Stannylcupration of acetylenes followed by reaction with epoxides: A novel annulation strategy for the synthesis of cyclobutenes

Full text of DOI:10.1021/jo980874s

J . Org. Chem. 1998, 63, 7531-7533
7531
Sch em e 1
Sta n n ylcu p r a tion of Acetylen es F ollow ed
by Rea ction w ith Ep oxid es: A Novel
An n u la tion Str a tegy for th e Syn th esis of
Cyclobu ten es
the general reaction. It provides an easy entry to the
synthesis of potentially useful small tin-synthons of wide
synthetic applicability. In this paper, we report the
stannyl cupration of acetylenes followed by reaction with
epoxides as a simple and efficient route to the synthesis
of cyclobutenes.
Asuncio´n Barbero, Purificacio´n Cuadrado,
Carlos Garc´ıa, J uan A. Rinco´n, and Francisco J . Pulido*
Departamento de Quı´mica Orga´nica, Facultad de Ciencias,
Universidad de Valladolid, Valladolid 47011, Spain
Received May 7, 1998
Several strategies have been reported in the literature
for the synthesis of cyclobutenes. The most available
route to cyclobutenes is the photochemical7 or thermal8
[2 + 2] cycloaddition between an alkyne and an alkene.
These methods have been thoroughly reviewed.9 Extru-
sion of sulfur dioxide from appropriate cyclic sulfones
leads to the formation of cyclobutenes. This reaction,
known as the Ramberg-Ba¨cklund rearrangement, has
been used widely in synthesis.10 A third approach
involves the introduction of a double bond into a pre-
formed cyclobutane ring, typically via an elimination
reaction.11 A number of less general routes for making
cyclobutenes have also been described.12-15
The metallocupration of allenes and acetylenes is a
powerful and synthetically useful reaction because it
generates two adjacent and usually well differentiated
carbon atoms that react sequentially with a wide range
of electrophiles (Scheme 1).
Our results in this area have been extensively pub-
lished in the past years.1,2 Other examples of stoichio-
metric3 or catalytic4 metallometalations of unactivated
CdC π bonds have been reported recently, including the
addition of silicon-magnesium,5 silicon-aluminum,5 and
silicon-zinc5 bonds to allenes.
The stannylcupration of acetylenes has been widely
studied in our group,6 and it is a particular example of
Some time ago, we reported in a short paper16 two
examples of cyclobutene ring formation from vinylstan-
nanes initiated by treatment with butyllithium.
(1) SiCu of allenes and acetylenes: (a) Fleming, I.; Pulido, F. J . J .
Chem. Soc., Chem. Commun. 1986, 1010. (b) Cuadrado, P.; Gonza´lez,
A. M.; Pulido, F. J .; Fleming, I. Tetrahedron Lett. 1988, 29, 1825. (c)
Cuadrado, P.; Gonza´lez, A. M.; Pulido, F. J .; Fleming, I.; Rowley, M.
Tetrahedron 1989, 45, 413. (d) Barbero, A.; Cuadrado, P.; Gonza´lez,
A. M.; Pulido, F. J .; Fleming, I. J . Chem. Soc., Perkin Trans. 1 1991,
2811. (e) Blanco, F. J .; Cuadrado, P.; Gonza´lez, A. M.; Pulido, F. J .;
Fleming, I. Tetrahedron Lett. 1994, 35, 8881. (f) Barbero, A.; Cuadrado,
P.; Gonza´lez, A. M.; Pulido, F. J .; Fleming, I.; Sa´nchez, A. J . Chem.
Soc., Perkin Trans. 1 1995, 1525. (g) Blanco, F. J .; Cuadrado, P.;
Gonza´lez, A. M.; Pulido, F. J . Synthesis 1996, 42.
(2) SnCu of allenes: (a) Barbero, A.; Cuadrado, P.; Gonza´lez, A. M.;
Pulido, F. J .; Fleming, I. J . Chem. Soc., Chem. Commun. 1990, 1030.
