fails; instead of
III, imidazolones, dequaternisation products or azide–amide
mixtures were found.3a In the isomeric azoliums V, the methyl
taneously, only 4c was utilised (without separation from 3c).
Access to the unknown precursors 1f–i and 2a was also
effected by standard procedures, i.e. by alkylation of 1b and 1a,
† For naming IV and VI as ‘2H-pyrrolo . . . azole’ (instead of using the
Chem. Abstr. name ‘2-substituted 1H-pyrrolo . . . azolium, inner salt’),
cf. the established literature practice.5 From their electronic structure,
mesoionic bicycles such as IV and VI, like the related 2H-pyrrolo-
[1,2-c]imidazole6b,c and the analogues of ref. 5, belong in Ramsden’s
classification6a to ‘type C heteropentalene mesomeric betaines’.
720
J. Chem. Soc., Perkin Trans. 1, 2001, 720–728
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b007873p

View Article Online
Scheme 3 Reagents and conditions: i, NaOAc–AcOH, heat; ii, 6–12 M
HCl, heat (with 5c,d: KOH–EtOH; then 12 M HCl, heat); iii, 12 M HCl,
heat.
MeOSO3; vide supra), we checked the mother liquor of 5b,c for
derivatives 6b,c and found that some were formed, 6c being
isolated in turn (20% yield). This led us to extend the above
procedure to the separately prepared salts 4a,b,d–h (X = BF4);
as expected, all of these (save 4e) gave the desired pyrrolo-
tetrazoles 6.
Defunctionalisation of 5 and 6 could be achieved easily with
mineral acid (cf. refs. 4a, 10), but in the case of 5c,d prolonged
heating with alkali was required for hydrolysis of the ester
group. Regarding the two different routes shown for 7a, the
second approach (1b→1f→3b→5b→7a) proved altogether the
more convenient one.
Cyclisation of 3 and 4 in the presence of an acylating agent
leads to the pyrrolotetrazoles 11 and 12 (Scheme 4). This kind
of reaction has already been described for the salt 3a which on
treatment with acetic anhydride and triethylamine gave com-
pound 11c along with some 11d.8b In like manner we now
obtained analogous 2H-isomers: (i) 12e from 4f, (ii) a mixture
of 12f and 12g from 4g (in parallel with the finding with 3a),
and (iii) 12g from 4h. Formylating agents converted 3e and 4e–h
into the 6-unsubstituted derivatives 11a and 12a–d, respectively;
the corresponding 6-methyl congeners of 12a–d which are con-
ceivable side products were not observed. These cyclisations
proceed via intermediates such as 9 and 10 (cf. refs. 15, 16).
Accordingly, the enamine 1j, after being phenacylated to 9b,
could also be transformed into a derivative of type 11, albeit in
low yield (cf. ref. 16a).
Formation of the crucial intermediates 9 and 10 will fail if
the acylating compound acts as a dehydrating agent (and
thereby leads to 5 and 6). For example, treatment of the
salt 3b (Z = Br) with N,N-dimethylformamide diethyl acetal
(DMF–DEA), instead of generating 9e, gave rise to the
pyrrolotetrazole 5b (cf. ref. 16b) (Scheme 5).17 Likewise, triethyl
orthoformate, while suitable for making 11a, did not convert
the salt 4h into the expected compound 12d [via 10d (OEt in
place of OϪ)] but produced a mixture of 6h and the 5-acetyl
Scheme 2 Reagents and conditions: i, BrCH2COR4–AgBF4, warm;
ii, (MeO)2SO2, rt; iii, BrCH2COR4–AgBF4 (for 4a, b, d, g) or ICH2-
COMe–AgBF4 (for 4e, f, h), warm.
respectively. To provide the earlier described 1e,12a we more
practically condensed 1d with ethyl acetate in the presence of
base (cf. ref. 12b). The derivative 2c was advantageously pre-
pared by adoption of the ring transformation process reported
for 5-methyl-3-[(nitrophenyl)triazeno)]isoxazoles.13 However,
success with the present phenyl analogue required an inverse
protocol for making the starting triazene: here the areneamine,
i.e. aniline, had to be treated with the diazotised isoxazolamine
(instead of reacting benzenediazonium chloride with the
isoxazolamine as suggested by the procedure efficient with
the nitrophenyl derivatives13). Failing this, 1,3-diphenyltriazene
was the sole product. We also tried to obtain 2a in that modified
way but could only observe the formation of the corresponding
1,3-bis(isoxazolyl)triazene.
Cyclisation of the substrates 3 and 4 was first attempted by
heating 3a with aqueous sodium hydrogencarbonate, i.e. by
applying the traditional base. The material obtained indeed
turned out to be the desired compound 5a. But as the yield was
very poor (< 5%), we repeated the reaction using sodium acetate
in acetic acid (the latter for activation of the carbonyl group14)
(Scheme 3). This modification resulted in a considerable
improvement; the method was then applied to both the ana-
logues 3e,g and the ester-functionalised derivatives 3b–d,f.
Regarding cyclisation of the latter, there was no appreciable
change in reactivity. Since the precursors 3b–d,f were accom-
panied by minor quantities of the isomers 4b–d,f (X =
J. Chem. Soc., Perkin Trans. 1, 2001, 720–728
721

View Article Online
Scheme 5 Reagents and conditions: i, DMF–DEA, heat; ii, DMF–
POCl3, rt, then heat; iii, 12 M HCl, heat.
Scheme 4 Reagents and conditions: i, Ac2O–Et3N, heat (with 3a; cf.
ref. 8b); HC(OEt)3, heat; then base, heat (with 3e); ii, BrCH2COPh,
warm; then NaOAc–AcOH, heat; iii, Ac2O–Et3N, heat (with 4f–h);
HCOOAc–Et3N, warm (with 4e–h).
derivative of 8a (with the latter predominating).18 Vilsmeier
reagent also showed this unwanted behaviour in that it gave rise
to 6h instead of 10h.18 Moreover, it may transform acetyl
functions into 1-chloro-2-formylvinyl groups; we encountered
this trouble in the course of making 11a.17
Removal of the functional groups from the cyclisation
products 11 and 12 is partly feasible, rendering 11a and 12b,e,g
suitable precursors of the pyrrolotetrazoles 7a and 8f,d,g,
respectively (Scheme 5); the low yields of the parent substances
7f and 8f reflect the instability typical of azapentalenes which
have an unsubstituted pyrrolic half-ring (cf. ref. 10c). As
observed with 12e and 12g, defunctionalisation proceeds step-
wise, with the group attached to C-5 being removed first.18
Interestingly, efforts to convert 11b17 as well as 12a,c,d18 into
the deacylated pyrrolotetrazoles remained unrewarded.
It is well known that diacylpyrroloazoles related to 11 can
also be obtained on heating the corresponding C-methyl-
azolium salts II with an acylating agent and base.10d,19 In the
tetrazole series, however, this reaction does not take place to a
considerable extent: treatment of the salt 3h or its N-acetonyl
congener with acetic anhydride–triethylamine at elevated tem-
perature gave only small amounts of the expected compounds
11c (2%)17 and 11d (6%).8b Minor quantities of these materials
(3% and < 1%, respectively)8b were also observed as side
products during the preparation of the N-ylide 13 from the salt
3h. Regarding the mechanism, there is evidence (from a series
of model reactions17) that 11c (Scheme 6) does not arise via
anhydride-mediated cyclisation of 13 into the benzoyl deriv-
ative 14, followed by acetylation of the latter (as one might
suppose in view of the theory advanced in ref. 10d), nor does
11d originate from 11c. Precursors of these products should be
Scheme 6 Reagents and conditions: i, Ac2O–Et3N, rt.
the ‘C-ylides’ 9c and 9d (the latter formally derived from 9c by
benzoyl–acetyl exchange). Indeed, heating of separately pre-
pared 9c with acetic anhydride and base not only gave the
bicycle 11c but in addition the diacetyl congener 11d (ratio
1:2).17 This experiment may likewise illuminate the joint form-
ation of the two pyrrolotetrazoles 12f and 12g from the salt 4g
shown in Scheme 4.
