Highly Stereoselective Synthesis of Conjugated Polyenes via a Homocoupling Reaction of Unsaturated Silanes

Article abstract of DOI:10.1021/jo9700437

A new method for the synthesis of conjugated polyenes containing up to eight double bonds with all-E configuration is reported.The procedure is based upon a homocoupling reaction of dienyl-, trienyl, or tetraenylsilanes, promoted by PdCl2 in methanol and in the presence of LiCl and CuCl2.Configurational and conformational assignments were rigorously made on the basis of NMR spectra.The compounds obtained represent a novel interesting class of symmetrically substituted polyenes with potential optical and electrooptical properties.By changing the solvent, the homocoupling process can be switched to the halogenation of the silyl-substituted terminal double bond, thus leading to polyenyl halides.

Full text of DOI:10.1021/jo9700437

J . Org. Chem. 1997, 62, 3291-3298
3291
High ly Ster eoselective Syn th esis of Con ju ga ted P olyen es via a
Hom ocou p lin g Rea ction of Un sa tu r a ted Sila n es
Francesco Babudri, Angela R. Cicciomessere, Gianluca M. Farinola, Vito Fiandanese,
Giuseppe Marchese, Roberta Musio, Francesco Naso,* and Oronzo Sciacovelli
Centro CNR di Studio sulle Metodologie Innovative di Sintesi Organiche, Dipartimento di Chimica,
Universita` di Bari, via Amendola 173, 70126 Bari, Italy
Received J anuary 7, 1997X
A new method for the synthesis of conjugated polyenes containing up to eight double bonds with
all-E configuration is reported. The procedure is based upon a homocoupling reaction of dienyl-,
trienyl-, or tetraenylsilanes, promoted by PdCl2 in methanol and in the presence of LiCl and CuCl2.
Configurational and conformational assignments were rigorously made on the basis of NMR spectra.
The compounds obtained represent a novel interesting class of symmetrically substituted polyenes
with potential optical and electrooptical properties. By changing the solvent, the homocoupling
process can be switched to the halogenation of the silyl-substituted terminal double bond, thus
leading to polyenyl halides.
In tr od u ction
molecular electronic system (molecular wires).7 More-
over, R,ω-disubstituted polyolefinic systems bearing an
electron-accepting group on one end and a donor group
on the opposite end, the so-called “push-pull” polyenes,
show a preferential one-way electron transfer, and such
molecular wires should simulate a rectifying component.7
Polyenes with a defined length of the π-system are also
taken as discrete models of polymeric conjugated materi-
als. For example, the behavior of anionic species gener-
ated from R,ω-diphenylpolyenes has been investigated in
order to clarify the charge transfer mechanism in trans-
polyacetylene.8
In this framework, the presence of a stereoregular all-E
structure in the polyenes is of importance. Thus, it is
not surprising that considerable efforts have been made
to search for stereoselective methods of synthesis of these
conjugated systems. The availability of some polycon-
jugated stereodefined carbonyl compounds, such as cro-
cetin dialdehyde or 2,7-dimethyloctatriendial,9a structur-
ally derived from carotenoids, opens the access to
carotenoid-like polyenes with a more extended π-system,
via Wittig or Wittig-like olefination. Following these
synthetic procedures, polyenes which combine the struc-
tural features of carotenoids and various terminal groups
such as anthryl,9 naphthyl,9a thienyl,10 pyridyl,9b,11 and
5,10,15,20-tetraphenylporphyrinyl9a,d or push-pull poly-
enes with a similar structure have been synthesized.12
However, referring to the stereochemistry of the new
double bonds formed, Wittig olefination and related
The concept of molecular electronics,1 i.e. the possibility
of performing electronic functions in molecular scale, has
led to extensive investigations about electrical2 and
optical3 properties of organic molecules.
Among the various classes of organic compounds which
are of particular importance in these studies, molecules
with a long conjugated π-system are envisaged as the
most promising materials for future applications in
molecular-electronic devices.
Both conjugated polymers and polyenes with a defined
length of the π-system are well-known to provide large
and fast second-order and third-order nonlinear optical
responses.3a,4 In particular, the third-order nonlinear
susceptibility, ø3, has been determined for R,ω-diphe-
nylpolyenes up to six conjugated double bonds,5 and an
enhancement in the values of ø3 is expected for bipo-
laronic states of these and other R,ω-disubstituted poly-
enes.6
Owing to the presence of high polarizable π-electrons,
similar molecules should act as connectors permitting
electron flow to occur between different elements of a
X Abstract published in Advance ACS Abstracts, March 15, 1997.
(1) (a) Carter, F. L., Ed. Molecular Electronic Devices; Marcel
Dekker: New York, 1982; (b) Ashwell, G. J ., Ed. Molecular Electronics;
Research Studies Press LTD: Taunton, 1992.
(2) For a general review on this topic, see: Skotheim, T. A., Ed.
Handbook of Conducting Polymers; Marcel Dekker: New York, 1986.
Kiess, H. G., Ed. Conjugated Conducting Polymers; Springer Verlag:
Heidelberg, 1992.
(3) For
a
general review on this topic, see: (a) Prasad, P. N.,
(7) (a) Aviram, A.; Ratner, M. A. Chem. Phys. Lett. 1974, 29, 277-
283. (b) Lehn, J . M. Angew. Chem., Int. Ed. Engl. 1990, 29, 1304-
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Clays, K.; Persoons, A.; Marder, S. R.; Bre´das, J . L. J . Am. Chem. Soc.
1995, 117, 10127-10128.
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(b) Effenberger, F.; Niesert, C. P. Synthesis 1992, 1137-1144. (c)
Effenberger, F.; Schlosser, H.; Bau¨erle, S. M.; Maier, S.; Port, H.; Wolf,
H. C. Angew. Chem., Int. Ed. Engl. 1988, 27, 281-284. (d) Effenberger,
F.; Strobel, H. Chem. Ber. 1993, 126, 1683-1691.
Williams, D. J ., Eds. Introduction to Nonlinear Optical Effects in
Molecules and Polymers; J ohn Wiley: New York, 1991. (b) Marder,
S. R., Sohn, J . E., Stucky, G. D., Eds. Materials for Nonlinear Optics;
ACS Symposium Series 455; Washington, 1991. (c) Chemla, D. S.;
Zyss, J ., Eds. Nonlinear Optical Properties of Organic Molecules and
Crystals; Academic Press: New York, 1987. Munn, R. W., Ironside,
C. N., Eds. Principles and Applications of Nonlinear Optical Materials;
Chapman and Hall: London, 1993; Wagnie`re, G. H. Linear and
Nonlinear Optical Properties of Molecules; Verlag Helvetica Chimica
Acta: Basel, 1993. Optical Nonlinearities in Chemistry; special issue
of Chem. Rev. 1994, 94.
(4) Bre´das, J . L., Chance, R. R., Eds. Conjugated Polymeric Materi-
als: Opportunities in Electronics, Optoelectronics and Molecular Elec-
tronics; Kluwer: Dordrecht, 1990.
(5) Bunning, T. J .; Natarajan, L. V.; Schmitt, M. G.; Epling, B. L.;
Crane, R. L. Appl. Opt. 1991, 30, 4341-4349.
(10) Kajzar, F.; Sentein, C.; Zamboni, R.; Ferracuti, P.; Rossini, S.;
Danieli, R.; Ruani, G.; Taliani, C. Synth. Met. 1991, 41, 3177-3180.
(11) Blanchard-Desce, M.; Arrhenius, T. S.; Lehn, J . M. Bull. Soc.
Chim. Fr. 1993, 130, 266-272.
(6) (a) Spangler, C. W.; Pei-Kang, L.; Havelka, K. O. J . Chem. Soc.,
Perkin Trans. 2 1992, 1207-1211. (b) Nickel, E. G.; Spangler, C. W.;
Tang, N.; Hellwarth, R.; Dalton, L. In Organic Materials for Non-linear
Optics III; Ashwell, G. J ., Bloor, D., Eds.; Royal Society of Chemistry:
Cambridge, 1993; pp 237-242.
(12) (a) Hagen, S.; Roth, S.; Hanack, M. Synth. Met. 1991, 41, 1557-
1561. (b) Blanchard-Desce, M.; Ledoux, I.; Lehn, J . M.; Malthete, J .;
Zyss, J . J . Chem. Soc., Chem. Commun. 1988, 737-739. (c) Effen-
berger, F.; Heid, S.; Merkle, R.; Zimmermann, P. Synthesis 1995,
1115-1120.
S0022-3263(97)00043-1 CCC: $14.00 © 1997 American Chemical Society

3292 J . Org. Chem., Vol. 62, No. 10, 1997
Babudri et al.
