N-(3-benzo[b]thienyl)iminophosphoranes toward the synthesis of benzo[b]thieno[3,2-b]pyridines: Reactivity and alternative regioselectivity with α,β-unsaturated ketones and aldehydes

Article abstract of DOI:10.1016/S0040-4020(00)00037-5

The novel N-(3-benzo[b]thienyl)iminophosphoranes 1b-d react with α,β- unsaturated aldehydes and ketones 2a-e to give varying mixtures of the regioisomeric benzothieno[3,2-b]pyridines 3a-d and 4a-d as a result of preferential attack of either imino nitroge

Full text of DOI:10.1016/S0040-4020(00)00037-5

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 1517–1521
N-(3-Benzo[b]thienyl)iminophosphoranes toward the Synthesis of
Benzo[b]thieno[3,2-b]pyridines: Reactivity and Alternative
Regioselectivity with a,b-unsaturated Ketones and Aldehydes
b,
Carlo Bonini,a Lucia Chiummiento,a Maria Funicelloa, and Piero Spagnolo
*
*
a
`
Dipartimento di Chimica, Universita della Basilicata, Via N.Sauro 85, 85100 Potenza, Italy
b
`
Dipartimento di Chimica Organica ‘A. Mangini’, Universita di Bologna, Viale Risorgimento 4, 40136 Bologna, Italy
Received 19 October 1999; revised 13 December 1999; accepted 6 January 2000
Abstract—The novel N-(3-benzo[b]thienyl)iminophosphoranes 1b–d react with a,b-unsaturated aldehydes and ketones 2a–e to give
varying mixtures of the regioisomeric benzothieno[3,2-b]pyridines 3a–d and 4a–d as a result of preferential attack of either imino nitrogen
or a-thienyl carbon at the enone carbonyl group. The findings indicate that the progressive replacement of phenyl with methyl P-substituent
greatly enhances the reactivity of the phosphorane 1 and concomitantly enhances the propensity of the phosphorane itself for addition to the
enone by the a-thienyl carbon. ᭧ 2000 Elsevier Science Ltd. All rights reserved.
Introduction
phosphorane compounds proved to be useful nitrogen inter-
mediates for the construction of benzothieno[b]pyridines,
which represent a class of pharmacological bioactive
compounds of special interest as isosters with indolopyri-
dines3 and as annelated NADH models.4 In fact, mild
thermal reaction of the phosphorane 1a (and its positional
isomer) with a,b-unsaturated aldehydes directly yielded
moderate yields of corresponding benzothienopyridines
that were considered to form through electrocyclization
and eventual dehydrogenation of the initial aza Wittig
imine products (Scheme 1).
Iminophosphoranes are important intermediates which have
found extensive use in the production of acyclic and,
especially, heterocyclic nitrogen-containing compounds.1
N-aryl- and certain N-heteroaryl-iminophosphoranes have
been largely investigated; instead, those derived from five-
membered heteroarenes containing one heteroatom remain
virtually unexplored, despite the fact that their preparation
from readily available azido precursors is now feasible.2
In previous work we first prepared N-(3-benzo[b]thienyl)-
iminotriphenylphosphorane 1a and its N-(2-benzo[b]thienyl)-
substituted analogue by Staudinger reaction of 3-azido- and
2-azido-benzothiophene with triphenylphosphine.2 Both
Strong support to the postulated aza Wittig-electrocycliza-
tion mechanism arose from successful detection of certain
azahexatriene intermediates. Moreover, consistent with the
Scheme 1.
Keywords: azides; iminophosphoranes; annulation reactions; fused pyridines.