Properties
The prepared pyrrolotetrazoles are well crystallised, reasonably
stable substances that can be stored for a prolonged period of
time. Limitations to storage (even below 0 ЊC) concern only
derivatives devoid of a C-attached phenyl, acyl or ester group,
i.e. the compounds 7d and 8d,g; especially unstable are the
parents 7f and 8f (cf. supra). The 1H-pyrrolotetrazoles are
colourless materials (in contrast to the 2H-isomers), but should
be protected from light, in particular representatives having an
722
J. Chem. Soc., Perkin Trans. 1, 2001, 720–728

View Article Online
Table 1 Comparison of UV–vis spectra (λmax > 210 nm) of selected pairs of isomeric pyrrolotetrazoles 5–6 and 7–8 (including fluorescence data of
two derivatives of the series 7 and 8)
Compound
λmax [MeOH]/nm (log ε)
Compound
λmax [MeOH]/nm (log ε)
5a
310 (3.97), 223 (4.27)
6a
357 (3.90), 282 (4.23), 220 (4.32)
356 (3.97), 267 (4.37), 233 (4.41)
350 (3.71), 257 (4.27)
377 (3.57), 296 (4.08), 271 (4.23), 245 (4.29)
323 (4.19), 261 (4.04)
392 (3.53), 293 (4.03), 278 (4.07)
426 (3.74), 331 (4.32), 254 (4.32)
5b
302 (3.83), 257 (4.34), 220 (4.43)
297 (3.47), 263 (3.97), 221 (4.07)
324 (3.45), 268 (4.26), 243 (4.22)
326 (4.19), 259 (4.04), 222 (4.10)
338 (3.34), 2.64 (4.15)
6bb
6f
5f
7a
8ab
8a–Acc
8b
7a–Aca
7b
7e
342 (3.68), 279 (4.32), 249 (4.41)
8e
a 5-Acetyl-1-methyl-6-phenyl-1H-pyrrolo[1,2-d ]tetrazole (for preparation, see ref. 21). b Fluorescence (excitation wavelength 350 nm): λmax
481 [CCl4]/489 [MeOH] (6b); 520 and 495 nm [CCl4] (8a; no fluorescence in MeOH). c 5-Acetyl-2-methyl-6-phenyl-2H-pyrrolo[1,2-d ]tetrazole (for
preparation, see ref. 21).
unsubstituted 5-position. The 2H-isomers, on the whole, are
photochemically less sensitive.
UV–vis spectra were determined on a Philips PU-8730
spectrometer. Fluorescence spectra were measured on
a
In agreement with the properties of related mesoionic
azapentalenes,5c,20 the electronic spectra of the 2H-pyrrolo-
tetrazoles are characterised by a pronounced bathochromic
shift of the longest wavelength compared to that of the 1H-
isomers (see Table 1; the 5-acetyl derivative is an exception);
they also display green or blue fluorescence (cf. ref. 6c). Within
either series common substituent effects become apparent on
going (i) from the derivatives 7a/8a to 7b/8b, (ii) from 7a/8a to
5a,b/6a,b, and (iii) from 7a/8a to 7e/8e; the extreme bathochro-
mic shift observed with 8e reflects the unhindered conjugative
interaction of the phenyl group and the heterocycle, which is
not possible to that extent with 7e. Likewise in accord with the
literature,5c,20 the 13C NMR spectra of the 2H-derivatives show
a marked deshielding of the bridgehead carbon atom compared
to the 1H-series (Table 2). A salient mass spectrometric feature
constitutes intense [M Ϫ 15] and [M Ϫ 31] peaks observed with
the acetyl and ester derivatives of the 2H-system (Table 3;
cf. also ref. 5c). These signals can be assigned to the ketenic
species 15 and 16; thus, from the doubly functionalised com-
pound 12b both 15b and 16b arise. The 1H-isomers do not
Kontron SFM 25 instrument. Mass spectra were taken on
a Finnigan MAT 8430/8400 machine.
Tetrazoles 1a,22 1b,23 1c,7 1d,24 1j25 and 2b23 were made by
literature procedures, as were the tetrazolium salt 3a,7 silver
tetrafluoroborate26 and the precursor of 1a, 6-methylpyrimidin-
4(3H)-one.27 CAUTION: Regarding preparation of the latter,
application of the alternate method described in ref. 28 is
strongly discouraged, since we experienced a violent explosion
after the reaction mixture had been partly concentrated
in vacuo!
(1-Phenyl-1H-tetrazol-5-yl)acetone 1e
To a solution of potassium tert-butoxide (3.36 g, 30 mmol) in
anhydrous THF (40 cm3) were added successively with stirring
at 0 ЊC the 1H-tetrazole 1d (1.60 g, 10 mmol) and ethyl acetate
(1.76 g, 20 mmol). The mixture was heated under reflux for
30 min, concentrated to half its volume, diluted with water
(20 cm3) and acidified with 12 M HCl. The product was
extracted with dichloromethane and recrystallised from
ethanol; yield 1.47 g (73%), mp 101–103 ЊC (lit.,12a 103–
104.5 ЊC); νmax(KBr)/cmϪ1 1715; δH(CDCl3) 2.28 (3 H, s), 4.14
(2 H, s), 7.41–7.50 (2 H, m) and 7.54–7.61 (3 H, m); δC(CDCl3)
30.0 (q), 38.4 (t), 125.1 (2 × d), 130.0 (2 × d), 130.8 (d), 133.5
(s), 149.6 (s) and 200.2 (s).
(Substituted) methyl (1-phenacyl/acetonyl-1H-tetrazol-5-yl)-
acetates 1f–i. General procedure
To a cooled suspension of the N-unsubstituted tetrazole 1b
(2.84 g, 20 mmol) and the respective α-bromoketone (20 mmol)
in acetone (20 cm3) was added dropwise triethylamine (2.02 g,
20 mmol). The mixture was stirred at room temperature for 1 h
whereupon the precipitate of triethylammonium bromide was
filtered off. The products were isolated from the concentrated
filtrate as follows: 1f–h by crystallisation from acetone–diethyl
ether; 1i by column chromatography on silica gel using
chloroform–ethyl acetate (4 : 1) as eluent [with the first frac-
tion being the 2H-isomer methyl (2-acetonyl-2H-tetrazol-5-yl)-
acetate].
1f: Yield 1.92 g (37%), mp 103–104 ЊC (Found: C, 55.4;
H, 4.7; N, 21.5. C12H12N4O3 requires C, 55.4; H, 4.65; N,
21.5%); νmax(KBr)/cmϪ1 1745 and 1695; δH(CDCl3) 3.71 (3 H, s),
4.10 (2 H, s), 6.10 (2 H, s), 7.45–7.82 (3 H, m) and 7.95–8.13
(2 H, m); δC(CDCl3) 29.9 (t), 53.0 (q), 53.6 (t), 128.3 (2 × d),
129.3 (2 × d), 133.5 (s), 135.0 (d), 150.6 (s), 167.4 (s) and
189.5 (s).
produce fragments of that kind, since here loss of molecular
nitrogen from the tetrazolic half-ring predominates. Regarding
IR spectra, the ketonic and ester derivatives of either title
system exhibit, as known from monocyclic pyrroles, low-
frequency carbonyl absorptions; 5-unsubstituted represent-
atives are characterised by a sharp C–H absorption at ≥ 3130
cmϪ1
.
We have shown that the originally desired pyrrolotetrazoles
III and VI (Scheme 1) are readily accessible via vicarious cyclis-
ations of acceptor-substituted tetrazolium salts. In the follow-
ing paper21 we will report on SE-reactions of these systems.
Experimental
Mps were determined on a Kofler microscope. IR spectra were
taken on Pye-Unicam SP 1100, SP3-200 or Philips PU-9800
FTIR instruments. 1H NMR spectra were run on a Varian
EM-390 or Bruker AM 400 spectrometer (J- and N-values in
Hz); 13C NMR spectra were recorded on a Bruker AM 400
instrument (tetramethylsilane or CDCl3 as internal standard).
1g: Yield 1.40 g (26%), mp 78–81 ЊC (Found: C, 57.0; H, 5.3;
N, 20.3. C13H14N4O3 requires C, 56.9; H, 5.15; N, 20.4%);
νmax(KBr)/cmϪ1 1745 and 1695; δH(CDCl3) 2.02 (3 H, d, J 7.4),
3.63 (3 H, s), 3.94/4.14 (2 H, AB, J 17.1), 6.41 (1 H, q, J 7.4),
7.52–7.56 (2 H, m), 7.65–7.69 (1 H, m) and 7.96–7.99 (2 H, m);
δC(CDCl3) 17.6 (q), 30.2 (t), 53.0 (q), 59.3 (d), 128.7 (2 × d),
J. Chem. Soc., Perkin Trans. 1, 2001, 720–728
723

View Article Online
129.3 (2 × d), 133.5 (s), 134.6 (d), 149.2 (s), 167.2 (s) and
193.4 (s).
1h: Yield 2.15 g (32%), mp 142–146 ЊC (Found: C, 42.4; H,
3.3; N, 16.4. C12H11BrN4O3 requires C, 42.5; H, 3.3; N, 16.5%);
νmax(KBr)/cmϪ1 1750 and 1695; δH(CDCl3) 3.72 (3 H, s), 4.10
(2 H, s), 6.04 (2 H, s) and 7.74/7.91 (4 H, AAЈBBЈ, N 8).
1i: Yield 1.03 g (26%), oil; δH(CDCl3) 2.32 (3 H, s), 3.72 (3 H,
s), 4.04 (2 H, s) and 5.43 (2 H, s); δC(CDCl3) 27.3 (q), 29.8 (t),
53.1 (q), 56.3 (t), 150.1 (s), 167.4 (s) and 198.1 (s).—2H-Isomer
of 1i: Yield 0.35 g (9%), oil; δH(CDCl3) 2.23 (3 H, s), 3.75 (3 H,
s), 4.03 (2 H, s) and 5.46 (2 H, s); δC(CDCl3) 27.1 (q), 31.6 (t),
52.6 (q), 60.9 (t), 160.7 (s), 168.6 (s) and 197.7 (s).
