Regio- and stereoselective synthesis of the 1,3-cyclohexadiene nucleus by [2 + 2 + 2] cycloaddition reactions catalyzed by titanium aryloxide compounds

Article abstract of DOI:10.1021/ja970516r

A variety of titanium aryloxide reagents catalyze the cross coupling of two alkyne units with 1 equiv of olefin to produce the 1,3-cyclohexadiene nucleus. Catalysts include isolated titanacyclopentadiene or titanacyclopentane complexes. The reaction proceeds via attack of the olefin upon a titanacyclopentadiene compound initially formed by coupling of two alkyne units. The reaction is limited to bulky alkyne substrates that undergo slow catalytic cyclotrimerization via competing attack of a third alkyne upon the titanacyclopentadiene ring. The organic products isolated are typically the result of an isomerization within the initially produced 1,3-cyclohexadiene nucleus. Mechanistic studies show that these isomerization processes occur via sequential, metal-mediated 1,5-hydrogen shifts upon a single face of the six-membered ring, exclusively leading to a cis-stereochemistry within the final products. In the reactions of the diynes R-C≡C(CH₂)₄C≡C-R (R = Et, SiMe₃), coupling with ethylene and α-olefins produces a variety of substituted hexalins. A combination of NMR spectroscopy, photochemistry, and molecular mechanics calculations has been applied to determine the stereochemistry and ground state conformations adopted by the product 1,3-cyclohexadienes and hexalins. The primary and secondary photoproducts obtained from some of these 1,3-cyclohexadiene compounds have been characterized.

Full text of DOI:10.1021/ja970516r

J. Am. Chem. Soc. 1997, 119, 7685-7693
7685
Regio- and Stereoselective Synthesis of the 1,3-Cyclohexadiene
Nucleus by [2 + 2 + 2] Cycloaddition Reactions Catalyzed by
Titanium Aryloxide Compounds
Eric S. Johnson, Gary J. Balaich, and Ian P. Rothwell*
Contribution from the Department of Chemistry, 1393 Brown Building, Purdue UniVersity,
West Lafayette, Indiana 47907-1393
ReceiVed February 18, 1997X
Abstract: A variety of titanium aryloxide reagents catalyze the cross coupling of two alkyne units with 1 equiv of
olefin to produce the 1,3-cyclohexadiene nucleus. Catalysts include isolated titanacyclopentadiene or titanacyclopentane
complexes. The reaction proceeds via attack of the olefin upon a titanacyclopentadiene compound initially formed
by coupling of two alkyne units. The reaction is limited to bulky alkyne substrates that undergo slow catalytic
cyclotrimerization via competing attack of a third alkyne upon the titanacyclopentadiene ring. The organic products
isolated are typically the result of an isomerization within the initially produced 1,3-cyclohexadiene nucleus.
Mechanistic studies show that these isomerization processes occur via sequential, metal-mediated 1,5-hydrogen shifts
upon a single face of the six-membered ring, exclusively leading to a cis-stereochemistry within the final products.
In the reactions of the diynes RsCtC(CH2)4CtCsR (R ) Et, SiMe3), coupling with ethylene and R-olefins produces
a variety of substituted hexalins. A combination of NMR spectroscopy, photochemistry, and molecular mechanics
calculations has been applied to determine the stereochemistry and ground state conformations adopted by the product
1,3-cyclohexadienes and hexalins. The primary and secondary photoproducts obtained from some of these 1,3-
cyclohexadiene compounds have been characterized.