* Corresponding authors. Tel.: ϩ39-971-202241; fax:ϩ39-971-202223; e-mail: funicello@unibas.it; e-mail: spagnolo@ms.fci.unibo.it
0040–4020/00/$ - see front matter ᭧ 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00037-5

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C. Bonini et al. / Tetrahedron 56 (2000) 1517–1521
Figure 1.
postulated mechanism, the reactions with cinnamaldehyde,
crotonaldehyde and methacrylaldehyde occurred in a
regiospecific fashion to give a single 4- or 3-substituted
benzothienopyridine.2 However, our subsequent efforts to
enlarge the scope of these novel annulation reactions by
using but-3-en-2-one as the carbonyl substrate showed
that both triphenylphosphoranes were virtually inert with
the ketone. We were therefore led to prepare the mono-,
di-, and trimethyl-P-substituted (3-benzothienylimino)phos-
phoranes 1b–d (Fig. 1) and thence to examine their possible
use with a,b-unsaturated ketones and aldehydes.
Compounds 1b–d were predicted to be more reactive than
the triphenyl counterpart 1a since the electron-donating
methyl group(s) should decrease the positive charge on
the phosphorus and concomitantly increase the negative
charge on the imino nitrogen.1a
electrocyclization pyridine product) and the 4-methyl posi-
tional isomer 4a (Fig. 1 and Table 1; entry 1). Under
comparable conditions the dimethylphosphorane 1c with
2a similarly furnished both isomeric pyridines 3a and 4a,
but in this case their overall yield was significantly higher
and, additionally, the proportion of the isomer 4a was
greatly enhanced (Table 1; entry 2). Like the phosphorane
1c, in the presence of 2a the rather unstable trimethyl
derivative 1d also yielded the pyridine 4a in preference to
the isomer 3a, although in a less efficient fashion (Table 1;
entry 3). With trans-4-phenyl-3-buten-2-one 2b the
compound 1b reacted to give a modest yield of the sole
disubstituted pyridine 3b (Fig. 1 and Table 1; entry 4),
whereas the more reactive dimethyl analogue 1c could
afford, besides the above pyridine 3b, significant amounts
of its regioisomer 4b (Table 1; entry 5). Moreover, with
Herein we report the results of our study on the reactions of
the phosphoranes 1b–d (and 1a) with the enones 2a–e
shown in Fig. 1.
Table 1. Reactions of the phosphoranes 1a–d with the a,b-unsaturated
ketones 2a–c and aldehydes 2d, e (reactions were normally carried out in
PhMe at 70ЊC by using equimolar amounts of phosphorane 1 and enone 2)
Entry
Phosphorane
Enone
Benzothienopyridine(s)
(% yield)a
Results and Discussion
1
2
3
4
5
6
7
8
1b
1c
1d
1b
1c
1a
1b
1c
1a
1b
1c
1a
1b
1c
1dc
2a
2a
2a
2b
2b
2c
2c
2c
2d
2d
2d
2e
2e
2e
2e
3a (25)ϩ4a (25)
3a (15)ϩ4a (60)
3a (10)ϩ4a (40)
3b (26)
3b (33)ϩ4b (15)
3c (30)
3c (46)ϩ4c (27)
3c (47)ϩ4c (42)
3d (45)b
3d (30)ϩ4d (25)
3d (15)ϩ4d (40)
4a (62)b
The phosphoranes 1b–d were readily prepared by Staudinger
reaction of 3-azidobenzothiophene with the appropriate
phosphine, following an analogous procedure to that
previously employed for the triphenyl derivative 1a. The
mono- and dimethyl-phosphoranes 1b,c were isolated as
fairly stable solid compounds, whereas the trimethyl
analogue 1c was obtained as a crude oil which showed a
tendency to decompose and thence was directly used
without purification.
9
10
11
12
13
14
15
4a (41)ϩ3a (30)
4a (20)ϩ3a (51)
4a (16)ϩ3a (30)
In contrast with the previous triphenylphosphorane 1a,
the methylphosphorane 1b succeeded in reacting with but-
3-en-2-one 2a, in toluene solution at 70ЊC, to furnish, in
moderate overall yield, equal amounts of 2-methylbenzo-
[b]thieno[3,2-b]pyridine 3a (the expected aza Wittig-
a Yield isolated by column chromatography.
b See Ref. 2.
c Reaction carried out at 45ЊC.

