From β-nitrothiophenes to ring-fused nitrobenzenes: An overall ring-enlargement process via a facile, aromatization-driven, thermal 6π electrocyclization

Article abstract of DOI:10.1021/jo051059x

In prosecution of previous work on the thermal cyclization of 1-aryl-4-methanesulfonyl-2-nitro-3-phenylsulfonyl-1,3-butadienes (7), the 3-unsubstituted derivatives 8, deriving from the initial ring opening of 3-nitrothiophene (2), have been likewise found herein to undergo cyclization, followed by aromatization, in analogous mild experimental conditions, leading to the ring-fused homo- or heteroaromatic nitro derivatives 10. The concerted electrocyclic nature of the process is strongly supported by the outcome of tests based on the variation of the polarity of the solvent or of the electron density on the aryl of 8. Thus, the successful application of the process to the non-phenylsulfonyl-activated 8 significantly widens the scope of a synthetically valuable overall ring-opening/ring-closing procedure from nitrothiophenes. Support to the recently renewed interest in thermal 6π electrocyclizations as a tool for the construction of the benzene ring is furthermore provided.

Full text of DOI:10.1021/jo051059x

From â-Nitrothiophenes to Ring-Fused Nitrobenzenes: An Overall
Ring-Enlargement Process via a Facile, Aromatization-Driven,
Thermal 6π Electrocyclization1
Lara Bianchi,† Carlo Dell’Erba,† Massimo Maccagno,† Giovanni Petrillo,*,† Egon Rizzato,‡
Fernando Sancassan,† Elda Severi,† and Cinzia Tavani†
Dipartimento di Chimica e Chimica Industriale, Universita` di Genova, Via Dodecaneso 31,
I-16146 Genova, Italy, and Dipartimento di Chimica Organica “A. Mangini”,
Universita` di Bologna, Via San Giacomo 11, I-40126 Bologna, Italy
petrillo@chimica.unige.it
Received May 27, 2005
In prosecution of previous work on the thermal cyclization of 1-aryl-4-methanesulfonyl-2-nitro-3-
phenylsulfonyl-1,3-butadienes (7), the 3-unsubstituted derivatives 8, deriving from the initial ring
opening of 3-nitrothiophene (2), have been likewise found herein to undergo cyclization, followed
by aromatization, in analogous mild experimental conditions, leading to the ring-fused homo- or
heteroaromatic nitro derivatives 10. The concerted electrocyclic nature of the process is strongly
supported by the outcome of tests based on the variation of the polarity of the solvent or of the
electron density on the aryl of 8. Thus, the successful application of the process to the
non-phenylsulfonyl-activated 8 significantly widens the scope of a synthetically valuable overall
ring-opening/ring-closing procedure from nitrothiophenes. Support to the recently renewed interest
in thermal 6π electrocyclizations as a tool for the construction of the benzene ring is furthermore
provided.
Introduction
thermal 6π electrocyclization has reportedly3 received
little attention as far as its potentialities in organic
synthesis are concerned. More recently, though, the
interest in the thermal electrocyclization of conjugated
trienes for the construction of the benzene ring has found,
in particular, renewed strength: this is due to the
possibility to exploit the presence of a suitable leaving
group (Y) capable of driving the reaction toward aroma-
tization after cyclization of the triene to a cyclohexadiene
intermediate (Scheme 1).4
As compared to the photochemical counterpart,2 not-
withstanding an undeniable theoretical significance the
* Corresponding author. Phone: +39-10-353-6121. Fax: +39-10-
353-6118.
† Universita` di Genova.
‡ Universita` di Bologna.
(1) Synthetic Exploitation of the Ring-Opening of Nitrothiophenes,
Part XVII. For part XVI, see ref 5a.
(2) For the photochemical cyclization of stilbenes to phenanthrenes
see: Lewis, F. D.; Kurth, T. L.; Kalgutkar, R. S. Chem. Commun. 2001,
1372-1373. Mallory, F. B.; Mallory, C. W. In Organic Reactions; John
Wiley & Sons: New York, 1984. Doyle, T. D.; Benson, W. R.; Filipescu,
N. J. Am. Chem. Soc. 1976, 98, 3262-3267. Liu, L.; Yang, B.; Katz, T.
J.; Poindexter, M. K. J. Org. Chem. 1991, 56, 3769-3775. Rodier, J.-
M.; Myers, A. B. J. Am. Chem. Soc. 1993, 115, 10791-10795. Caldwell,
R. A.; Mizuno, K.; Hansen, P. E.; Vo, L. P.; Frentrup, M.; Ho, C. D. J.
Am. Chem. Soc. 1981, 103, 7263-7269. Laarhoven, W. H. Pure Appl.