(b) Barbero, A.; Cuadrado, P.; Gonza´lez, A. M.; Pulido, F. J .; Fleming,
I. J . Chem. Soc., Perkin Trans. 1 1992, 327. (c) Barbero, A.; Cuadrado,
P.; Gonza´lez, A. M.; Pulido, F. J .; Fleming, I. J . Chem. Res. 1990, 297,
291. (d) See also ref 1c.
(3) (a) Sharma, S.; Oehlschlager, A. C. J . Org. Chem. 1991, 56, 770.
(b) Singer, R. D.; Hutzinger, M. W.; Oehlschlager, A. C. J . Org. Chem.
1991, 56, 4933. (c) Singer, R. D.; Hutzinger, M. W.; Oehlschlager, A.
C. J . Am. Chem. Soc. 1990, 112, 9397. (d) Piers, E.; Gavai, A. V. J .
Org. Chem. 1990, 55, 2374 and 2380. (e) Piers, E.; Chong, J . M. Can.
J . Chem. 1988, 66, 1425. (f) Cox, S. D.; Wudl, F. Organometallics 1983,
2, 184. (g) Lipshutz, B. H.; Sharma, S.; Reuter, D. C. Tetrahedron Lett.
1990, 31, 7253. (h) Lipshutz, B. H.; Reuter, D. C. Tetrahedron Lett.
1989, 30, 4617 and 2065. (i) Magriotis, P. A.; Scott, M. E.; Kim, K. D.
Tetrahedron Lett. 1991, 32, 6085. (j) Marino, J . P.; Edmonds, M. V.
M.; Stengel, P. J .; Oliveira, A. R. M.; Simonelli, F.; Ferreira, J . T. B.
Tetrahedron Lett. 1992, 33, 49. (k) Beaudet, I.; Parrain, J . L.; Quintard,
J . P. Tetrahedron Lett. 1991, 32, 6333. (l) Marek, I.; Alexakis, A.;
Normant, J . F. Tetrahedron Lett. 1991, 32, 6337. (m) Pereira, O. Z.;
Chan, T. H. Tetrahedron Lett. 1995, 36, 8749. (n) Pereira, O. Z.; Chan,
T. H. J . Org. Chem. 1996, 61, 5406. (o) See also ref 1c and citations
therein.
(4) (a) Sharma, S.; Oehlschlager, A. C. Tetrahedron Lett. 1986, 27,
6161. (b) Sharma, S.; Oehlschlager, A. C. Tetrahedron Lett. 1988, 29,
261. (c) Nozaki, K.; Wakamatsu, K.; Nonaka, T.; Tu¨ckmantel, W.;
Oshima, K.; Utimoto, K. Tetrahedron Lett. 1986, 27, 2007. (d) Nonaka,
T.; Okuda, Y.; Matsubara, S.; Oshima, K.; Utimoto, K.; Nozaki, H. J .
Org. Chem. 1986, 51, 4716. (e) Mitchell, T. N.; Wickenkamp, R.;
Amaria, A.; Dicke, R.; Schneider, U. J . Org. Chem. 1987, 52, 4868. (f)
Mitchell, T. N. J . Organomet. Chem. 1992, 437, 127. (g) See also ref
1c and citations therein.
We now report in full an apparently general method
for the synthesis of 1- and 3-substituted cyclobutenes
from acetylenes and epoxides using our stannylcupration
methodology. Reaction of acetylenes 1a -c with lithium
methyl(tributylstannyl)cuprate6b or lithium bis(tributyl-
stannyl)cuprate,6b in THF at -78 °C, leads to cis-2-
(tributylstannyl)vinyl cuprates 2a -c, which are syntheti-
cally equivalent to cis-1,2-ethylene dianions (Scheme 2).
Addition of the tin-copper pair across the triple bond
occurs syn-stereospecifically, thus providing an easy
entry to the synthesis of Z-vinylstannanes.6 As we noted
previously,6 phenylacetylene (1b) reacts with our tin
cuprate with regiochemistry opposite to that of 1-decyne
(1c). The intermediate cuprates 2 react well with eth-
ylene oxide at low temperature (-78 to 0 °C), giving the
(7) (a) Fuks, R.; Viehe, H. G. In Chemistry of Acetylenes; Viehe, H.