Introduction
Scheme 1
The 1,3-cyclohexadiene nucleus has a rich and diverse
reaction chemistry.1 Two important areas of study are the
utilization of 1,3-cyclohexadienes in Diels-Alder condensa-
tions2 and in photochemical ring opening to produce a variety
of primary and secondary photoproducts.3 The study of the
photochemistry of substituted 1,3-cyclohexadienes gains im-
portance from their direct relevance to photoinduced transfor-
mations in the vitamin D field.4 The stereochemical outcome
of the photochemical and thermal interconversions of 1,3-
cyclohexadienes and acyclic trienes was an important component
in the development of the Woodward-Hoffman rules.5
Existing routes to the 1,3-cyclohexadiene nucleus include
isomerization of 1,4-cyclohexadienes generated by Birch reduc-
tion6 and a limited number of other methods.7 Of direct
relevance to the work described here is the pioneering studies
of Volhardt et al. on the cobalt-mediated [2 + 2 + 2]
cycloaddition of 2 equiv of alkyne with an olefin.8 This is
conceptually the simplest and potentially the most powerful
method for the synthesis of 1,3-cyclohexadienes. We report
here our understanding of a titanium aryloxide catalyst system
which produces 1,3-cyclohexadienes with a high degree of regio-
and stereoselectivity. Some aspects of this work have been
communicated.9
Results and Discussions
X Abstract published in AdVance ACS Abstracts, August 1, 1997.
(1) Okamura, W. H.; De Lera, A. R. In ComprehensiVe Organic
Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: New York,
1991; Vol 5, Chapter 6.2.
(2) Fringuelli, F.; Taticchi, A. Dienes in the Diels-Alder Reaction; John
Wiley: New York, 1990.
(3) Jacobs, H. J. C.; Havinga, E. AdV. Photochem. 1979, 11, 305.
(4) Dauben, W. G.; Kellog, M. S.; Seeman, J. I.; Vietmeyer, N. D.;
Wendshuh, P. H. Pure Appl. Chem. 1973, 33, 197.
(5) Woodward, R. B.; Hoffmann, R. The ConserVation of Orbital
Symmetry; Verlag Chemie: Weinheim, 1970.
Synthesis of 1,3-Cyclohexadienes. Previously, we have
shown that the titanacyclopentadiene compounds 1 and 2 can
be obtained in high yield by sodium amalgam reduction of the
dichloride [Ti(OC6H3Ph2-2,6)2Cl2] (OC6H3Ph2-2,6 ) 2,6-di-
phenylphenoxide) in the presence of 3-hexyne or ButCtCH
(Scheme 1).10 In the presence of excess reagent alkyne, 1 and
2 will slowly produce hexaethylbenzene and 1,3,5-tri-tert-
butylbenzene under ambient conditions (Scheme 1). In contrast,
small terminal alkynes exothermically yield copious amounts
of 1,2,4- and 1,3,5-trisubstituted benzene upon addition to 1 or
(6) Organic Reactions; Paquette, L. A., Ed.; John Wiley: New York,
1992; Vol. 42, pp 1-334.
(7) Mironov, V. A.; Federovich, A. D.; Akhrem, A. A. Russ. Chem. ReV.
1983, 52, 61.
(9) Balaich, G. J.; Rothwell, I. P. J. Am. Chem. Soc. 1993, 115, 1581.
(10) Hill, J. E.; Balaich, G. J.; Fanwick, P. E.; Rothwell, I. P.
Organometallics 1993, 12, 2911.
(8) (a) Vollhardt, K. P. C. Angew. Chem., Int. Ed. Engl. 1984, 23, 539.
(b) Shore, N. E. Chem. ReV. 1988, 88, 1081.
S0002-7863(97)00516-7 CCC: $14.00 © 1997 American Chemical Society

7686 J. Am. Chem. Soc., Vol. 119, No. 33, 1997
Johnson et al.
Scheme 2
Scheme 4
Scheme 5
Scheme 3
of 1 with ethylene versus 3-hexyne (leading to cyclotrimeriza-
tion). These gross features control the selectivity of formation
of 1,3-cyclohexadienes below, although more intimate mecha-
nistic details will be discussed later in the paper. Another
important property of this catalytic system is the extensive
isomerization observed leading to a 1,3-cyclohexadiene regio-
chemistry not directly predicted on the basis of alkyne/olefin
structure. The product regio- and stereochemistry can be
rationalized on the basis of either kinetically and/or thermody-
namically controlled 1,5-hydrogen shifts mediated by the
titanium metal center (see mechanistic section below). In the
formation of cis-7 from 3-hexyne/ethylene, two sequential 1,5-
hydrogen shifts within metal bound 5 and 6 (Scheme 2) are
envisaged.
