Thermal [2+2] cycloaddition of allenynes: Easy construction of bicyclo[6.2.0]deca-1,8-dienes, bicyclo[5.2.0]nona-1,7-dienes, and bicyclo[4.2.0]octa-1,6-dienes

Article abstract of DOI:10.1021/jo070513p

(Chemical Equation Presented) The simple refluxing of allenynes, having a phenylsulfonyl functionality on the allenyl group, in xylene (or mesitylene) without microwave irradiation resulted in the efficient formation of bicyclo[5.2.0]nona-1,7-dienes and b

Full text of DOI:10.1021/jo070513p

Thermal [2+2] Cycloaddition of Allenynes: Easy Construction of
Bicyclo[6.2.0]deca-1,8-dienes, Bicyclo[5.2.0]nona-1,7-dienes, and
Bicyclo[4.2.0]octa-1,6-dienes
Chisato Mukai,* Yasuyuki Hara, Yusuke Miyashita, and Fuyuhiko Inagaki
DiVision of Pharmaceutical Sciences, Graduate School of Natural Science and Technology, Kanazawa
UniVersity, Kakuma-machi, Kanazawa 920-1192, Japan
cmukai@kenroku.kanazawa-u.ac.jp
ReceiVed March 12, 2007
The simple refluxing of allenynes, having a phenylsulfonyl functionality on the allenyl group, in xylene
(or mesitylene) without microwave irradiation resulted in the efficient formation of bicyclo[5.2.0]nona-
1,7-dienes and bicyclo[4.2.0]octa-1,6-dienes in high yields. This method was shown to be successfully
applicable to the first construction of bicyclo[6.2.0]deca-1,8-dienes. Construction of the corresponding
oxa- and azabicyclo[m.2.0] frameworks could also be attained. This thermal ring-closing reaction involves
the formal [2+2] cycloaddition in which the distal double bond of an allenyl moiety exclusively served
as one of the π-components regardless of the position of the phenysulfonyl functionality on the allenyl
moiety.
Introduction
groups: Brummond and Chen1a reported the construction of the
bicyclo[5.2.0] derivative 2 from the allene-alkynone derivative
1, while two successful examples forming other types of bicyclo-
[5.2.0] derivatives 4 from the allene-propiolate derivatives 3
under similar conditions were described by Oh and co-workers.1b
They claimed that the transformation of 3 into 4 could not occur
under the stated conditions1b without microwave irradiation
(Scheme 1).
A novel method for the preparation of bicyclo[5.2.0]nona-
1,7-diene skeletons1 based on the intramolecular [2+2] cy-
cloaddition reaction of allenynes2,3 with use of microwave
irradiation has recently been independently developed by two
* To whom correspondence should be addressed. Phone: +81-76-234-4411.
Fax: +81-76-234-4410.
(1) (a) Brummond, K. M.; Chen, D. Org. Lett. 2005, 7, 3473-3475. (b)
Oh, C. H.; Gupta, A. K.; Park, D. I.; Kim, N. Chem. Commun. 2005, 5670-
5672. In both references, the preparation of bicyclo[4.2.0]octa-1,6-dienes
skeleton with microwave irradiation conditions was also reported.
(2) For the intramolecular thermal [2+2] cycloaddition of allenynes for
the construction of the bicyclo[3.2.0]hepta-1,5-diene skeleton without
microwave irradiation, see: (a) Gillmann, T.; Hu¨lsen, T.; Massa, W.;
Wocadlo, S. Synlett 1995, 1257-1259. (b) Cao, H.; Flippen-Anderson, J.;
Cook, J. M. J. Am. Chem. Soc. 2003, 125, 3230-3231. (c) Cao, H.; Van
Ornum, S. G.; Deschamps, J.; Flippen-Anderson, J.; Laib, F.; Cook, J. M.
J. Am. Chem. Soc. 2005, 127, 933-943.
(3) For the intramolecular thermal [2+2] cycloaddition of allenynes for
the construction of the bicyclo[4.2.0]octa-1,6-diene skeleton without
microwave irradiation, see: (a) Ikemoto, C.; Kawano, T.; Ueda, I.
Tetrahedron Lett. 1998, 39, 5053-5056. (b) Ohno, H.; Mizutani, T.; Kadoh,
Y.; Miyamura, K.; Tanaka, T. Angew. Chem., Int. Ed. 2005, 44, 5113-
5115.
On the other hand, during our studies on the scope and
limitations of the Rh(I)-catalyzed intramolecular Pauson-
Khand-type reaction of phenylsulfonylallenynes,4,5 compound
5a was exposed to a catalytic amount of [RhCl(CO)dppp]2 in
(4) For the Rh(I)-catalyzed Pauson-Khand reaction of phenylsulfonyl-
allenynes, see: (a) Mukai, C.; Nomura, I.; Yamanishi, K.; Hanaoka, M.
Org. Lett. 2002, 4, 1755-1758. (b) Mukai, C.; Nomura, I.; Kitagaki, S. J.
Org. Chem. 2003, 68, 1376-1385. (c) Mukai, C.; Inagaki, F.; Yoshida, T.;
Kitagaki, S. Tetrahedron Lett. 2004, 45, 4117-4121. (d) Mukai, C.; Inagaki,
F.; Yoshida, T.; Yoshitani, K.; Hara, Y.; Kitagaki, S. J. Org. Chem. 2005,
70, 7159-7171. (e) Mukai, C.; Hirose, T.; Teramoto, S.; Kitagaki, S.
Tetrahedron 2005, 61, 10983-10994.
(5) For the Rh(I)-catalyzed Pauson-Khand reaction of phenylsulfonyl-
allenenes, see: Inagaki, F.; Mukai, C. Org. Lett. 2006, 8, 1217-1220.
10.1021/jo070513p CCC: $37.00 © 2007 American Chemical Society
Published on Web 05/18/2007
4454
J. Org. Chem. 2007, 72, 4454-4461

Thermal [2+2] Cycloaddition of Allenynes
TABLE 1. Thermal [2+2] Cycloaddition of 5a
SCHEME 1
T
(°C)
t
yield
(%)
entry
solvent
(h)
Rh(I)-catalysta
1
2
3
toluene
toluene
xylene
80
reflux
reflux
40
25
2
none
none
none
23b
86
91
40c
46
SCHEME 2
4
5
toluene
xylene
100
reflux
20
1
[RhCl(CO)2]2
[RhCl(CO)2]2
a 2.5 mol % of Rh(I)-catalyst was used. b The starting material 5a was
recovered in 53% yield. c The starting material 5a was recovered in 38%
yield.
Results and Discussion
Our initial evaluation for the intramolecular [2+2] cycload-
dition of a phenylsulfonylallenyne 5a10 was carried out in
toluene at 80 °C in a nitrogen atmosphere instead of CO to
give 7a in 23% yield together with the recovery of the starting
material in 53% yield after a prolonged reaction time (Table 1,
entry 1). Refluxing of 5a in toluene for 25 h significantly
improved the chemical yield (86%) (entry 2). Changing the
solvent from toluene to xylene led to a shortening of the reaction
time and the highest yield (91%) (entry 3). When this cycload-
dition reaction was carried out in the presence of a rhodium
catalyst, significantly lower yields were observed (entries 4 and
5). These results indicated that the transformation of 5a into 7a
would mainly proceed via the thermal [2+2] cycloaddition rather
than the rhodium catalyst-mediated ring-closing reaction.11-13
We next investigated the scope of this thermal [2+2] ring-
closing reaction using several substrates 5b-f under xylene
refluxing conditions. These results are summarized in Table 2.