G., Ed.; Dekker: New York, 1969; p 434. (b) Cargill, R. L.; Beckham,
M. E.; Siebert, A. E.; Dorn, J . J . Org. Chem. 1965, 30, 3647. (c) Scharf,
H. D.; Mattay, J . J ustus Liebigs Ann. Chem. 1977, 772.
(8) (a) Vos, G. J . M.; Benders, P. H.; Reinhoudt, D. N.; Egberink, R.
J . M.; Harkema, S.; Van Hummel, G. J . J . Org. Chem. 1986, 51, 2004.
(b) Cook, A. G. In Enamines: Synthesis, Structure and Reactions; Cook,
A. G., Ed.; Dekker: New York, 1988. (c) Ficini, J .; d’Angelo, J .
Tetrahedron Lett. 1976, 687.
(9) Carbocyclic Four-Membered Ring Compounds, Houben-Weyl
Methods of Organic Chemistry; deMeijere, A., Ed.; Thieme: Stuttgart,
1997; Vol. 17f, E17e-f.
(10) (a) Paquette, L. A. Acc. Chem. Res. 1968, 1, 209. (b) Paquette,
L. A.; Photis, J . M. J . Am. Chem. Soc. 1974, 96, 4715.
(11) (a) Aben, R. W.; Scheeren, H. W. J . Chem. Soc., Perkin Trans.
1 1979, 3132. (b) Halazy, S.; Krief, A. Tetrahedron Lett. 1980, 21, 1997.
(12) Sohn, M. B.; J ones, M., J r. J . Am. Chem. Soc. 1972, 94, 8280.
(13) (a) Vincens, M.; Dumont, C.; Vidal, M. Bull. Soc. Chim. Fr.
1984, Part 2, 59. (b) Vincens, M.; Dumont, C.; Vidal, M. Tetrahedron
Lett. 1986, 27, 2267.
(5) Morizawa, Y.; Oda, H.; Oshima, K.; Nozaki, H. Tetrahedron Lett.
1984, 25, 1163.
(6) SnCu of acetylenes: (a) Barbero, A.; Cuadrado, P.; Gonza´lez, A.
M.; Pulido, F. J .; Fleming, I. J . Chem. Soc., Chem. Commun. 1992,
351. (b) Barbero, A.; Cuadrado, P.; Gonza´lez, A. M.; Pulido, F. J .; Rubio,
R.; Fleming, I. J . Chem. Soc., Perkin Trans. 1 1993, 1657.
(14) (a) Pettit, R.; Henery, J . Org. Synth. 1970, 50, 36. (b) Vogel,
E.; Hasse, K. J ustus Liebigs Ann. Chem. 1958, 615, 22.
(15) Negishi, E.; Boardman, L. D.; Sawada, H.; Bagheri, V.; Stoll,
A. T.; Tour, J . M.; Rand, C. L. J . Am. Chem. Soc. 1988, 110, 5383.
(16) Barbero, A.; Cuadrado, P.; Gonza´lez, A. M.; Pulido, F. J .; Rubio,
R.; Fleming, I. Tetrahedron Lett. 1992, 33, 5841.
S0022-3263(98)00874-3 CCC: $15.00 © 1998 American Chemical Society
Published on Web 09/24/1998

7532 J . Org. Chem., Vol. 63, No. 21, 1998
Notes
Sch em e 2
Sch em e 3
Sch em e 4
Ta ble 1. Syn th esis of Cyclobu ten es 4a -c a n d 7a ,b a n d
Cyclobu ta n es 10a ,b
temperature, 4b undergoes electrocyclic ring opening to
a considerable extent. Yields of cyclobutenes 4 and 7
refer to isolated pure compounds; however, conversion
of tosylated alcohols into cyclobutenes seems to be
complete as was shown by GC and NMR analysis of the
crude product.