Chem. 1984, 56, 1225. Mallory, F. B.; Mallory, C. W. Org. React. 1984,
30, 1. Floyd, A. J.; Dyke, S. F.; Ward, S. E. Chem. Rev. 1976, 76, 509.
For the photochemical heterostilbene to heterophenanthrene cycliza-
tion see: Lewis, F. D.; Kalgutkar, R. S.; Yang, J.-S. J. Am. Chem. Soc.
2001, 123, 3878-3884. Irie, M. Chem. Rev. 2000, 100, 1685-1716.
Rawal, V. H.; Jones, R. J.; Cava, M. P. Tetrahedron Lett. 1985, 26,
2423-2426.
In this line, within a long-standing research project on
the synthetic exploitation of the versatile butadiene
building-blocks deriving from the ring-opening of ni-
(3) Okamura, W. H.; De Lera, A. R. In Comprehensive Organic
Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon: New York, 1991;
Vol. 5, pp 699-750.
(4) (a) Ogura, K.; Takeda, M.; Xie, J. R.; Akazome, M.; Matsumoto,
S. Tetrahedron Lett. 2001, 42, 1923-1925. (b) Guner, V. A.; Houk, K.
N.; Davies, I. W. J. Org. Chem. 2004, 69, 8024-8028. (c) Davies, I.
W.; Marcoux, J. F.; Kuete, T. F.; Lankshear, M. D.; Taylor, J. D. O.;
Tsou, N.; Dormer, P. G.; Hughes, D. L.; Houk, K. N.; Guner, V. J. Org.
Chem. 2004, 69, 1298-1308. (d) de Koning, C. B.; Rousseau, A. L.;
van Otterlo, W. A. L. Tetrahedron 2003, 59, 7-36 and references
therein.
10.1021/jo051059x CCC: $30.25 © 2005 American Chemical Society
Published on Web 09/30/2005
8734
J. Org. Chem. 2005, 70, 8734-8738

A Facile Thermal 6π Electrocyclization
SCHEME 1
On these grounds we have extended our methodology
to 8, characterized by a less activated side chain, to verify
the feasibility of the cyclization/aromatization process
also in less favorable electronic conditions.4b,8 We have
also run suitable tests to support the electrocyclic,
nonionic nature of the process. Such goals would defi-
nitely contribute to assign to thermal 6π electrocycliza-
tions a more significant role in the panorama of the
synthetic methodologies available for the construction of
aromatic rings.
trothiophenes with secondary amines,5 we have recently
reported5b an appealing access to ring-fused homo- and
heteroaromatic derivatives (9) from 3-nitro-4-(phenyl-
sulfonyl)thiophene (1) (Scheme 2). The final 7 to 9 ring-
closure step in the scheme has been interpreted as a 6π
electrocyclization followed by methanesulfinic acid elimi-
nation from the nonisolated intermediate 11 (X ) PhSO2)
(Scheme 3). The experimental conditions for the cycliza-
tion/aromatization step appear surprisingly mild for a
process involving the initial loss of aromaticity of the Ar
moiety.6 Such a mildness has been justified on the
grounds (a) of a proper spatial arrangement of 7 [to which
the (1E,3E) configuration5b allows the attainment of the
s-cis conformation necessary for cyclization]4b and/or (b)
of the cis relation between SO2Me and the bridgehead H
atom in 11 (X ) PhSO2),7 suitable for a concerted syn
â-elimination of MeSO2H. The latter process effectively
drives the system to the final product with aromatization
of the condensed polycycle.
Results and Discussion
Compounds 8 have been prepared starting from 3-ni-
trothiophene (2) following a procedure similar to that
already described for the synthesis of derivatives 7 from
3-nitro-4-(phenylsulfonyl)thiophene (1). The yields of 8
and of the methylthio precursors 6 [Scheme 2, steps c
and b, respectively] are reported in Table 1,10 together
with the experimental details relevant to the thermal
treatment of 8 in the same conditions previously reported
for the phenylsulfonyl derivatives 7.5b In the last column
of the table, yields and reaction times for the cyclization
of the latter compounds5b are also reported, for compari-
son sake.