The allenynes 5b4d and 5c,10 having an oxygen atom on the
alkyl tether and a substituent at the alkyne terminus, consistently
produced the corresponding oxabicyclic compounds 7b and 7c
in reasonable yields, although prolonged reaction times, com-
pared to that of 5a (2 h), were required (entries 1 and 2). When
compound 5d,4d which has a terminal alkyne group, was exposed
to the standard conditions, no formation of the oxabicyclo[5.2.0]
derivative could be detected and the gradual decomposition of
the starting material was observed (entry 3). Both the aza- and
carbon-congeners 5e4d and 5f10 are also susceptible to this ring-
closing reaction that produced the corresponding 5-azabicyclo-
[5.2.0]nona- and bicyclo[5.2.0]nona-1,7-dienes 7e,f in high
yields (entries 4 and 5). On the basis of the results in Tables 1
and 2, it might be concluded that the thermal [2+2] cycload-
dition of 3-phenylsulfonyl-9-substituted-1,2-nonadien-8-yne and
its congeners possessing a heteroatom on the alkyl appendage
refluxing toluene under an atmosphere of CO (optimized
conditions4 for Rh(I)-catalyzed Pauson-Khand-type reaction of
other allenynes) that produced the Pauson-Khand product 6a
in 46% yield along with the unexpected 5-oxabicyclo[5.2.0]-
nona-1,7-diene derivative 7a in 27% yield as a byproduct.6
Compound 7a became a major product (44%) when [RhCl-
6
(CO)2]2 was used instead of [RhCl(CO)dppp]2 (Scheme 2).
Thus, the formation of the oxabicyclo[5.2.0]nona-1,7-diene
skeleton 7a by the simple heating of the allenyne 5a in toluene
without any microwave irradiation prompted us to search for
the optimal conditions for this conversion7-9 as well as study
its scope and limitations. We now describe an efficient and very
simple procedure for the construction of bicyclo[4.2.0]octa-1,6-
dienes, bicyclo[5.2.0]nona-1,7-dienes, and bicyclo[6.2.0]deca-
1,8-dienes. We note, in advance, that this is the first example
of the construction of the bicyclo[6.2.0]deca-1,8-diene frame-
works by the [2+2] cycloaddition of allenynes.
(6) Under similar Pauson-Khand-type conditions, the homologues of
5a, having a carbon or nitrogen atom instead of an oxygen atom with a
different kind of terminal substituent, did not produce the corresponding
bicyclo[5.2.0]nona-1,7-diene compounds, see ref 4.
(7) For reviews of the [2+2] cycloaddition of allenes, see: (a) Pasto, D.
J. Tetrahedron 1984, 40, 2805-2827. (b) Murakami, M.; Matsuda, T. In
Modern Allene Chemistry; Krause, N., Hashmi, A. S. K., Eds.; Wiley-
VCH: Weinheim, Germany, 2004; Vol. 2, pp 727-815. (c) Ma, S. Chem.
ReV. 2005, 105, 2829-2872.
(8) Extensive studies of the intramolecular thermal [2+2] cycloaddition
of phenylsulfonylallenenes have been made by Padwa; see: (a) Padwa,
A.; Filipkowski, M. A.; Meske, M.; Watterson, S. H.; Ni, Z. J. Am. Chem.
Soc. 1993, 115, 3776-3777. (b) Padwa, A.; Meske, M.; Murphree, S. S.;
Watterson, S. H.; Ni, Z. J. Am. Chem. Soc. 1995, 117, 7071-7080. (c)
Padwa, A.; Lipka, H.; Watterson, S. H.; Murphree, S. S. J. Org. Chem.
2003, 68, 6238-6250 and references cited therein.
(10) The preparation and characterization of the unknown allenynes are
described in the Supporting Information.
(9) Additional examples for intramolecular thermal [2+2] cycloaddition
of allenenes; see: (a) Yeo, S.-K.; Shiro, M.; Kanematsu, K. J. Org. Chem.
1994, 59, 1621-1632. (b) Yoshida, M.; Hidaka, Y.; Nawata, Y.; Rudzinski,
J. M.; Osawa, E.; Kanematsu, K. J. Am. Chem. Soc. 1988, 110, 1232-
1238. (c) Hansen, T. V.; Skattebol, L.; Stenstrom, Y. Tetrahedron 2003,
59, 3461-3466. (d) Alcaide, B.; Almendros, P.; Aragoncillo, C. Org. Lett.
2003, 5, 3795-3798. (e) Alcaide, B.; Almendros, P.; Aragoncillo, C.;
Redondo, M. C.; Torres, M. R. Chem. Eur. J. 2006, 12, 1539-1546. (f)
Na¨rhi, K.; Franze´n, J.; Ba¨ckvall, J.-E. J. Org. Chem. 2006, 71, 2914-2917
and references cited therein.
(11) The Mo(CO)6-catalyzed intramolecular [2+2] cycloaddition reaction
of allenynes resulting in the formation of bicyclo[4.2.0]octa-1,6-dienes was
reported; see: Shen, Q.; Hammond, G. B. J. Am. Chem. Soc. 2002, 124,
6534-6535.
(12) The PdCl2(PPh3)2-catalyzed intramolecular [2+2] cycloaddition
reaction of allenynes resulting in the formation of bicyclo[m.2.0]-1,(m+2)-
diene derivatives (m ) 3, 4) was reported, see ref 1b.
(13) The PtCl2-catalyzed cycloisomerization of allenynes resulting in the
formation of bicyclo[3.2.0] frameworks was reported; see: Matsuda, T.;
Kadowaki, S.; Goya, T.; Murakami, M. Synlett 2006, 575-578.
J. Org. Chem, Vol. 72, No. 12, 2007 4455

Mukai et al.
TABLE 2. Thermal [2+2] Cycloaddition of 5b-f
TABLE 3. Thermal [2+2] Cycloaddition of 14a-d
t
yield
(%)
t
yield
entry
substrate
R
X
Z
(h)
product
entry substrate
X
Z
solvent
xylene
xylene
(h) product (%)
62a
30
28
41a
74
75
1
2
3
4
5
5b
5c
5d
5e
5f
TMS
Me
H
TMS
TMS
O
O
O
NTs
CH2
H
H
H
H
20
40
20
11
10
7b
7c
7d
7e
7f
1
2
3
4
5
6
14a
14b
14a
14b
14c
14d
O
NTs
O
H
H
H
H
15a
15b
15a
15b
15c
15d
63b
c
-
mesitylene 10
mesitylene
91
80
NTs
7
88
60b
CO2Me
CH2 CO2Me mesitylene 11
CH2 mesitylene 18
c
H
-
a The starting material 5b was recovered in 4% yield. b The starting
material 5c was recovered in 10% yield. c The starting material 5d was
recovered in 26% yield.
a The starting material 14a was recovered in 28% yield. b The starting
material 14c was recovered in 9% yield. c The starting material 14d was
recovered in 70% yield.
SCHEME 3
TABLE 4. Thermal [2+2] Cycloaddition of 16a-f
yield
entry
substrate
R
X
product
(%)
1
2
3
4
5
6
16a
16b
16c
16d
16e
16f
Ph
O
O
O
NTs
NTs
17a
17b
17c
17d
17e
17f
64a
98
Me
TMS
H
90
b
-
nPr
100
94
nBu
C(CO2Me)2
a The allene 16a was too reactive to purify. Thus, the crude 16a was
heated in toluene at 40 °C for 18 h to give compound 17a in 64% overall
yield from the corresponding propargyl alcohol precursor. b The starting
material was completely decomposed.
produces the corresponding bicyclo[5.2.0] frameworks in good
to high yields by simply refluxing in xylene.
The next phase of this investigation was to confirm the
compatibility of the substituent at the allenic terminus of 5
during this ring-closing reaction. A solution of the monomethyl
derivative 84d in xylene was refluxed in a nitrogen atmosphere
for 6 h to give the bicyclo[5.2.0] derivative 9 in 86% yield
(Scheme 3). The dimethyl derivative 10,10 however, was
transformed into two different products 114d and 12.14 The
expected [2+2] compound 13 could not be detected in the
reaction mixture. The formation of another type of bicyclo[5.2.0]
skeleton 11 could be rationalized in terms of the intermediacy
of the triene derivative 11′,4d which should be formed via the
thermal ene-type reaction of 10, the former of which would
simultaneously undergo the 4π-electronic cyclization reaction
and collapse into 11. These observations obviously indicated
that allenynes having a tetrasubstituted-allenyl moiety, such as
10, seem to be unsuitable substrates for this thermal [2+2]
cycloaddition reaction (Scheme 3).