Although 1,2-disubstituted cyclobutenes could be ob-
tained starting from disubstituted acetylenes, we re-
ported previously6 that the intermediate cuprates derived
from disubstituted acetylenes show a low reactivity
toward electrophiles, including ethylene oxide, and there-
fore, yields of 1,2-disubstituted cyclobutenes are poor.18
The procedure herein described is highly versatile.
Thus, through the choice of allenes 8a ,b as starting
materials and our usual cuprate, it is possible to prepare
the alcohols 9a ,b regioselectively (Scheme 4). Following
the same protocol as before (TsCl, rt, and BuLi, -78 °C)
alcohols 9 are converted into methylenecyclobutanes
10a ,b in very acceptable yields (Scheme 4, Table 1).
In summary, we report a new [2 + 2] annulation
strategy for the synthesis of cyclobutenes by coupling of
a C2 acetylenic synthon and a C2 epoxide synthon, where
the key step for the success of the synthesis is the syn
addition of the tincuprate to the acetylene that controls
the cis stereochemistry required for the final cyclization
step.
a
b
Isolated yields. Isolated as the dibromo derivative (bp 66-
69 °C/22 mmHg). c Isolated as the dibromo derivative (bp 82-87
°C/20 mmHg).
primary alcohols 3a -c (Scheme 2). The use of TMEDA
increases yields significantly. We prepared the p-tolu-
enesulfonates of alcohols 3a -c by standard procedures.
When we treated the former p-toluenesulfonates with
butyllithium (THF, -40 to 0 °C, 1 h), the major products
were the 1-substituted cyclobutenes 4a -c (Scheme 2,
Table 1). It should be noted that the tin-lithium
exchange takes place faster than the attack of butyl-
lithium to the tosylate group.
The same methodology but using a different strategy
enabled us to prepare 3-substituted cyclobutenes. There-
fore, substituted epoxides 5a ,b react with the cis-2-
(tributylstannyl)vinyl cuprate 2a resulting from the
stannylcupration of acetylene 1a , in the presence of BF3‚
Et2O, to give the alcohols 6a ,b17 (Scheme 3). Tosylation
of 6a ,b followed by intramolecular nucleophilic displace-
ment initiated by treatment with BuLi affords the
3-substituted cyclobutenes 7a ,b (Scheme 3, Table 1).
Cyclobutenes 4a -c and 7a ,b are quite stable. They can
be distilled under reduced pressure and stored for a long
time in the refrigerator. However, after 2 weeks at room
Exp er im en ta l Section
All boiling points are uncorrected. All reagents were of
commercial quality from freshly opened containers or were
purified before use. THF was distilled under N2 from purple
solutions of sodium benzophenone ketyl. Acetylene 1a (99.6%),
allene 8a (97%), and ethylene oxide (99.9%) were supplied by
Air-Products in lecture bottles. Commercial reagents 1b,c and
5a ,b were purchased from Aldrich. Preparation of allene 8b was
reported in a previous paper.1c IR spectra were recorded on a
FT/IR spectrophotometer as neat liquid films. 1H and 13C NMR
spectra were taken at 200 and 50 MHz, respectively. GC/MS
were recorded operating either in CI mode or EI mode (70 eV).
(17) Alcohol 6b is obtained along with a small amount (11%) of the
regioisomeric alcohol resulting from attack of 2a to the substituted
end of the epoxide. In the absence of BF3‚Et2O, the reaction gives poor
yields.
(18) A typical reaction using diphenylacetylene led to only a 15% of
1,2-diphenylcyclobutene.

Notes
J . Org. Chem., Vol. 63, No. 21, 1998 7533
Purification of products were performed by flash chromatography
on silica gel 60 (Merck, 230-400 mesh). Lithium bis(tributyl-
stannyl)cuprate was prepared and used as reported in our
original work.6b Nonaqueous reactions were carried out under
nitrogen atmosphere. Compounds 3a ,b and 9a were described
in previous papers.2b,6b The very well-known compounds 4a and
10a were isolated as 1,2-dibromo derivatives, due to their low
boiling point. Unless otherwise noted, yields of all compounds
are of purified material.
Gen er a l P r oced u r e for th e P r ep a r a tion of Alcoh ols 3.
