A convenient one-pot synthesis of 1 4-dihalobutadienes from alkynes via ' titanacyclopentadienes and their transformation to a series of silole derivatives

Full text of DOI:10.1021/jo981533h

10060
J . Org. Chem. 1998, 63, 10060-10062
Sch em e 1
A Con ven ien t On e-P ot Syn th esis of
1,4-Dih a lobu ta d ien es fr om Alk yn es via
Tita n a cyclop en ta d ien es a n d Th eir
Tr a n sfor m a tion to a Ser ies of Silole
Der iva tives
Shigehiro Yamaguchi,† Ren-Zhi J in,†
Kohei Tamao,*,† and Fumie Sato‡
Institute for Chemical Research, Kyoto University, Uji,
Kyoto 611-0011, J apan, and Department of Biomolecular
Engineering, Tokyo Institute of Technology,
4259 Nagatsuta-cho, Midori-ku, Yokohama,
Kanagawa 226-8501, J apan
convenient one-pot synthesis of exocyclic and 2,3-unsub-
stituted-1,4-dihalobutadienes by the halogenolysis of
titanacyclopentadienes9 instead of zirconacyclopenta-
dienes. Transformation of the 1,4-dihalobutadienes to a
series of silole derivatives1c-e,4e-g,5 will also be described.
Received J uly 31, 1998
In tr od u ction
Butadienes having halogen functionalities on the 1,4-
positions constitute an important class of compounds as
1,4-dianion precursors. Indeed, a number of metalloles
containing main group elements have been prepared from
1,4-dihalobutadienes through halogen-metal exchange.1-5
Among a limited number of synthetic routes to 1,4-
dihalobutadienes reported so far,2-7 the most practical
way may be the iodination of zirconacyclopentadienes
which are prepared from two alkynes.4,6 This method has
recently been improved by Takahashi and co-workers to
proceed smoothly and cleanly using CuCl as an additive.5
1,4-Diiodobutadienes having a variety of substitution
modes can be now accessed by these procedures. How-
ever, this zirconacyclopentadiene route has not been
applied to the preparation of exocyclic 1,4-dihalobuta-
dienes and 2,3-unsubstituted-1,4-dihalobutadienes,8 which
are crucial precursors to bicyclic and 3,4-unsubstituted
metalloles, respectively. We now report a new and
Resu lts a n d Discu ssion
Our procedure involves the preparation and subse-
quent halogenolysis of titanacyclopentadienes derived
from alkynes with a divalent titanium complex, (η2-
propene)Ti(O-i-Pr)2, prepared in situ from Ti(O-i-Pr)4 and
i-PrMgCl, as originally reported by Sato and co-workers
(Scheme 1).10,11 Thus, the titanacyclopentadienes were
cleanly formed within 2 h at -50 °C, which were then
treated with a slight excess of iodine or bromine, followed
by stirring at room temperature for several hours, to
afford the corresponding 1,4-dihalobutadienes in good to
excellent yields. The entire procedure was carried out in
one pot. The results are summarized in Table 1.
There are several significant features to be noted. (1)
The present procedure affords various types of exocyclic
1,4-diiodobutadienes containing a four-membered ring as
well as a five- and a six membered ring from 1,5-, 1,6-,
and 1,7- diynes (entries 1-7).12b,13 As terminal groups of
the diynes, silyl (entries 1 and 2), phenyl (entries 3-5),
and even heteroaromatic groups, such as pyridyl (entry
6) and thienyl (entry 7), are applicable. (2) Intermolecular
cyclization of internal alkynes to titanacyclopentadienes
followed by iodination successfully affords tetrasubsti-
tuted 1,4-diiodobutadienes, as exemplified by entry 8.
Worthy of special note is that the present method is also
applicable to terminal alkynes (entries 9 and 10). This
is in sharp contrast to the methodologies using the
biscyclopentadienyls “Cp2M” (M ) Ti and Zr).6,12 The
reaction proceeds in a highly regioselective head-to-head
manner to produce the corresponding 2,3-unsubstituted
† Kyoyo University.
‡ Tokyo Institute of Technology.
(1) (a) Leavitt, F. C.; Manuel, T. A.; J ohnson, F. J . Am. Chem. Soc.
1959, 81, 3163. (b) Leavitt, F. C.; Manuel, T. A.; J ohnson, F.;
Matternas, L. U.; Lehman, D. S. J . Am. Chem. Soc. 1960, 82, 5099. (c)
Ru¨hlmann, K. Z. Chem. 1965, 5, 354. (d) Curtis, M. D. J . Am. Chem.