Sch em e 1
Sch em e 2
methods often lead to an E/Z mixture of products, from
which the all-E isomer has to be isolated.9a
a diene cytotoxic fatty acid, â-parinaric acid methyl
ester,20c with a tetraenic structure, and other trienic
compounds of biological interest such as the (6E) isomer
and a structural analogue of leukotriene B3,20b benzoleu-
kotriene B3, a LTB4 antagonist,20d and some natural
dienic amides.20e
In the present work we illustrate the versatility and
the efficient synthetic potential of silyl derivatives 1 and
2 for the highly stereoselective preparation of polyenes
with more extended conjugated π-systems.
Wittig or Horner-Emmons-Wadsworth approaches
are also useful for the preparation of symmetrically
substituted polyenes with 6-10 double bonds and a
variety of terminal groups (such as quinone or hydro-
quinone,13 aryl,14a alkylthiophenyl,6a alkoxyphenyl,6a
alkoxythienyl,6a,14c ferrocenyl14d-f) and without angular
methyl groups in the polyenic chain. The lack of sub-
stituents appears to favor the all-E configuration of these
polyenes.
Resu lts a n d Discu ssion
The Wittig procedure has been also adopted for the
synthesis of both bis([2.2.2]paracyclophanyl)butadiene
and hexatriene.15
Syn th esis of P olyen es. Our strategy for the synthe-
sis of polyenes is based upon the homocoupling reactions
of unsaturated silanes 2a -g (Scheme 2).
In principle, the reaction is particularly attractive in
view of the possibility to double in one step the number
of conjugated double bonds. Obviously, the critical point
of all the process is represented by the stereochemistry,
i.e. the preservation of the geometry of the double bonds
Besides the Wittig procedure other synthetic ap-
proaches have attracted attention for the preparation of
conjugated polyenes. 6-(Cyclopentadienyl)pentafulvenes16
with up to five double bonds have been prepared by
condensation of sodium cyclopentadienide with vinami-
dinium salts. Mixture of isomers of tert-butyl-capped
polyenes containing even or odd numbers of double bonds
up to 15 have been obtained by ring-opening methathesis
oligomerization of 7,8-bis(trifluoromethyl)tricyclo[4.2.2.02,5]-
deca-3,7,9-triene promoted by tungsten catalyst, followed
by retro-Diels-Alder reaction.17 However, a mixture of
isomers of various lengths is obtained, and photochemical
isomerization is required for inversion to the all-E
counterpart. all-E tetraenedioates and pentaenedioates
have been prepared in moderate yields by palladium-
catalyzed reaction of vinylic halides with shorter conju-
gated derivatives.18 More recently, R,ω-dialkyl-substi-
tuted linear polyenes with up to 10 conjugated double
bonds have been prepared by Stille coupling of distan-
nylated polyenes with polyenic iodides. Once again
photoirradiation of the isomeric final mixture has been
used to obtain the required E structure.19
(13) Duhamel, L.; Duhamel, P.; Ple´, G.; Ramondec, Y. Tetrahedron
Lett. 1993, 34, 7399-7400.
(14) (a) Spangler, C. W.; McCoy, R. K.; Dembek, A. A.; Sapochak,
L. S.; Gates, B. D. J . Chem. Soc., Perkin Trans. 1 1989, 151-154. (b)
Spangler, C. W.; Pei-Kang, L.; Dembek, A. A.; Havelka, K. O. J . Chem.
Soc., Perkin Trans. 1 1991, 799-802. (c) Spangler, C. W.; Pei-Kang,
L. J . Chem. Soc., Perkin Trans. 2 1992, 1959-1963. (d) Sachtleben,
M. L.; Spangler, C. W.; Tang, N.; Hellwarth, R.; Dalton, L. In Organic
Materials for Non-linear Optics III; Ashwell, G. J ., Bloor, D., Eds.;
Royal Society of Chemistry: Cambridge, 1993; pp 231-236. (e) Ribou,
A. C.; Launay, J . P.; Satchleben, M. L.; Li, H.; Spangler, C. W. Inorg.
Chem. 1996, 35, 3735-3740. (f) Tolbert, L. M.; Zhao, X.; Ding, Y.;
Bottomley, L. A. J . Am. Chem. Soc. 1995, 117, 12891-12892.
(15) Heirtzler, F. R.; Hopf, H.; Lehne, V. Liebigs Ann. 1995, 1521-
1528.
(16) (a) Eiermann, M.; Stowasser, B.; Hafner, K.; Bierwirth, K.;
Frank, A.; Lerch, A.; Reusswig, J . Chem. Ber. 1990, 123, 1421-1431.
(b) J utz, C.; Amschler, H. Chem. Ber. 1964, 97, 3331-3348.
(17) Knoll, K.; Schrock, R. R. J . Am. Chem. Soc. 1989, 111, 7989-
8004.
In our previous studies dealing with the synthesis of
stereodefined conjugated polyenes,20 we reported a syn-
thetic methodology based upon the chemoselective acy-
lation of (1E,3E)-1,4-bis(trimethylsilyl)-1,3-butadiene 1a
(n ) 0) (Scheme 1) and (1E,3E,5E)-1,6-bis(trimethylsilyl)-
1,3,5-hexatriene 1b (n ) 1) to afford, in good yields, all-E
silylated ketones 2, or dicarbonyl compounds 3, with
sequential double acylation reactions.20a
(18) Fischetti, W.; Mak, K. T.; Stakem, F. G.; Kim, J .; Rheingold,
A. L.; Heck, R. F. J . Org. Chem. 1983, 48, 948-955.
(19) Kiehl, A.; Eberhardt, A.; Mu¨ller, K. Liebigs Ann. 1995, 223-
230.
(20) (a) Babudri, F.; Fiandanese, V.; Marchese, G.; Naso, F. J . Chem.
Soc., Chem. Commun. 1991, 237-239. (b) Babudri, F.; Fiandanese,
V.; Naso, F. J . Org. Chem. 1991, 56, 6245-6248. (c) Babudri, F.;
Fiandanese, V.; Naso, F.; Punzi, A. Synlett 1992, 221-223. (d)
Babudri, F.; Fiandanese, V.; Marchese, G.; Punzi, A. Synlett 1995,
817-818. (e) Babudri, F.; Fiandanese, V.; Naso, F.; Punzi, A.
Tetrahedron Lett. 1994, 35, 2067-2070. (f) Babudri, F.; Fiandanese,
V.; Mazzone, L.; Naso, F. Tetrahedron Lett. 1994, 35, 8847-8850. (g)
Fiandanese, V.; Mazzone, L. Tetrahedron Lett. 1992, 33, 7067-7068.
This methodology was successfully applied to the
synthesis of natural products such as ostopanic acid,20b

Synthesis of Conjugated Polyenes
J . Org. Chem., Vol. 62, No. 10, 1997 3293
Sch em e 3
Ta ble 1. Con ju ga ted P olyen es 4a -g via Hom ocou p lin g
Rea ction of Tr im eth ylsilyl P olyen es 2a -g
optimize the yields of these homocoupling products, we
tested also a different palladium catalyst, i.e. palladium-
(II) bis(acetonitrile) dichloride in HMPA, which is effec-
tive in promoting the coupling of vinylstannanes to
dienes.23 On applying this procedure to ketones 2a and
2b, in the presence of the CuCl2/LiCl couple, which is
necessary to reoxidize palladium from the lower oxidation
state, the yields in polyenes 4a ,b were nearly the same
as those obtained with PdCl2/CuCl2/LiCl (Table 1).
reaction
products
reaction
time (h)
compd
(yield, %)a
catalytic system and solvent
2a
2b
2c
2d
2e
2f
4a (50)
4b (61)
4c (30)
4d (41)
4e (51)
4f (51)
4g (52)
4a (51)
3.5
3
4
5
2
4
10
2
PdCl2/CuCl2/LiCl/MeOH
PdCl2/CuCl2/LiCl/MeOH
PdCl2/CuCl2/LiCl/MeOH
PdCl2/CuCl2/LiCl/MeOH
PdCl2/CuCl2/LiCl/MeOH
PdCl2/CuCl2/LiCl/MeOH
PdCl2/CuCl2/LiCl/MeOH
Pd(MeCN)2Cl2/CuCl2/LiCl/
HMPA
The stereochemical aspects of the reaction were inves-
tigated. For polyenes 4a -f a complete and detailed NMR
study allowed us to ascertain the configuration of all the
double bonds of the polyenic chain. The all-E configu-
ration and, as a consequence, the stereospecificity of the
homocoupling reaction24 were unambiguously demon-
strated (see the following section).
2g
2a
2b
4b (47)
3.5
Pd(MeCN)2Cl2/CuCl2/LiCl/
HMPA
a
Based on isolated materials.
NMR Da ta for P olyen es 4a -f. The configuration of
present in the starting silanes and the stereoselectivity
in the formation of the new carbon-carbon bond.