Typically, a solution of the acetylene 1 (4 mmol) in THF (4 mL)
was added dropwise to the lithium bis(tributylstannyl)cuprate6b
reagent (4 mmol) cooled with a solid carbon dioxide-acetone
bath, and the mixture was stirred for 1 h. TMEDA (4.5 mmol)
was added to the stannylcupration mixture at -70 °C. After 5
min, ethylene oxide (8 mmol) was added at -70 °C, and the
resulting mixture was warmed to 0 °C for 1 h, with continuous
stirring. Saturated aqueous ammonium chloride (10 mL) was
added to the mixture. Extraction with diethyl ether, drying
(MgSO4), and chromatography (hexanes-EtOAc) gave the al-
cohols 3a -c (Scheme 2). We described compounds 3a (93%) and
3b (84%) in a previous paper.6b
68 (base). Anal. Calcd for C12H22: C, 86.67; H, 13.33. Found:
C, 86.98; H, 13.56
3-P h en ylcyclobu ten e (7a ): colorless liquid (78%); bp 48-
51 °C/1 mmHg; IR (neat) 3050-3030, 1592 cm-1 1H NMR
;
(CDCl3) δ 7.43-7.20 (m, 5H), 6.21 (d with fine couplings, J )
1.9 Hz, 1H), 6.02 (d, J ) 1.9 Hz, 1H), 4.23 (dd, J ) 5.4, 2.6 Hz,
1H), 3.19 (dd, J ) 15.4, 5.2 Hz, 1H), 2.37 (dd, J ) 15.4, 2.3 Hz,
1H); 13C NMR (CDCl3) δ 143.7, 135.5, 131.9, 128.3, 127.6, 126.8,
68.6, 59.21; MS (EI) m/z 130 (M+), 129 (base). Anal. Calcd for
C10H10: C, 92.26; H, 7.74. Found: C, 92.58; H, 7.85.
3-Octylcyclobu ten e (7b): colorless liquid (85%); bp 52-55
°C/1 mmHg; IR (neat) 3045 cm-1; 1H NMR (CDCl3) δ 6.08 (d, J
) 1.8 Hz, 1H), 5.96 (d with fine couplings, J ) 1.8 Hz, 1H), 2.75
(m, 1H), 2.64 (dd, J ) 11.2, 3.1 Hz, 1H), 2.03 (dd, J ) 11.2, 1.1
Hz, 1H), 1.57-1.20 (m, 14H), 0.82 (t, J ) 7.3 Hz, 3H); 13C NMR
(CDCl3) δ 140.4, 135.9, 62.3, 53.8, 44.1, 38.5, 37.1, 35,3, 32,6,
26.14, 22.6, 14.6; MS (EI) m/z 166 (M+), 54 (base). Anal. Calcd
for C12H22: C, 86.67; H, 13.33. Found: C, 86.87; H, 13.50.
Gen er a l P r oced u r e for th e P r ep a r a tion of Alcoh ols 9.
The allene 81c (4 mmol) in THF (4 mL) was added to the lithium
bis(tributylstannyl)cuprate6b (4 mmol) at -70 °C, and the
mixture was stirred for 1 h. Ethylene oxide (8 mmol) was added
to the stannylcupration mixture at -70 °C, and the resulting
mixture was warmed to 0 °C for 1 h. The usual workup and
chromatography (hexane/EtOAc) gave the alcohols 9a ,b (Scheme
4). We described alcohol 9a (78%) in a previous paper.2b
(E)-5-P h en yl-4-(tr ibu tylsta n n yl)p en t-4-en -1-ol (9b): col-
orless oil (86%); IR (neat) 3350 cm-1; 1H NMR (CDCl3) δ 7.31-
7.18 (m, 5H), 6.53 (s with fine couplings, 1H), 3.62 (t, J ) 7.1
Hz, 2H), 2.42 (t, J ) 6.7 Hz, 2H), 1.87 (m, 2H), 1.69 (broad s,
1H), 1.65-0.78 (m, 27H); 13C NMR (CDCl3) δ 157.7, 146.2, 137.0,
129.2, 128.7, 127.3, 63.2, 45.1, 32.8, 29.1, 27.3, 14.5, 10.1; MS
(CI) m/z 453 (M + H)+, 395 (base). Anal. Calcd for C23H40OSn:
C, 61.22; H, 8.94. Found: C, 61.35; H, 9.03.