Soc. 1967, 89, 4241. (e) Dubac, J .; Laporterie, A.; Manuel, G. Chem.
Rev. 1990, 90, 215 and references therein.
(2) Atwell, W. H.; Weyenberg, D. R.; Gilman, H. J . Org. Chem. 1967,
32, 885.
(3) (a) Ashe, A. J ., III; Drone, F. J . Organometallics 1984, 3, 495.
(b) Ashe, A. J ., III; Drone, F. J . Organometallics 1985, 4, 1478.
(4) (a) Ashe, A. J ., III; Kampf, J . W.; Al-Taweel, S. M. J . Am. Chem.
Soc. 1992, 114, 372. (b) Ashe, A. J ., III; Kampf, J . W.; Al-Taweel, S.
M. Organometallics 1992, 11, 1491. (c) Ashe, A. J ., III; Kampf, J . W.;
Pilotek, S.; Rousseau, R. Organomettallics 1994, 13, 4067. (d) Ashe,
A. J ., III; Al-Ahmad, S.; Pilotek, S.; Puranik, D. B.; Elschenbroich, C.;
Behrendt, A. Organometallics 1995, 14, 2689. (e) Bankwitz, U.; Sohn,
H.; Powell, D. R.; West, R. J . Organomet. Chem. 1995, 499, C7. (f)
Freeeman, W. P.; Tilley, T. D.; Liable-Sands, L. M.; Rheingold, A. L.
J . Am. Chem. Soc. 1996, 118, 10457. (g) Yamaguchi, S.; J in, R.-Z.;
Tamao, K. J . Organomet. Chem. 1998, 559, 73.
(5) Xi, C.; Huo, S.; Afifi, T. H.; Hara, R.; Takahashi, T. Tetrahedron
Lett. 1997, 38, 4099.
(6) (a) Negishi, E.; Cederbaum, F. E.; Takahashi, T. Tetrahedron
Lett. 1986, 27, 2829. (b) Negishi, E.; Holmes, S. J .; Tour, J . M.; Miller,
J . A.; Cederbaum, F. E.; Swanson, D. R.; Takahashi, T. J . Am. Chem.
Soc. 1989, 111, 3336. (c) Buchwald, S. L.; Nielson, R. B. J . Am. Chem.
Soc. 1989, 111, 2870.
(9) Iodination of titanacyclopentadienes: Hill, J . E.; Balaich, G.;
Fanwick, P. E.; Rothwell, I. P. Organometallics 1993, 12, 2911.
(10) (a) Urabe, H.; Hata, T.; Sato, F. Tetrahedron Lett. 1995, 36,
4261. (b) Urabe, H.; Sato, F. J . Org. Chem. 1996, 61, 6756 and
references therein.
(11) The generation of olefin-titanium complexes from Ti(OR)4 and
Grignard reagents was first reported by Kulinkovich et al., See:
Kulinkovich, O. G.; Sviridov, S. V.; Vasilevski, D. A. Synthesis 1991,
234. See also: Corey, E. J .; Rao, S. A.; Noe, M. C. J . Am. Chem. Soc.
1994, 116, 9345.
(12) (a) Nugent, W. A.; Calabrese, J . C. J . Am. Chem. Soc. 1984,
106, 6422. (b) Nugent, W. A.; Thorn, D. L.; Harlow, R. L. J . Am. Chem.
Soc. 1987, 109, 2788.
(13) Tillack, A.; Baumann, W.; Lefeber, A. O. C.; Spannenberg, A.;
Kempe, R.; Rosenthal, U. J . Organomet. Chem. 1996, 520, 187.
(7) Reich, I. L.; Haile, C. L.; Reich, H. J . J . Org. Chem. 1978, 43,
2402.
(8) In the course of the present study, the preparation of the
exocylclic 1,4-dihalobutadienes by the zirconacyclopentadiene route has
been reported: Ubayama, H.; Xi, Z.; Takahashi, T. Chem. Lett. 1998,
517.
10.1021/jo981533h CCC: $15.00 © 1998 American Chemical Society
Published on Web 12/02/1998

Notes
Ta ble 1. P r ep a r a tion of 1,4-d ih a lobu ta d ien esa
J . Org. Chem., Vol. 63, No. 26, 1998 10061
Sch em e 2
istries of 2c-e and 2i, 2j have been determined by X-ray
crystallography, which will be reported elsewhere to-
gether with the aspects of their unique thermoisomer-
ization. (5) The present procedures do not require any
additives such as CuCl. This is a superior advantage for
the titanacyclopentadiene route in comparison with the
zirconacyclopentadiene route.14 (6) From an economical
point of view, the titanium reagent Ti(O-i-Pr)4 is about
one-tenth less expensive than Cp2ZrCl2, thus providing
the most convenient and practically useful methodology
for the synthesis of 1,4-dihalobutadienes.