The thermal [2+2] cycloaddition of the one-carbon homolo-
gated allenynes 1410 for the synthesis of the bicyclo[6.2.0]-
decadienes was the next subject. Thus, a solution of 14a in
xylene was refluxed for 30 h to afford 2-phenylsulfonyl-6-
oxabicyclo[6.2.0]deca-1,8-diene (15a) in 41% yield along with
14a in 28% yield (Table 3, entry 1). Similarly, the aza-congener
15b was obtained from 14b in 74% yield (entry 2). Improvement
of the chemical yield for both compounds, accompanied by a
significant shortening of the reaction time, was realized by using
mesitylene instead of xylene to furnish 15a and 15b in the
respective yields of 75% and 88% (entries 3 and 4). Further-
more, the carbon homologue 15c could be synthesized in a good
yield under similar conditions (entry 5). However, the simpler
carbon analogue 14d without a bis(methoxycarbonyl) group did
not give the ring-closed product 15d, presumably due to the
loss of the Thorpe-Ingold-type effects (entry 6).15
To further extend the scope of this simple method, we
examined the construction of the bicyclo[4.2.0]octa-1,6-diene
derivative. The results are summarized in Table 4. As can be
predicted from the literature,2,3 the easy formation of the bicyclo-
[4.2.0]octa-1,6-diene frameworks 17 from allenynes 16 could
be attained in high yields except for compound 16d, and the
reaction occurred much faster than those of the bicyclo[5.2.0]-
nona-1,7-dienes and bicyclo[6.2.0]deca-1,8-dienes. Because the
phenyl derivative 16a was extremely reactive and gradually
transformed into the cyclized product 17a during its preparation
steps, compound 17a was straighforwardly synthesized in a 64%
overall yield from the propargyl alcohol precursor by successive
treatment with PhSCl and mCPBA, followed by heating in
toluene at 40 °C for 18 h (entry 1). In the case of compound
(15) For a recent review, see: Jung, M. E.; Piizzi, G. Chem. ReV. 2005,
105, 1735-1766.
(14) The stereochemistry was determined by an NOE analysis.
4456 J. Org. Chem., Vol. 72, No. 12, 2007

Thermal [2+2] Cycloaddition of Allenynes
SCHEME 4
SCHEME 5
16d (entry 4), no characteristic products could be isolated from
the reaction mixture after refluxing in xylene for 20 min. This
result is in good accordance with the result of compound 5d in
Table 2, entry 3. Two additional examples of the thermal [2+2]
cycloaddition are depicted in Scheme 4. The monomethyl
derivative 1810 underwent the [2+2] cycloaddition in refluxing
xylene to afford the bicyclo[4.2.0] compound 19 in 99% yield,
whereas the dimethyl congener 20 under similar conditions
provided the triene derivative 21 via the thermal ene-type
reaction. The bicyclo[4.2.0] derivative 21′, which may be formed
via the 4π-electronic cyclization reaction of 21, could never be
detected. This result is in good agreement with the previous
observations.4c,d
The thermal [2+2] cycloaddition of the phenylsulfonylal-
lenynes, such as compounds 5, 14, and 16 (1-phenylsulfonyl-
1-substituted-allene species) as well as 8 and 18 (1-phenylsulfonyl-
1,3-disubstituted-allene species), exclusively gave the correspond-
ing bicyclo[m.2.0] derivatives (m ) 4, 5, 6), in which the distal
double bond of the allenyl moiety consistently took part in the
ring-closing process. Some additional experiments with various
allenynes were performed to confirm the effect of a phenylsul-
fonyl group on the allenyl moiety in this ring-closing reaction
(Scheme 5). The allenyne 22,10 having a methyl group instead
of a phenylsulfonyl one, was submitted to the xylene refluxing
conditions to furnish the bicyclo[5.2.0] compound 23 in 80%
yield along with the recovery of the starting material (10%),
strongly indicating that a phenylsulfonyl group on the allenyl
moiety seems not to be mandatory for this regioselective thermal
[2+2] cycloaddition. Upon heating in refluxing xylene for 40
h, however, compound 24,10 without an additional functional
group at the C1-position of the allenyl moiety (1-substituted-
allene), gradually decomposed and no expected products like
25 could be found except for the starting material. Presumably,
the instability of 24 and/or 25 under high-temperature conditions,
compared to those of the phenysulfonylallenynes,16 may have
caused the decomposition.
material completely disappeared (2 h) to give the bicyclo[4.2.0]
derivative 27 in 53% yield through the [2+2] cycloaddition
between a distal double bond of an allenyl functionality and a
triple bond. The corresponding azabicyclo[3.2.0]heptene skel-
eton 27′ with an exomethylene group, which should have been
formed by the reaction of a triple bond with the proximal double
bond of the allenyl group, could not be obtained. This
experiment revealed that the thermal reaction of the 1-phenyl-
sulfonyl-3-substituted-allene 26 required a longer reaction time
and resulted in a lower chemical yield in comparison to those
of the 1-phenylsulfonyl-1-substituted-allenes depicted in Table
4 (20 min, 90-100%). For the one-carbon homologated
1-phenylsulfonyl-3-substituted-allenes 2810 and 30,10 a much
higher temperature (180 °C), compared to that for the 1-phe-
nylsulfonyl-1-substituted-allenes 5 (xylene reflux, see Table 2,
e.g.), was necessary to produce the ring-closed products 29 and
31 in moderate yields (51% and 47% yield, respectively). In
fact, 29 was obtained in only13% yield when 28 was treated in
refluxing xylene for 6 h. Thus, it was found that the [2+2]
cycloaddition of the phenylsulfonylallenynes exclusively oc-
curred between the distal double bond of the allenyl functionality
and a triple bond irrespective of the position of the phenylsul-
fonyl group in sharp contrast to the [2+2] cycloaddition of the
allenenes reported by Padwa,8 in which a distal or a proximal
double bond of the allenyl moiety reacted with an olefin
depending on the position of the phenylsulfonyl group on the
allenyl moiety.
The mechanism for the regioselective formation of the
bicyclo[m.2.0] frameworks is uncertain at this stage, but a simple
explanation involving biradical intermediates might be tenta-
tively rationalized based on the literature precedents.1-3,7-9 For
the thermal reaction of 5a, for instance, there are two pathways
via biradical intermediates that can be considered. One is route
a in which the allyl radical intermediate A (A′) would be formed
by the initial combination between the sp-hybridized carbon
center of the allenyl moiety and that of the internal alkyne
carbon. The resulting seven-membered biradical intermediate
A (A′), having an allyl as well as phenylvinyl radical species,
would immediately collapse into compound 7a. An alternative
To obtain more information on the effect of the phenylsul-
fonyl group, it would be interesting to investigate the thermal
[2+2] cycloaddition of the 1-phenylsulfonyl-3-substituted spe-
cies, which might clarify the role of the phenylsulfonyl group
in the regioselectivity observed in this ring-closing reaction.
Thus, compound 26,10 possessing the 1-phenylsulfonyl-3-
substituted framework, was refluxed in xylene until the starting
(16) The easy formation of phenylsulfonylbicyclo[m.2.0] skeletons might
reflect the marked stability of phenylsulfonylallenes under high-temperature
conditions.
J. Org. Chem, Vol. 72, No. 12, 2007 4457

Mukai et al.