The nitrobutadienes 8a-i actually undergo, much as
the phenylsulfonyl-activated counterparts 7, a thermal
intramolecular cyclization to yield benzocondensed homo-
or heteroaromatic systems (Chart 1) as a consequence of
the neat loss of methanesulfinic acid. The data in Table
1 bring to evidence that the reaction on 8 is generally
characterized by appreciably longer times and/or sizably
lower yields of isolated products. Some degradation at
the experimental temperature is partly responsible for
the latter result, as can be deduced when confronting the
final yields with those based on the consumed substrate
after quenching before completion in some representative
cases (namely 8a, 8d, and 8f: cf. footnotes g, j, and m of
Table 1, respectively). Nonetheless, even if some time-
dependent yield reduction of 5b is allowed for, the overall
comparison between the 7 to 9 and the 8 to 10 transfor-
mations definitely enlightens a significant favorable
effect played by the PhSO2 group in the cyclization of 7.
Although such an outcome is well in line with the cited
recent reports4b,8 on the role played by electron-with-
drawing groups on thermal electrocyclizations, the onset
of sizable electronic effects could cast some doubts on the
real pericyclic nature of the cyclization step in favor of
the participation of some ionic component. Actually, an
electrophilic-aromatic-substitution component has al-
ready been proposed,11 and recently reaffirmed to justify
the effect of substituents on the phenyl ring, within the
thermal cyclization/aromatization process on sulfonyl-
activated phenylbutadienes in MeCN in the presence of
iodine.9 Furthermore, as already pointed out,5b an aspect
of our system that is surely intriguing is represented by
the mildness of the experimental conditions (reflux in
Very recent reports have enlightened (both on experi-
mental8 and on computational grounds4b) the favorable
role played by electron-withdrawing groups (such as the
phenylsulfonyl group) on the hexatriene chain in lowering
the activation-energy barrier for the hexatriene to cyclo-
hexadiene thermal electrocyclization. On the other hand,
in the thermal cyclization/aromatization of sulfonyl-
activated phenylbutadienes in MeCN in the presence of
iodine,9 the occurrence of an electrocyclic process has been
recently questioned in favor of a more classical electro-
philic substitution pathway of ionic character.
(5) (a) Bianchi, L.; Dell’Erba, C.; Maccagno, M.; Morganti, S.; Novi,
M.; Petrillo, G.; Rizzato, E.; Sancassan, F.; Severi, E.; Spinelli, D.;
Tavani, C. Tetrahedron 2004, 60, 4967-4973. (b) Bianchi, L.; Dell’Erba,
C.; Maccagno, M.; Mugnoli, A.; Novi, M.; Petrillo, G.; Sancassan, F.;
Tavani, C. J. Org. Chem. 2003, 68, 5254-5260. (c) Bianchi, L.;
Dell’Erba, C.; Gasparrini, F.; Novi, M.; Petrillo, G.; Sancassan, F.;
Tavani, C. Arkivoc 2002, 142-158. (d) Bianchi, L.; Dell’Erba, C.;
Gabellini, A.; Novi, M.; Petrillo, G.; Tavani, C. Tetrahedron 2002, 58,
3379-3385. (e) Armaroli, T.; Dell’Erba, C.; Gabellini, A.; Gasparrini,
F.; Mugnoli, A.; Novi, M.; Petrillo, G.; Tavani, C. Eur. J. Org. Chem.
2002, 1284-1291, and previous papers in the series. For a survey of
relevant earlier literature see: (f) Spinelli, D.; Consiglio, G.; Dell’Erba,
C.; Novi, M. In The Chemistry of Heterocyclic Compounds, Thiophene
and its Derivatives; Gronowitz, S., Ed.; J. Wiley: New York, 1991; Vol.
44, pp 295-396. (g) Dell’Erba, C.; Novi, M.; Petrillo, G.; Tavani, C. In
Topics in Heterocyclic Systems: Synthesis, Reactions and Properties;
Attanasi, O. A., Spinelli, D., Eds.; Research Signpost: Trivandrum,
India, 1996; Vol. 1, pp 1-12. (h) Consiglio, G.; Spinelli, D.; Dell’Erba,
C.; Novi, M.; Petrillo, G. Gazz. Chim. Ital. 1997, 127, 753-769.