1
compounds 4a -f was determined by H NMR spectros-
A
copy. In compound 4a the analysis of the 1H-NMR
spectrum was straightforward. In compounds 4b-f the
complexity and the extensive overlap of the resonance
signals limit the amount of information that can be
obtained from single resonance spectra. H(1)/H(1′) pro-
tons25 give origin to a distinct doublet in all the com-
pounds examined, and H(2)/H(2′), H(3)/H(3′), H(4)/H(4′)
resonances were assigned by homonuclear decoupling
experiments. Chemical shifts and coupling constants of
the outer protons, H(1)/H(1′) and H(2)/H(2′), were in all
reaction of this type has only one precedent in the
literature. Indeed, it has been reported that (E)-1-
phenyl-2-(trimethylsilyl)ethene can be transformed in
(1E,3E)-1,4-diphenyl-1,3-butadiene.21 This reaction was
performed in the presence of palladium dichloride in
methanol, and the suggested mechanism (Scheme 3)
involves the addition of PdCl2 across the double bond of
the vinylsilane, followed by elimination of trimethylsilyl
chloride. The addition of the â-styrylpalladium chloride
intermediate to a second molecule of vinylsilane, followed
by elimination of trimethylsilyl chloride, affords a bis-â-
styrylpalladium species which undergoes a reductive
elimination of Pd(0) with formation of the diene.
Copper dichloride and lithium chloride are added to
reoxidize Pd(0) to Pd(II), and the entire process is made
catalytic in palladium. The reported yield in dimeriza-
tion product was 30%. The cause of the moderate yield
was attributed21 to the proton desilylation of the starting
vinylsilane promoted by hydrogen chloride derived from
the methanolysis of the trimethylsilyl chloride. In an-
hydrous conditions and in the presence of 1 equiv of
tertiary amine such as dicyclohexylethylamine, the yield
rises to 79%. However, under these conditions the
reaction is stoichiometric in PdCl2, the CuCl2 being
ineffective in reoxidizing Pd(0).
1
cases obtained directly from H single resonance spectra.
For the hydrogen atoms bound to the central carbon
atoms, NMR parameters could not be extracted by direct
inspection of the spectra, because of second-order effects
and extensive overlap of the resonance signals. Even in
COSY spectra, cross-peaks originated from second-order
effects precluded the possibility to obtain vicinal coupling
constants 3J HH reliable enough to assign the configuration
at the central double bonds of the polyenic chain. Least-
squares analysis of the spectra was the only way to obtain
3
chemical shifts and J HH values which permitted the
required configurations to be determined unambiguously.
Therefore, a modified version of the LAOCN-526 program
was used. The eight central protons of the polyenic
chains in compounds 4b-e, H(3)/H(3′), H(4)/H(4′), H(5)/
H(5′), and H(6)/H(6′), were analyzed as an AA′BB′CC′DD′
spin system. The resonances of H(3)/H(3′), H(5)/H(5′),
and H(6)/H(6′) are located in a narrow range (50 Hz), and
spin-tickling experiments were necessary for a correct
With the aim of applying a similar procedure to more
complex systems, we prepared the series of polyenylsi-
lanes 2a -g and investigated their transformation into
longer polyenes 4a -g (Table 1).
By performing preliminary experiments in conditions
ranging from stoichiometric to catalytic in Pd(II), the best
results were obtained by using a 4:1 molar ratio between
starting silanes and palladium salt. The presence of a
large excess of anhydrous CuCl2, to ensure the reoxida-
tion of Pd(0) to Pd(II), and of LiCl was also necessary to
the catalytic system.22 In our hands, strictly catalytic
conditions gave poor results; also the stoichiometric
conditions, tested with the silane 2a in methanol and in
the presence of 1 equiv of dicyclohexylethylamine, gave
a low yield (27%) of the product 4a . In an attempt to
(23) Tolstikov, G. A.; Miftakhov, M. S.; Danilova, N. A.; Vel’der, Ya.
L.; Spirikhin, L. V. Synthesis 1989, 633-634.
(24) In order to increase the extent of the conjugated π-system, we
transformed the diketo polyenes 4c, 4d , and 4e in R,ω-diphenylhexa-
decaoctaenes by reduction of the two carbonyl functions and dehydra-
tion of the resulting diols. The products were reddish amorphous
solids, completely insoluble in all common organic solvents and
therefore very difficult to characterize. For the polyene derived from
4c, a solid state 1H NMR and 13C NMR analysis confirmed the
structure of 1,16-diphenylhexadecaoctaene, but no information about
the configuration of the double bonds could be derived.
(25) For the sake of clarity the two carbon atoms at the ends of
polyenic chains bound to carbonyl groups (and consequently the two
hydrogen atoms bound to them) have been numbered as 1 and 1′. Other
hydrogen and carbon atoms have been numbered in increasing order
moving toward the center of the chain. This numeration, although
differing from IUPAC rules, has been adopted in order to point out
the symmetry of these molecules.
(21) Weber, W. P.; Felix, R. A.; Willard, A. K.; Koenig, K. E.
Tetrahedron Lett. 1971, 4701-4704.
(22) Smidt, J .; Hafner, W.; J ira, R.; Sedlmeier, R.; Sieber, R.;
Ru¨ttinger, R.; Kojer, H. Angew. Chem. 1959, 71, 176-182.
(26) Cassidei, L.; Sciacovelli, O. QCPE Bull. 1983, 3, 45.

3294 J . Org. Chem., Vol. 62, No. 10, 1997
Babudri et al.
Sch em e 4
Ta ble 2. 1H NMR Ch em ica l Sh iftsa a n d Vicin a l Cou p lin g Con sta n tsb for P olyen es 4a -f
compd
H(1)
H(2)
H(3)
H(4)
H(5)
H(6)
H(7)
H(8)
4a
4b
4c
4d
4e
4f
7.07 (14.82)
6.99 (14.89)
6.23 (15.23)
6.21 (15.28)
6.22 (15.23)
6.97 (14.9)
7.48 (10.74)
7.48 (11.40)
7.25 (11.39)
7.25 (11.42)
7.26 (11.34)
7.47 (11.5)
6.65 (14.99)
6.53 (14.80)
6.33 (14.74)
6.33 (14.69)
6.34 (14.78)
6.49 (14.7)
6.76 (11.23)
6.69 (10.16)
6.65 (10.65)
6.64 (11.19)
6.65 (11.0)
6.72 (11.0)
6.43 (14.12)
6.38 (15.12)
6.38 (14.09)
6.38 (14.19)
6.42 (15.0)
6.48 (11.95)
6.46 (10.79)
6.45 (11.85)
6.45 (11.09)
6.48 (10.0)
6.43 (14.83)
6.40 (11.40)
a
b
1H NMR chemical shifts are listed in ppm vs TMS in CDCl3. Vicinal coupling constants of each proton with the following one in the
polyenic chain are reported in parentheses (in hertz).
3
assignment of the experimental frequencies to the cal-
culated transitions. COSY spectra were helpful in esti-
mating the proton chemical shift values used to start the
iterative analysis.
system.27 The J HH values across single carbon-carbon
bonds, which are in the range 10.0-11.8, suggest the
occurrence of a nearly planar arrangement of the polyenic
chains.27 However, on this basis a distinction between
s-trans (structure a) or s-cis conformation (structure b)
was not possible.
For compound 4f decoupling of H(4)/H(4′) allowed the
H(3)/H(3′) and H(5)/H(5′) resonances to be localized; these
resonances strongly overlap with H(6)/H(6′), H(7)/H(7′)
and H(8)/H(8′) resonances. Since the signals arising from
these 10 protons are located in a range of 90 Hz, it was
not possible to carry out the spectral analysis of the spin
system H(5)/H(5′), H(6)/H(6′), H(7)/H(7′), and H(8)/H(8′).
The stereochemistry of the fragment C(7)-C(8)-C(8′)-
C(7′) was determined for the partially and selectively
deuterated octaene 4h , prepared following the same
procedure adopted for the nondeuterated analogue, start-
ing from 3,4,5,6-tetradeuterated bis(trimethylsilyl) tet-
raene 1d (Scheme 4). This in turn was prepared by
nickel-catalyzed cross-coupling reaction of 2 mol of
[2-(trimethylsilyl)ethenyl]magnesium bromide with 1-bro-
mo-4-(phenylthio)-1,3-butadiene-1,2,3,4-d4 (1e) obtained
by adapting the procedure described for the light
counterpart.20f
Con for m a tion a l Stu d ies on 4a ,b a n d 4f. The
conformation of 4a was fully determined by 13C-NMR and
2D NOESY spectra. The 2D NOESY spectrum shows
correlation peaks of significative intensities between the
pairs of protons H(1)/H(1′)-H(3)/H(3′) and H(2)/H(2′)-
H(4)/H(4′). This suggest an s-trans (a) conformation of
the polyenic chain. Such a conformation is confirmed also
by the 3J (CH) values between C(1)/C(1′) and H(3)/H(3′), 3.8
Hz, and C(2)/C(2′) and H(4)/H(4′), 5.0 Hz.28
In the 13C-coupled spectrum, the carbonyl carbon
resonance shows a quintet-like multiplicity, which indi-
cates that the couplings over three bonds to H(2)/H(2′)
and the aromatic protons in the ortho position to the
carbonyl group have equal values, about 4.5 Hz, that are
1
The H-NMR spectrum of the four central protons of
4h was analyzed as an AA′BB′ spin system. The coupling
constants between H(7)/H(7′) and the deuterium atoms
on C(6)/C(6′) (∼2 Hz) were taken into account as first-
order perturbations. In all cases coupling constants over
four (-0.58 to -0.87 Hz) and five (+0.32 to +0.69 Hz)
bonds were also considered in performing the spectral
analysis.