SCHEME 6
initial connection of the sp-hybridized carbon of the allenyl
moiety with the external alkyne carbon might lead to the eight-
membered intermediate B (B′) containing allyl and vinyl
radicals. The ring-closing reaction of B (B′) would give rise to
the production of compound 7a′ (route b). The fact that
compound 5a exclusively gave 7a in a high yield (Table 1)
would strongly reflect the preferential formation of A (A′) over
B (B′) due to its easier formation, the latter of which has an
eight-membered ring, while the former has a seven-membered
one. Similarly, the exclusive formation of bicyclo[4.2.0]-
octadiene derivatives 17 and the bicyclo[6.2.0]decadiene deriva-
tives 15 would be interpreted by considering the ring size of
the biradical species (6- versus 7-membered ring and 8- versus
9-membered ring).17 It is well-known that the Myers-Saito
cycloaromatization (C2-C7 cyclization)18 of enyne-allenes 32
predominantly proceeds via the biradical C when 32 does not
have a substituent at the alkyne terminus (route c), whereas aryl
groups or sterically demanding substituents at the acetylene
terminus of compound 32 change the reaction pathway from
the C2-C7 mode combination to the C2-C6 one (Schmittel
cyclization)19 resulting in the formation of biradical D, the vinyl
radical center of which is stabilized by the attached substituent
(R).19 The plausible route a, leading to 7a, might be regarded
as an analogy to route d (C2-C6 cyclization), both of which
produce a vinyl radical center stabilized by the phenyl group
(when R ) Ph), although the nonconjugated allenyne group of
compound 5a is not the same as that of 32 having a conjugated
enyne-allene functionality. As mentioned in Tables 2 and 4,
compounds 5d and 16d, both of which have a terminal acetylene
moiety, did not provide the corresponding [2+2] cycloadducts
unlike the other substrates possessing a substituent at the triple
bond terminus. This observation might be rationalized by
considering the stability of the vinyl radical center due to the
attached substituents.20 On the other hands, route b would be
regarded as analogous to route c (C2-C7 cyclization). In contrast
to the biradical intermediate A (A′), the stability of the vinyl
radical center of the biradical intermediate B (B′) could not be
directly increased by the presence of the attached substituent
(a terminal substituent of the acetylene group of the starting
allenyne). As a result, route a would become a favorable
pathway over route b due to (i) the ring size of the biradical
intermediate and/or (ii) the stabilization of the vinyl radical by
the attached substituent resulting in the exclusive formation of
compound 7a.
Our next effort involved capturing the possible biradical
intermediate A (A′). Thus, compound 18 was refluxed in xylene
in the presence of TEMPO (7 equiv) for 1 h, hoping to obtain
compound 33, but the only isolatable compound from the
reaction mixture was 19 in a rather lower yield (57%), compared
to the reaction without TEMPO (99%, Scheme 4). When 18
was treated with 1,4-cyclohexadiene (1,4-CHD) (20 equiv) in
refluxing toluene, compound 19 was again isolated in 63% yield.
Furthermore, refluxing of compound 8 in 1,4-CHD19f,h did not
afford compound 34 at all.21
Schemittel19 reported that the phenyl group of the benzene-
conjugated allenynes, such as compound 32 (R′ ) Ph) in
Scheme 6, participated in the ring-closing reaction through a
biradical intermediate D. Wang22 also described similar ring-
closing reactions of the benzene-conjugated aza-allenyne con-
geners.23 On the basis of these results, we presumed that the
allyl-benzyl radical intermediate E (F) resulting from the
allenyne 35 having a phenyl group at the allenic terminus would
be susceptible to a subsequent ring-closing reaction to produce
the tricyclic product 37 via the 1,5-hydrogen-shift of 36 (Scheme
8).
(17) The exclusive formation of 27, 29, and 31 from the corresponding
1-phenylsulfonyl-1,3-disubstituted-allenes 26, 28, and 30 would also be
interpreted by a similar consideration on the stability of the biradical
intermediates.
Thus, the allenyne 3810 was heated in toluene under reflux
to give the [2+2] cycloadduct 39 in 72% yield along with the
expected tricyclic derivative 40 in 18% yield (Scheme 9).
Refluxing of 38 in xylene afforded a similar result. The low
(18) (a) Myers, A. G. Tetrahedron Lett. 1987, 28, 4493-4496. (b) Myers,
A. G.; Kuo, E. Y.; Finney, N. S. J. Am. Chem. Soc. 1989, 111, 8057-
8059. (c) Nagata, R.; Yamanaka, H.; Okazaki, E.; Saito, I. Tetrahedron
Lett. 1989, 30, 4995-4998. (d) Nagata, R.; Yamanaka, H.; Murahashi, E.;
Saito, I. Tetrahedron Lett. 1990, 31, 2907-2910. (e) Myers, A. G.;
Dragovich, P. S.; Kuo, E. Y. J. Am. Chem. Soc. 1992, 114, 9369-9386.
(19) (a) Schmittel, M.; Strittmatter, M.; Kiau, S. Tetrahedron Lett. 1995,
36, 4975-4978. (b) Schmittel, M.; Strittmatter, M.; Vollmann, K.; Kiau,
S. Tetrahedron Lett. 1996, 37, 999-1002. (c) Schmittel, M.; Strittmatter,
M.; Kiau, S. Angew. Chem., Int. Ed. Engl. 1996, 35, 1843-1845. (d)
Schmittel, M.; Maywald, M.; Strittmatter, M. Synlett 1997, 165-166. (e)
Schmittel, M.; Keller, M.; Kiau, S.; Strittmatter, M. Chem. Eur. J. 1997, 3,
807-816. (f) Schmittel, M.; Steffen, J.-P.; Auer, D.; Maywald, M.
Tetrahedron Lett. 1997, 38, 6177-6180. (g) Schmittel, M.; Steffen, J.-P.;
Wencesla AÄ ngel, M. AÄ .; Engels, B.; Lennartz, C.; Hanrath, M. Angew.
Chem., Int. Ed. 1998, 37, 1562-1564. (h) Engels, B.; Lennartz, C.; Hanrath,
M.; Schmittel, M.; Strittmatter, M. Angew. Chem., Int. Ed. 1998, 37, 1960-
1963. (i) Schmittel, M.; Steffen, J.-P.; Engels, B.; Lennartz, C.; Hanrath,
M. Angew. Chem., Int. Ed. 1998, 37, 2371-2373.
(21) Reaction was monitored by 1H NMR, and no peaks due to compound
35 could be detected except for those of 8 and 9.
(22) (a) Shi, C.; Wang, K. K. J. Org. Chem. 1998, 63, 3517-3520. (b)
Shi, C.; Zhang, Q.; Wang, K. K. J. Org. Chem. 1999, 64, 925-932. (c)
Zhang, Q.; Shi, C.; Zhang, H.-R.; Wang, K. K. J. Org. Chem. 2000, 65,
7977-7983. (d) Lu, X.; Peterson, J. L.; Wang, K. K. J. Org. Chem. 2002,
67, 5412-5415. (e) Lu, X.; Peterson, J. L.; Wang, K. K. J. Org. Chem.
2002, 67, 7797-7801. (f) Dai, W.; Peterson, J. L.; Wang, K. K. J. Org.
Chem. 2005, 70, 6647-6652.
(23) A similar ring-closing reaction of benzene-conjugated allenynes was
used for preparation of polycyclic aromatics; see: (a) Wang, K. K.; Zhang,
H.-R.; Peterson, J. L. J. Org. Chem. 1999, 64, 1650-1656. (b) Li, H.; Zhang,
H.-R.; Peterson, J. L.; Wang, K. K. J. Org. Chem. 2001, 66, 6662-6668.
(c) Li, H.; Peterson, J. L.; Wang, K. K. J. Org. Chem. 2001, 66, 7804-
7810. (d) Yang, Y.; Peterson, J. L.; Wang, K. K. J. Org. Chem. 2003, 68,
5832-5837. (e) Yang, Y.; Peterson, J. L.; Wang, K. K. J. Org. Chem. 2003,
68, 8545-8549. (f) Han, X.; Zhang, Y.; Wang, K. K. J. Org. Chem. 2005,
70, 2406-2408.
(20) Proton transfer from plausible biradical intermediates, similar to A
with a dimethyl substituent at the allenic terminus, generated from allenes
10 and 20 may rationalize the formation of triene derivatives 11′ (actually,
compound 11 was isolated instead of 11′) and 21, see refs 17a,c,e.