(2-Methyl-2H-tetrazol-5-yl)acetone 2a
To a solution of the N-unsubstituted tetrazole 1a (0.99 g, 7.8
mmol) and triethylamine (0.81 g, 8.0 mmol) in acetone (30 cm3)
was added methyl iodide (1.14 g, 8.0 mmol) in the same solvent
(ca. 15 cm3). The mixture was heated under reflux for 18 h and
then kept at 5–10 ЊC for 10 h whereupon the triethylammonium
iodide was filtered off. The filtrate was concentrated and the
residue chromatographed on silica gel using chloroform–diethyl
ether (10 : 3) as eluent to afford successively: the product 2a
and its 1H-isomer (1-methyl-1H-tetrazol-5-yl)acetone 1c
(0.45 g, 41%; identical with the material described in ref. 7).
Yield 0.63 g (58%), mp 50 ЊC (from dichloromethane–diethyl
ether) (Found: C, 42.5; H, 5.9; N, 40.3. C5H8N4O requires C,
42.85; H, 5.75; N, 40.0%); νmax(KBr)/cmϪ1 1721; δH(CDCl3) 2.29
(3 H, s), 4.05 (2 H, s) and 4.36 (3 H, s); δC(CDCl3) 29.6 (q), 39.4
(q), 40.3 (t), 160.2 (s) and 202.0 (s).
(2-Phenyl-2H-tetrazol-5-yl)acetone 2c
To a vigorously stirred solution of 5-methylisoxazol-3-amine
(2.00 g, 20.4 mmol) in 4 M HCl (30 cm3), cooled below 5 ЊC,
was rapidly added sodium nitrite (1.90 g, 27.5 mmol) in
the minimum amount of water. After 45 min the mixture was
treated with urea and extracted with dichloromethane (2 × 30
cm3). The aqueous layer was added to a stirred solution of
aniline (1.86 g, 20.0 mmol) in water (50 cm3) at 5 ЊC. The yellow
precipitate was filtered off 30 min later, dissolved in acetone (50
cm3) and, after addition of 3 M NH3 (10 cm3), heated at 50 ЊC
for 10 min. The mixture was cooled to 5 ЊC and diluted with
water (100 cm3) whereupon the product precipitated. It was
collected by filtration and purified through column chrom-
atography on silica gel using petroleum ether–ethyl acetate
(10 : 3) as eluent. Yield 2.31 g (57%), mp 95–96 ЊC (from petrol-
eum ether–ethyl acetate) (Found: C, 59.2; H, 5.1; N, 27.8.
C10H10N4O requires C, 59.4; H, 5.0; N, 27.7%); νmax(KBr)/cmϪ1
1710; δH(CDCl3) 2.33 (3 H, s), 4.15 (2 H, s), 7.47–7.58 (3 H, m)
and 8.09–8.13 (2 H, m); δC(CDCl3) 29.8 (q), 40.6 (t), 119.9
(2 × d), 129.7 (2 × d), 129.8 (d), 136.7 (s), 160.5 (s) and 201.8
(s).
Quaternisation of the 1H-tetrazoles 1f–i. General procedure
A mixture of the respective 1H-tetrazole 1 (10 mmol) and dime-
thyl sulfate (6.30 g, 50 mmol) was kept at room temperature for
48 h [in the case of 1h, the mixture was diluted with chloroform
(10 cm3) and heated under reflux for 1 h prior to treatment as
above]. Then the unconsumed reagent was removed by shaking
with diethyl ether (4 × 20 cm3) and the residual oil consisting of
an inseparable mixture of 1,4-disubstituted and 2,4-disubstituted
5-(methoxycarbonylmethyl)tetrazolium methylsulfate 3b–d,f
and 4b–d,f, respectively, was directly used for cyclisation as
shown below.
3b–4b (Z = MeOSO3) (7 : 3): δH[(CD3)2SO] 3.69 (2.1 H, s)/
3.64 (0.9 H, s), 4.44 (2.1 H, s)/4.80 (0.9 H, s), 4.88 (1.4 H, s)/4.67
(0.6 H, s), 6.76 (1.4 H, s)/6.81 (0.6 H, s), 7.64–7.68 (2 H, m),
7.79–7.82 (1 H, m) and 8.07–8.09 (2 H, m).
3c–4c (7 : 3): δH[(CD3)2SO] 1.95 (3 H, d), 3.53 (2.1 H, s)/3.48
724
J. Chem. Soc., Perkin Trans. 1, 2001, 720–728

View Article Online
Table 3 Comparison of EI mass spectra (significant peaks) of selected isomeric pyrrolotetrazoles 5–6 and 7–8 (including the spectrum of 12b)
Compound
m/z (70 eV)a (%)
Compound
m/z (70 eV)a (%)
5a
240 (Mϩ, 38), 212 (14), 142 (100)
6a
6b
240 (Mϩ, 60), 225d (100), 43 (8)
256 (Mϩ, 100), 225d (44), 43 (32)
198 (Mϩ, 66), 102 (68), 43 (100)
240 (Mϩ, 100), 225e (78), 43 (62)
212 (Mϩ, 74), 102 (77), 43 (100)
5b
256 (Mϩ, 47), 225 (2), 196 (81), 142 (100)
198 (Mϩ, 8), 170 (23), 143 (39), 102 (100)
240 (Mϩ, 37), 169 (100), 43 (11)
7a
8a
7a–Acb
7b
8a–Acc
8b
12b
212 (Mϩ, 28), 184 (29), 143 (26), 102 (100)
222 (Mϩ, 100), 207f (84), 191g (80), 43 (46)
a Ion-source temperature, ЊC: 5a, 25; 5b, 71; 6a, 100; 6b, 29; 7a, 82; 7a–Ac, 35; 7b, 20; 8a, 73; 8a–Ac, 70; 8b, 51; 12b, 80. b 5-Acetyl-1-methyl-6-phenyl-
1H-pyrrolo[1,2-d ]tetrazole (for preparation, see ref. 21). c 5-Acetyl-2-methyl-6-phenyl-2H-pyrrolo[1,2-d ]tetrazole (for preparation, see ref. 21).
d–g Peaks corresponding to 15a, 16a, 15b and 16b, respectively.
(0.9 H, s), 4.43 (2.1 H, s)/4.83 (0.9 H, s), 4.96 (1.4 H, s)/4.33 (0.6
H, s), 7.22 (1 H, m), 7.56–7.88 (3 H, m) and 8.10–8.24 (2 H, m).
3d–4d (Z = MeOSO3) (6 : 4): δH[(CD3)2SO] 3.73 (1.8 H, s)/
3.66 (1.2 H, s), 4.46 (1.8 H, s)/4.82 (1.2 H, s), 4.91 (1.2 H, s)/4.67
(0.8 H, s), 6.79 (1.2 H, s)/6.83 (0.8 H, s), 7.86–8.15 (4 H,
AAЈBBЈ).
3f–4f (Z = MeOSO3) (6 : 4): δH[(CD3)2SO] 2.35 (3 H, s); 3.73
(3 H, s), 4.41 (1.8 H, s)/4.76 (1.2 H, s), 4.82 (1.2 H, s)/4.57 (0.8
H, s), 6.08 (1.2 H, s)/6.11 (0.8 H, s).
diethyl ether (4g); analytical figures of 4a,f–h were only
approximate.
4a: Yield 1.97 g (57%), mp 159–161 ЊC; νmax(KBr)/cmϪ1 1726
and 1699; δH[(CD3)2SO] 2.27 (3 H, s), 4.77 (2 H, s), 4.79 (3 H, s),
6.69 (2 H, s), 7.64–7.68 (2 H, m), 7.78–7.82 (1 H, m) and 8.07–
8.31 (2 H, m); δC[(CD3)2SO] 29.7 (q), 37.5 (t), 43.8 (q), 56.4 (t),
128.6 (2 × d), 129.0 (2 × d), 133.1 (s), 134.9 (d), 157.2 (s), 188.5
(s) and 199.5 (s).
4b: Yield 2.95 g (81%), mp 123–124 ЊC (Found: C, 43.2; H,
4.1; N, 15.3. [C13H15N4O3]BF4 requires C, 43.1; H, 4.2; N,
15.5%); νmax(KBr)/cmϪ1 1760 and 1709; δH[(CD3)2SO] 3.65 (3 H,
s), 4.67 (2 H, s), 4.80 (3 H, s), 6.81 (2 H, s), 7.65–7.69 (2 H, m),
7.78–7.83 (1 H, m) and 8.07–8.10 (2 H, m); δC[(CD3)2SO] 29.3
(t), 44.0 (q), 52.9 (q), 56.8 (t), 128.7 (2 × d), 129.1 (2 × d), 133.1
(s), 135.0 (d), 156.8 (s), 165.5 (s) and 188.7 (s).