(27) (a) J ackman, L. M.; Sternhell, S. Applications of Nuclear
Magnetic Resonance Spectroscopy in Organic Chemistry; Pergamon
Press: London, 1962. (b) Wernly, J .; Lauterwein, J . Helv. Chim. Acta
1983, 66, 1576-1587. Wernly, J .; Lauterwein, J . Magn. Reson. Chem.
1985, 23, 170-176. (c) Harris, R. K.; Cunliffe, A. V. Org. Magn. Reson.
1977, 9, 483-488.
(28) Marshall, J . L. Carbon-Carbon and Carbon-Proton NMR Cou-
plings: Application to Organic Stereochemistry and Conformational
Analysis; Verlag Chemie International: Deerfield Beach, FL, 1983.
Chemical shifts and vicinal coupling constants are
reported in Table 2. Vicinal coupling constants across
double bonds are in the range 14.2-15.3 Hz, thus
indicating the all-E configuration of the conjugated

Synthesis of Conjugated Polyenes
J . Org. Chem., Vol. 62, No. 10, 1997 3295
Ta ble 3. Ha logen a tion Rea ction s of Tr im eth ylsilyl Dien es 2a a n d 2g to Ha lo Dien es 5-7
reaction
products
(yield, %)a
reaction
time (h)
compd
E/Z ratiob
catalytic system and solvent
2a
2a
2a
2a
2g
2g
5a ,b (76)
6a ,b (59)
5a ,b (45)
6a ,b (60)
7a ,b (50)
7a ,b (41)
50:50
50:50
61:39
55:45
64:36
31:69
3.5
1
48
1
1
1
PdCl2/CuCl2/LiCl/MeCN
Pd(OAc)2/CuBr2/LiBr/MeCN
CuCl2/LiCl/MeCN
CuBr2/LiBr/MeCN
Pd(OAc)2/CuBr2/LiBr/MeCN
CuBr2/LiBr/MeCN
a
b
Based on isolated materials. Isomers ratio of the isolated materials, determined by 1H NMR and/or GLC.
Sch em e 5
in agreement with a nearly planar arrangement of the
coupled nuclei.28 Moreover, the presence in the NOESY
spectrum of a quite intense correlation peak between
H(1)/H(1′) and the protons in ortho position in the
aromatic ring suggests that the oxygen atoms are in
antiperiplanar position to H(1)/H(1′) (structure c).
H(1)/H(1′) resonances and (ii) the intense correlation peak
observed in NOESY spectra between H(1)/H(1′) and the
two hydrogen atoms in the ortho position of the benzene
ring.
Ha logen a tion Rea ction s of Silyl P olyen es. In our
studies directed toward an optimization of the homocou-
pling reaction of the ketosilane 2a , we found interesting
byproducts, represented by compounds deriving from
chlorodesilylation reaction. Since these compounds could
represent synthetically useful starting materials in vari-
ous processes (e.g. cross-coupling reactions), we per-
formed experiments in order to check the possibility of
diverting the reaction toward their formation. Indeed,
replacing methanol with acetonitrile and starting from
ketone 2a gave the mixture of isomeric chloro derivatives
5a and 5b (Scheme 5) as the main product.
A further support to this conclusion came from H(1)/
H(1′) chemical shift which occurs at 7.0 ppm, compared
to the value of 6.3 ppm, predicted on the basis of the
substituent effects. This deshielding can be attributed
to the diamagnetic anisotropy of the benzene ring.
Indeed, a downfield shift of 0.8 ppm has been estimated
using Dreiding models and the J ohnson and Bovey
diagram29 for H(1)/H(1′) coplanar with the aromatic ring.
In the case of a syncoplanar conformation, the correla-
tion peak would appear between the hydrogen atom in
ortho position and H(2)/(H2′) (structure d). Moreover,
H(2)/H(2′) would be shifted to lower field by the diamag-
netic anisotropy of the benzene ring.
With CuBr2/LiBr and palladium(II) acetate in aceto-
nitrile, a mixture of bromides 6a and 6b was obtained.
In the same reaction conditions silyl diene 2g gave the
bromides 7a and 7b (Table 3).
For compound 4b, the extended s-trans conformation
of the polyenic chain is suggested from the 2D-NOESY
spectrum which shows significant correlation peaks
between the pairs of protons H(2)/H(2′)-H(4)/H(4′), H(4)/
H(4′)-H(6)/H(6′), H(3)/H(3′)-H(5)/-(5′). The correlation
peak between H(1)/H(1′) and protons in the ortho
positions in the benzene ring and the chemical shift value
of H(1)/H(1′) indicate that the conformation at the ends
of the conjugated system is the same as in 4a (i.e.
structure c).
In order to clarify the role of the different metal salts,
we performed the same halogenation reactions without
the palladium salt. Chlorination and bromination oc-
curred also in this case. However, lower yields and
reaction rates were observed in the case of chlorination
of 2a without Pd(II) salts. The bromination reaction of
2a and 2g proceeded at the same rate both in the
presence and in the absence of palladium salt, without
any marked influence upon the yields of the halogeno
derivatives 6a ,b and 7a ,b. The E/Z ratio in the dienyl
halide is somewhat influenced by the presence of palla-
dium(II) salt (Table 3).
It was not possible to obtain the 2D-NOESY and 13C
spectra of 4f because of its very low solubility. However,
3
the values of J HH across single bonds and the chemical
shifts of protons H(1)/H(1′) suggest that in solution 4f
assumes a conformation similar to those of 4a and 4b.
The planar arrangement of the polyenic chain is also
supported by AM130 calculations performed on 4a ,b and
4f with full geometry optimization. In all the compounds
examined, the most stable conformation is very similar
to the experimental one with the plane of the aromatic
rings rotated of about 30° with respect to the plane
containing the polyenic chain and the carbonyl group.
According to Dreiding models, this rotation angle is quite
consistent with (i) the observed downfield shift of the
Halogenation of vinylsilanes, with substitution of the
silyl group, has been performed with various reagents,31
but copper(II) halides have seldom been employed for
such a transformation. In one case the oxidation reaction
of alkenyl pentafluorosilicates with copper(II) bromide
or chloride to the corresponding alkenyl bromide or
chloride with cleavage of the silicon-carbon bond has
been reported.32 On the other hand, chlorination and
bromination of alkenes to 1,2-dihalo derivatives promoted
(29) J ohnson, C. E.; Bovey, F. A. J . Chem. Phys. 1958, 29, 1012-
1014.
(30) Dewar, M. J . S.; Zoebisch, E. G.; Healy, E. F.; Stewart, J . J . P.
J . Am. Chem. Soc. 1985, 107, 3902-3909.
(31) Fleming, I.; Dunogue`s, J .; Smithers, R. Org. React. (N.Y.) 1989,
37, 57-575.
(32) Yoshida, J .; Tamao, K.; Kakui, T.; Kurita, A.; Murata, M.;
Yamada, K.; Kumada, M. Organometallics 1982, 1, 369-380.

3296 J . Org. Chem., Vol. 62, No. 10, 1997
Babudri et al.
on a fused silica capillary column SE 30, 30 m. Melting points
are uncorrected. (1E,3E)-1,4-Bis(trimethylsilyl)-1,3-butadiene
(1a),35 (1E,3E,5E)-1,6-bis(trimethylsilyl)-1,3,5-hexatriene (1b),36
(1E,3E,5E,7E)-1,8-bis(trimethylsilyl)-1,3,5,7-octatetraene(1c),37
(2E,4E)-1-phenyl-5-(trimethylsilyl)-2,4-pentadien-1-one (2a ),20a
(2E,4E,6E)-1-phenyl-7-(trimethylsilyl)-2,4,6-heptatrien-1-
one (2b ),20a (3E,5E,7E)-1-phenyl-8-(trimethylsilyl)-3,5,7-oc-
tatrien-2-one (2c),20c and (1E,3E)-1-phenyl-4-(trimethylsilyl)-
1,3-butadiene (2g)40 were prepared as reported in the literature.