As one example of the synthetic application of 1,4-
dihalobutadienes, we have prepared a series of silole
derivatives, as shown in Scheme 2. The iodo-lithium
exchange of 1,4-diiodobutadienes 2 with n-BuLi in ether
followed by the coupling with Si(OMe)4 gave siloles 4 in
moderate to good yields. All these siloles except for 4j
are new compounds.1e In particular, 2,5-disilylsiloles, 4a ,
4b, and 4i, are hardly accessible by other conventional
methods, despite their potentials as useful precursors for
various 2,5-difunctionalized siloles.15
Exp er im en ta l Section
Gen er a l. 1H, 13C, and 29Si NMR spectra were measured using
a J EOL EX-270 (270 MHz for 1H, 67.8 MHz for 13C, and 53.5
MHz for 29Si) spectrometer in appropriate solvents. Titanium
tetraisopropoxide was purchased from the Wako Co. and used
without further purification. Tetramethoxysilane was purchased
from the Shin-Etsu Chemical Co. and distilled before use. Diynes
1c-g were prepared by the Pd(0)-catalyzed coupling reaction
of the corresponding diynes and aryl halides in the presence of
PdCl2(PPh3)2/CuI in Et2NH.16
1,4-diiodobutadienes in both cases of (trimethylsilyl)-
acetylene (entry 9) and phenylacetylene (entry 10). The
ratio of the head-to-head product and the head-to-tail
product (1,3-disilyl- or 1,3-diphenyl-1,4-diiodobutadiene)
is 95/5 for entry 9 and 93/7 for entry 10 as determined
by 1H NMR and isolated yields, respectively. This is in a
contrast to the head-to-tail reaction observed in a similar
reaction mediated by (ArO)2TiCl2/Na where Ar denotes
the bulky 2,6-diphenylphenyl group.9 (3) 1,4-Dibromo-
butadienes were also successfully prepared by the forma-
tion of titanacyclopentadienes followed by bromination
with bromine (entries 11-13). (4) The halogenolysis of
the titanacyclopentadienes proceeds stereospecifically
with complete retention of geometry to exclusively form
(Z,Z)-1,4-dihalobutadienes in all cases. The stereochem-
(14) For comparison of the present method with the zirconacyclo-
pentadiene route, we conducted a similar reaction using 1,6-diyne 1a
with “Cp2Zr” prepared in situ from Cp2ZrCl2 and n-BuLi in THF.6a
The bicyclic zirconacyclopentadiene was cleanly formed. However, the
iodination resulted in the formation of a complex mixture even using
an excess amount of iodine, while, under Takahashi’s condition using
a 1 molar amount of CuCl as the additive,5 the iodination proceeded
at room temperature for 2 h to afford 2a in 71% yield.
(15) Synthesis of 2,5-difunctionalized siloles from 2,5-disilylsiloles:
Yamaguchi, S.; J in, R.-Z.; Ohno, S.; Tamao, K. Organometallics 1998,
17, 5133.
(16) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahadron Lett.
1975, 50, 4467.

10062 J . Org. Chem., Vol. 63, No. 26, 1998
Notes
A Typ ica l P r oced u r e for th e P r ep a r a tion of 1,4-Dih a -
lobu ta d ien es. Syn th esis of (Z,Z)-1,4-Diiod o-2,3-tetr a m eth -
ylen e-1,4-bis(tr im eth ylsilyl)-1,3-bu ta d ien e (2b). To an ether
(15 mL) solution of Ti(O-i-Pr)4 (0.36 mL, 1.20 mmol) and 1b (0.25
g, 1.00 mmol) was added an ether solution of i-PrMgCl (1.92
mL, 1.25 M, 2.40 mmol) at -70 °C. The mixture was warmed to
-50 °C over 1 h. After stirring for an additional 1 h, iodine (0.63
g, 2.50 mmol) was added as a solid to the mixture at -50 °C.