The 2,4-di-tert-butyltitanacyclopentadiene complex 2 reacts
with ethylene in the presence of excess ButCtCH to produce
the 1,3-cyclohexadienes 9, 10 (major component) and 11
(Scheme 4) along with small amounts of 1,3,5-tri-tert-butyl-
benzene 12. Separation and purification of the components of
this reaction mixture is hampered by facile dehydrogenation
(aromatization) on prolonged exposure to air and on silica TLC
plates.
We have extensively investigated the products obtained by
the catalytic [2 + 2 + 2] cycloaddition of styrene with a variety
of alkynes. These reactions can be carried out either by addition
of styrene to isolated titanacyclopentadienes 1 or 2 in the
presence of alkyne or, alternatively, by utilization of the
diphenyltitanacyclopentane 1311a as the catalyst precursor
(Scheme 5). This compound reacts with 3-hexyne, ButCtCH,
or Me3SiCtCH to initially produce titanacyclopentadienes 1,
2, and 14 quantitatively (1H NMR) along with 2 equiv of styrene
(Scheme 5). Use of either of these two catalyst precursors leads
to the phenyl-substituted 1,3-cyclohexadienes shown (Scheme
6, Table 1). Utilization of either ButCtCH or Me3SiCtCH
generates a series of 1,3,5-tris-substituted-1,3-cyclohexadienes.
In the But-substituted compounds, the product ratio of 18/19 is
kinetically controlled by the reaction conditions (Table 2),
whereas for the trimethylsilyl compounds, kinetically produced
2.10 We have also shown that compound 1 reacts with ethylene
to produce a thermally stable titanacyclopentane 3 as the
organometallic product (Scheme 2).11 Surprisingly, we discov-
ered that the organic byproduct was a pentaethyl-1,3-cyclo-
hexadiene (4) whose stereochemistry is now known to be
exclusively trans. When ethylene is added to a mixture of 1
and excess 3-hexyne, catalytic formation of cis-1,2,5,6-tetra-
ethyl-1,3-cyclohexadiene (cis-7) occurs (Scheme 2). Upon
exhaustion of all of the 3-hexyne, the titanium system then
catalyzes the cross coupling of cis-7 with a further equivalent
of ethylene to produce trans-4 (Scheme 2). We have carried
out a separate study of the regio- and stereochemistry of the
cross coupling of olefins with 1,3-cyclohexadienes catalyzed
by titanium aryloxides and these results have been com-
municated12 and full details will be reported elsewhere. In the
presence of excess 3-hexyne, compound 1 reacts with 1-butene
to exclusively produce cis-1,2,3,4,5-pentaethyl-1,3-cyclohexa-
diene (cis-4, Scheme 2).
The addition of 1 to hydrocarbon solutions containing an
excess of both 3-hexyne and ethylene can generate three
organotitanium species: titanacyclopentadiene 1; titanacyclo-
pentane 3; as yet unisolated titanacyclopent-2-ene 8 (Scheme
1
3). Analysis of the H NMR spectrum of a mixture of 1,
3-hexyne, and ethylene in C6D6 reveals the majority of the
titanium to be present as 1. The selective formation of 1,3-
cyclohexadiene, therefore, originates in the stability of 1 over
3 and 8 within the reaction media coupled with a faster reaction
(11) (a) Thorn, M. G.; Hill, J. E.; Waratuke, S. A.; Johnson, E. S.;
Fanwick, P. E.; Rothwell, I. P. In press. (b) Hill, J. E.; Fanwick, P. E.;
Rothwell, I. P. Organometallics 1991, 10, 15.
(12) Waratuke, S. A.; Johnson, E. S.; Thorn, M. G.; Fanwick, P. E.;
Rothwell, I. P. J. Chem. Soc., Chem. Commun. 1996, 2617.