Copper(II) bromide and copper(II) chloride were commercial
products, dried at 150 °C (0.1 mbar) for 2 h, and stored in a
nitrogen atmosphere. Palladium(II) chloride, palladium(II)
acetate, bis(acetonitrile)palladium(II) chloride, anhydrous
lithium chloride, and lithium bromide were commercial prod-
ucts and were used without further purification. Acetonitrile
was dried by refluxing on Linde 4 Å molecular sieves and
distilled; a second distillation from P2O5 was performed
immediately prior to use.
Sch em e 6
by copper(II) halides are well documented.33 This reac-
tion is highly favored in solvents which behave as
stabilizing ligands for copper(I), and acetonitrile is the
most useful among them.33c
In our case addition of halogen to the silicon bearing
the double bond promoted by copper(II) halide may be
followed by the elimination of trimethylsilyl halide to give
the dienyl halide (Scheme 6).
However, at least in the case of chlorination, we cannot
rule out the possibility of a parallel route to the polyenyl
chloride, involving Pd(0) elimination from an intermedi-
ate polyenylpalladium chloride.
(1E,3E,5E,7E)-1,8-Bis(t r im et h ylsilyl)-1,3,5,7-oct a t et -
r a en e-3,4,5,6-d 4 (1d ). The synthesis of 1d required the
preliminary preparation of (1E,3E)-1-bromo-4-(phenylthio)-1,3-
butadiene-1,2,3,4-d4 (1e), following the procedure previously
described for the corresponding light compound.20f For this
purpose acetylene-d2 was bubbled into a solution of benzene-
sulfenyl chloride (21.4 g, 148 mmol) in ethyl acetate (150 mL),
leading to (E)-1-chloro-2-(phenylthio)ethene-1,2-d2 (8.65 g, 34%
yield). GC/MS analysis showed a complete deuteration of the
olefinic positions. This compound (8.65 g, 50 mmol) in 105
mL of THF was reacted with [2-(trimethylsilyl)ethynyl]mag-
nesium bromide (0.43 N solution in THF, 118 mL, 51 mmol)
in the presence of NiCl2(dppe) (0.79 g, 1.50 mmol). After the
usual workup and purification on Florisil column (petroleum
ether as eluant), (3E)-4-(phenylthio)-1-(trimethylsilyl)-3-buten-
1-yne-3,4-d2 was obtained as yellow oil (11.36 g, 97% yield).
Desilylation reaction of this compound (11.36 g, 48.5 mmol)
with KF (27.9 g, 481 mmol) in 103 mL of methanol-d1 gave,
after flash chromatography (elution with petroleum ether),
5.57 g (71% yield) of (1E)-1-(phenylthio)-1-buten-3-yne-1,2,4-
d3 with a complete deuteration. The deuteriozirconation/
bromination reactions of this enyne (3.02 g, 18.5 mmol) with
zirconocene chloride deuteride (5.30 g, 20.6 mmol) and N-
bromosuccinimide (3.4 g, 19.11 mmol) in 122 mL of benzene,
performed as described,20f afforded 2.27 g (50% yield) of 1e;
GC/MS analysis confirmed the full deuteration of the obtained
compound. In diene 1e (1.87 g, 7.63 mmol) in 75 mL of THF
both the bromine atom and the phenylthio group were
substituted in a cross-coupling reaction with [(E)-2-(trimeth-
ylsilyl)ethenyl]magnesium bromide (0.38 N solution in THF,
90.5 mL, 34.4 mmol) in the presence of NiCl2(dppe) (0.39 g,
0.74 mmol), at room temperature. After the usual workup and
purification of the crude product on Florisil column (elution
with petroleum ether), 0.85 g (44% yield) of the tetraene 1d
was obtained as yellow oil: 1H NMR (500 MHz, CDCl3) δ 0.10
(s, 18H), 5.89 (d, J ) 18.3 Hz, 2H), 6.54 (d, J ) 18.3 Hz, 2H);
GC/MS m/e 254 (M+, 15), 239 (2), 166 (14), 151 (35), 73 (100).
(3E,5E,7E)-1-(4-Meth ylp h en yl)-8-(tr im eth ylsilyl)-3,5,7-
octa tr ien -2-on e (2d ). The product was prepared following
our procedure,20a starting from 1b (1.71 g, 7.62 mmol), 4-me-
thylphenylacetyl chloride (1.42 g, 8.42 mmol), and AlCl3 (1.10
g, 8.25 mmol) in 50 mL of CH2Cl2 (1 h reaction time at room
temperature). After preliminary purification of the crude
Con clu sion
Conjugated polyenes 4a -g with an all-E configuration
of the π-system, as rigorously established by a detailed
NMR study, have been obtained following a synthetic
procedure based upon an operatively very simple homo-
coupling reaction of the unsaturated silanes 2a -g. These
compounds can be easily derived from bis(trimethylsilyl)
polyenes 1a -c. The methodology opens the access to
symmetrically substituted polyenes with carbonyl groups
at both ends of the conjugated π-system. The influence
of two substituents with the same electronic effect on the
nonlinear optical properties of various polyenes has been
recently addressed. In particular, both electron-donor
and electron-acceptor substituents enhance the second
hyperpolarizability, γ, of bisaryl and thienyl polyenes.34
These results show that not only push-pull polyenes but
also the symmetrically substituted ones are suitable for
providing materials with large nonlinear optical coef-
ficients. With this background, our diketo polyenes
represent a new attractive class of compounds, whose
potential nonlinear optical behavior is now open to
investigation.
Finally, an interesting aspect of our work is the finding
of a new method which permits the exchange of the
trimethylsilyl group for a halogen atom with formation
of polyenyl halides. In principle, these are useful inter-
mediates in the synthesis of more extended conjugated
systems via cross-coupling reactions.
Exp er im en ta l Section
Flash chromatography was performed with silica gel (par-
ticle size 0.043-0.063 mm). Petroleum ether was the 40-70
°C boiling fraction. GLC analyses were performed with a
SPB-1 (methylsilicone 30 m × 0.25 mm i.d.) capillary column.
1H NMR data were measured at 200 and 500 MHz, and 13C
NMR data at 50.3 and 125.7 MHz. NMR spectral data were
taken in CDCl3 using the residual CHCl3 as the standard for
1H data, and the triplet centered at δ 77.0 as the standard for
13C spectra. GLC/mass spectrometry analyses were performed
product on
a Florisil column (elution with 1:1 CH2Cl2-
petroleum ether) and subsequent distillation with Kugelrohr
(35) Seyferth, D.; Vick, S. C. J . Organomet. Chem. 1978, 144, 1-12.
Bock, H.; Seidl, J . J . Am. Chem. Soc. 1968, 90, 5694-5700.
(36) Naso, F.; Fiandanese, V.; Babudri, F. In Encyclopedia of
Reagents for Organic Synthesis; Paquette, L. A., Ed.; J ohn Wiley:
Chichester, 1995; Vol. 1, pp 594-595.
(33) (a) Arganbright, R. P.; Yates, W. F. J . Org. Chem. 1962, 27,
1205-1208. (b) Koyano, T. Bull. Chem. Soc. J pn. 1970, 43, 1439-
1443. Koyano, T.; Watanabe, O. Bull. Chem. Soc. J pn. 1971, 44, 1378-
1381. Uemura, S.; Tabata, A.; Kimura, Y.; Ichikawa, K. Bull. Chem.
Soc. J pn. 1971, 44, 1973-1975. (c) Baird, W. C., J r.; Surridge, J . H.;
Buza, M. J . Org. Chem. 1971, 36, 3324-3330. (d) Or(Orochov), A.;
Levy, M.; Asscher, M.; Vofsi, D. J . Chem. Soc., Perkin Trans. 2 1974,
857-861.
(34) (a) Spangler, C. W.; Havelka, K. O.; Becker, M. W.; Kelleher,
T. A.; Cheng, L.-T. A. Proc. SPIE 1991, 1560, 139-147. (b) Spangler,
C. W.; Liu, P.-K.; Kelleher, T. A.; Nickel, E. G. Proc. SPIE 1992, 1626,
406-414.
(37) 1c was prepared by means of Miyaura-Suzuki38 cross-coupling
of (1E,3E)-1-iodo-4-(trimethylsilyl)-1,3-butadiene and 2-[(1E,3E)-4-
(trimethylsilyl)-1,3-butadienyl]-1,3,2-benzodioxaborole. Both these
compounds were obtained from 1a , adopting our recently reported
procedure.39 Details will be given elsewhere.
(38) Suzuki, A.; Miyaura, N. Chem. Rev. 1995, 95, 2457-2483.
(39) Farinola, G. M.; Fiandanese, V.; Mazzone, L.; Naso, F. J . Chem.
Soc., Chem. Commun. 1995, 2523-2524.