4458 J. Org. Chem., Vol. 72, No. 12, 2007

Thermal [2+2] Cycloaddition of Allenynes
SCHEME 7
[2+2] cycloadduct 42a in 66% yield. When a substituent on
the sulfonyl group was changed to the sterically more hindered
tert-butyl group, a remarkable improvement in the chemical
yield of the tricyclic compound was attained. In fact, the tert-
butylsulfonyl derivative 41b10 provided a tricyclic compound
43b in 50% yield along with 42b in 47% yield. Finally, we
examined the electronic effect of a substituent on the phenyl
group at the allenic terminus using the tert-butylsulfonyl
derivative, which gave the highest yield of the tricyclic
compound. As depicted in Scheme 9, the behavior of 4410
similar to that of 41b was observed irrespective of the electronic
property of substituent on the benzene ring. In the case of 44b,
the tricyclic compound 46b was formed in 47% yield ac-
companied by desilylation. Although direct evidence for the
intermediacy of the biradical species such as A during the
thermal transformation of the allenynes to the bicyclo[m.2.0]
skeletons could not yet be obtained, a series of experiments in
Scheme 9 indirectly but strongly suggested the possibility of
the intermediacy of the biradical species because the ratio of
the azabicyclo[4.2.0]octadienes 39, 42, and 45 to tricyclic
compounds 40, 43, and 46 obviously depended on the bulkiness
of a substituent on the sulfonyl group of starting allenynes 38,
41, and 44. These results would not only support the ring-closing
process via biradical intermediates leading to the [2+2] cy-
cloadducts, but it would also rule out the possibility of a
concerted [4+2] cycloaddition pathway for the formation of
tricyclic compounds.24
SCHEME 8
In summary, we have described the thermal [2+2] cycload-
dition of allenynes by refluxing in xylene that leads to the
formation of the bicyclo[5.2.0]nona-1,7-dienes, in which the
distal double bond of the allenyl moiety exclusively served as
the π-component irrespective of the position of the sulfonyl
group on the allenyl moiety. This simple method was shown to
be successfully applicable to the first construction of the one-
carbon homologated bicyclo[6.2.0]deca-1,8-dienes. One-carbon
smaller-sized bicyclo[4.2.0]octa-1,6-dienes could also be ob-
tained in high yields. When the starting allenynes have a phenyl
group at the allenic terminus, tricyclic compounds incorporating
a terminal phenyl group were obtained along with the normal
[2+2] cycloadducts. Thus, we developed a general procedure
for the preparation of bicyclo[m.2.0]alka-1,(m+2)-diene skel-
etons (m ) 4-6). Further studies on the scope and limitations
of this method are now in progress.
SCHEME 9
Experimental Section
8-Phenyl-2-(phenylsulfonyl)-5-oxabicyclo[5.3.0]deca-1,7-dien-
9-one (6a) and 8-Phenyl-2-(phenylsulfonyl)-5-oxabicyclo[5.2.0]-
nona-1,7-diene (7a). [RhCl(CO)dppp]2 (2.9 mg, 2.5 × 10-3 mmol)
was added to a solution of allenyne 5a (33.9 mg, 0.100 mmol) in
toluene (1.0 mL). The reaction mixture was refluxed under a CO
atmosphere for 1 h. Toluene was evaporated off, and the residual
oil was chromatographed with CH2Cl2 to afford 6a (16.9 mg, 46%)
and 7a (9.0 mg, 27%); 6a: colorless needles, mp 203-204 °C
yield of 40 may be attributed to the low ratio of the intermediate
F (R′ ) Ph) compared to its isomer F′ (see Scheme 8). We
thought that the substituent (R′) sterically more hindered than
a phenyl group on the sulfonyl functionality would significantly
increase the nonbonding interaction with the pentadienyl radical
moiety as shown in the structure of intermediate F′ resulting in
the increased ratio of intermediate F. As a result, the mesity-
lenesulfonyl drivative 41a10 was reacted under standard condi-
tions (refluxed in xylene for 1 h) to afford the tricyclic
compound 43a in a slightly higher yield (22%) and the normal
1
(AcOEt), IR 1713, 1308, 1151 cm-1; H NMR δ 7.94-7.91 (m,
2H), 7.70-7.55 (m, 3H), 7.46-7.40 (m, 3H), 7.28-7.24 (m, 2H),
4.70 (s, 2H), 3.92 (t, 2H, J ) 6.1 Hz), 3.76 (s, 2H), 3.06 (t, 2H, J
) 6.1 Hz); 13C NMR δ 200.6, 163.4, 145.83, 145.78, 140.3, 133.8,
(24) If the ring-closing reaction of 38, 41, and 44 leading to tricyclic
compounds 40, 43, and 46 proceeds via a concerted [4+2] cycloaddition
pathway in which the distal double bond of the allenyl moiety and one of
the π bonds of the benzene ring serve as a 1,3-diene part and an alkyne
group functions as a dienophile, the bulkiness of the substituent on the
sulfonyl functionality should not affect their reactivity.
J. Org. Chem, Vol. 72, No. 12, 2007 4459

Mukai et al.
133.3, 129.6, 129.5, 129.2, 128.5, 127.6, 69.2, 63.9, 41.1, 29.3;
MS m/z 366 (M+, 8.7). HRMS calcd for C21H18O4S 366.0926, found
366.0925. Anal. Calcd for C21H18O4S: C, 68.83; H, 4.95. Found:
C, 68.53; H, 5.04. 7a: colorless needles, mp 216-218 °C (AcOEt);
IR 1680, 1304, 1151 cm-1; 1H NMR δ 7.92-7.90 (m, 2H), 7.61-
7.52 (m, 3H), 7.45-7.36 (m, 3H), 7.28-7.24 (m, 2H), 4.60 (t, 2H,
J ) 3.2 Hz), 3.92 (t, 2H, J ) 4.9 Hz), 3.70 (t, 2H, J ) 3.2 Hz),
2.69 (t, 2H, J ) 4.9 Hz); 13C NMR δ 148.5, 147.4, 141.2, 139.9,
132.94, 132.88, 129.7, 129.1, 128.9, 127.6, 127.5, 122.7, 70.5, 68.9,
36.3, 33.5; MS m/z 338 (M+, 79.4). HRMS calcd for C20H18O3S
338.0977, found 338.0977. Anal. Calcd for C20H18O3S: C, 70.98;
H, 5.36. Found: C, 70.70; H, 5.46.
General Procedure for Ring-Closing Reaction of Allenynes
under an Atmosphere of N2. To a solution of allenyne (0.10 mmol)
in toluene was added xylene or mesitylene (1 mL) with refluxed
under a N2 atmosphere until the starting material completely
disappeared (monitored by TLC). Solvent was evaporated off, and
the residual oil was chromatographed with hexane-AcOEt to afford
cyclized products. Chemical yields are summarized in Tables 1-4
and Schemes 3-5 and 9.
N-(4-Methylbenzenesulfonyl)-2-(phenylsulfonyl)-8-(trimethyl-
silyl)-5-azabicyclo[5.2.0]nona-1,7-diene (7e): colorless plates, mp
134-136 °C (AcOEt); IR 1666, 1350, 1306, 1159 cm-1; 1H NMR
δ 7.83-7.82 (m, 2H), 7.63-7.53 (m, 5H), 7.26-7.25 (m, 2H), 3.96
(br s, 2H), 3.39 (t, 2H, J ) 5.0 Hz), 3.26 (br s, 2H), 2.66 (t, 2H,
J ) 5.0 Hz), 2.42 (s, 3H), 0.16 (s, 9H); 13C NMR δ 160.5, 151.9,
149.2, 143.7, 140.7, 135.5, 133.1, 129.8, 129.2, 127.7, 127.0, 121.8,
49.6, 48.6, 37.9, 32.2, 21.5, -2.2; MS m/z 487 (M+, 2.0). HRMS
calcd for C24H29NO4S2Si 487.1307, found 487.1303. Anal. Calcd
for C24H29NO4S2Si: C, 59.10; H, 5.99; N, 2.87. Found: C, 58.77;
H, 6.08; N, 2.86.