C. Bonini et al. / Tetrahedron 56 (2000) 1517–1521
1519
methyl trans-4-oxo-2-pentenoate 2c both methylated phos-
phoranes 1b,c led, in high yields, to the corresponding
disubstituted pyridines 3c and 4c, which isomers occurred
in a ratio of ca. 2:1 and 1:1 on passing respectively from 1b
to 1c (Fig. 1 and Table 1; entries 7 and 8).
the methylated phosphoranes 1b and, especially, 1c,d
showed a fair tendency to produce the respective benzo-
thienopyridines 4a–d (and 3a) at the expense of the
isomeric aza Wittig-electrocyclization ones 3a–d (and
4a). The compounds 1b–d presumably led to the pyridines
4a–d and 3a through the reaction sequences outlined in
Scheme 2. These involve primary addition of the a-thienyl
carbon of 1b–d to the carbonyl carbon of the enones 2a–e
leading to an intermediate phosphorane 5, which, upon
subsequent fragmentation, undergoes cyclization to pyri-
dine with eventual dehydrogenation. Analogous type of
reaction sequences have already been invoked in the
reaction of certain (vinylimino)phosphoranes with cinna-
maldehydes similarly leading to cyclized pyridines.6,7
In the present work the triphenylphosphorane 1a was found
to fail to react with the ketone 2b, while, in the presence of
the (activated) keto ester 2c, it could successfully afford
only the aza Wittig-electrocyclization pyridine 3c, albeit
in modest yield (Table 1; entry 6). When the benzothienyl
phosphoranes 1b–d were reacted with trans-cinnamalde-
hyde 2d and trans-crotonaldeyde 2e, interestingly, the
ensuing chemical trend was strictly comparable with that
displayed by the corresponding reactions with the ketones
2a–c. Indeed, with the aldehydes 2d,e the methylated
derivatives 1b–d, unlike the triphenylphosphorane 1a,2
similarly furnished varying mixtures of the respective
4-substituted-, 3d and 4a, and 2-substituted-benzothieno-
pyridines, 4d and 3a, in relative ratios reversing on going
from 1b to 1c,d (Fig. 1 and Table 1; entries 9–15).
Structural assignment to the previously known benzo-
thienopyridines 3a,d,4a and to those hitherto unknown
3b,c,4b–d was generally performed on the basis of elemen-
tal analysis in addition to 1H and 13C NMR spectral data. In
However, it is worth noting that in the presence of enones 2
the vinyl phosphoranes are normally envisaged to yield
pyridines as a result of (frontier orbital-controlled) addition
to the enone b-vinyl carbon rather than of alternative
(charge-controlled) addition to the carbonyl one.6 On this
basis, in the observed production of the pyridines 4a–d and
3a the compounds 1b–d would be generally entitled to add
to the enones 2a–e in a mode unusual for the vinyl counter-
parts. At this stage we have no clear explanation of the
actual reasons that might cause a different addition mode
by those types of related compounds, but it is possible that
kinetic and thermodynamic factors in the addition of those
phosphoranes at either enone carbonyl or vinyl carbon can
play a relative role to a different extent.
1
particular, H NMR spectroscopy clearly showed that the
the hydrogen and/or methyl substituents attached at the
a-position of the pyridine moiety absorb at a significantly
lower field than when they are attached at the g-position.
Moreover, the values of the coupling constant of the vicinal
a- and b-hydrogens in the compounds 3d,4a (Jˆca. 6 Hz)
were found to be expectedly lower than that observed for the
b- and g-hydrogens in the compound 3a (Jˆ8.5 Hz).
Regardless of mechanistic implications, our overall results
now indicate that the thermal reactions of the phosphoranes
1 with unsaturated aldehydes and ketones can offer a con-
venient, general protocol for the production of
benzothieno[3,2-b]pyridines, for which compounds the
few literature methods are rather difficult and/or give
(very) low yields.3,4,8 Such a protocol, in principle, should
be of wide utility for achieving b-fusion9 of a pyridine
ring onto five-membered heteroarenes by using the a- and
b-azido derivatives as the nitrogen precursors.10,11 Of
special interest is our present observation that the
Thus, our present and previous findings revealed that the
progressive replacement of phenyl with methyl P-substi-
tuent can greatly enhance the reactivity of benzothienyl-
phosphorane
1
towards enones 2, concomitantly
enhancing the propensity of 1 to behave like the N-vinyl
congeners5 by adopting the b-(a-thienyl-)carbon instead
of the imino nitrogen. In fact, with all the enones 2a–e
Scheme 2.