(6) (a) Kajikawa, S.; Nishino, H.; Kurosawa, K. Tetrahedron Lett.
2001, 42, 3351-3354. (b) Valkovich, P. B.; Conger, J. L.; Castiello, F.
A.; Brodie, T. B.; Weber, W. P. J. Am. Chem. Soc. 1975, 97, 901-902.
(c) Banciu, M. D.; Brown, R. F. C.; Coulston, K. J.; Eastwood, F. W.;
Macrae, T. Aust. J. Chem. 1998, 51, 695-701. (d) Padwa, A.; Caruso,
T.; Nahm, S.; Rodriguez, A. J. Am. Chem. Soc. 1982, 104, 2865-2871.
(e) Olsen, R. J.; Minniear, J. C.; Mack Overton, W.; Sherrick, J. M. J.
Org. Chem. 1991, 56, 989-991. (f) de Koning, C. B.; Rousseau, A. L.;
van Otterlo, W. A. L. Tetrahedron 2003, 59, 7-36 and references
therein.
(10) (a) The ring-opening of 3-nitrothiophene with pyrrolidine/
AgNO3 in EtOH, followed by S-methylation with MeI has been reported
elsewhere.10b (b) Dell’Erba, C.; Gabellini, A.; Novi, M.; Petrillo, G.;
Tavani, C.; Cosimelli, B.; Spinelli, D. Tetrahedron 2001, 57, 8159-
8165.
(11) Harding, K. E.; Tiner, T. H. In Comprehensive Organic Syn-
thesis; Trost, B. M., Fleming, I., Eds.; Pergamon: Oxford, UK, 1991;
Vol. 3, pp 363-421.
(7) Woodward, R. B.; Hoffman, R. The Conservation of Orbital
Symmetry; Academic Press: New York, 1970.
(8) Magomedov, N. A.; Ruggiero, P. L.; Tang, Y. J. Am. Chem. Soc.
2004, 126, 1624-1625.
(9) Matsumoto, S.; Takahashi, S.; Ogura, K. Heteroatom Chem.
2001, 12, 385-391.
J. Org. Chem, Vol. 70, No. 22, 2005 8735

Bianchi et al.
SCHEME 2
SCHEME 3
TABLE 1. Experimental Details for Steps b, c, and d of Scheme 2 for X ) Hn
10a,d
9d,f
Ar
6a,b
8a,c
(reaction time)e
(reaction time)
Ph
6a: 90%
6b: 95%
6c: 88%
6d: 98%
6e: 87%
6f: 91%
6g: 89%
6h: 76%
6i: 78%
8a: 92%
8b: 94%
8c: 93%
8d: 98%
8e: 96%
8f: 98%
8g: 98%
8h: 92%
8i: 93%
10a: 86% (96 h)g
10b: 90% (80 h)
10c-10c′: 79% (90 h)h
10d: 84% (90 h)j
10e-10e′: 92% (90h)l
10f: 77% (3.5 h)m
10g: 75% (1 h)
9a: 96% (48 h)
2-MeC6H4
3-MeC6H4
4-MeC6H4
3-MeOC6H4
1-naphthyl
2-naphthyl
2-thienyl
9b: 98% (24 h)
9c-9c′: 93% (17 h)i
9d: 98% (24 h)k
9f: 88% (1.5 h)
9g: 98% (1 h)
9h: 90% (20 h)
9i: 98% (16 h)
10h: 90% (20 h)
10i: 72% (20 h)
3-thienyl
a Isolated yields. b [4]: ca. 0.08 M in THF. ArMgBr: 1.1 mol equiv; 0 °C; H3O+ quenching. c [6]: 0.07 M in CH2Cl2. m-Chloroperbenzoic
d
e
acid: 2 mol equiv; rt. [Substrate]: 5 × 10-3 M in dry p-xylene; reflux. Reaction driven to completion and followed by monitoring
(TLC) the disappearance of substrate. The reported times should be regarded as only indicative. f Data from ref 5b. g The yield is 72%
after 48 h (88% on the reacted substrate). h Mixture of isomeric 10c and 10c′ in a 57/43 molar ratio (1H NMR analysis), from which only
10c could be separated in pure form. i Mixture of isomeric 9c and 9c′ in a 66/34 molar ratio (1H NMR analysis).5b j The yield is 73% after
70 h (90% on the reacted substrate). k Optimized conditions and final-point detection with respect to the previous report (ref 5b). l Mixture
of isomeric 10e and 10e′ in a 81/19 molar ratio (1H NMR analysis). m The yield is 67% after 1.5 h (83% on the reacted substrate). n The
results for the cyclization/aromatization of compounds 75b are also reported in the last column for comparison sake.