Gen er a l P r oced u r e for th e P r ep a r a tion of Cyclobu ta n es
10. The alcohols 9a ,b (3 mmol) were stirred with tosyl chloride
(4 mmol) and triethylamine (4 mmol) in dichloromethane (12
mL) at room temperature overnight. Hexane (3 mL) was added
to precipitate the excess of tosyl chloride, and the solution was
filtered and concentrated. The crude tosylate (94-97%, 1H NMR
δ 3.97-4.08, CH2-OTs) was dissolved in THF (4 mL) and used
without further purification for better yields. BuLi (4.5 mmmol,
1.6 M in hexane) was added at -70 °C, and the mixture was
stirred at this temperature for a few minutes. Then, the
resulting brownish solution was allowed to warm to 0 °C during
2 h. Brine was added (5 mL), and the mixture was extracted
with Et2O and dried (MgSO4). Rotoevaporation of the solvent
and Kugelrohr distillation of the residue gave 10b (359 mg, 2.5
mmol, 83% from 9b) (Scheme 4, Table 1). The known compound
10a (57%, bp 42 °C, Aldrich) was isolated as the dibromo
derivative by addition of bromine to the reaction mixture before
the final workup (Table 1).
(Z)-4-(Tr ibu tylsta n n yl)d od ec-3-en -1-ol (3c): colorless oil
(87%); IR (neat) 3630, 3350 cm-1
;
1H NMR (CDCl3) δ 5.97 (t,
3
1H, J ) 7.2 Hz, J Sn-H ) 136 Hz), 3.63 (t, 2H, J ) 6.9 Hz), 2.38
(dt, 2H, J ) 7.2, 6.9 Hz), 2.17 (t, 2H, J ) 6.7 Hz), 1.65 (broad s,
1H), 1.55-0.8 (m, 42H); 13C NMR (CDCl3) δ 147.8, 135.9, 62.1,
41.1, 37.7, 32.4, 31.1, 30.0, 29.6, 29.1, 28.7, 28.2, 23.5, 14.7, 14.2,
10.2; MS (CI) m/z 475 (M + H)+, 247 (base). Anal. Calcd for
C24H50OSn: C, 60.90; H, 10.65. Found: C, 61.18; H, 10.81.
Gen er a l P r oced u r e for th e P r ep a r a tion of Alcoh ols 6.
A solution of BF3‚Et2O (4 mmol) in THF (4 mL) was added
dropwise to a THF solution (4 mL) of the epoxide 5 (4 mmol) at
-70 °C, and the mixture was stirred for 10 min. Immediately,
the cuprate 2a (4 mmol), prepared as before, in THF (4 mL) was
added from an adjacent flask, via cannula, at -70 °C, and the
resulting mixture was warmed to 0 °C for 1 h. An aqueous
workup using ammonium chloride, extraction with diethyl ether
(2 × 15 mL), drying with magnesium sulfate, and chromatog-
raphy (SiO2, hexane/EtOAc) gave the alcohols 6a (77%) and 6b
(69%) (Scheme 3).
(Z)-2-P h en yl-4-(tr ibu tylsta n n yl)bu t-3-en -1-ol (6a ): color-
less oil (77%); IR (neat) 3400 cm-1
;