4,5-Diacetonyl-1-methyl-1H-tetrazolium tetrafluoroborate 3e
To a solution of the 1H-tetrazole 1c (1.40 g, 10 mmol) in
anhydrous nitromethane (20 cm3) were added successively
bromoacetone (i; 1.03 g, 8 mmol) and silver tetrafluoroborate
(ii; 0.98 g, 5 mmol). The mixture was warmed at 50–55 ЊC for a
total of 12 d, while fresh reagents (i and ii, amounts as above)
were added twice at equal intervals. Filtration of silver bromide
followed by concentration of the filtrate in vacuo gave an oily
residue which, after extraction with boiling diethyl ether, was
crystallised from methanol–diethyl ether. Yield 0.93 g (33%),
mp 124–127 ЊC (Found: C, 33.75; H, 4.6; N, 19.6. [C8H13N4O2]-
BF4 requires C, 33.8; H, 4.6; N, 19.7%); νmax(KBr)/cmϪ1 1735;
δH[(CD3)2SO] 2.31 (6 H, s), 4.30 (3 H, s), 4.88 (2 H, s) and 5.93
(2 H, s); δC[(CD3)2SO] 26.9 (q), 29.9 (q), 36.4 (t), 37.2 (q), 58.1
(t), 150.6 (s), 197.66 (s) and 197.73 (s).
4d: Yield 3.62 g (82%), mp 107–109 ЊC (Found: C, 35.15; H,
3.2; N, 12.5. [C13H14BrN4O3]BF4 requires C, 35.4; H, 3.2; N,
12.7%); νmax(KBr)/cmϪ1 1737 and 1702; δH[(CD3)2SO] 3.65 (3 H,
s), 4.67 (2 H, s), 4.80 (3 H, s), 6.78 (2 H, s) and 7.90/8.00 (4 H,
AAЈBBЈ, N 8); δC[(CD3)2SO] 29.3 (t), 44.0 (q), 53.0 (q), 56.7 (t),
129.2 (s), 130.6 (2 × d), 132.2 (2 × d), 132.3 (s), 156.8 (s), 165.5
(s) and 188.0 (s).
4e: Yield 1.62 g (57%), dark oil; νmax(neat)/cmϪ1 1732;
δH(CF3CO2H; external C6D6) 2.712 (3 H, s), 2.714 (3 H, s), 4.83
(2 H, s), 4.91 (3 H, s) and 6.04 (2 H, s); δC(CF3CO2H; external
C6D6) 26.3 (q), 29.0 (q), 37.9 (t), 43.3 (q), 58.9 (t), 157.3 (s),
200.2 (s) and 204.6 (s).
Quaternisation of the 1H-tetrazole 1e
4f: Yield 1.80 g (60%), mp 145 ЊC; νmax(KBr)/cmϪ1 1745;
δH(CF3CO2H; external C6D6) 2.58 (3 H, s), 3.94 (3 H, s), 4.46
(2 H, s), 4.74 (3 H, s) and 5.99 (2 H, s); δC(CF3CO2H; external
C6D6) 26.2 (q), 30.0 (t), 43.4 (q), 54.4 (q), 59.4 (t), 157.3 (s),
168.1 (s) and 200.8 (s).
To a solution of the 1H-tetrazole 1e (2.02 g, 10 mmol)
in anhydrous nitromethane (20 cm3) were added phenacyl
bromide (1.99 g, 10 mmol) and silver tetrafluoroborate (1.95 g,
10 mmol), and the mixture was heated at 70 ЊC for 7 d. Work-up
as detailed with the salt 3e gave 2.00 g of a crystalline material
which, according to NMR (see below), was a 1 : 1 mixture of
5-acetonyl-4-phenacyl-1-phenyl- 3g and 5-acetonyl-3-phenacyl-
1-phenyl-1H-tetrazolium tetrafluoroborate X. Since separation
of the desired component 3g failed, the mixture was reacted
further as such. 3g–X (1 : 1): δH[(CD3)2SO] 2.18 (1.5 H, s)/1.99
(1.5 H, s), 5.37 (1 H, s)/5.09 (1 H, s), 6.62 (1 H, s)/6.81 (1 H, s),
7.60–7.95, 8.14–8.20 (10 H, m).
4g: Yield 3.26 g (80%), mp 210–211 ЊC; νmax(KBr)/cmϪ1 1728
and 1708; δH(CF3CO2H; external C6D6) 2.58 (3 H, s), 4.88 (2 H,
s), 6.58 (2 H, s), 7.64–7.68 (2 H, m), 7.75–7.79 (2 H, m), 7.82–
7.87 (2 H, m), 8.14–8.15 (2 H, m) and 8.28–8.30 (2 H, m);
δC(CF3CO2H; external C6H6) 29.1 (q), 38.6 (t), 57.5 (t), 121.1
(2 × d), 129.0 (2 × d), 129.9 (2 × d), 130.9 (2 × d), 132.4 (s),
134.7 (d), 135.3 (s), 137.1 (d), 157.8 (s), 190.2 (s) and 205.8 (s).
4h: Yield 2.08 g (60%), mp 145 ЊC; νmax(KBr)/cmϪ1 1734;
δH(CF3CO2H; external C6D6) 2.600 (3 H, s), 2.603 (3 H, s), 4.80
(2 H, s), 6.01 (2 H, s), 7.73–7.77 (2 H, m), 7.81–7.85 (1 H, m)
and 8.23–8.26 (2 H, m); δC(CF3CO2H; external C6D6) 26.4 (q),
29.1 (q), 38.4 (t), 59.5 (t), 121.1 (2 × d), 130.9 (2 × d), 134.7 (d),
135.2 (s), 157.4 (s), 201.0 (s) and 205.4 (s).
2,4-Disubstituted 5-acetonyl/(methoxycarbonylmethyl)-2H-
tetrazolium tetrafluoroborates 4a,b,d–h. General procedure
A mixture of the appropriate 2H-tetrazole 2 (10 mmol), the
respective α-bromoketone (12 mmol) and silver tetrafluoro-
borate (2.34 g, 12 mmol) in anhydrous nitromethane (20 cm3)
was stirred at 60 ЊC for 14 d (4a,g) or 10 d (4b,d). In the case of
4e,f and h, the reagents [iodoacetone (2.21 g, 12 mmol) and
silver tetrafluoroborate (2.34 g, 12 mmol)] were added portion-
wise at several intervals over a period of 10, 7 and 14 d, respec-
tively. Work-up as above afforded a sticky oil which, after
repeated extraction with diethyl ether and acetone–diethyl ether
(3 : 8), was crystallised from methanol–chloroform–diethyl
ether (attempts to crystallise 4e failed). Purification was effected
by recrystallisation from ethanol–diethyl ether (4a,b,d,f),
acetone–dichloromethane (4h) or ethanol–dichloromethane–
7-Functionalised 1H- and 2H-pyrrolotetrazoles 5a–g and
6a–d,f–h. General procedure
A stirred mixture of the appropriate tetrazolium salt 3 (5 mmol)
or 4 (4 mmol) and anhydrous sodium acetate [1.00 g, 12 mmol
(with 3); 2.00 g, 24 mmol (with 4)] in acetic acid [10.0 g, 167
mmol (with 3); 20.0 g, 334 mmol (with 4)] was heated at 100–
110 ЊC for 1 h (4a: 2 h); in the case of 3b–d,f, the crude material
containing 4b–d,f was employed. For isolation of the products
5, the cooled mixture was diluted with water (20 cm3) and
extracted with dichloromethane (3 × 20 cm3); the combined
J. Chem. Soc., Perkin Trans. 1, 2001, 720–728
725

View Article Online
organic layers were washed with aqueous sodium carbonate
and water, dried and concentrated. The residue was recrystal-
lised from dichloromethane–light petroleum (5a), chloroform–
diethyl ether (5b–f) or chloroform–light petroleum (5g). To
isolate the products 6 (derivatives a,b,d,f–h), the reaction mix-
ture was neutralised with aqueous sodium carbonate and
extracted with dichloromethane (3 × 50 cm3), and the residue
of the combined organic layers was chromatographed on silica
gel using chloroform–ethyl acetate (4 : 1) as eluent. To obtain
6c, the mother liquor of 5c was concentrated and chromato-
graphed as above. Recrystallisation was effected with dichloro-
methane–diethyl ether (6a), chloroform–diethyl ether (6b–d),
diethyl ether–light petroleum (6f), dichloromethane–light
petroleum (6g) or dichloromethane–diethyl ether–light petrol-
eum (6h).
requires C, 62.2; H, 5.2; N, 20.7%); νmax(KBr)/cmϪ1 1692;
δH(CDCl3) 2.40 (3 H, s), 3.81 (3 H, s), 4.46 (3 H, s) and 7.35–
7.44 (5 H, m); δC(CDCl3) 9.5 (q), 41.8 (q), 50.8 (q), 84.4 (s),
108.9 (s), 127.4 (d), 127.6 (2 × d), 130.5 (2 × d), 133.7 (s), 135.5
(s), 147.1 (s) and 163.5 (s).
6d: Yield 0.80 g (60%), mp 174 ЊC (Found: C, 46.5; H, 3.25;
N, 16.7. C13H11BrN4O2 requires C, 46.6; H, 3.3; N, 16.7%);
νmax(KBr)/cmϪ1 3142 and 1692; δH[(CD3)2SO] 3.84 (3 H, s), 4.45
(3 H, s), 7.19 (1 H, s) and 7.47/7.52 (4 H, AAЈBBЈ, N 8);
δC[(CD3)2SO] 41.9 (q), 51.0 (q), 84.7 (s), 100.2 (d), 122.2 (s),
131.0 (2 × d), 131.4 (2 × d), 132.8 (s), 138.4 (s), 149.0 (s) and
163.3 (s).