p-xylene) necessary to perform the cyclization on com-
pounds 7 or 8 as compared to typical literature examples
where electron couples of an aromatic sextet are similarly
involved in an electrocyclization.2,6 For instance, the
thermal benzocyclization of 1-aryl-1,3-butadienes until
recently has been reported to occur in much harsher
conditions such as flash vacuum pyrolysis,6b-d otherwise
acidic catalysis6a or photostimulation6e can be employed.
On these grounds, the successful extension of the process
to compounds 8, i.e. in the absence of the activating
PhSO2 group, under the same mild conditions applied to
7 seems even more surprising and therefore deserving
of some kind of confirmation for the occurrence of a
concerted pericyclic mechanism.
polarity and/or the introduction in the aromatic moiety
of groups characterized by strong electronic effects, to
cause appreciable variations in the electron density on
the aromatic ring itself.
Parallel tests have been carried out on 8a at reflux in
benzene and in acetonitrile, i.e., in two solvents with very
similar boiling points (80 and 81 °C, respectively) but
with completely different physical properties (benzene:
ETN 0.111, Aj 0.15, Bj 0.59, ꢀr 2.27; acetonitrile: ETN 0.460,
Aj 0.37, Bj 0.86, ꢀr 35.94).12 In a first experiment the
reaction mixtures have been refluxed for the time (96 h)
necessary to guarantee completion of the reaction in
p-xylene (see Table 1), observing a conversion (deter-
Clues on the intervention of ionic pathways can pos-
sibly be traced by means of the use of solvents of different
(12) Reichardt, C. Solvents and Solvent Effects in Organic Chemistry,
3rd ed.; Wiley-VCH: Weinheim, Germany, 2003.
8736 J. Org. Chem., Vol. 70, No. 22, 2005

A Facile Thermal 6π Electrocyclization
CHART 1
mined by 1H NMR) of approximately 4 ( 1% and 8 ( 1%
in benzene and in acetonitrile, respectively. The 4%
conversion in the former solvent, compared to the 100%
conversion in p-xylene after the same time, is perfectly
in line with the fact that benzene and p-xylene show
similar physical properties but very different boiling
points [∆(bp): 58 °C]. Interestingly, the reactivity dif-
ference between benzene and MeCN is significant but
seemingly not high enough to justify the involvement of
ionic intermediates. In a second experiment, where the
reaction time was prolonged to 19 days, 23% and 27% of
10a was isolated from the two solvents, with an overall
balance of 98% and 87% (23% and 31% of conversion),
respectively: thus, only a meagre, although sizable,
favorable effect played by the solvent polarity is definitely
reaffirmed on more sound quantitative grounds.
As far as the electronic effects on the aryl moiety of
the substrate are concerned, the completion of the
cyclization/aromatization process on 8e, which contains
the strongly electron-donating methoxy group, required
4 days, leading to an overall 92% yield of 10e and 10e′
(see Table 1). These results are closely comparable with
those for either the parent phenyl derivative 8a or the
3-methyl derivative 8c and thus definitely exclude any
significant concurrence of an aromatic electrophilic sub-
stitution pathway. For comparison sake, a 3-methoxy
group on the aromatic moiety has been shown to play a
strong (>15-fold) accelerative effect in the previously
cited cyclization of 1-aryl-1,3-butadienes in MeCN/I2, to
support the proposed ionic pathway.9
steric effect (likely due to the peri hindrance) that
conversely could not be observed in the case of the thienyl
derivatives h and i, for which different steric require-
ments are not expected.