1520
C. Bonini et al. / Tetrahedron 56 (2000) 1517–1521
regiochemistry of the outcoming substituted pyridines can
be largely governed by a proper choice of the phosphorane 1
reagent since phenyl substituents on the phosphorus can
favor attack of the imino nitrogen on the enone carbonyl
group and instead methyl substituents favor alternative
attack of the a-thienyl carbon. This observation will be
useful in the future planning of the synthesis of benzo-
thieno[b]pyridines bearing specific substituents at the 2-,
3- and/or 4-positions of the pyridine moiety.
time the starting reagents were normally shown by TLC to
be largely absent (but the essayed mixture of 1a and 2b was
shown to remain virtually unchanged). The excess of
solvent was removed under vacuum and the residual
material chromatographed. The reaction of the most
reactive phosphorane 1d with the aldehyde 2e was carried
out in a similar fashion but using a lower temperature (45ЊC)
and a reduced time (1.5 h). Yields of the isolated
benzo[b]thieno[3,2-b]pyridines 3a–d, 4a–d are given in
Table 1. Physical and analytical data for every compound
3,4 were as follows.
Experimental
2-Methylbenzo[b]thieno[3,2-b]pyridine (3a).13 Thick oil
[1H NMR (300 MHz) 8.59–8.51 (m, 1H), 8.08 (d, 1H,
Jˆ8.5 Hz), 7.90–7.82 (m, 1H), 7.60–7.51 (m, 2H), 7.26
(d, 1H, Jˆ8.5 Hz), 2.79 (s, 3H); 13C NMR (75 MHz) d
155.1, 140.0, 134.8, 132.1, 128.4, 125.1, 124.8, 123.2,
122.9, 122.5, 121.0, 28.5; MS m/z 199 (Mϩ, 100). Anal.
Calcd for C12H9NS: C, 72.33; H, 4.55; N, 7.03; S, 16.09.
Found: C, 72.11; H, 4.58; N, 7.06; S, 16.05%].
The enones 2a–e were commercially available. 3-Azido-
benzo[b]thiophene was prepared according to a literature
method.12 Column chromatography was carried out on
Merck silica gel (0.063–0.200 mm particle size) by pro-
1
gressive elution with hexane–ethyl acetate mixtures. H
and 13C NMR spectra were normally carried out in CDCl3
solutions, using tetramethylsilane as the internal standard.
Massa spectra were obtained with a Hewlett-Packard 5971
mass-selective detector on a Hewlett-Packard 5890 gas
chromatograph [OV-1 capillary column between 70–
250ЊC (20ЊC minϪ1)].
4-Methylbenzo[b]thieno[3,2-b]pyridine (4a).13 Thick oil
[1H NMR (300 MHz) d 8.64 (d, 1H, Jˆ5.6 Hz), 8.52–
8.44 (m, 1H), 7.92–7.82 (m, 1H), 7.61–7.50 (m, 2H), 7.20
(d, 1H, Jˆ5.6 Hz), 2.61 (s, 3H); 13C NMR (75 MHz) d
146.8, 143.9, 141.3, 136.2, 134.8, 132.0, 128.4, 125.0,
123.2, 122.9, 121.5, 30.1; MS m/z 199 (Mϩ, 100). Anal.
Calcd for C12H9NS: C, 72.33; H, 4.55; N, 7.03; S, 16.09.
Found: C, 72.21; H, 4.55; N, 7.11; S, 16.15%].