(40) Fiandanese, V.; Marchese, G.; Mascolo, G.; Naso, F.; Ronzini,
L. Tetrahedron Lett. 1988, 29, 3705-3708.

Synthesis of Conjugated Polyenes
J . Org. Chem., Vol. 62, No. 10, 1997 3297
apparatus (ot 165 °C, 2 × 10-4 mbar), 0.43 g of a yellow oil
6.80 (m, 2H, 5a ), 7.00 (d, J ) 15.0 Hz, 1H, 5a ), 7.08 (d, J )
15.3 Hz, 1H, 5b), 7.28-7.38 (m, 1H, 5a ), 7.40-7.65 (m, 3H),
7.80 (ddd, J ) 15.3, 10.8, 0.8 Hz, 1H 5b), 7.90-8.00 (m, 2H);
13C NMR (125.7 MHz, CDCl3) δ 125.81, 127.39, 128.12, 128.29,
128.35, 128.43, 128.61, 130.37, 132.24, 132.93, 136.53, 137.65,
139.85, 189.91, 190.29; MS (70 eV) m/e isomer 5b 194 (M + 2,
14), 192 (M+, 39), 157 (100), 129 (38), 105 (30), 77 (58), 51 (58);
isomer 5a 194 (M + 2, 18), 192 (M+, 53), 157 (100), 129 (55),
105 (48), 77 (72), 51 (69). Anal. Calcd for C11H9OCl: C, 68.58;
H, 4.71; Cl, 18.40. Found: C, 68.23; H, 5.18; Cl, 18.15.
Further elution gave 0.17 g (50% yield) of compound 4a : mp
213-214 °C (CHCl3/diethyl ether); IR (KBr) 1656, 1600, 1556,
1019, 772, 697; 1H NMR (500 MHz, CDCl3) 6.61-6.71 (m, 2H),
6.72-6.81 (m, 2H), 7.07 (d, J ) 14.8 Hz, 2H), 7.43-7.61 (m,
8H), 7.92-7.97 (m, 4H); 13C NMR (50.3 MHz, CDCl3, trace
DMSO-d6) δ 126.87, 128.38, 128.64, 132.86, 134.75, 137.98,
140.48, 143.49, 190.12. Anal. Calcd for C22H18O2: C, 84.05;
H, 5.77. Found: C, 84.28; H, 5.66.
Meth od B. A solution of the silyl ketone 2a (0.50 g, 2.17
mmol) in 7 mL of HMPA was added dropwise to a stirred
solution of Pd(MeCN)2Cl2 (0.028 g, 0.099 mmol), CuCl2 (0.86
g, 6.39 mmol), and LiCl (0.09 g, 2.12 mmol) in 5 mL of
anhydrous HMPA, under nitrogen atmosphere. The solution
was warmed to 55 °C, and the reaction, monitored by capillary
GLC analysis, was completed after 2 h. The mixture was then
diluted with water and extracted with CH2Cl2. The organic
extracts were washed with aqueous HCl (1 N) and with water,
dried over anhydrous sodium sulfate, and concentrated to give
the solid product. Recrystallization from CH2Cl2/diethyl ether
gave 0.175 g (51% yield) of 4a .
(2E,4E,6E,8E,10E,12E)-1,14-Dip h en yl-2,4,6,8,10,12-tet-
r a d eca h exa en e-1,14-d ion e (4b). Meth od A. Following the
same procedure described for the synthesis of 4a , compound
4b was prepared starting from 2b (0.60 g, 2.34 mmol) and
using PdCl2 (0.11 g, 0.62 mmol), CuCl2 (0.72 g, 5.35 mmol),
and LiCl (0.087 g, 2.05 mmol) in 10 mL of CH3OH (3 h reaction
time). Concentration of the solvent gave a solid residue which
was recrystallized from CHCl3/diethyl ether to give 0.260 g
(61% yield) of 4b: mp 220-222 °C; IR (KBr) 1645, 1575, 1535,
1010, 765, 690 cm-1; 1H NMR (500 MHz, CDCl3) δ 6.43-6.57
(m, 6H), 6.69 (dd, J ) 14.8, 10.2 Hz, 2H), 6.99 (d, J ) 14.9 Hz,
2H), 7.42-7.62 (m, 8H), 7.90-7.97 (m, 4H); 13C NMR (125.7
MHz, CDCl3) δ 125.73, 128.35, 128.58, 132.31, 132.58, 134.60,
136.83, 138.44, 141.53, 144.13, 190.24. Anal. Calcd for
C26H22O2: C, 85.22; H, 6.05. Found: C, 85.48; H, 6.34.
Meth od B. The same procedure described for compound
4a was used starting from 2b (0.60 g, 2.34 mmol), Pd-
(MeCN)2Cl2 (0.03 g, 0.11 mmol), CuCl2 (0.72 g, 5.36 mmol),
and LiCl (0.09 g, 2.12 mmol) in 10 mL of HMPA (3.5 h reaction
time). After the usual workup, the recrystallization of the
residue from CH2Cl2/diethyl ether afforded 0.20 g (47% yield)
of 4b.
(3E,5E,7E,9E,11E,13E)-1,16-Diph en yl-3,5,7,9,11,13-h exa-
d eca h exa en e-2,15-d ion e (4c). The synthesis of 4c was
performed following the procedure described in method A for
compounds 4a and 4b, starting from 2c (0.30 g, 1.11 mmol),
PdCl2 (0.05 g, 0.28 mmol), LiCl (0.03 g, 0.71 mmol), and CuCl2
(0.31 g, 2.29 mmol) in 5 mL of CH3OH (4 h reaction time).
After the usual workup, the crude product was purified by
flash chromatography (elution with CH2Cl2): 0.065 g (30%
yield) of a red solid were isolated; mp 190-193 °C (ethanol);
IR (KBr) 1636, 1580, 1009, 740, 702 cm-1; 1H NMR (500 MHz,
CDCl3) δ 3.82 (s, 4H), 6.23 (d, J ) 15.2 Hz, 2H), 6.33 (dd, J )
14.7, 11.4 Hz, 2H), 6.30-6.50 (m, 4H), 6.65 (dd, J ) 14.7, 10.7
Hz, 2H), 7.0-7.34 (m, 12H); 13C NMR (125.7 MHz, CDCl3) δ
48.50, 126.93, 128.59, 128.73, 129.43, 131.89, 134.43, 134.62,
136.72, 141.33, 142.66, 197.09. Anal. Calcd for C28H26O2: C,
85.25; H, 6.64. Found: C, 85.04; H, 6.52.
was obtained (20% yield): IR (neat) 1681, 1249, 1011, 864,
1
840 cm-1; H NMR (500 MHz, CDCl3) δ 0.23 (s, 9H), 2.45 (s,
3H), 3.92 (s, 2H), 6.27 (d, J ) 17.1 Hz, 1H), 6.35 (d, J ) 15.3
Hz, 1H), 6.36-6.47 (m, 1H), 6.65-6.75 (m, 2H), 7.22-7.30 (m,
4H), 7.37 (dd, J ) 15.3, 11.2 Hz, 1H); MS (70 eV) m/e 284 (M+,
7), 269 (7), 256 (14), 179 (84), 105 (38), 73 (100), 59 (23). Anal.
Calcd for C18H24OSi: C, 76.00; H, 8.50. Found: C, 76.10; H,
8.60.
(3E,5E,7E)-1-(4-n -Decylp h en yl)-8-(tr im eth ylsilyl)-3,5,7-
octa tr ien -2-on e (2e). The product was prepared following
the same procedure described above, starting from 1b (1.72 g,
7.67 mmol), 4-n-decylphenylacetyl chloride41 (2.27 g, 7.70
mmol), and AlCl3 (1.03 g, 7.73 mmol) in 55 mL of CH2Cl2
(reaction time 1.5 h). After the usual workup, the crude
product was purified by flash chromatography (elution with
1:1 CH2Cl2-petroleum ether); 1.40 g (yield 44%) of a yellow
oil was obtained. An analytical sample was obtained by
Kugelrohr distillation (ot 225 °C, 2.7 × 10-4 mbar): IR (neat)
1682, 1598, 1249, 1010, 773, 726 cm-1 1H NMR (500 MHz,
;
CDCl3) δ 0.08 (s, 9H), 0.88 (t, J ) 6.7 Hz, 3H), 1.15-1.40 (m,
14H), 1.53-1.64 (m, 2H), 2.56 (t, J ) 7.7 Hz, 2H), 3.78 (s, 2H),
6.13 (d, J ) 17.0 Hz, 1H), 6.21 (d, J ) 15.3 Hz, 1H), 6.08-
6.32 (m, 1H), 6.50-6.62 (m, 2H), 7.11 (s, 4H), 7.23 (dd, J )
15.3, 11.2 Hz, 1H). Anal. Calcd for C27H42OSi: C, 78.95; H,
10.31. Found: C, 78.80; H, 10.45.
(2E,4E,6E,8E)-1-P h en yl-9-(t r im et h ylsilyl)-2,4,6,8-n on -
a tetr a en -1-on e (2f). The product was prepared following the
procedure reported above starting from 1c (2.21 g, 8.83 mmol),
benzoyl chloride (1.35 g, 9.60 mmol), and AlCl3 (1.29 g, 9.67
mmol) in 72 mL of CH2Cl2 at -20 °C for 20 min. After
preliminary purification on a Florisil column (elution with 4:6
CH2Cl2-petroleum ether) and subsequent distillation with
Kugelrohr apparatus (ot 170 °C, 1 × 10-4 mbar), 1.108 g of a
yellow oil was obtained (44% yield): IR (neat) 1650, 1607, 1570,
1522, 1278, 1247, 1013, 867, 834, 771, 689; 1H NMR (500 MHz,
CDCl3) δ 0.1 (s, 9H), 6.05 (d, J ) 18.2 Hz, 1H), 6.33 (dd, J )
14.8, 10.5 Hz, 1H), 6.41 (dd, J ) 14.8, 9.8 Hz, 1H), 6.48 (dd, J
) 14.8, 11.5 Hz, 1H), 6.58 (dd, J ) 18.2, 9.8 Hz, 1H), 6.69 (dd,
J ) 14.8, 10.5 Hz, 1H), 6.97 (d, J ) 14.8 Hz, 1H), 7.42-7.57
(m, 4H), 7.90-7.95 (m, 2H). Anal. Calcd for C18H22OSi: C,
76.54; H, 7.85. Found: C, 76.25; H, 8.18.