Conclusions
Experimental tests devised to bring to evidence the
involvement of pathways of ionic nature for the intramo-
lecular cyclization step of the overall 8 to 10 transforma-
tion of Scheme 1 have altogether furnished an essentially
negative response. Thus, the results reported herein seem
to reasonably confirm the previously advanced5b 6π
electrocyclic nature of a process that reveals on the other
hand to be surprisingly facile most likely because of a
subsequent favorable aromatization via a concerted syn
â-elimination of methanesulfinic acid. The successful
extension of the process to the non-phenylsulfonyl-
activated compounds 8 is particularly interesting from
a synthetic point of view. As a matter of fact, the result
significantly widens the range of applicability of the
process and thus adds on to the recently renewed interest
in thermal electrocyclizations4,8 as a valuable tool in
homo- and heterocyclic synthesis. Actually, besides the
undoubtedly interesting mechanistic aspects, the system
herein is definitely endowed with the practical advantage
of providing a relatively mild access to variously func-
tionalized ring-fused homo- or heteroaromatic nitro
compounds which generally cannot be achieved other
than with rather long and tedious syntheses, often
characterized by very low overall yields.
As a matter of fact, rather than by the electronic
density on the Ar moiety of the substrate, the reaction
herein is clearly influenced by the aromaticity13 of the
homo- or heteroring that participates in the cyclization.
Thus, while for the phenyl compounds a-e the indicative
reaction times based on the disappearance of substrate
vary within very narrow ranges around mean values of
24 and 90 h for 7 and 8, respectively, the cyclization step
is sizably faster for the naphthyl or the thienyl deriva-
tives f-i; such a higher reactivity is coupled with a higher
similarity in the behavior between 7 and 8, although the
latter still led to somewhat lower yields.
The overall ring-opening/ring-closure process can also
be envisaged as a ring enlargement, which leads from
nitrothiophenes to ring-fused nitrobenzenes via extrusion
of the sulfur atom and uptake of two carbons from the
Ar moiety to build the final nitrobenzene ring.
Experimental Section
Reactions of 4 with Aromatic Organometallic Re-
agents. The reactions were typically performed on 0.5 g (2.33
mmol) of substrate, following the procedure previously re-
ported for the synthesis of 6d.10b Yields of compounds 6a-i
are collected in Table 1.
As a final comment, the reaction times relevant to the
derivatives f and g reveal the occurrence of a significant
(1E,3Z)-(4-Methylsulfanyl-2-nitrobuta-1,3-dien-1-yl)-
benzene (6a). Yellow solid, mp 85.7-86.8 °C (ethanol); νmax
1
(Nujol) 1630, 1570, 1309 cm-1; H NMR (CDCl3) δ 2.25 (3H,
(13) Bird, C. W. Tetrahedron 1992, 48, 335-340. Bean, P. G. J. Org.
Chem. 1998, 63, 2496-2506. Balaban, A. T.; Oniciu, D. C.; Katritzky,
A. R. Chem. Rev. 2004, 104, 2777-2812. Bird, C. W. Tetrahedron 1985,
41, 1409-1414.
s), 6.46 (1H, d, J ) 10.4 Hz), 6.61 (1H, d, J ) 10.4 Hz), 7.36-
7.45 (3H, m), 7.51-7.59 (2H, m), 8.05 (1H, s); 13C NMR (CDCl3)
δ 17.6, 114.3, 128.8, 130.6, 130.8, 131.4, 134.4, 139.0, 145.0.
J. Org. Chem, Vol. 70, No. 22, 2005 8737

Bianchi et al.
Anal. Calcd for C11H11NO2S (221.28): C, 59.71; H, 5.01; N,
6.33. Found: C, 59.82; H, 5.10; N, 6.19.
(1E,3Z)-1-(4-Methylsulfanyl-2-nitrobuta-1,3-dien-1-yl)-
naphthalene (6f). Yellow oil. νmax (neat) 3049, 2921, 1688,
Thermal Cyclization of Compounds 8 to 10.5b In a flask
the appropriate substrate (1 mmol) was dissolved in dry
p-xylene (200 mL) and the solution was refluxed until TLC
showed complete disappearance of the substrate (1-98 h). The
solvent was then evaporated under reduced pressure and the
residue purified by column chromatography and/or by crystal-
lization. Yields are reported in Table 1.