Cycloaddition Reactions Catalyzed by Ti Compounds
J. Am. Chem. Soc., Vol. 119, No. 33, 1997 7687
Scheme 6
Table 1. Product Yields and Distributionsa
[olefin] (equiv per Ti)
[alkyne] (equiv per Ti)
yield %c
product distributiond
PhCHdCH2; 1.9 M (40)
PhCHdCH2; 1.9 M (40)
PhCHdCH2; 1.9 M (40)
Me3SiCHdCH2; 2.1 M (45)
PhCHdCH2; 3.7 M (78)
EtCtCEt; 3.1 M (65)
t-BuCtCH; 1.4 M (28)
Me3SiCtCH; 2.7 M (55)
Me3SiCtCH; 2.8 Me (60)
Me3SiCtC(CH2)4CtCSiMe3; 1.0 M (20)
54
24
52
51
42b
15 (13), 16 (35), 17 (53)
18 (66), 19 (28), 12 (6)
20 (57), 21 (25), 22 (18)
23 (61), 22 (39)
36 (>95)
a Catalyst used 13, 0.048 M; solvent C6D6; alkyne and olefin mixed with 13 and maintained at 25 °C unless otherwise stated. b 105 °C. c Isolated
yield of product mixture based upon alkyne reagent. d GC analysis. e Alkyne added slowly over 3 days.
Table 2. Effect of Initial 3,3-Dimethylbutyne/Styrene
Scheme 7
Concentration on the Product Distributiona
reagents (M)
product distribution (%)
2.90
1.45
2.90
4.35
1.45
1.45b
47
62
74
48
75b
34
30
20
45
20b
19
8
6
7
5
2.90
2.90
1.45
1.45
a [2] ) 0.072 M; solvent C6D6. b Styrene-d8; T ) 25 °C.
20 can subsequently be isomerized thermally by the reaction
mixture to produce 21 as the dominant product. These
observations are of mechanistic significance (Vide infra).
The coupling of vinyltrimethylsilane with Me3SiCtCH can
be achieved using 13 as the catalyst precursor. In this case,
only a single 1,3-cyclohexadiene product (23) is generated,
although large amounts of 1,3,5-tris(trimethylsilyl)benzene (22)
are also produced (Scheme 6, Table 1). To minimize cyclo-
trimerization, the alkyne was added in small batches over a three
day period to a mixture of 13/vinyltrimethylsilane.
hexalin nucleus from entirely acyclic precursors.13 In these
reactions the intermediate titanacyclopentadienes 24 and 25
(Scheme 7)14 are observed in C6D6 solution. Although ethylene
generates the product mixture shown (Scheme 7), the [2 + 2 +
2] cyclization of R-olefins RCHdCH2 (R ) Ph, Bun, and
CH2Ph) with 3,9-dodecadiyne leads almost exclusively to a
series of cis-1,2,4-trisubstituted-1,2,5,6,7,8-hexahydronaphtha-
(13) Hillard, R. L.; Vollhardt, K. P. C. J. Am. Chem. Soc. 1977, 99,
4058.
(14) Balaich, G. J.; Fanwick, P. E.; Rothwell, I. P. Organometallics 1994,
13, 4117.
Utilizing 3,9-dodecadiyne or 1,8-bis(trimethylsilyl)-1,7-octa-
diyne as the alkyne component allows the synthesis of the

7688 J. Am. Chem. Soc., Vol. 119, No. 33, 1997
Johnson et al.
Scheme 8
Scheme 9
3J(H5-H6) coupling constants within the saturated unit will
typically indicate whether substituents occupy pseudoaxial or
pseudoequatorial sites. A powerful, complementary analysis
3
of the J(H4-H5/6) coupling constants by Knowles et al. is of
significance to this work.18 A detailed analysis of chorismate
in a variety of solvents demonstrates the magnitude of this
parameter can be successfully used to determine the predominant
ground state conformational structure.