6f: Yield 0.26 g (33%), mp 104–105 ЊC (Found: C, 49.4; H,
5.2; N, 28.8. C8H10N4O2 requires C, 49.5; H, 5.2; N, 28.85%);
νmax(KBr)/cmϪ1 1688; δH(CDCl3) 2.55 (3 H, s), 3.90 (3 H, s),
4.43 (3 H, s) and 7.00 (1 H, s); δC(CDCl3) 13.4 (q), 41.6 (q), 50.8
(q), 85.8 (s), 100.0 (d), 136.4 (s), 148.3 (s) and 164.2 (s).
6g: Yield 0.97 g (80%), mp 161–163 ЊC (Found: C, 71.1; H,
4.7; N, 18.8. C18H14N4O requires C, 71.5; H, 4.7; N, 18.5%);
νmax(KBr)/cmϪ1 3097 and 1635; δH(CDCl3) 2.60 (3 H, s), 7.24
(1 H, s), 7.38–7.44 (3 H, m), 7.55–7.62 (5 H, m) and 8.22–8.24
(2 H, m); δC(CDCl3) 29.7 (q), 97.0 (s), 101.2 (d), 120.3 (2 × d),
127.9 (2 × d), 128.1 (d), 129.7 (2 × d), 129.8 (2 × d), 130.6 (d),
134.2 (s), 137.2 (s), 140.6 (s), 149.9 (s) and 189.3 (s).
6h: Yield 0.16 g (17%), mp 149–150 ЊC (Found: C, 64.9; H,
5.1; N, 23.3. C13H12N4O requires C, 65.0; H, 5.0; N, 23.3%);
νmax(KBr)/cmϪ1 3130 and 1636; δH(CDCl3) 2.60 (3 H, s), 2.67
(3 H, s), 7.07 (1 H, s), 7.50–7.59 (3 H, m) and 8.13–8.17 (2 H,
m); δC(CDCl3) 14.4 (q), 29.4 (q), 97.9 (s), 101.0 (d), 120.1
(2 × d), 129.8 (2 × d), 130.3 (d), 137.3 (s), 138.3 (s), 149.6 (s)
and 190.0 (s).
5a: Yield 0.16 g (66%) [from 0.35 g (1 mmol) 3a], mp 92–
94 ЊC (lit.,1 92–94 ЊC) (Found: C, 64.95; H, 5.1; N, 23.4.
C13H12N4O requires C, 65.0; H, 5.0; N, 23.3%); νmax(KBr)/cmϪ1
3155 and 1640; for δH and δC, see Table 2.
5b: Yield 0.73 g (82%; based on 7 : 3 mixture of 3b–4b), mp
128–129 ЊC (lit.,1 128–129 ЊC) (Found: C, 61.0; H, 4.7; N, 21.9.
C13H12N4O2 requires C, 60.9; H, 4.7; N, 21.9%); for νmax/cmϪ1
δH and δC, see ref. 1.
,
5c: Yield 0.49 g (52%; based on 7 : 3 mixture of 3c–4c), mp
123–125 ЊC (Found: C, 62.4; H, 5.2; N, 20.7. C14H14N4O2
requires C, 62.2; H, 5.2; N, 20.7%); νmax(KBr)/cmϪ1 1713;
δH(CDCl3) 2.39 (3 H, s), 3.65 (3 H, s), 4.39 (3 H, s) and 7.32–
7.43 (5 H, m); δC(CDCl3) 9.1 (q), 36.7 (q), 50.4 (q), 83.0 (s),
111.4 (s), 127.2 (d), 127.6 (2 × d), 130.5 (2 × d), 130.8 (s), 134.0
(s), 134.8 (s) and 163.8 (s).
5d: Yield 0.71 g (64%; based on 6 : 4 mixture of 3d–4d), mp
117–118 ЊC (lit.,1 114–116 ЊC) (Found: C, 46.6; H, 3.3; N, 16.7.
C13H11BrN4O2 requires C, 46.6; H, 3.3; N, 16.7%); νmax(KBr)/
cmϪ1 3160 and 1680; δH(CDCl3) 3.72 (3 H, s), 4.40 (3 H, s), 7.16
(1 H, s) and 7.35/7.51 (4 H, AAЈBBЈ, N 8.6); δC(CDCl3) 36.8 (q),
50.7 (q), 83.5 (s), 102.6 (d), 121.9 (s), 130.9 (2 × d), 131.3
(2 × d), 133.0 (s), 134.5 (s), 136.2 (s) and 163.5 (s).
Defunctionalised 1H- and 2H-pyrrolotetrazoles 7a–f and 8a–g.
General procedure
The appropriate pyrrolotetrazole 5, 6, 11 or 12 (2 mmol; with 5a
1 mmol, with 11a 2.5 mmol) was heated under reflux as detailed
below: 5a,e in 6 M HCl (15 and 10 cm3, respectively; 1 h); 5b in
12 M HCl (10 cm3; 4 h); 5c,d in potassium hydroxide–ethanol
(1.00 g, 9 cm3; 20 h), followed by neutralisation with 12 M HCl
and heating after addition of further 12 M HCl (10 cm3; 0.5 h);
5g in 12 M HCl–ethanol (1 : 1) (20 cm3; 1 h); 6b–d,f in 12 M
HCl (10 cm3; 2 h); 6g in 12 M HCl (10 cm3; 1.5 h); 11a in 12 M
HCl (10 cm3; 2.5 h); 12b in 12 M HCl (10 cm3; 1 h); 12e in
12 M HCl (10 cm3; 5.5 h); 12g in 12 M HCl (10 cm3; 2 h). The
cooled reaction mixture was neutralised with sodium carbonate
(or hydrogencarbonate), in the case of 8 after dilution with
water (20 cm3); then 8e was filtered off, while the remaining
products 7 and 8 were extracted with dichloromethane (3 × 30
cm3). Recrystallisation (after possible filtration over a short
column of silica gel) was effected with chloroform (7a,e),
chloroform–light petroleum (7b), dimethylformamide–water
(7c), ethanol (picrate of 7d), chloroform–diethyl ether (8a),
dichloromethane–diethyl ether–light petroleum (8b,d) or
dichloromethane–diethyl ether (8c,e). The derivatives 7f, 8f and
8g were purified by sublimation (45–50, 60–70 and 40 ЊC,
respectively; 25 Pa). Analytical figures of 7d,f and 8f were only
approximate.
5e: Yield 0.77 g (86%), mp 152–154 ЊC (lit.,1 152–154 ЊC)
(Found: C, 53.8; H, 5.7; N, 31.4. C8H10N4O requires C, 53.9; H,
5.7; N, 31.4%); νmax(KBr)/cmϪ1 3155 and 1630; δH(CDCl3) 2.42
(3 H, s), 2.44 (3 H, d, J 1.0), 4.49 (3 H, s) and 6.96 (1 H, d,
J 1.0); δC(CDCl3) 14.9 (q), 29.3 (q), 37.4 (q), 98.0 (s), 102.6 (d),
129.0 (s), 136.9 (s) and 191.1 (s).
5f: Yield 0.33 g (57%), mp 105–108 ЊC (Found: C, 49.1; H,
5.3; N, 28.9. C8H10N4O2 requires C, 49.5; H, 5.2; N, 28.85%);
νmax(KBr)/cmϪ1 3140 and 1685; δH(CDCl3) 2.39 (3 H, d, J 1.1),
3.83 (3 H, s), 4.34 (3 H, s) and 6.96 (1 H, d, J 1.1); δC(CDCl3)
13.4 (q), 36.3 (q), 50.5 (q), 84.5 (s), 102.2 (d), 131.3 (s), 135.8 (s)
and 164.3 (s).
5g: Yield 0.62 g (82%; based on 1 : 1 mixture of 3g–X), mp
95–96 ЊC (lit.,1 95–96 ЊC) (Found: C, 71.45; H, 4.6; N, 18.65.
C18H14N4O requires C, 71.5; H, 4.7; N, 18.5%); νmax(KBr)/cmϪ1
3155 and 1630; δH(CDCl3) 1.89 (3 H, s), 7.24 (1 H, s), 7.40–7.45
(5 H, m) and 7.48–7.56 (5 H, m); δC(CDCl3) 29.4 (q), 98.4 (s),
102.7 (d), 125.7 (2 × d), 128.2 (d), 128.31 (2 × d), 128.33
(2 × d), 129.5 (d), 130.0 (2 × d), 133.7 (s), 134.7 (s), 134.9 (s),
135.4 (s) and 191.0 (s).
6a: Yield 0.10 g (10%), mp 167–169 ЊC (Found: C, 65.95;
H, 5.05; N, 23.3. C13H12N4O requires C, 65.0; H, 5.0; N,
23.3%); νmax(KBr)/cmϪ1 3138 and 1630; for δH and δC, see
Table 2.