7.13-7.11 (m, 2H), 5.32-5.31 (m, 2H), 4.27 (s, 2H), 3.42-3.38
(m, 2H), 2.80-2.77 (m, 2H), 2.34 (s, 3H), 2.01 (s, 3H); 13C NMR
δ 143.6, 142.1, 139.1, 138.8, 137.1, 135.6, 133.3, 131.6, 129.6,
129.3, 128.5, 128.3, 128.1, 127.7, 123.2, 122.1, 85.6, 82.0, 46.6,
38.2, 26.7, 21.7, 21.4; MS m/z 519 (M+, 0.6). HRMS calcd for
C29H29NO4S2 519.1538, found 519.1541.
9-Phenyl-2-(phenylsulfonyl)-6-oxabicyclo[6.2.0]deca-1,8-di-
ene (15a): colorless needles, mp 175-176.5 °C (AcOEt); IR 1302,
1
1150 cm-1; H NMR δ 7.92-7.91 (m, 2H), 7.59-7.56 (m, 1H),
7.54-7.51 (m, 2H), 7.45-7.42 (m, 2H), 7.40-7.37 (m, 1H), 7.34-
7.32 (m, 2H), 4.55 (t, 2H, J ) 3.1 Hz), 3.75 (t, 2H, J ) 3.1 Hz),
3.70 (t, 2H, J ) 6.1 Hz), 2.62-2.60 (m, 2H), 1.77-1.72 (m, 2H);
13C NMR δ 151.3, 148.4, 141.8, 139.5, 133.0, 132.7, 129.8, 129.1,
128.9, 127.9, 127.6, 123.4, 69.0, 65.4, 37.1, 28.0, 24.5; MS m/z
352 (M+, 0.1). HRMS calcd for C21H20O3S 352.1133, found
352.1134.
N-(4-Methylbenzenesulfonyl)-9-phenyl-2-(phenylsulfonyl)-6-
azabicyclo[6.2.0]deca-1,8-diene (15b): colorless needles, mp
1
198.5-200 °C (AcOEt); IR 1346, 1304, 1157 cm-1; H NMR δ
7.89-7.86 (m, 2H), 7.69-7.29 (m, 12H), 4.28-4.26 (m, 2H),
3.70-3.69 (m, 2H), 3.26 (t, 2H, J ) 5.9 Hz), 2.58-2.54 (m, 2H),
2.42 (s, 3H), 1.79-1.70 (m, 2H); 13C NMR δ 153.0, 148.3, 143.7,
141.3, 135.3, 134.6, 132.9, 132.5, 130.2, 129.8, 129.1, 129.0, 127.8,
127.6, 127.2, 122.8, 46.3, 45.4, 37.3, 28.2, 24.3, 21.5; MS m/z 505
(M+, 0.5). Anal. Calcd for C28H27NO4S2: C, 66.51; H, 5.38; N,
2.77. Found: C, 66.24; H, 5.56; N, 2.86.
4,4-Bis(methoxycarbonyl)-9-phenyl-2-(phenylsulfonyl)bicyclo-
[6.2.0]deca-1,8-diene (15c): pale yellow plates, mp 183-185 °C
1
(AcOEt); IR 1728, 1306, 1151 cm-1; H NMR δ 7.87-7.86 (m,
2H), 7.59-7.36 (m, 8H), 3.80 (s, 6H), 3.64 (s, 2H), 3.20 (s, 2H),
2.67-2.64 (m, 2H), 2.27-2.24 (m, 2H), 1.68-1.66 (m, 2H); 13C
NMR δ 171.4, 155.3, 151.6, 141.8, 140.9, 133.4, 132.7, 129.7,
129.1, 128.8, 127.7, 127.4, 117.9, 57.9, 52.8, 36.7, 30.7, 28.0, 24.3,
22.6; MS m/z 466 (M+, 0.2). Anal. Calcd for C26H26O6S: C, 66.93;
H, 5.62. Found: C, 66.69; H, 5.81.
4,4-Bis(methoxycarbonyl)-8-(trimethylsilyl)-2-(phenylsulfonyl)-
bicyclo[5.2.0]nona-1,7-diene (7f): colorless needles, mp 133-
1
135 °C (AcOEt); IR 1734, 1304, 1155 cm-1; H NMR δ 7.93-
7.90 (m, 2H), 7.61-7.52 (m, 3H), 3.58 (s, 6H), 3.27-3.25 (m,
2H), 2.97 (s, 2H), 2.50-2.43 (m, 2H), 2.24-2.19 (m, 2H), 0.14
(s, 9H); 13C NMR δ 170.7, 160.3, 155.7, 151.0, 141.2, 132.8, 129.0,
127.8, 117.9, 57.3, 52.7, 37.7, 36.1, 30.9, 25.1, -2.0; MS m/z 448
(M+, 10.4). HRMS calcd for C22H28O6SSi 448.1376, found
448.1376. Anal. Calcd for C22H28O6SSi: C, 58.90; H, 6.29.
Found: C, 58.53; H, 6.38.
N-(4-Methylbenzenesulfonyl)-2-(phenylsulfonyl)-7-propyl-4-
azabicyclo[4.2.0]octa-1,6-diene (17e): a colorless oil; IR 1350,
1
1306, 1159 cm-1; H NMR δ 7.87-7.83 (m, 2H), 7.67-7.46 (m,
5H), 7.20-7.17 (m, 2H), 4.07 (s, 2H), 3.95-3.94 (m, 2H), 3.02
(s, 2H), 2.40 (s, 3H), 2.21-2.15 (m, 2H), 1.56-1.42 (m, 2H), 0.96-
0.90 (m, 3H); 13C NMR δ 155.1, 146.9, 143.6, 140.5, 134.54,
134.49, 133.3, 129.5, 129.3, 127.6, 127.4, 114.0, 42.8, 41.8, 38.5,
32.6, 21.5, 19.8, 14.0; MS m/z 443 (M+, 0.4). HRMS calcd for
C23H25NO4S2 443.1225, found 443.1218.
9-Methyl-N-(4-methylbenzenesulfonyl)-8-phenyl-2-(phenylsul-
fonyl)-5-azabicyclo[5.2.0]nona-1,7-diene (9): colorless plates, mp
1
205.5-207 °C (AcOEt); IR 1344, 1304, 1153 cm-1; H NMR δ
7.86 (d, 2H, J ) 7.6 Hz), 7.64-7.60 (m, 3H), 7.56-7.53 (m, 2H),
7.48-7.39 (m, 3H), 7.31 (d, 2H, J ) 7.6 Hz), 7.27-7.25 (m, 2H),
4.37-4.26 (m, 2H), 4.09-4.07 (m, 1H), 3.52-3.48 (m, 1H), 3.42-
3.38 (m, 1H), 2.74-2.69 (m, 1H), 2.63-2.58 (m, 1H), 2.41 (s,
3H), 1.59 (d, 3H, J ) 6.6 Hz); 13C NMR δ 155.2, 152.3, 143.7,
140.7, 135.5, 134.3, 133.1, 131.6, 129.9, 129.13, 129.05, 127.8,
127.5, 127.0, 121.2, 48.6, 48.2, 43.9, 32.5, 21.5, 17.4; MS m/z 505
(M+, 3.5). Anal. Calcd for C28H27NO4S2: C, 66.51; H, 5.38; N,
2.77. Found: C, 66.29; H, 5.50; N, 2.73.
4,4-Bis(methoxycarbonyl)-7-butyl-2-(phenylsulfonyl)bicyclo-
[4.2.0]nona-1,6-diene (17f): a colorless oil; IR 1736, 1306, 1155
1
cm-1; H NMR δ 7.88-7.87 (m, 2H), 7.61-7.58 (m, 1H), 7.55-
7.52 (m, 2H), 3.49 (s, 6H), 3.28 (br s, 2H), 2.89 (s, 2H), 2.70 (br
s, 2H), 2.33 (t, 2H, J ) 7.3 Hz), 1.55 (quin, 2H, J ) 7.3 Hz), 1.37
(sex, 2H, J ) 7.3 Hz), 0.93 (t, 3H, J ) 7.3 Hz); 13C NMR δ 170.1,
155.8, 148.4, 140.8, 137.5, 132.7, 128.9, 127.8, 113.6, 55.5, 52.8,
38.2, 30.3, 29.2, 28.4, 28.0, 22.5, 13.7; MS m/z 418 (M+, 87.2).