lenes (Scheme 8). These reactions are complicated, however,
by the formation of significant quantities of the 3,9-dodecadiyne
trimerization product 29.13
The photochemistry of 1,3-cyclohexadienes has been ex-
tremely well documented. The conrotatory photochemical ring
opening of a 1,3-cyclohexadiene to produce a hexatriene
backbone as the primary photoproduct is typically followed by
secondary photoreactions producing a variety of cyclic and
acyclic products.4,19 Detailed studies have shown that the
position of substituents in the triene primary photoproduct are
controlled by the “principal of least motion” (PLM); pseudoaxial
groups occupy the Z-sites in the terminal methylene groups.20
More recently molecular mechanics methods have been
brought to bear on the problem of ground state structures of
1,3-cyclohexadienes and in particular for the conformational
analysis of partially hydrogenated polycyclic aromatic hydro-
carbons.16
The series of ethyl derivatives 4 and 7 (Scheme 2) have
complex patterns in the aliphatic region of the 1H NMR
spectrum, precluding analysis of the 3J(H5-H6) coupling
constants to indicate the absolute stereochemistry. The 3J(H4-
H5) parameter is, however, highly informative. A low value
of <2 Hz in both cis-4 and cis-7 indicates that H5 occupies a
pseudoaxial site in these compounds, whereas the larger, 6.5
Hz coupling in trans-4 is consistent with a pseudoequatorial
site for H5 in this compound (Scheme 9).18 Steric considerations
argue that the ethyl groups at C-6 will occupy a pseudoaxial
The titanacyclopentane compound 13 has been shown to react
with 3 equiv of 3,9-dodecadiyne to stoichiometrically (1H NMR)
produce 24 and 2 equiv of cis-33 (Scheme 8). Addition of
excess styrene to 24 then regenerates 13 along with an additional
1 equiv of cis-33.
One of the cleanest [2 + 2 + 2] cycloaddition reactions we
have identified is the reaction of styrene with 1,8-bis(trimeth-
ylsilyl)-1,7-octadiyne15 catalyzed by 25 (Scheme 8, Table 1).
Although much slower than the corresponding reactions with
3,9-dodecadiyne (presumable a steric consequence), this reaction
produces a single hexalin product (cis-36) with no contaminating
cyclotrimerization products.
Product 1,3-Cyclohexadiene Stereochemistry. A thorough
understanding of the stereochemistry of these 1,3-cyclohexa-
diene products is not only of synthetic importance but is also
crucial to any comprehension of the mechanism of their
formation and/or isomerization by the titanium aryloxide
catalysts. The conformational ground state structure of 1,3-
cyclohexadiene and its substituted derivatives has been exten-
sively studied by a variety of methods, and we have utilized
three particular techniques in this study.
(17) (a) Lightner, D. A.; Bouman, T. D.; Gawronski, J. K.; Gawronska,
K.; Chappuis, J. L.; Crist, B. V.; Hansen, A. E. J. Am. Chem. Soc. 1981,
103, 5314. (b) Karabelas, K.; Hallberg, A. J. Org. Chem. 1988, 53, 4909.
(18) Copley, S. D.; Knowles, J. R. J. Am. Chem. Soc. 1987, 109, 5008.
(19) Woning, J.; Lijten, F. A.; Laarhoven, W. H. J. Org. Chem. 1991,
56, 2427 and references therein.
(20) (a) Padwa, A.; Brodsky, L.; Clough, S. J. Am. Chem. Soc. 1972,
94, 6767. (b) Courtot, P.; Rumin, R.; Salaun, J. Y. Recl. TraV. Chim. Pays-
Bas 1979, 98, 192. (c) Lamberts, J. J. M.; Laarhoven, Recl. TraV. Chim.
Pays-Bas 1984, 103, 131. (d) Spangler, C. W.; Hennis, R. P. J. Chem. Soc.,
Chem. Commun. 1972, 24.
1
Routine H NMR methods have been successfully applied
to the determination of the ground state conformations adopted
by 5- and 5,6-substituted-1,3-cyclohexadienes.16,17 Analysis of
(15) (a) Birkofer, L.; Hansel, E.; Steigel, A. Chem. Ber. 1982, 115, 2574.
(b) Brandsma, L.; Verkryijsse, H. D. Synthesis of Acetylenes, Allenes, and
Cumulenes; Elsevier: New York, 1981, p 57.
(16) The Conformational Analysis of Cyclohexenes, Cyclohexadienes and
Related Hydroaromatic Compounds; Rabideau, P. W., Ed.; VCH Publishers,
Inc.: New York, 1989.