1630, 1572, 1513, 1460, 1433, 1399, 1319, 1245, 1004 cm-1
;
1H NMR (CDCl3) δ 1.95 (3H, s), 6.35 (1H, d, J ) 10.6 Hz),
6.45 (1H, d, J ) 10.6 Hz), 7.32-7.58 (4H, m), 7.72-7.87 (2H,
m), 7.92-8.02 (1H, m), 8.60 (1H, s); 13C NMR (CDCl3) δ 17.6,
113.7, 123.6, 125.04, 126.2, 126.9, 127.4, 128.5, 128.7, 130.8,
131.4, 131.6, 133.3, 138.2, 146.3. Anal. Calcd for C15H13NO2S
(271.33): C, 66.40; H, 4.83; N, 5.16. Found: C, 66.53; H, 4.89;
N, 5.11.
2-Methyl-7-nitronaphthalene (10c)14 and 1-Methyl-6-
nitronaphthalene (10c′).15 The crude product (0.148 g, 79%)
from the cyclization of 8c was a chromatographically unsepa-
rable mixture of 10c (0.084 g, 45%) and 10c′ (0.064 g, 34%)
(as deduced by 1H NMR). Compound 10c could be isolated by
crystallization as a pale yellow solid, mp 99.9-101.0 °C
(1E,3Z)-2-(4-Methylsulfanyl-2-nitrobuta-1,3-dien-1-yl)-
thiophene (6h). Orange solid, mp 49.1-50.0 °C (light petro-
leum/toluene); νmax (Nujol) 1617, 1575, 1414, 1291, 1251, 1073,
1052, 1024 cm-1; 1H NMR (CDCl3) δ 2.34 (3H, s), 6.32 (1H, d,
J ) 10.2 Hz), 6.75 (1H, d, J ) 10.2 Hz), 7.15 (1H, dd, J ) 5.1
and 3.6 Hz), 7.46 (1H, d, J ) 3.6 Hz), 7.62 (1H, d, J ) 5.1 Hz),
8.27 (1H, s); 13C NMR (CDCl3) δ 17.3, 113.9, 127.9, 128.4,
133.2, 134.3, 135.7, 141.5, 142.2. Anal. Calcd for C9H9NO2S2
(227.30): C, 47.56; H, 3.99; N, 6.16. Found: C, 47.78; H, 3.92;
N, 6.13.
Oxidation of Compounds 6 to 8. The reactions were
performed on 2 mmol of the appropriate substrate, according
to the conditions previously described.5b Relevant yields are
reported in Table 1.
1
(ethanol) [lit.14 mp 105 °C]; H NMR (CDCl3) δ 2.57 (3H, s),
7.53 (1H, d, J ) 8.4 Hz), 7.80 (1H, s), 7.85 (1H, d, J ) 8.4 Hz),
7.91 (1H, d, J ) 8.8 Hz), 8.17 (1H, dd, J ) 8.8 and 2.1 Hz),
1
8.72 (1H, d, J ) 2.1 Hz). H NMR signals of compounds 10c′
could be deduced by the mixture spectrum: 1H NMR (CDCl3)
δ 2.75 (3H, s), 7.51-7.56 (2H, m), 7.89 (1H, d, J ) 9.6 Hz),
8.11 (1H, d, J ) 9.4 Hz), 8.26 (1H, dd, J ) 9.4 and 2.4 Hz),
8.79 (1H, d, J ) 2.4 Hz).
2-Methoxy-7-nitronaphthalene (10e).16 Yellow solid (0.152
g, 75%), mp 111.5-111.8 °C (ethanol); νmax (Nujol) 1629, 1610,
1523, 1397, 1343, 1263, 1222, 1199, 1181, 1145, 1086, 1033
cm-1 1H NMR (CDCl3) δ 3.97 (3H, s), 7.29 (1H, d, J ) 2.6
;
(1E,3Z)-(4-Methanesulfonyl-2-nitrobuta-1,3-dien-1-yl)-
benzene (8a). Yellow solid, mp 146.6-147.8 °C (ethanol); νmax
(Nujol) 1657, 1596, 1516, 1327, 1311, 1299, 1212, 1192, 1157,
1139, 1048 cm-1; 1H NMR (CDCl3) δ 2.98 (3H, s), 6.78 (1H, d,
J ) 11.3 Hz), 6.95 (1H, dd, J ) 11.3 and 1.5 Hz), 7.45-7.53
(5H, m), 8.18 (1H, d, J ) 1.5 Hz); 13C NMR (CDCl3) δ 41.4,
129.2, 130.5, 130.6, 131.3, 131.8, 135.9, 137.7, 141.7. Anal.