HRMS calcd for C22H26O6S 418.1450, found 418.1438.
9-Methyl-N-(4-methylbenzenesulfonyl)-2-[(Z)-phenylmethyl-
ene]-7-(phenylsulfonyl)-4-azabicyclo[5.2.0]non-1(9)-ene (11): col-
orless needles, mp 153-154 °C (AcOEt); IR 1360, 1157, 1146
8-Methyl-N-(4-methylbenzenesulfonyl)-2-(phenylsulfonyl)-7-
(trimethylsilyl)-4-azabicyclo[4.2.0]octa-1,6-diene (19): colorless
1
plates, mp 119-120 °C (AcOEt); IR 1346, 1306, 1157 cm-1; H
1
cm-1; H NMR δ 7.88-7.84 (m, 2H), 7.66-7.20 (m, 12H), 6.47
NMR δ 7.89-7.86 (m, 2H), 7.71-7.57 (m, 3H), 7.39-7.36 (m,
2H), 7.16-7.13 (m, 2H), 4.23-4.13 (m, 2H), 4.02-3.96 (m, 1H),
3.86 (dd, 1H, J ) 17.3, 3.5 Hz), 3.58-3.54 (m, 1H), 2.39 (s, 3H),
1.12 (d, 3H, J ) 6.9 Hz), 0.12 (s, 9H); 13C NMR δ 164.0, 153.1,
148.3, 143.6, 140.2, 135.0, 133.6, 129.6, 129.4, 127.6, 127.4, 114.7,
48.0, 42.9, 42.7, 21.4, 17.5, -1.8; MS m/z 487 (M+, 1.6). HRMS
calcd for C24H29NO4S2Si 487.1307, found 487.1311. Anal. Calcd
for C24H29NO4S2Si: C, 59.10; H, 5.99; N, 2.87. Found: C, 58.79;
H, 6.05; N, 2.87.
(s, 1H), 4.98 (d, 1H, J ) 16.8 Hz), 4.17-4.08 (m, 2H), 3.74-3.63
(m, 1H), 2.75-2.69 (m, 1H), 2.53 (d, 1H, J ) 14.9 Hz), 2.39 (s,
3H), 2.16-2.04 (m, 2H), 1.60 (s, 3H); 13C NMR δ 143.0, 142.9,
138.8, 137.5, 136.1, 135.8 134.3, 133.8, 129.6, 129.5, 128.9, 128.8,
128.5, 128.4, 127.5, 126.9, 68.8, 50.0, 49.9, 42.6, 34.0, 21.4, 15.2;
MS m/z 519 (M+, 0.7). Anal. Calcd for C29H29NO4S2: C, 67.02;
H, 5.62; N, 2.70. Found: C, 66.81; H, 5.67; N, 2.66.
N-[(E)-5-Methyl-3-(phenylsulfonyl)hexa-3,5-dienyl]-N-(3-phenyl-
2-propynyl)-(4-methylbenzene)sulfonamide (12): colorless plates,
1-(4-Methylbenzenesulfonyl)-5-(phenylsulfonyl)-4-(1-propen-
2-yl)-3-[(Z)-(trimethylsilyl)methylene]-1,2,3,6-tetrahydropyri-
dine (21): colorless plates, mp 144-145.5 °C (AcOEt); IR 1352,
mp 102-103.5 °C (AcOEt); IR 1599, 1491, 1348, 1306, 1161 cm-1
;
1H NMR δ 7.89-7.87 (m, 2H), 7.73-7.71 (m, 2H), 7.58-7.55
(m, 1H), 7.48-7.44 (m, 2H), 7.40 (s, 1H), 7.32-7.23 (m, 5H),
1
1308, 1161, 1153 cm-1; H NMR δ 7.88-7.85 (m, 2H), 7.69-
4460 J. Org. Chem., Vol. 72, No. 12, 2007

Thermal [2+2] Cycloaddition of Allenynes
7.63 (m, 1H), 7.57-7.48 (m, 4H), 7.16-7.13 (m, 2H), 6.01 (s,
1H), 5.07 (s, 1H), 4.25 (br s, 3H), 4.08 (s, 1H), 3.63 (br s, 1H),
2.37 (s, 3H), 1.73 (s, 3H), 0.21 (s, 9H); 13C NMR δ 149.8, 143.8,
141.2, 140.8, 139.3, 137.8, 134.1, 133.6, 131.3, 129.6, 129.1, 128.2,
127.6, 117.3, 47.6, 45.6, 23.9, 21.4, -0.4; MS m/z 501 (M+, 76.5).
HRMS calcd for C25H31NO4S2Si 501.1464, found 501.1466.
2-Methyl-N-(4-methylbenzenesulfonyl)-8-phenyl-5-azabicyclo-
[5.2.0]nona-1,7-diene (23): colorless needles, mp 193-194.5 °C
aqueous Na2S2O3 and NaHCO3. The resulting mixture was extracted
with CH2Cl2, which was washed with water and brine, dried, and
concentrated to dryness. The residual oil was passed through a short
pad of silica gel with hexane-AcOEt (7:3) to afford the crude
allenyne 16a. A solution of the crude allenyne 16a in toluene (1.0
mL) was stirred for 18 h at 40 °C under a N2 atmosphere. The
solvent was evaporated off, and the residual oil was chromato-
graphed with hexane-AcOEt (7:3) to afford 17a (32.0 mg, 64%,
for three steps) as pale yellow plates: mp 188-189.5 °C (AcOEt);
1
(AcOEt); IR 1344, 1159 cm-1; H NMR δ 7.72-7.71 (m, 2H),
1
7.38-7.20 (m, 7H), 4.32-4.31 (m, 2H), 3.48-3.46 (m, 2H), 2.99-
2.98 (m, 2H), 2.44-2.42 (m, 5H), 1.64 (s, 3H); 13C NMR δ 143.2,
137.5, 137.0, 136.3, 134.6, 131.5, 129.6, 128.6, 127.4, 127.1, 126.0,
121.0, 49.5, 49.1, 37.9, 33.0, 21.5, 18.2; MS m/z 365 (M+, 12.0).
Anal. Calcd for C22H23NO2S: C, 72.30; H, 6.34; N, 3.83. Found:
C, 72.12; H, 6.35; N, 3.95.
IR 1306, 1157 cm-1; H NMR δ 7.93-7.91 (m, 2H), 7.63-7.60
(m, 1H), 7.56-7.53 (m, 2H), 7.43-7.35 (m, 3H), 7.28-7.26 (m,
2H), 4.52 (t, 2H, J ) 2.9 Hz), 4.34 (s, 2H), 3.75 (t, 2H, J ) 2.9
Hz); 13C NMR δ 145.4, 145.1, 140.9, 136.1, 133.2, 132.7, 129.8,
129.3, 128.9, 127.5, 127.3, 119.0, 62.44, 62.39, 37.0; MS m/z 324
(M+, 48.1). HRMS calcd for C19H16O3S 324.0820, found 324.0813.