Cycloaddition Reactions Catalyzed by Ti Compounds
J. Am. Chem. Soc., Vol. 119, No. 33, 1997 7689
Table 3. Selected Coupling Constants (hertz) for 1,3,5-Trisubstituted-1,3-Cyclohexadienes
R1
R3
But
Ph
SiMe3
SiMe3
SiMe3
R5
2J(H6c-H6t)
3J(H5-H6t)
3J(H5-H6c)
3J(H4-H5)
18
19
20
21
23
Ph
But
16.3
15.0
16.5
16.3
16.5
13.2
14.8
14.8
9.8
8.7
7.0
8.1
4.0
4.0
3.5
<2
3.2
5.6
5.6
But
But
SiMe3
Ph
SiMe3
Ph
SiMe3
SiMe3
9.5
Scheme 10
Scheme 11
a pseudoequatorial conformer for 18 and 19 is confirmed by
their photochemical conversion to 47 and 48 (Scheme 11).
Mechanistic Considerations. The formation of 1,3-cyclo-
hexadienes studied here has some mechanistic similarities to
the [2 + 2 + 2] cyclotrimerization of alkynes.10 In this latter
case, a long-standing mechanistic dilemma has been the exact
nature of intermediate organometallic species. The addition of
ethylene to a titanacyclopentadiene may lead (via an olefin
adduct) to the concerted formation of the two new carbon-
carbon bonds or else proceed in a stepwise fashion via a
titanacycloheptatriene (Scheme 12). The concerted pathway has
many similarities with the ubiquitous Diels-Alder reaction.
Three observations argue strongly against a stepwise pathway
for these reactions. First, the facile insertion of olefins into the
Ti-C bonds of neutral species [(ArO)2TiR2]21 (R ) alkyl, aryl,
or part of a metallacyclic ring) has not been observed. Although
the expansion of titanacyclopent-3-ene rings upon addition of
ethylene and R-olefins occurs readily, it proceeds via coupling
of the olefin with a diene double bond.22 Second, seven-
membered titanacyclic rings undergo â-hydrogen abstraction/
elimination processes (whether concerted or stepwise) at a much
faster rate than five-membered analogues.11a,22 In a number of
cases this would lead to the formation of 1,3,5-trienes, which
we have synthesized by photochemical experiments but do not
detect in the [2 + 2 + 2] cycloaddition reaction mixtures.
Finally, we have no evidence in our previous work on titanium
aryloxides for the facile reductive/elimination (coupling) of
adjacent Ti-C bonds in [(ArO)2TiR2] species.
site in all three compounds to minimize interactions with the
ethyl substituent at C-1. This argument is strongly supported
by molecular mechanics calculations on the compound 1,2,3,5,6-
pentamethyl-1,3-cyclohexadiene where, in both the cis- and
trans-isomers, a preference of a pseudoaxial substituent at C-6
was calculated (see the Supporting Information). The above
arguments, therefore, lead to the stereochemistry assigned to
these three molecules (shown in Scheme 9). We have also
carried out the photolysis of these three products. The
magnitude of the relevant vicinal coupling constants in the
product trienes 37-39 (Scheme 9) confirms the ground state
conformational position of the substituents at C5.
Directly analogous arguments, when applied to the three
hexalin compounds 33-35 (Scheme 8), show the product
stereochemistry to be cis. Molecular mechanics calculations
on the model compound 1,2,4-trimethylhexalin (see the Sup-
porting Information) show the substituent at C1 is pseudoaxial,
1
while H NMR data and photochemical studies of 34 and 35
show the substituent at C-2 is pseudoequatorial (Scheme 10).
Extended photolysis of trienes 41 and 44 (Scheme 10) was found
to lead to the allene compounds 42 and 45 as the major
secondary photoproducts. In contrast photolysis of the 2-phenyl
derivative, 33 did not produce significant quantities of a triene.