Calcd for C11H11NO4S (253.27): C, 52.16; H, 4.38; N, 5.53.
Found: C, 52.09; H, 4.22; N, 5.63.
Hz), 7.34 (1H, dd, J ) 2.6 and 9.2 Hz), 7.84 (1H, d, J ) 9.2
Hz), 7.88 (1H, d, J ) 9.0 Hz), 8.10 (1H, dd, J ) 9.0 and 2.4
Hz), 8.70 (1H, d, J ) 2.4 Hz); 13C NMR (CDCl3) δ 55.5, 107.3,
117.1, 122.8, 123.2, 129.1, 129.4, 131.4, 133.5, 146.1, 159.0.
Anal. Calcd for C11H9NO3 (203.19): C, 65.02; H, 4.46; N, 6.89.
Found: C, 65.09; H, 4.41; N, 6.99.
Acknowledgment. Financial support was provided
by grants from the University of Genova and from
Ministero dell’Istruzione, dell’Universita` e della Ricerca
(MIUR, PRIN-2002).
(1E,3Z)-1-(4-Methanesulfonyl-2-nitrobuta-1,3-dien-1-
yl)naphthalene (8f). Yellow solid, mp 131.3-132.8 °C (toluene/
petroleum ether); νmax (Nujol) 1620, 1510, 1301, 1137 cm-1
;
1H NMR (CDCl3) δ 2.99 (3H, s), 6.67 (1H, d, J ) 11.4 Hz),
6.80 (1H, dd, J ) 11.4 and 1.8 Hz), 7.46-7.70 (4H, m), 7.87-
8.04 (3H, m), 8.86 (1H, s); 13C NMR (CDCl3) δ 41.3, 123.8,
125.2, 127.1, 127.7, 127.8, 129.0, 130.1, 130.4, 131.5, 132.3,
133.4, 135.3, 136.0, 143.8. Anal. Calcd for C15H13NO4S
(303.33): C, 59.39; H, 4.32; N, 4.62. Found: C, 59.28; H, 4.37;
N, 4.78.
Supporting Information Available: General experimen-
tal information and physical, microanalytical, and/or spectro-
scopic characterization of all the reported compounds. This
material is available free of charge via the Internet at
http://pubs.acs.org.
(1E,3Z)-2-(4-Methanesulfonyl-2-nitrobuta-1,3-dien-1-
yl)thiophene (8h). Yellow solid, mp 162.9-164.1 °C (ethanol);
νmax (Nujol) 1647, 1598, 1497, 1323, 1299, 1185, 1139, 1058
JO051059X
1
cm-1; H NMR (CDCl3) δ 3.02 (3H, s), 6.84 (1H, d, J ) 11.2
(14) Vesely´, V.; Pa´cˇ, J. Collect. Czech. Chem. Commun. 1937, 2, 471-
485; Chem. Abstr. 1930, 24, 5296.
Hz), 7.05 (1H, dd, J ) 11.2 and 1.5 Hz), 7.22 (1H, dd, J ) 5.0
and 3.8 Hz), 7.52 (1H, d, J ) 3.8 Hz), 7.74 (1H, d, J ) 5.0 Hz),
8.37 (1H, s); 13C NMR (CD3COCD3) δ 41.9, 129.6, 129.8, 130.2,
135.0, 135.6, 137.7, 138.9, 140.3. Anal. Calcd for C9H9NO4S2
(259.30): C, 41.69; H, 3.50; N, 5.40. Found: C, 41.87; H, 3.33;
N, 5.34.
(15) Vesely´, V.; Sˇtursa, F.; Olejn´icˇek H.; Rein, E. Collect. Czech.
Chem. Commun. 1936, 1, 493-515; Chem. Abstr. 1930, 24, 611.
(16) Lammers, J. G.; Cornelisse, J. Isr. J. Chem. 1977, 16, 299-
303. Lammers, J. G.; de Gunst, G. P.; Havinga, E. Recl. Trav. Chim.
Pays-Bas 1973, 92, 1386-1388. Beijersbergen van Henegouwen, G.
M. J.; Havinga, E. Recl. Trav. Chim. Pays-Bas 1970, 89, 907-912.
8738 J. Org. Chem., Vol. 70, No. 22, 2005