The mixture was warmed to room temperature and stirred for
2 h. A saturated aqueous solution of Na2S2O3 was added, and
the mixture was extracted with hexane. The combined extract
was washed with brine, dried over MgSO4, filtered, and evapo-
rated. The residue was subjected to column chromatography on
silica gel using hexane as an eluent (Rf ) 0.5) to afford 2b (0.45
g, 0.89 mmol) in 89% yield as a white solid: mp 70-72 °C. 1H
NMR (CDCl3) δ 0.30 (s, 18 H), 1.43-1.62 (m, 2 H), 1.80-1.95
(m, 2 H), 2.12-2.25 (m, 2 H), 2.80-2.89 (m, 2 H). 13C NMR
(CDCl3) δ 1.71, 29.09, 36.43, 101.58, 165.95. MS (EI) m/z (rel
(CDCl3) δ 0.83, 29.00, 35.92, 119.96, 156.23. MS (EI) m/z (rel
int) 410 (M+, 5), 331 (100). IR (KBr) 2925, 2860, 1580, 1440 cm-1
.
Anal. Calcd for C14H26Br2Si2: C, 40.98; H, 6.39. Found: C, 40.71;
H, 6.36.
A Typ ica l P r oced u r e for th e Syn th esis of Siloles. Syn -
th esis of 1,1-Dim eth oxy-2,5-bis(tr im eth ylsilyl)silole (4i). To
a solution of 2i (3.70 g, 8.2 mmol) in Et2O (30 mL) was added a
hexane solution of n-BuLi (10.6 mL, 1.59 M, 16.9 mmol) at -78
°C. The solution was stirred for 1 h. Tetramethoxysilane (1.21
mL, 8.2 mmol) was added to the mixture at the same temper-
ature. The resulting mixture was gradually warmed to room
temperature and stirred for 12 h. The mixture was hydrolyzed
with water and extracted with hexane. The combined extract
was washed with brine, dried over MgSO4, filtered, and evapo-
rated. The residue was passed through a short silica gel column
and then subjected to HPLC on silica gel (hexane/EtOAc ) 60/
1; Rf ) 0.12) to afford 4i (1.60 g, 5.6 mmol) in 68% yield as light
yellow oil: 1H NMR (CDCl3) δ 0.11 (s, 18H), 3.44 (s, 6H), 7.19
(s, 2H). 13C NMR (CDCl3) δ -1.00, 50.12, 138.72, 155.20. 29Si
NMR (CDCl3) δ -6.89, -7.51. MS (EI) m/z (rel int) 286 (M+,
42), 271 (100). IR (film) 2950, 2850, 1550, 1250 cm-1. Anal. Calcd
for C12H26O2Si3: C, 50.29; H, 9.14. Found: C, 50.27; H, 9.35.
int) 504 (M+, 1.2), 73 (100). IR (KBr) 2930, 2850, 1570 cm-1
.
Anal. Calcd for C14H26I2Si2: C, 33.34; H, 5.20. Found: C, 33.48;
H,5.26.
A Typ ica l P r oced u r e for th e Syn th esis of (Z,Z)-1,4-
Dibr om obu ta d ien e: Syn th esis of (Z,Z)-1,4-Dibr om o-2,3-
tetr a m eth ylen e-1,4-bis(tr im eth ylsilyl)-1,3-bu ta d ien e (3b).
To an ether (10 mL) solution of Ti(O-i-Pr)4 (0.37 mL, 1.26 mmol)
and 1b (0.25 g, 1.00 mmol) was added an ether solution of
i-PrMgCl (1.59 mL, 1.70 M, 2.70 mmol) at -78 °C. The mixture
was warmed to -50 °C over 1 h. After stirring at the same
temperature for an additional 1 h, bromine (113 µL, 2.20 mmol)
was added at -78 °C. The mixture was warmed to room
temperature and stirred for 2 h. A saturated aqueous solution
of Na2S2O3 was added. The mixture was extracted with hexane.
The combined extract was washed with brine, dried over MgSO4,
filtered, and evaporated. The residue was subjected to column
chromatography on silica gel using hexane as an eluent to give
3b (0.32 g, 0.78 mmol) in 78% yield as a white solid: mp 53-55
°C. 1H NMR (CDCl3) δ 0.28 (s, 18 H), 1.35-1.63 (m, 2 H), 1.79-
1.98 (m, 2 H), 2.00-2.15 (m, 2 H), 2.66-2.80 (m, 2 H). 13C NMR
Ack n ow led gm en t. This work was partly supported
by Grant-in-Aids (No. 07555280 and 09239103) from the
Ministry of Education, Science, Sports and Culture,
J apan, and by the J apan High Polymer Center.
Su p p or tin g In for m a tion Ava ila ble: The detailed ex-
perimental procedures and spectral and analytical data for
compounds 2-4 (7 pages). 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.
J O981533H