1H NMR (CDCl3) δ 7.45-
3
7.25 (m, 5H), 6.72 (dd, J ) 12.3, 6.2 Hz, J Sn-H ) 132 Hz, 1H),
2
6.18 (d, J ) 12.3 Hz, J Sn-H ) 55.5 Hz, 1H), 3.81-3.68 (m, 2H),
3.28 (q with fine couplings, J ) 6.2 Hz, 1H), 1.61 (broad s, 1H),
1.45-0.9 (m, 27H); 13C NMR (CDCl3) δ 148.1, 140.5, 132.6, 128.1,
127.0, 126.2, 66.4, 55.8, 29.4, 27.3, 13.7, 9.1; MS (CI) m/z 439
(M + H)+, 269 (base). Anal. Calcd for C22H38OSn: C, 60.43; H,
8.76. Found: C, 60.61; H, 8.89.
Gen er a l P r oced u r e for th e Syn th esis of Cyclobu ten es
4 a n d 7. The alcohols 3 and 6 were tosylated by standard
procedures (TsCl, Et3N, CH2Cl2, rt, 4 h). The former tosylates
(2.8 mmol) in THF (3 mL) were treated with BuLi (4.2 mmol,
1.6 M in hexane) at -40 °C, and the resulting solution was
warmed to 0 °C for 1 h with continuous stirring. Brine was
added (5 mL) and the mixture extracted with diethyl ether (2 ×
10 mL) and dried with MgSO4. Careful rotoevaporation of the
solvent and microdistillation of the oily residue gave the final
products 4 and 7 (Schemes 2 and 3, Table 1). The known
compound 4a (72%, bp 2 °C) was isolated as the 1,2-dibromo
derivative by addition of bromine to the reaction mixture before
the final workup (Table 1).
Ben zylid en ecyclobu ta n e (10b): colorless liquid (83%); bp
67-72 °C/3 mmHg (lit.20 bp 112-113 °C/15 mmHg); IR (neat)
1672 cm-1; 1H NMR (CDCl3) δ 7.41-7.18 (m, 5H), 6.14 (m, 1H),
3.14-2.88 (m, 4H), 2.19 (quintet, J ) 6 Hz, 2H); 13C NMR
(CDCl3) δ 141.27, 132.7, 129.3, 128.6, 127.5, 115.9, 34.5, 30.5,
18.1; MS (EI) m/z 144 (M+), 129 (base).
Ack n ow led gm en t. This work was supported by the
D.G.E.S. (Project PB-96/0357) from the Ministry of
Education and Science of Spain.
1-P h en ylcyclobu ten e (4b): colorless liquid (67%); bp 62-
Su p p or tin g In for m a tion Ava ila ble: Full spectroscopic
and analytical data for compound 6b. Experimental procedure
for the tosylation of alcohols 3 and 6, as well as 1H NMR
characterization data of all tosylates (1 page). This material
is contained in libraries on microfiche, immediately follows this
article in the microfilm version of the journal, and can be
ordered from the ACS; see any current masthead page for
ordering information.
65 °C/3 mmHg (lit.19 bp 68-70 °C/3.5 mmHg); IR (neat) 1623
1
cm-1; H NMR (CDCl3) δ 7.24-7.15 (m, 5H), 6.21 (s, 1H), 2.84
(m, 2H), 2.45 (m, 2H); 13C NMR (CDCl3) δ 148.4, 134.8, 128.2,
127.9, 127.1, 126.4, 37.1, 30.9; MS (EI) m/z 130 (M+), 51 (base).
1-Octylcyclobu ten e (4c): colorless liquid (82%); bp 45-48
1
°C/1.5 mmHg; IR (neat) 1642 cm-1; H NMR (CDCl3) δ 5.67 (s
with fine couplings, 1H), 2.38 (t, J ) 2.8 Hz, 2H), 2.29 (t, J )
2.8 Hz, 2H), 1.97 (t, J ) 7.5 Hz, 2H), 1.50-1.21 (m, 12H), 0.93
(t, J ) 7.2 Hz, 3H); 13C NMR (CDCl3) δ 151.3, 128.6, 35.7, 32.9,
32.1, 31.7, 29.6, 29.5, 28.7, 28.1, 23.3, 14.2; MS (EI) m/z 166 (M+),
J O980874S
(20) Schweizer, E. E.; Thompson, J . G.; Ulrich, T. A. J . Org. Chem.
1968, 33, 3082.
(19) Wilt, J . W.; Roberts, D. D. J . Org. Chem. 1962, 27, 3430.