Instead, the major photoproduct appears to be a bicyclo[3.1.0]-
hexene, whose stereochemistry we have not assigned. The
stereochemical outcome of the photochemical conversion of
phenyl-substituted 1,3-cyclohexadienes to bicyclo[3.1.0]hexenes
has been reported.20
The kinetics of formation of the hexalin cis-36 by reaction
of styrene with 1,8-bis(trimethylsilyl)-1,7-octadiyne were in-
vestigated. This reaction was chosen for study because only a
single isomer is produced with no cyclotrimerization side
reaction. The kinetics were carried out by adding titanacyclo-
pentane 13 to a mixture of styrene (excess) and 1,8-bis-
The situation with the five 1,3,5-tris-substituted-1,3-cyclo-
hexadienes is more straightforward. In this case, the resolution
3
and analysis of J coupling constants reveals the 5-substituent
in 18-20 to be predominantly pseudoequatorial in solution
(Table 3). This data is consistent with reported studies of 5-tert-
butyl-1,3-cyclohexadiene.16,17a It is interesting to note that the
values of the coupling constants indicate that the SiMe3
substituents in 21 and 2317b imply that significant amounts of
the pseudoaxial conformer are present. The predominance of
(21) (a) Chesnut, R. W.; Durfee, L. D.; Fanwick, P. E.; Rothwell, I. P.;
Folting, K.; Huffman, J. C. Polyhedron 1987, 6, 2019. (b) Hill, J. E.;
Fanwick, P. E.; Rothwell, I. P. Organometallics 1990, 9, 2211. (c) Hill, J.
E.; Fanwick, P. E.; Rothwell, I. P. Organometallics 1991, 10, 15.
(22) Balaich, G. J.; Hill, J. E.; Waratuke, S. A.; Fanwick, P. E.; Rothwell,
I. P. Organometallics 1995, 14, 656.

7690 J. Am. Chem. Soc., Vol. 119, No. 33, 1997
Johnson et al.
Scheme 13
Figure 1. Plot showing the appearance of cis-36 (equivalents per Ti)
at 105 °C during the [2 + 2 + 2] cycloaddition of 1,8-bis-
(trimethylsilyl)-1,7-octadiene with styrene.
Scheme 12
pounds leading to an overall 1,5-hydrogen shift (Scheme 13).25,26
During the formation of cis-7 (Scheme 2) and many other
products, two sequential 1,5-hydrogen shifts are necessary. The
mediating metal center remaining bound to a single face of the
cyclohexadiene nucleus will lead exclusively to the observed
cis-stereochemistry. An indiscriminate isomerization process
would lead to the thermodynamically more stable trans-isomer.
In the reaction of 3,9-dodecadiyne and 1,8-bis(trimethylsilyl)-
1,7-octadiyne with R-olefins (Scheme 8), the initially formed
titananorbornene may exist as either an exo- or endo-stereo-
isomer. On the basis of steric arguments, the endo-isomer (alkyl
trans to the titanium metal center) is preferred. The stereo-
chemistry of the isolated products could only originate via a
metal-mediated 1,5-shift within the endo-isomer; the exo-isomer
can only produce the trans-stereoisomer (Scheme 13). Fur-
thermore, the endo-isomer also has available an alternative
hydrogen for migration (Scheme 13). This pathway would lead
to a regiochemistry that is not observed, indicating that the metal
center is highly selective at abstracting and migrating a hydrogen
from the methylene group.
(trimethylsilyl)-1,7-octadiyne in C6D6 solvent. Analysis of the
initial reaction mixture by H NMR spectroscopy reveals the
1
clean conversion of 13 into 25 (Scheme 8). The solutions were
then heated at 105 °C, and the reaction was monitored at various
time intervals by 1H NMR. The reactions were found to
demonstrate a zero-order dependence on [diyne] and a first-
order dependence on both [styrene] and [Ti]. In Figure 1 is
shown a plot of the appearance of cis-36 utilizing 25 equiv of
diyne per Ti and 65 or 130 equiv of styrene. Under the
conditions shown, the product cis-36 is produced at rates of
1.9(1) and 4.1(2) equiv Ti-1 h-1, respectively.