N-[(4-Methylbenzene)sulfonyl]-8-phenyl-9-(phenylsulfonyl)-
5-azabicyclo[5.2.0]]nona-1,7-diene (29). A solution of 28 (15 mg,
3.0 × 10-2 mmol) in mesitylene (2 mL) was heated at 180 °C in
a sealed tube for 1 h. Mesitylene was evaporated off, and the
residual oil was chromatographed with hexane-AcOEt (3:1) to
afford 29 (7.6 mg, 51%) as a pale yellow oil: IR 1361, 1340, 1159,
N-(4-Methylbenzenesulfonyl)-7-phenyl-8-(phenylsulfonyl)-4-
azabicyclo[4.2.0]octa-1,6-diene (27): a pale yellow oil; IR 1350,
1
1307, 1163, 1138 cm-1; H NMR δ 7.65 (d, 2H, J ) 8.1 Hz),
7.61-7.57 (m, 3H), 7.41-7.34 (m, 7H), 7.24 (d, 2H, J ) 7.8 Hz),
5.41-5.39 (m, 1H), 4.97 (s, 1H), 4.34-4.30 (m, 1H), 3.98 (dd,
1H, J ) 17.1, 4.4 Hz), 3.89 (d, 1H, J ) 17.1 Hz), 3.75 (dd, 1H, J
) 17.1, 3.2 Hz), 2.41 (s, 3H); 13C NMR δ 143.8, 140.6, 136.4,
136.0, 134.3, 134.0, 132.1, 131.2, 129.6, 129.1, 128.9, 128.4, 127.4,
127.0, 109.6, 70.2, 44.1, 42.7, 21.5; MS m/z 477 (M+, 5.5); HRMS
calcd for C26H23NO4S2 477.1069, found 477.1070.
1
1136 cm-1; H NMR δ 7.66-7.54 (m, 5H), 7.41-7.28 (m, 9H),
5.60 (t, 1H, J ) 4.2 Hz), 4.91-4.90 (m, 1H), 4.33 (dd, 1H, J )
17.7, 2.4 Hz), 3.76 (dd, 1H, J ) 17.7, 1.8 Hz), 3.56-3.51 (m, 1H),
2.99-2.93 (m, 1H), 2.60-2.53 (m, 1H), 2.47-2.39 (m, 4H); 13C
NMR δ 145.1, 143.6, 137.5, 136.1, 135.6, 133.8, 132.2, 131.3,
129.8, 129.4, 129.0, 128.8, 128.1, 127.2, 127.0, 118.8, 67.7, 49.2,
48.6, 32.6, 21.5; MS m/z 491 (M+, 47.9); HRMS calcd for
C27H25O4S2N 491.1225, found 491.1223.
N-(4-Methylbenzenesulfonyl)-8-phenyl-2-(phenylsulfonyl)-7-
(trimethylsilyl)-4-azabicyclo[4.2.0]octa-1,6-diene (39): colorless
plates, mp 189-190.5 °C (AcOEt); IR 1348, 1308, 1157 cm-1; 1H
NMR δ 7.52-7.49 (m, 1H), 7.43 (d, 2H, J ) 8.3 Hz), 7.31-7.17
(m, 7H), 7.05 (d, 2H, J ) 7.1 Hz), 6.90 (d, 2H, J ) 7.1 Hz), 4.61
(d, 1H, J ) 2.4 Hz), 4.38 (dd, 1H, J ) 17.1, 1.5 Hz), 4.15 (ABq,
2H, J ) 17.1 Hz), 3.89 (dd, 1H, J ) 17.3, 3.7 Hz), 2.46 (s, 3H),
-0.03 (s, 9H); 13C NMR δ 162.4, 151.9, 150.6, 143.6, 139.8, 138.4,
135.1, 133.1, 129.9, 129.0, 128.2, 128.1, 127.44, 127.37, 127.2,
114.8, 56.4, 42.7, 42.5, 21.6, -1.9; MS m/z 549 (M+, 1.2). HRMS
calcd for C29H31NO4S2Si 549.1464, found 549.1472.
Ring-Closing Reaction of 18 with TEMPO under an Atmo-
sphere of N2. To a solution of 18 (48.0 mg, 9.85 × 10-2 mmol) in
xyene (1.0 mL) was added TEMPO (110 mg, 0.70 mmol) at room
temperature. The reaction mixture was refluxed under a N2
atmosphere for 1 h and toluene was evaporated off. The residual
oil was chromatographed with hexane-AcOEt to afford 19 (27.2
mg, 57%).
N-(4-Methylbenzenesulfonyl)-4-(phenylsulfonyl)-10-trimeth-
ylsilyl-1,2,3,4-tetrahydrobenz[g]isoquinoline (40): colorless plates,
Ring-Closing Reaction of 18 with 1,4-CHD under an Atmo-
sphere of N2. To a solution of 18 (55.0 mg, 0.113 mmol) in xyene
(1.1 mL) was added 1,4-CHD (0.21 mL, 2.3 mmol). The reaction
mixture was refluxed under a N2 atmosphere for 1 h and toluene
was evaporated off. The residual oil was chromatographed with
hexane-AcOEt to afford 19 (34.9 mg, 63%).
1
mp 228-229 °C (AcOEt); IR 1348, 1308, 1163, 1134 cm-1; H
NMR δ 8.13 (d, 1H, J ) 8.3 Hz), 7.88 (s, 1H), 7.79-7.77 (m,
1H), 7.53-7.45 (m, 5H), 7.38-7.37 (m, 2H), 7.26-7.23 (m, 2H),
7.15 (d, 2H, J ) 8.1 Hz), 4.56-4.52 (m, 2H), 4.06 (ABq, 2H, J )
15.1 Hz), 3.37-3.34 (m, 1H), 2.33 (s, 3H), 0.46 (s, 9H); 13C NMR
δ 143.9, 137.14, 137.06, 136.7, 134.9, 133.8, 133.6, 132.7, 131.9,
130.1, 129.6, 129.3, 128.3, 127.8, 127.6, 126.5, 125.6, 121.8, 65.2,
49.2, 43.3, 21.4, 3.8; MS m/z 549 (M+, 0.9). HRMS calcd for
C29H31NO4S2Si 549.1464, found 549.1480.
Acknowledgment. This work was supported in part by a
Grant-in-Aid for Scientific Research from the Ministry of
Education, Culture, Sports, Science, and Technology, Japan, for
which we are thankful.
7-Phenyl-2-(phenylsulfonyl)-4-oxabicyclo[4.2.0]octa-1,6-di-
ene (17a). PhSCl (90 mg, 0.62 mmol) was gradually added to a
solution of 4-(3-phenyl-2-propynyloxy)-2-butyn-1-ol (31.0 mg,
0.155 mmol) and Et3N(0.1 mL, 0.71 mmol) in THF (1.5 mL) at
-78 °C. After being stirred for 2 h at the same temperature, the
mixture was quenched by addition of saturated aqueous NaHCO3.
The resulting mixture was extracted with AcOEt, which was washed
with water and brine, dried, and concentrated to dryness. The
residual oil was passed through a short pad of silica gel with
hexane-AcOEt (2:1) to afford the crude sulfoxide. mCPBA (35
mg, 0.20 mmol) was added to a solution of the crude sulfoxide in
CH2Cl2 (1.3 mL) at 0 °C. After being stirred for 1 h at the same
temperature, the mixture was quenched by addition of saturated
Supporting Information Available: 1H spectra for compounds
6a, 7a,e,f, 9-11, 14b, 15b,c, 16e, 18, 19, 22, 23, and 55, H and
1
13C NMR spectra for compounds 5a,c,f, 7b,c, 12, 14a, 15a, 16b-
d,f, 17a-c,e,f, 20, 21, 24, 26-31, 38-40, 41a,b, 42a,b, 43a,b,
44a,b, 45a,b, 46a,b, 49, 50, 54, 57, 58, 60, 65, 67, 69, 70, 73, 76,
77, 80, 81, 84, 89, and 90, characterization data for compounds
7b,c 17b,c, 31, 42a,b, 43a,b, 45a,b, and 46a,b, and preparation
and characterization data for compounds 5a-f, 8, 10, 14a-d, 16b-
f, 18, 20, 22, 24, 26, 28, 30, 38, 41a,b, and 44a,b. This material is
available free of charge via the Internet at http://pubs.acs.org.
JO070513P
J. Org. Chem, Vol. 72, No. 12, 2007 4461