(2E,4E,6E,8E)-1-P h en yl-9-(t r im et h ylsilyl)-2,4,6,8-n on -
a tetr a en -1-on e-4,5,6,7-d 4 (2h ). The product was prepared
following the same procedure adopted for the synthesis of
tetraene 2f, starting from 1d (0.850 g, 3.34 mmol), benzoyl
chloride (0.510 g, 3.63 mmol), and AlCl3 (0.480 g, 3.60 mmol)
in 27 mL of CH2Cl2. The crude product was purified on a
Florisil column (elution with 7:3 CH2Cl2/petroleum ether); 0.36
g of a yellow oil was obtained (yield 38%): 1H NMR (500 MHz,
CDCl3) δ 0.1 (s, 9H), 6.05 (d, J ) 18.3 Hz, 1H), 6.58 (d, J )
18.3 Hz, 1H), 6.97 (d, J ) 14.9 Hz, 1H), 7.42-7.55 (m, 4H),
7.90-7.95 (m, 2H).
(2E,4E,6E,8E)-1,10-Dip h en yl-2,4,6,8-d eca tetr a en e-1,10-
d ion e (4a ). Meth od A. A solution of silyl ketone 2a (0.50 g,
2.17 mmol) in 3.5 mL of methanol was added dropwise to a
stirred suspension of palladium(II) chloride (0.10 g, 0.56
mmol), lithium chloride (0.07 g, 1.65 mmol), and anhydrous
copper(II) chloride (0.60 g, 4.46 mmol) in 4 mL of methanol
under a nitrogen atmosphere. The resulting mixture was
stirred at room temperature, and the reaction was monitored
by capillary GLC analysis. After reaction completion (3.5 h),
the solvent was removed at reduced pressure. By means of
flash chromatography of the residue (9:1 CH2Cl2-petroleum
ether) 0.040 g (10% yield) of a mixture of the chloride isomers
5a and 5b was eluted first: IR (neat) 1680, 1630, 1020, 780,
1
725 cm-1; H NMR (200 MHz, CDCl3) δ 6.44 (dt, J ) 7.2, 0.8
Hz, 1H, 5b), 6.57 (ddd, J ) 10.8, 7.2, 0.7 Hz, 1H, 5b), 6.65-
(3E,5E,7E,9E,11E,13E)-1,16-Bis(4-m eth ylph en yl)-3,5,7,9,-
11,13-h exa d eca h exa en e-2,15-d ion e (4d ). The synthesis of
4d was performed following the procedure described above for
compound 4a (method A) starting from 2d (0.43 g, 1.51 mmol),
PdCl2 (0.07 g, 0.39 mmol), LiCl (0.05 g, 1.18 mmol), and CuCl2
(0.42 g, 3.12 mmol) in 7.5 mL of CH3OH (5 h reaction time).
After the usual workup, the crude product was purified by
flash chromatography (elution with CH2Cl2); 0.130 g (41%
yield) of a red solid was isolated: mp 209-211 °C (ethanol);
(41) This acyl chloride was prepared by a standard procedure
starting from the corresponding acid. 4-n-Decylphenylacetic acid was
prepared following a procedure reported for the synthesis of homolo-
gous compounds:42 mp 74-76 °C (ethyl ether); IR (KBr) 1737, 1712,
1255 cm-1 1H NMR (500 MHz, CDCl3 + D2O) δ 0.84 (t, J ) 6.8 Hz,
;
3H), 1.18-1.38 (m, 14H), 1.50-1.63 (m, 2H), 2.57 (t, J ) 7.8 Hz, 2H),
3.60 (s, 2H), 7.13 (d, J ) 8.1 Hz, 2H), 7.18 (d, J ) 8.1 Hz, 2H). Anal.
Calcd for C18H28O2: C, 78.21; H, 10.21. Found: C, 78.33; H, 10.12.
(42) Morgan, E. D. Tetrahedron 1967, 23, 1735-1738.

3298 J . Org. Chem., Vol. 62, No. 10, 1997
Babudri et al.
IR (KBr) 1682, 1640, 1586, 1010, 800; 1H NMR (500 MHz,
CDCl3) δ 2.30 (s, 6H), 3.75 (s, 4H), 6.21 (d, J ) 15.3 Hz, 2H),
6.33 (dd, J ) 14.7, 11.3 Hz, 2H), 6.37-6.48 (m, 4H), 6.64 (dd,
J ) 14.7, 10.6 Hz, 2H), 7.09 (d, J ) 8.2 Hz, 4H), 7.12 (d, J )
8.2 Hz, 4H), 7.25 (dd, J ) 15.3, 11.4 Hz, 2H); 13C NMR (125.7
MHz, CDCl3) δ 21.02, 48.16, 128.59, 129.29, 129.45, 131.49,
131.93, 134.41, 136.56, 136.66, 141.23, 142.54, 197.34. Anal.
Calcd for C30H30O2: C, 85.27; H, 7.16. Found: C, 85.47; H,
7.05.
was stirred at room temperature until the disappearance of
the starting compound 2a (GLC, 3.5 h reaction time). After
the usual workup, flash chromatography of the residue (elution
with 40:60 CH2Cl2-petroleum ether) afforded 0.19 g (76%
yield) of a mixture of 5a and 5b isomers (E/Z ratio 50:50
1
determined by H NMR).
The same reaction was performed also in the absence of
PdCl2 starting from 2a (0.40 g, 1.74 mmol), CuCl2 (0.55 g, 4.09
mmol), and LiCl (0.07 g, 1.65 mmol) in 7 mL of CH3CN (48 h
reaction time). In this case 0.15 g (45% yield) of 5a ,b was
(3E,5E,7E,9E,11E,13E)-1,16-Bis(4-n -decylph en yl)-3,5,7,9,-
11,13-h exa d eca h exa en e-2,15-d ion e (4e). The synthesis of
4e was performed following the procedure described above for
compound 4a (method A) starting from 2e (1.25 g, 3.04 mmol),
PdCl2 (0.13 g, 0.73 mmol), LiCl (0.10 g, 2.36 mmol), and CuCl2
(0.84 g, 6.24 mmol) in 7.5 mL of CH3OH (2 h reaction time).
After the usual workup, the crude product was purified by
flash chromatography (elution with 9:1 CH2Cl2-petroleum
ether); 0.520 g (51% yield) of a red solid was isolated: mp 169-
1
obtained (E/Z ratio 61:39 determined by H NMR).
(2E,4E)- a n d (2E,4Z)-1-P h en yl-5-br om o-2,4-p en ta d ien -
1-on e (6a a n d 6b). The bromo derivatives 6a ,b were pre-
pared following the same procedure described above for the
chloro derivatives 5a ,b, starting from 2a (0.28 g, 1.22 mmol)
and Pd(OAc)2 (0.07 g, 0.31 mmol), CuBr2 (0.56 g, 2.52 mmol),
and LiBr (0.15 g, 1.73 mmol) in 5 mL of CH3CN (1 h reaction
time). Flash chromatography (elution with 40:60 CH2Cl2-
petroleum ether) of the crude product gave 0.17 g (59% yield)
of a mixture of 4E and 4Z isomers 6a and 6b (E/Z ratio 50:50
171 °C (ethanol); IR (KBr) 1679, 1584, 1075, 1009 cm-1 1H
;
NMR (500 MHz, CDCl3) δ 0.85 (t, J ) 6.8 Hz, 6H), 1.20-1.40
(m, 28H), 1.50-1.70 (m, 4H), 2.56 (t, J ) 7.8 Hz, 4H), 3.58 (s,
4H), 6.22 (d, J ) 15.2 Hz, 2H), 6.34 (dd, J ) 14.8, 11.3 Hz,
2H), 6.37-6.48 (m, 4H), 6.65 (dd, J ) 14.8, 11.0 Hz, 2H), 7.05-
7.15 (m, 8H), 7.26 (dd, J ) 15.2, 11.3 Hz, 2H); 13C NMR (125.7
MHz, CDCl3) δ 14.10, 22.67, 29.31, 29.35, 29.49, 29.57, 29.60,
31.43, 31.88, 35.58, 48.17, 128.55, 128.78, 129.25, 131.59,
131.92, 134.43, 136.70, 141.31, 141.65, 142.58, 197.47. Anal.