The methylphosphoranes 1b–d were prepared from
3-azidobenzothiophene (350 mg, 2 mmol) and the appro-
priate phosphine (2 mmol) by following the same procedure
as previously described for the triphenyl analogue 1a.2
Chromatographic purification gave N-(3-benzo[b]thienyl)-
methyldiphenylphosphorane (1b) (555 mg, 80%) as an
orange solid, mp 105–107ЊC [1H NMR (300 MHz) d
8.18–8.10 (m, 1H), 7.92–7.81 (m, 5H), 7.78–7.70 (m,
1H), 7.60–7.48 (m, 5H), 7.40–7.27 (m, 2H), 5.64 (s, 1H),
2-Methyl-4-phenylbenzo[b]thieno[3,2-b]pyridine (3b).
Yellow solid, mp 75–78ЊC [1H NMR (300 MHz) d 8.62–
8.52 (m, 1H), 7.89–7.74 (m, 3H), 7.68–7.48 (m, 5H), 7.35
(s, 1H), 2.85 (s, 3H); 13C NMR (75 MHz) d 156.0, 144.1,
143.1, 139.0, 137.5, 131.5, 129.1, 128.5, 128.1, 127.5,
127.3, 127.0, 126.8, 122.5, 121.0, 31.1; MS m/z 275 (Mϩ,
100). Anal. Calcd for C18H13NS: C, 78.51; H, 4.76; N, 5.09;
S, 11.64. Found: C, 78.48, H, 4.81; N, 5.03; S, 11.70%].
2
2.20 (d, 3H, JPHˆ15.8 Hz); IR (Nujol) nmax 1520, 1340,
1250, 970, 880 cmϪ1. Anal. Calcd for C21H18NPS: C,
72.60; H, 5.22; N, 4.03; S, 9.23. Found: C, 72.32; H, 5.20;
N, 4.10; S, 9.13%].
4-Methyl-2-phenylbenzo[b]thieno[3,2-b]pyridine (4b).
Yellow solid, mp 82–85ЊC [1H NMR (300 MHz) d 8.62–
8.55 (m, 1H), 7.92–7.85 (m, 1H), 7.67 (s, 1H), 7.65–7.40
(m, 7H), 2.69 (s, 3H); 13C NMR (75 MHz) d 154.9, 152.9,
141.8, 139.9, 134.8, 131.0, 130.6, 129.0, 128.5, 128.3,
128.1, 126.9, 124.0, 123.3, 122.7, 118.7, 118.6, 29.3; MS
m/z 275 (Mϩ, 100). Anal. Calcd for C18H13NS requires C,
78.51; H, 4.76; N, 5.09; S, 11.64. Found: C, 78.55; H, 4.78;
N, 5.13; S, 11.68].
Chromatographic purification gave N-(3-benzo[b]thienyl)-
dimethylphenylphosphorane (1c) (445 mg, 78%) as an
orange solid, mp 145–147ЊC [1H NMR (300 MHz) d
8.04–7.98 (m, 1H), 7.76–7.70 (m, 1H), 7.60–7.48 (m, 5H),
7.40–7.27 (m, 2H), 5.71 (s, 1H), 1.98 (d, 6H, 2JPHˆ 17.6 Hz);
IR (Nujol) nmax 1570, 1320, 1230, 970, 930, 880 cmϪ1. Anal.
Calcd for C16H16NPS: C, 67.35; H, 5.65; N, 4.91; S, 11.24.
Found: C, 67.30; H, 5.67; N, 4.98; S, 11.18%].
The crude N-(3-benzo[b]thienyl)trimethylphosphorane (1d)
(334 mg, 75%) was obtained as a viscous oil which showed
a tendency to decompose under work-up conditions and was
thence directly employed without purification [1H NMR
(300 MHz) d.7.90–7.86 (m, 1H), 7.28–7.22 (m, 1H),
7.40–7.27 (m, 2H), 6.08 (s, 1H), 1.71 (d, 6H,
Methyl 2-methylbenzo[b]thieno[3,2-b]pyridine-4-carboxyl-
ate (3c). Yellow solid, mp 120–122ЊC [1H NMR (300 MHz)
d 8.54–8.48 (m, 1H), 7.94–7.88 (m, 1H), 7.86 (s, 1H),
7.62–7.5 (m, 2H), 4.09 (s, 3H), 2.84 (s, 3H); 13C NMR
(75 MHz) 166.0, 156.1, 154.0, 141.5, 134.5, 131.5, 131.0,
129.1, 125.0, 122.0, 121.5, 120.5, 53.1, 29.0; MS m/z 257
(Mϩ, 100). Anal. Calcd for C14H11NO2S: C, 65.35; H, 4.31;
N, 5.44; S, 12.46. Found: C, 65.30; H, 4.38; N, 5.42; S,
12.55%].