7a: Yield 0.13 g (66%) (from 5a) and 0.30 g (76%) (from 5b),
mp 140–142 ЊC (lit.,1 140–142 ЊC) (Found: C, 66.6; H, 5.1; N,
28.2. C11H10N4 requires C, 66.65; H, 5.1; N, 28.3%); for νmax
cmϪ1, δH and δC, see ref. 1.
/
6b: Yield 0.62 g (60%), mp 145–146 ЊC (Found: C, 60.6; H,
4.7; N, 21.8. C13H12N4O2 requires C, 60.9; H, 4.7; N, 21.9%);
νmax(KBr)/cmϪ1 3138 and 1693; δH(CDCl3) 3.85 (3 H, s), 4.45
(3 H, s), 7.21 (1 H, s), 7.34–7.43 (3 H, m) and 7.60–7.62 (2 H,
m); δC(CDCl3) 41.8 (q), 51.0 (q), 84.8 (s), 100.2 (d), 127.8
(2 × d), 127.9 (d), 129.8 (2 × d), 133.9 (s), 139.7 (s), 148.9 (s)
and 163.4 (s).
7b: Yield 0.36 g (85%), mp 86–88 ЊC (Found: C, 68.25; H, 5.9;
N, 26.35. C12H12N4 requires C, 67.9; H, 5.7; N, 26.4%);
δH(CDCl3) 2.64 (3 H, s), 3.99 (3 H, s), 5.60 (1 H, s), 7.26–7.30
(1 H, m), 7.39–7.43 (2 H, m) and 7.47–7.50 (2 H, m); δC(CDCl3)
10.0 (q), 34.4 (q), 71.5 (d), 107.5 (s), 126.4 (d), 128.3 (2 × d),
128.5 (2 × d), 130.4 (s), 131.3 (s) and 136.5 (s).
6c: Yield 0.08 g (20%; based on 7 : 3 mixture of 3c–4c), mp
177–179 ЊC (Found: C, 62.15; H, 5.5; N, 20.7. C14H14N4O2
7c: Yield 0.32 g (58%), mp 201–203 ЊC (lit.,1 201–203 ЊC)
(Found: C, 47.6; H, 3.2; N, 20.1. C11H9BrN4 requires C, 47.7; H,
726
J. Chem. Soc., Perkin Trans. 1, 2001, 720–728

View Article Online
3.3; N, 20.2%); νmax(KBr)/cmϪ1 3150; δH[(CD3)2SO] 4.06 (3 H,
s), 6.10 (1 H, d, J 1.4), 7.57/7.64 (4 H, AAЈBBЈ, N 8.6) and 7.96
(1 H, d, J 1.4).
(2 × d), 133.7 (s), 134.7 (d), 156.9 (s), 188.0 (s) and 189.5
(2 × s).
7d: Yield 0.18 g (66%), oil (mp < 0 ЊC) (lit.,1 oil); νmax(neat)/
cmϪ1 3141; for δH and δC, see Table 2. Picrate: mp 102–104 ЊC
(Found: C, 39.5; H, 3.1; N, 26.9. [C6H9N4]C6H2N3O7 requires C,
39.5; H, 3.0; N, 26.8%).
Reaction of the ylide 9c with acetic anhydride–base
A suspension of 9c (0.50 g, 1.7 mmol) in acetic anhydride (10
cm3) and triethylamine (0.3 cm3, 2.2 mmol) was heated at 100–
110 ЊC for 1 h and then cooled to room temperature. Hydrolysis
by addition of water (20 cm3) and extraction with dichloro-
methane (3 × 20 cm3) gave a residue whose 1H NMR spectrum
showed a 3 : 4 mixture of 7-acetyl-5-benzoyl- 11c and 5,7-
diacetyl-1,6-dimethyl-1H-pyrrolo[1,2-d]tetrazole 11d (identified
by comparison with authentic samples8b). Fractional crystal-
lisation from chloroform–diethyl ether afforded 0.04 g (8%) 11c
and 0.06 g (16%) 11d (mps and spectroscopic data consistent
with ref. 8b).
7e: Yield 0.42 g (81%), mp 127–129 ЊC (lit.,1 127–129 ЊC)
(Found: C, 73.8; H, 4.4; N, 21.7. C16H12N4 requires C,
73.8; N, 4.65; N, 21.5%); νmax(KBr)/cmϪ1 3140; δH(CDCl3)
6.13 (1 H, d, J 1.4), 7.25–7.41 (4 H, m), 7.50–7.62 (4 H, m),
7.52 (1 H, d, J 1.4) and 7.72–7.80 (2 H, m); δC(CDCl3) 75.4 (d),
98.5 (d), 117.3 (2 × d), 126.1 (2 × d), 126.7 (d), 127.2 (d), 128.8
(2 × d), 129.6 (s), 129.8 (2 × d), 134.6 (s), 135.1 (s) and 135.9 (s).
7f: Yield 0.02 g (7%), mp 34–35 ЊC; νmax(KBr)/cmϪ1 3135;
for δH and δC, see Table 2.
8a: Yield 0.39 g (98%), mp 129–131 ЊC (Found: C, 66.2; H,
5.2; N, 28.2. C11H10N4 requires C, 66.7; H, 5.1; N, 28.3%);
νmax(KBr)/cmϪ1 3144; δH(CDCl3) 4.25 (3 H, s), 6.17 (1 H, d,
J 1.2), 7.20–7.26 (1 H, m), 7.34–7.39 (2 H, m), 7.42 (1 H, d,
J 1.2) and 7.62–7.64 (2 H, m); δC(CDCl3) 41.2 (q), 76.2 (d), 94.2
(d), 126.3 (2 × d), 127.0 (d), 128.7 (2 × d), 135.6 (s), 136.7 (s)
and 147.0 (s).
8b: Yield 0.34 g (80%), mp 90–91 ЊC (Found: C, 67.8; H, 5.7;
N, 26.4. C12H12N4 requires C, 67.9; H, 5.7; N, 26.4%);
δH(CDCl3) 2.61 (3 H, s), 4.32 (3 H, s), 6.00 (1 H, s), 7.26–7.31
(1 H, m), 7.38–7.43 (2 H, m) and 7.51–7.54 (2 H, m); δC(CDCl3)
10.5 (q), 41.2 (q), 77.0 (d), 103.3 (s), 126.5 (d), 128.5 (2 × d),
128.6 (2 × d), 133.9 (s), 136.7 (s) and 144.4 (s).
8c: Yield 0.55 g (99%), mp 212–214 ЊC (Found: C, 47.5; H,
3.3; N, 20.1. C11H9BrN4 requires C, 47.7; H, 3.3; N, 20.2%);
νmax(KBr)/cmϪ1 3142; δH[(CD3)2SO] 4.40 (3 H, s), 6.32 (1 H, s),
7.57/7.70 (4 H, AAЈBBЈ, N 8) and 7.94 (1 H, s); δC[(CD3)2SO]
41.6 (q), 75.6 (d), 94.8 (d), 119.8 (s), 127.8 (2 × d), 131.6 (2 × d),
134.0 (s), 134.6 (s) and 146.4 (s).
8d: Yield 0.20 g (73%) (from 6f) and 0.27 g (99%) (from 12e),
mp 39–40 ЊC (Found: C, 52.8; H, 6.1; N, 41.0. C6H8N4 requires
C, 52.9; H, 5.9; N, 41.15%); νmax(KBr)/cmϪ1 3123; for δH and
δC, see Table 2.
5,7-Diacetyl-1-methyl-1H-pyrrolo[1,2-d]tetrazole 11a
The finely powdered tetrazolium salt 3e (0.57 g, 2 mmol) was
heated with triethyl orthoformate (3.00 g, 20 mmol) in
anhydrous ethanol (3 cm3) under reflux for 5 h. Concentration
in vacuo gave a sticky brown oil which was taken up with pyrid-
ine (10 cm3) and piperidine (1 cm3) and again heated under
reflux for 1 h. After evaporation of the volatiles the product
was isolated by chromatography [silica gel; chloroform–diethyl
ether (4 : 1) as eluent] and crystallisation from chloroform–
diethyl ether. Yield 0.17 g (41%), mp 178–180 ЊC (Found: C,
52.4; H, 4.9; N, 27.0. C9H10N4O2 requires C, 52.4; H, 4.9;
N, 27.2%); νmax(KBr)/cmϪ1 3100 and 1650; for δH and δC, see
Table 2.