Calcd for C48H66O2: C, 85.40; H, 9.86. Found: C, 85.21; H,
9.64.
1
determined by H NMR). Further purification by Kugelrohr
distillation at 1 × 10-4 mbar was attempted, but the product
decomposed at 100 °C (ot): IR (KBr) 1657, 1595, 1019, 990,
759, 689 cm-1; 1H NMR (500 MHz, CDCl3) δ 6.67 (dt, J ) 7.2,
1 Hz, 1H, 6b), 6.88 (d, J ) 13.5 Hz, 1H, 6a ), 6.90 (ddd, J )
10.7, 7.2, 1 Hz, 1H, 6b), 6.96 (dd, J ) 13.5, 11.2 Hz, 1H, 6a ),
7.00 (d, J ) 15.0 Hz, 1H, 6a ), 7.13 (d, J ) 15.2 Hz, 1H, 6b),
7.30 (dd, J ) 15.0, 11.2 Hz, 1H, 6a ), 7.45-7.55 (m, 2H), 7.56-
7.60 (m, 1H), 7.71 (ddd, J ) 15.2, 10.7, 1 Hz, 1 H, 6b), 7.92-
7.96 (m, 2H); 13C NMR (125.7 MHz, CDCl3) δ 117.77, 119.00,
125.71, 128.36, 128,44, 128.62, 128.75, 131.26, 132.95, 136.05,
137.64, 137.68, 138.71, 140.87, 190.00, 190.29. Anal. Calcd
for C11H9OBr: C, 55.72; H, 3.83; Br, 33.70. Found: C, 55.96;
H, 4,06; Br, 33.85.
(2E,4E,6E,8E,10E,12E,14E,16E)-1,18-Dip h en yl-2,4,6,8,-
10,12,14,16-octa d eca octa en e-1,18-d ion e (4f). The synthe-
sis of 4f was performed following the procedure described
above for compound 4a (method A), starting from 2f (1.10 g,
3.89 mmol), PdCl2 (0.17 g, 0.96 mmol), LiCl (0.13 g, 3.06 mmol),
and CuCl2 (1.06 g, 7.90 mmol) in 53 mL of CH3OH (4 h reaction
time). The residue obtained from evaporation of the solvent
at reduced pressure and at 0 °C was extracted with CH2Cl2 in
a Soxhlet apparatus. By partial evaporation of the extraction
solvent, a deep red precipitate was obtained (0.411 g, yield
51%). This solid does not melt up to 240 °C and decomposes
The same reaction performed in the absence of Pd(OAc)2
afforded 0.17 g (60% yield) of a mixture of isomers (E/Z ratio
55:45).
(1E,3E)- a n d (1Z,3E)-1-Br om o-4-p h en yl-1,3-bu ta d ien e
(7a a n d 7b). The same procedure described for the other halo
derivatives was followed, starting from silyl diene 2g, (0.29 g,
1.43 mmol), Pd(OAc)2 (0.04 g, 0.17 mmol), CuBr2 (0.69 g, 3.09
mmol), and LiBr (0.13 g, 1.49 mmol) in 7 mL of CH3CN. After
reaction completion the solvent was evaporated at 0 °C under
reduced pressure. The residue was chromatographed on a
Florisil column with petroleum ether as eluant. Subsequent
distillation of the obtained oil with a Kugelrohr apparatus (ot
150 °C, 1 mbar) afforded 0.15 g (50% yield) of a mixture of 3E
and 3Z isomers 7a and 7b (E/Z ratio 64:36, determined by GLC
analysis): IR (neat) 1627, 1570, 971, 770, 702 cm-1; 1H NMR
(500 MHz, CDCl3) δ 6.24 (dt, J ) 7.1, 1 Hz, 1H, 7b), 6.43 (d,
J ) 13.5 Hz, 1H, 7a ), 6.57 (d, J ) 15.6 Hz, 1H, 7a ), 6.67 (dd,
J ) 15.6, 10.6 Hz, 1H, 7a ), 6.75 (d, J ) 15.8 Hz, 1H, 7b), 6.79
(ddd, J ) 10.2, 7.1, 1 Hz, 1H, 7b), 6.88 (dd, J ) 13.5, 10.6 Hz,
1H, 7a ), 7.13 (ddd, J ) 15.8, 10.2, 1 Hz, 1H, 7b), 7.25-7.40
(m, 3H), 7.45-7.52 (m, 2H); 13C NMR (125.7 MHz, CDCl3) δ
108.43, 108.87, 124.40, 126.03, 126.50, 126.81, 128.02, 128.29,
128.69, 132.74, 133.37, 136.12, 136.73, 137.66. Anal. Calcd
for C10H9Br: C, 57.44; H, 4.34; Br, 38.22. Found: C, 57.54;
H, 4.87; Br, 37.90.
at this temperature: IR (KBr) 1650, 1561, 1008, 771, 694 cm-1
;
1H NMR (500 MHz, CDCl3) δ 6.35-6.55 (m, 10H), 6.72 (dd, J
) 14.7, 11.0 Hz, 2H), 6.97 (d, J ) 14.9 Hz, 2H), 7.40-7.55 (m,
8H), 7.90-7.94 (m, 4H). Anal. Calcd for C30H26O2: C, 86.09;
H, 6.26. Found: C, 85.83; H, 6.00.
(1E,3E,5E,7E)-1,8-Dip h en yl-1,3,5,7-oct a t et r a en e (4g).
Tetraene 4g was prepared following the procedure described
in method A for compound 4a , using diene 2g (0.30 g, 1.49
mmol), PdCl2 (0.06 g, 0.34 mmol), CuCl2 (0.42 g, 3.12 mmol),
and LiCl (0.05 g, 1.18 mmol) in 3 mL of CH3OH. The residue
obtained from evaporation of the solvent at reduced pressure
was a yellow solid, which could be crystallized from chloroform;
0.10 g was obtained (52% yield): mp 229-232 °C. The IR and
MS spectra were compared with those of an authentic sample.
(2E,4E,6E,8E,10E,12E,14E,16E)-1,18-Dip h en yl-2,4,6,8,-
10,12,14,16-o c t a d e c a o c t a e n e -1,18-d io n e -4,5,6,7,12,-
13,14,15-d 8 (4h ). Octaene 4h was prepared following the
same procedure described for the nondeuterated analogue 4f,
starting from 2h (0.12 g, 0.42 mmol), PdCl2 (0.019 g, 0.11
mmol), CuCl2 (0.11 g, 0.82 mmol), and LiCl (0.014 g, 0.33
mmol) in 4 mL of CH3OH.
The crude product was purified on a Florisil column (eluent
9:1 CH2Cl2/petroleum ether) and recrystallized from CH2Cl2
to give 0.049 g of a red solid (55% yield): mp 240 °C with
decomposition; 1H NMR (500 MHz, CDCl3) δ 6.38-6.42 (m, 4H),
6.97 (d, J ) 14.9 Hz, 2H), 7.43-7.55 (m, 8H), 7.91-7.95 (m,
4H). Within the limits of the technique, 1H NMR spectroscopy
showed full deuteration at the 4,5,6,7,12,13,14,15-positions.
(2E,4E)- a n d (2E,4Z)-1-P h en yl-5-ch lor o-2,4-p en ta d ien -
1-on e (5a a n d 5b). A solution of the silyl ketone 2a (0.30 g,
1.30 mmol) in 2.5 mL of CH3CN was added, under a nitrogen
atmosphere, to a stirred suspension of PdCl2 (0.05 g, 0.28
mmol), LiCl (0.04 g, 0.94 mmol), and CuCl2 (0.36 g, 2.68 mmol)
in 3 mL of freshly distilled CH3CN. The resulting mixture
The same reaction performed in the absence of Pd(OAc)2
gave 0.12 g (41% yield) of a mixture of isomers (E/Z ratio 31:
69 GLC).
Ack n ow led gm en t. This work was financially sup-
ported in part by Ministero dell’Universita` e della
Ricerca Scientifica e Tecnologica (MURST, 40% and
60%), Rome. We thank Dr. G. Quinto for preliminary
experiments and Bruker Analytische Messtechnik GM-
BH-Rheinstetter/Karlsruhe (FRG) and Bruker Spectro-
spin Italiana SRL Milano (I) for solid state 1H NMR and
13C NMR spectra.
J O9700437