2
2JPHˆ13 Hz), 1.54 (d, 3H, JPHˆ15 Hz)].
Thermal reactions of the phosphoranes 1a–d with the
enones 2a–e.
Methyl 4-methylbenzo[b]thieno[3,2-b]pyridine-2-carboxyl-
ate (4c). Bright yellow solid, mp 105–107ЊC [1H NMR
(300 MHz) d 8.58–8.51 (m, 1H), 8.09 (s, 1H), 7.94–7.86
(m, 1H), 7.76–7.51 (m, 2H), 4.09 (s, 3H), 2.68 (s, 3H); 13C
General procedure. A mixture of the appropriate imino-
phosphorane 1 (0.12 mmol) and enone 2 (0.12 mmol) in dry
toluene (3 ml) was stirred at 70ЊC for 16–24 h, after which

C. Bonini et al. / Tetrahedron 56 (2000) 1517–1521
1521
1090; Levacher, V.; Boussad, N.; Dupas, G.; Bourgoignon, J.
Tetrahedron 1992, 48, 831–840.
NMR (75 MHz) d 167.0, 152.0, 146.1, 143.1, 135.0, 131.0,
129.1, 128.5, 125.1, 124.0, 122.6, 122.1, 53.0, 29.0; MS m/z
257 (Mϩ, 100). Anal. Calcd for C14H11NO2S: C, 65.35; H,
4.31; N, 5.44; S, 12.46. Found: C, 65.38; H, 4.35; N, 5.43; S,
12.48%].
5. N-Vinyliminophosphoranes are found to react at the b-vinylic
carbon with compounds bearing two electrophilic centres such as
a-bromo ketones and a,b-unsaturated aldehydes and ketones (cf.
Nitta, M. Reviews on Heteroatom Chemistry; Oae, S. Ed.; MYU:
Tokyo, 1993, vol 9, 87). However, certain (alkoxycarbonyl)vinyl
derivatives are reported to undergo a normal aza Wittig reaction
with saturated or unsaturated aldehydes (cf. Barluenga, J.; Ferrero,
M.; Palacios, F. J. Chem. Soc., Perkin Trans. 1 1990, 2193–2196;
Molina, P.; Pastor, A.; Vilaplana, M. J. Tetrahedron 1993, 49,
7769–7778; Palacios, F.; Perez de Heredia, I.; Rubiales, G.
J. Org. Chem. 1995, 60, 2384–2390).
6. Kobayashi, T.; Nitta, M. Chem. Lett. 1986, 1549–1552; Iino,
Y.; Nitta, M. Bull. Chem. Soc. Jpn. 1988, 61, 2235–2237; Nitta,
M.; Ohnuma, M.; Iino, Y. J. Chem. Soc., Perkin Trans. 1 1991,
1115–1118; Nitta, M.; Iino, Y. J. Chem. Soc., Perkin Trans. 1
1990, 435–439.
4-Phenylbenzo[b]thieno[3,2-b]pyridine (3d).14 Yellow
solid, mp 73–75ЊC [1H NMR (300 MHz) d 8.84 (d, 1H,
Jˆ6.0 Hz), 8.58–8.53 (m, 1H), 7.90–7.87 (m, 1H), 7.83–
7.79 (m, 2H), 7.62–7.54 (m, 5H), 7.45 (d, 1H, Jˆ6.0 Hz);
13C NMR (75 MHz) d 147.5, 144.5, 140.2, 139.2, 138.7,
137.0, 134.5, 129.6, 129.3, 128.5, 128.1, 125.4, 125.2,
123.2, 122.5, 121.0; MS m/z 261 (Mϩ, 100). Anal. Calcd
for C17H11NS: C, 78.13; H, 4.24; N, 5.36; S, 12.27. Found:
C, 78.20; H, 4.26; N, 5.29; S, 12.25%].