5-Benzoyl-1-phenyl-1H-pyrrolo[1,2-d]tetrazole 11b
The 1H-tetrazole 1j (2.15 g, 10 mmol) and phenacyl bromide
(2.39 g, 12 mmol) were warmed in nitromethane (20 cm3) at 50–
55 ЊC for 3 d. After removal of the solvent under reduced pres-
sure and repeated extraction of the residual mass with diethyl
ether, acetic acid (20.0 g, 334 mmol) and anhydrous sodium
acetate (2.00 g, 24 mmol) were added and the mixture was
heated at 100–110 ЊC for 1 h. Work-up as described for the 1H-
pyrrolotetrazoles 5 left a material which was chromatographed
on silica gel [chloroform–ethyl acetate (4 : 1) as eluent] and
recrystallised from chloroform–diethyl ether. Yield 0.17 g (6%),
mp 171–172 ЊC (Found: C, 70.5; H, 4.1; N, 19.4. C17H12N4O
requires C, 70.8; H, 4.2; N, 19.4%); νmax(KBr)/cmϪ1 3130 and
1615; δH(CDCl3) 6.08 (1 H, d, J 4.5), 7.37 (1 H, d, J 4.5), 7.41–
7.60 (6 H, m) and 7.80–7.89 (4 H, m); δC(CDCl3) 81.7 (d), 117.9
(s), 118.5 (2 × d), 128.2 (d), 128.3 (2 × d), 128.8 (2 × d), 129.6
(d), 130.1 (2 × d), 131.5 (d), 134.4 (s), 134.9 (s), 138.8 (s) and
181.8 (s).
8e: Yield 0.51 g (98%), mp 198–199 ЊC (Found: C, 73.4;
H, 4.8; N, 21.5. C16H12N4 requires C, 73.8; N, 4.65; N,
21.5%); νmax(KBr)/cmϪ1 3133; δH(CDCl3) 6.31 (1 H, d, J 1.2),
7.28–7.33 (1 H, m), 7.40–7.50 (3 H, m), 7.53–7.58 (3 H, m),
7.68–7.72 (2 H, m) and 8.15–8.18 (2 H, m); δC(CDCl3) 77.3 (d),
94.3 (d), 119.9 (2 × d), 126.4 (2 × d), 127.3 (d), 128.8 (2 × d),
129.50 (d), 129.54 (2 × d), 135.4 (s), 137.9 (s), 138.7 (s) and
147.3 (s).
8f: Yield 0.04 g (15%), mp 36–38 ЊC; νmax(KBr)/cmϪ1 3132;
for δH and δC, see Table 2.
8g: Yield 0.39 g (98%), mp 86–88 ЊC (Found: C, 66.6; H, 5.1;
N, 28.0. C11H10N4 requires C, 66.7; H, 5.1; N, 28.3%);
δH(CDCl3) 2.39 (3 H, s), 5.83 (1 H, s), 7.06 (1 H, s), 7.44–7.47
(1 H, m), 7.51–7.56 (2 H, m) and 8.12–8.14 (2 H, m); δC(CDCl3)
14.0 (q), 80.1 (d), 96.2 (d), 119.8 (2 × d), 129.2 (d), 129.5
(2 × d), 135.5 (s), 138.2 (s) and 146.8 (s).
5,7-Functionalised 2H-pyrrolotetrazoles 12a–g. General
procedure
The appropriate tetrazolium salt 4 (4 mmol) was dissolved or
suspended in acetic formic anhydride (i; 10–20 cm3) and acetic
anhydride (ii; 20–30 cm3), respectively. After cautious addition
of triethylamine (1.5 cm3, ca. 11 mmol) the mixture was heated
with stirring for 2 h at 60–65 ЊC (i) or 90–100 ЊC (ii). Work-up
for 12a–d: the cooled reaction mixture was diluted with water
(20–30 cm3), made weakly alkaline with sodium hydrogen-
carbonate and extracted with dichloromethane (3 × 50 cm3).
The products were isolated by flash chromatography on silica
gel (40–63 µm) using dichloromethane–diethyl ether (10 : 3) as
eluent and recrystallised from dichloromethane–light petrol-
eum (12a–c) or dichloromethane–diethyl ether (12d). Work-up
for 12e–g: Dilution with water (60 cm3) to allow hydrolysis of
the anhydride, followed by addition of sodium carbonate (until
pH 8) and extraction with dichloromethane (3 × 50 cm3) gave
crude materials which were purified on silica gel [chloroform–
ethyl acetate (4 : 1) as eluent] and recrystallised from dichloro-
1-Methyl-4-phenacyl-1H-tetrazolium-5-(ꢀ-acetylacetonylide) 9c
Triethylamine (0.6 cm3, 4 mmol) was added dropwise to a sus-
pension of the tetrazolium salt 3a (0.69 g, 2 mmol) in acetic
anhydride (10 cm3) and the mixture was stirred at 20 ЊC for 4 h.
After dilution with water (20 cm3) to allow hydrolysis of the
unconsumed reagent, it was concentrated in vacuo to half its
volume and extracted with dichloromethane (3 × 20 cm3) to
afford the product. Yield 0.27 g (45%), mp 134–137 ЊC
(from dichloromethane–diethyl ether) (Found: C, 60.1; H, 5.4;
N, 18.7. C15H16N4O3 requires C, 60.0; H, 5.4; N, 18.7%);
δH(CDCl3) 2.33 (6 H, s), 3.99 (3 H, s), 5.87 (2 H, s), 7.51–7.55
(2 H, m), 7.65–7.69 (1 H, m) and 7.93–7.95 (2 H, m); δC(CDCl3)
29.9 (2 × q), 37.1 (q), 56.0 (t), 93.7 (s), 128.2 (2 × d), 129.1
J. Chem. Soc., Perkin Trans. 1, 2001, 720–728
727

View Article Online
1996, 32, 114; T. A. Kuz’menko, V. V. Kuz’menko and V. A.
methane–light petroleum. Analytical figures of 12a were only
approximate.
Anisimova, Russ. J. Org. Chem., 1996, 32, 103; ( f ) F. S. Babichev
and V. A. Kovtunenko, Ukr. Khim. Zh. (Russ. Ed.), 1975, 41, 252;
F. S. Babichev, V. A. Kovtunenko and E. Ya. Shapiro, Ukr. Khim.
Zh. (Russ. Ed.), 1975, 41, 1053.
12a: Yield 0.31 g (39%), mp 233–234 ЊC; νmax(KBr)/cmϪ1
3090 and 1644; for δH and δC, see Table 2.
12b: Yield 0.28 g (32%), mp 186–188 ЊC (Found: C, 48.4; H,
4.5; N, 25.2. C9H10N4O3 requires C, 48.6; H, 4.5; N, 25.2%);
νmax(KBr)/cmϪ1 3104, 1718 and 1647; δH(CDCl3) 2.53 (3 H, s),
3.94 (3 H, s), 4.61 (3 H, s) and 7.98 (1 H, s); δC(CDCl3) 25.6 (q),
42.4 (q), 51.6 (q), 91.7 (s), 117.1 (s), 128.9 (s), 149.3 (s), 162.6 (s)
and 184.3 (s).
3 (a) D. Moderhack and A. Lembcke, Chem.-Ztg., 1985, 109, 432;
(b) A. Lembcke, Dissertation, Technische Universität Braunschweig
(Germany), 1985.
4 (a) F. S. Babichev, V. A. Kovtunenko and L. N. Didenko, Ukr. Khim.
Zh. (Russ. Ed.), 1974, 40, 245; (b) see also: V. A. Kovtunenko,
L. N. Didenko and F. S. Babichev, Ukr. Khim. Zh. (Russ. Ed.), 1974,
40, 402.
12c: Yield 1.27 g (96%), mp 220–221 ЊC (Found C, 68.6; H,
4.2; N, 16.8. C19H14N4O2 requires C, 69.1; H, 4.3; N, 17.0%);
νmax(KBr)/cmϪ1 3069, 1661 and 1625; δH(CDCl3) 2.68 (3 H, s),
7.51–7.59 (2 H, m), 7.61–7.66 (4 H, m), 7.90–7.92 (2 H, m), 7.99
(1 H, s) and 8.35–8.37 (2 H, m); δC(CDCl3) 28.2 (q), 103.0 (s),
116.9 (s), 120.9 (2 × d), 128.6 (2 × d), 128.7 (2 × d), 129.9
(2 × d), 130.7 (d), 131.4 (d), 132.1 (d), 136.9 (s), 137.8 (s), 150.2
(s), 182.1 (s) and 189.7 (s).
12d: Yield 0.32 g (29%), mp 211–212 ЊC (Found: C, 60.1; H,
4.35; N, 20.0. C14H12N4O2ؒ0.5 H2O requires C, 60.6; H, 4.7; N,
20.2%); νmax(KBr)/cmϪ1 3090 and 1639; δH(CDCl3) 2.58 (3 H, s),
2.68 (3 H, s), 7.61–7.66 (3 H, m), 8.05 (1 H, s) and 8.32–8.35
(2 H, m); δC(CDCl3) 26.0 (q), 28.1 (q), 102.5 (s), 117.5 (s), 120.9
(2 × d), 128.5 (d), 129.9 (2 × d), 131.4 (d), 136.8 (s), 149.7 (s),
184.6 (s) and 189.6 (s).
12e: Yield 0.62 g (66%), mp 212–213 ЊC (Found: C, 50.6; H,
5.2; N, 23.6. C10H12N4O3 requires C, 50.8; H, 5.1; N, 23.7%);
νmax(KBr)/cmϪ1 1703; δH(CDCl3) 2.60 (3 H, s), 2.87 (3 H, s),
3.92 (3 H, s) and 4.57 (3 H, s); δC(CDCl3) 13.3 (q), 29.8 (q), 42.3
(q), 51.2 (q), 90.9 (s), 116.7 (s), 143.8 (s), 148.9 (s), 163.4 (s) and
185.3 (s).
12f: Yield 0.19 g (14%), mp 236 ЊC (Found: C, 69.7; H, 4.6;
N, 16.0. C20H16N4O2 requires C, 69.75; H, 4.7; N, 16.3%);
νmax(KBr)/cmϪ1 1649 and 1623; δH(CDCl3) 2.54 (3 H, s), 2.76
(3 H, s), 7.48–7.52 (2 H, m), 7.57–7.64 (4 H, m), 7.70–7.72 (2 H,
m) and 8.24–8.26 (2 H, m); δC(CDCl3) 15.2 (q), 30.4 (q), 100.8
(s), 116.4 (s), 120.5 (2 × d), 128.4 (2 × d), 128.5 (2 × d), 129.9
(2 × d), 131.1 (d), 131.9 (d), 136.9 (s), 139.4 (s), 144.6 (s), 150.6
(s), 184.7 (s) and 191.0 (s).
5 For example: (a) G. Ege, R. Heck, K. Gilbert, H. Irngartinger,
U. Huber-Patz and H. Rodewald, J. Heterocycl. Chem., 1983, 20,
1683 (‘2H-pyrazolo[1,5-d ]tetrazole’ and, implicitly, ‘2H-[1,2,4]-
triazolo[1,5-d ]tetrazole’); (b) G. L’abbé, M. Gelinne and S. Toppet,
J. Heterocycl. Chem., 1989, 26, 729 (‘2H-imidazo[1,5-d]tetrazole’);
(c) D. Moderhack and B. Holtmann, J. Prakt. Chem., 2000, 342, 591
(‘2H-imidazo[1,2-d ]tetrazole’).
6 (a) C. A. Ramsden, Tetrahedron, 1977, 33, 3203; C. A. Ramsden,
in: Comprehensive Heterocyclic Chemistry, eds. A. R. Katritzky and
C. W. Rees, Pergamon, Oxford, 1984, vol. 6, p. 1027; (b) W. D. Ollis,
S. P. Stanforth and C. A. Ramsden, J. Chem. Soc., Perkin Trans. 1,
1989, 957; (c) B. Musicki, J. Org. Chem., 1990, 55, 910.
7 D. Moderhack and D.-O. Bode, Chem.-Ztg., 1991, 115, 331.
8 (a) D. Moderhack and A. Lembcke, J. Chem. Soc., Perkin Trans. 1,
1986, 1157 (see also p. 2009); (b) D. Moderhack and D.-O. Bode,
J. Chem. Soc., Perkin Trans. 1, 1992, 1483.
9 P. M. Kochergin, A. A. Druzhinina and R. M. Palei, Khim.
Geterotsikl. Soedin., 1976, 1549; P. M. Kochergin, A. A. Druzhinina
and R. M. Palei, Chem. Heterocycl. Compd. (USSR), 1976, 12, 1274.
10 (a) B. B. Molloy, D. H. Reid and F. S. Skelton, J. Chem. Soc., 1965,
65; (b) F. S. Babichev and A. F. Babicheva, Khim. Geterotsikl.
Soedin., 1967, 917; F. S. Babichev and A. F. Babicheva, Chem.
Heterocycl. Compd. (USSR), 1967, 3, 723; (c) V. Boekelheide and
N. A. Fedoruk, J. Am. Chem. Soc., 1968, 90, 3830; (d) V. A.
Kovtunenko and F. S. Babichev, Ukr. Khim. Zh. (Russ. Ed.), 1972,
38, 1244.
11 (a) J.-P. Dulcere, M. Tawil and M. Santelli, J. Org. Chem., 1990, 55,
571; (b) D. Moderhack and D. Decker, J. Org. Chem., 1996, 61, 5646.
12 (a) A. D’Adamo and R. A. LaForge, J. Org. Chem., 1956, 21, 340;
(b) C. R. Jacobson and E. D. Amstutz, J. Org. Chem., 1953, 18, 1183.
13 H. Kano and E. Yamazaki, Chem. Pharm. Bull., 1962, 10, 993;
H. Kano and E. Yamazaki, Tetrahedron, 1964, 20, 461.
14 S. Umio, K. Kariyone, K. Tanaka and H. Nakamura, Chem. Pharm.
Bull., 1969, 17, 559.
12g: Yield 0.19 g (17%) (from 4g) and 0.65 g (58%) (from
4h), mp 259 ЊC (Found: C, 63.8; H, 5.0; N, 19.7. C15H14N4O2
requires C, 63.8; H, 5.0; N, 19.85%); νmax(KBr)/cmϪ1 1657 and
1644; δH(CDCl3) 2.71 (3 H, s), 2.73 (3 H, s), 2.99 (3 H, s), 7.59–
7.67 (3 H, m) and 8.25–8.28 (2 H, m); δC(CDCl3) 13.9 (q), 30.1
(q), 30.5 (q), 100.9 (s), 116.8 (s), 120.4 (2 × d), 129.9 (2 × d),
131.1 (d), 136.9 (s), 145.0 (s), 149.9 (s), 185.9 (s) and 191.2 (s).
15 F. W. Kröck and F. Kröhnke, Chem. Ber., 1969, 102, 659; F. W.
Kröck and F. Kröhnke, Chem. Ber., 1969, 102, 669.
16 (a) A. Knoll and J. Liebscher, Z. Chem., 1988, 28, 214; (b) A. Copar,
B. Stanovnik and M. Tisler, J. Heterocycl. Chem., 1993, 30, 1577.
17 D. T. Decker, Dissertation, Technische Universität Braunschweig
(Germany), 1996.
18 B. Holtmann, Dissertation, Technische Universität Braunschweig
(Germany), 1998.
19 Yu. L. Briks and N. N. Romanov, Khim. Geterotsikl. Soedin., 1991,
549; Yu. L. Briks and N. N. Romanov, Chem. Heterocycl. Compd.
(USSR), 1991, 27, 438.
Acknowledgement
20 Review: D. Moderhack, in: Comprehensive Heterocyclic Chemistry
II, eds. A. R. Katritzky, C. W. Rees and E. F. Scriven, Pergamon,
Oxford, 1996, vol. 8 (ed. G. Jones), p. 227.
Measuring of fluorescence spectra by Dr H.-O. Burmeister of
this Institute is gratefully acknowledged.
21 D. Moderhack, D. Decker and B. Holtmann, J. Chem. Soc., Perkin
Trans. 1, 2001, DOI: 10.1039/b007874n.
22 I. Ya. Postovskii and N. B. Smirnova, Dokl. Akad. Nauk SSSR,
1966, 170, 604; I. Ya. Postovskii and N. B. Smirnova, Dokl. Chem.,
1966, 170, 920.
23 R. Raap and J. Howard, Can. J. Chem., 1969, 47, 813.—Compound
1b was also prepared (66% yield) by adoption of the recent general
method reported by K. Koguro, T. Oga, S. Mitsui and R. Orita,
Synthesis, 1998, 910.
24 E. K. Harvill, R. M. Herbst, E. C. Schreiner and C. W. Roberts,
J. Org. Chem., 1950, 15, 662.
25 G. W. Fischer and M. Herrmann, J. Prakt. Chem., 1988, 330, 963.
26 H. Meerwein, V. Hederich and K. Wunderlich, Arch. Pharm. Ber.
Dtsch. Pharm. Ges., 1958, 291, 541.
27 H. M. Foster and H. R. Snyder, Org. Synth., 1963, Coll. Vol. IV, 638.
28 R. R. Williams, A. E. Ruehle and J. Finkelstein, J. Am. Chem. Soc.,
1937, 59, 526; see also M. Forchiassin, G. Illuminati and G. Sleiter,
J. Heterocycl. Chem., 1969, 6, 879.
References
1 A few results on the 1H-pyrrolotetrazoles described herein have
been published in preliminary form: D. Moderhack and D. Decker,
Heterocycles, 1994, 37, 683; see also: D. Moderhack and D. Decker,
14th International Congress of Heterocyclic Chemistry, Antwerp,
1993, Abstracts of Papers, PO 3-211.
2 (a) A. E. Tschitschibabin, Ber. Dtsch. Chem. Ges., 1927, 60, 1607; A.
E. Tschitschibabin and F. N. Stepanov, Ber. Dtsch. Chem. Ges.,
1929, 62, 1068; (b) overview: J. Elguero, R. M. Claramunt and A. J.
H. Summers, Adv. Heterocycl. Chem., 1978, 22, 183; for
supplementary papers, see refs. 2c–f; (c) J. C. Brindley, D. G. Gillon
and G. D. Meakins, J. Chem. Soc., Perkin Trans. 1, 1986, 1255;
(d) P. M. Kochergin, R. M. Palei and S. A. Chernyak, Khim.
Geterotsikl. Soedin., 1993, 659; P. M. Kochergin, R. M. Palei and
S. A. Chernyak, Chem. Heterocycl. Compd., 1993, 29, 563; (e) T. A.
Kuz’menko, V. V. Kuz’menko and V. A. Anisimova, Zh. Org. Khim.,
728
J. Chem. Soc., Perkin Trans. 1, 2001, 720–728