2-Phenylbenzo[b]thieno[3,2-b]pyridine (4d). Pale yellow
solid, mp 85–87ЊC [1H NMR (300 MHz) d 8.66–8.61 (m,
1H), 8.25–8.18 (m, 3H), 7.94–7.82 (m, 2H), 7.62–7.42 (m,
5H); 13C NMR (75 MHz) d 153.8, 152.7, 140.5, 139.8,
134.9, 132.3, 130.9, 129.0, 128.8, 128.4, 128.0, 127.1,
124.9, 123.3, 123.1, 122.9, 118.1; MS m/z 261 (Mϩ, 100).
Anal. Calcd for C17H11NS: C, 78.13; H, 4.24; N, 5.36; S,
12.27. Found: C, 78.26; H, 4.28; N, 5.32; S, 12.35%].
7. Molina, P.; Pastor, A.; Vilaplana, M. J. J. Org. Chem. 1996, 61,
8094–8098.
8. (a) Klemm, L. H.; McCoy, D. R.; Klopfenstein, C. E. J. Hetero-
cycl. Chem. 1971, 8, 383–389. (b) Abramovitch, R. A.;
Inbasekaran, M. N.; Miller, A. L.; Hanna, M. J. J. Heterocycl.
Chem. 1982, 19, 509–512. (c) Klyuev, N. A.; Khmel’nitskii,
R. A.; Krymskii, Ya.Ya.; Abramenko, P. I.; Zhiryakov, V. G.
Tezisy Dokl.-Simp. Khim. Tekhnol. Geterotsikl. Soedin. Goryuch.
Iskop., 2nd 1973, 182–183 (Chem. Abstr. 1977, 86, 42623m). (d)
Abramenko, P. I. Khim. Geterotsikl. Soedin. 1971, 7, 468–470
(Chem. Abstr. 1972, 76, 25128e).
9. For a recent method to b-fused pyridines using five-membered
heteroaromatic o-aminothioaldehydes see: Degl’Innocenti, A.;
Funicello, M.; Scafato, P.; Spagnolo, P. Tetrahedron Lett. 1997,
38, 2171–2174.
Acknowledgements
Financial support from the University of Bologna and the
University of Basilicata as well as from MURST (COFIN.
98) is gratefully acknowledged.
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11. Davies, D.; Spagnolo, P.; Zanirato, P. J. Chem. Soc., Perkin
Trans. 1 1995, 613–614; Spagnolo, P.; Zanirato, P. J. Chem. Soc.,
Perkin Trans. 1 1996, 963–964 and references cited therein.
12. Spagnolo, P.; Zanirato, P. J. Org. Chem. 1978, 43, 3539.
13. The methylated benzothienopyridines 3a and 4a had been
previously reported, but the analytical data were not available
(cf. Refs. 8c,d and 2).
1. For leading reviews on the chemistry of iminophosphoranes and
their application in synthesis see: (a) Wamhoff, H.; Richard, G.;
Stolben, S. Adv. Heterocycl. Chem. 1995, 64, 159–249. (b) Molina,
P.; Vilaplana, M. J. Synthesis 1994, 1197–1218.
2. Degl’Innocenti, A.; Funicello, M.; Scafato, P.; Spagnolo, P.;
Zanirato, P. J. Chem. Soc., Perkin Trans. 1 1996, 2561–2563
and references cited therein.
3. Roques, B. P.; Prange, T.; Oberlin, R. Org. Magn. Reson. 1977,
9, 185–192.
4. Benoit, R.; Dupas, G.; Bourgoignon, J.; Queguiner, G. Synthesis
1987, 1124–1127; Cazin, J.; Trepouel, G.; Dupas, G.;
Bourgoignon, J.; Queguiner, G. Tetrahedron 1988, 44, 1079–
14. The benzothienopyridine 3d had been previously prepared, but
no analytical data had been provided (Ref. 2).