The kinetic results as well as the product regio- and
stereochemistry can be accounted for by a mechanistic pathway
in which rate-determining attack of olefin on the titanacyclo-
pentadiene produces a metal-bound 1,3-cyclohexadiene. On the
basis of related studies of the structure and bonding within the
niobium and tantalum species [(ArO)3M(η4-C6H8)] and [(ArO)2M-
(Cl)(η4-C6H8)]23 as well as related group 4 metal 1,3-diene
species,24 a titananorbornene bonding picture appears reasonable
for this molecule (Scheme 12). Direct dissociation of 1,3-
cyclohexadiene, releasing the extremely high-energy fragment
[Ti(OAr)2], is doubtful. Instead, displacement of the product
by alkyne or olefin present in solution will lead to regeneration
of the titanacyclopentadiene, titanacyclopentene and titana-
cyclopentane equilibrium mixture (Scheme 3).
We have also applied molecular mechanics methods to
determine the relative stabilities of all regio- and stereoisomers
of the model compounds pentamethyl-1,3-cyclohexadiene and
1,2,4-trimethylhexalins (see the Supporting Information).27
These results show that the cis-products observed are slightly
more stable than the isomers initially expected on the basis of
The isomerization process occurs within the titananorborna-
diene complex via intermediate cyclohexadienyl hydride com-
(25) (a) Lamanna, W.; Brookhart, M. J. Am. Chem. Soc. 1980, 102, 3490.
(b) Karel, K. J.; Brookhart, M.; Aumann, R. J. Am. Chem. Soc. 1981, 103,
2695.
(26) Fischer, M. B.; James, E. J.; McNeese, T. J.; Nyburg, S. C.; Posin,
B.; Wong-Ng, W.; Wreford, S. S. J. Am. Chem. Soc. 1980, 102, 4941.
(27) Dilworth, J. R.; Hanich J.; Krestel M. J. Organomet. Chem. 1986,
315, 9.
(23) (a) Visciglio, V. M.; Nguyen, M. T.; Clark, J. R.; Mulford, D. R.;
Fanwick, P. E.; Rothwell, I. P. J. Am. Chem. Soc. 1997, 119, 3490. (b)
Visciglio, V. M.; Nguyen, M. T.; Clark, J. R.; Fanwick, P. E.; Rothwell, I.
P. Polyhedron 1996, 15, 551.
(24) Diamond, G. M.; Green, M. L. H.; Walker, N. M.; Howard, J. A.
K.; Mason, S. A. J. Chem. Soc., Dalton Trans. 1992, 2641.

Cycloaddition Reactions Catalyzed by Ti Compounds
J. Am. Chem. Soc., Vol. 119, No. 33, 1997 7691
Scheme 14
Scheme 15
Figure 2. 1H NMR spectra (500 MHz, C6D6) of the olefinic and
aliphatic protons in the mixtures of 18/19 (A and C) and 18*/19* (B
and D) produced by the [2 + 2 + 2] cycloaddition of 3,3-dimethyl-
butyne with styrene and styrene-d8, respectively.
the proton at H6 occupies a pseudoaxial site, i.e., cis to the tert-
butyl substituent (Scheme 15, Figure 2).
A constant product ratio following formation of 18 and 19
indicates that the tert-butyl-1,3-cyclohexadiene products do not
revisit the titanium metal center following formation. In
contrast, the trimethylsilyl-substituted compound 20 can be
isomerized to 21 following completion of the [2 + 2 + 2]
cycloaddition process. It is interesting to note that excess alkyne
in the reaction mixture inhibits the isomerization while excess
styrene leads to slow conversion. We interpret this as indicating
that very stable titanacyclopentadiene 14 does not allow the
product cyclohexadiene to recoordinate, whereas the titana-
cyclopentane 13 is known to undergo facile fragmentation and
exchange of styrene for olefinic reagents in solution.
the olefin/alkyne structure. The analysis also shows that the
corresponding trans-isomers are much more stable. The lack
of observation of trans-products indicates that the isomerization
process is being controlled by the titanium reagent. The only
trans-isomer obtained, trans-4 (Scheme 2), is obtained via a
different pathway involving coupling of a preformed 1,3-
cyclohexadiene (cis-4) with ethylene.12
Support for this mechanism of formation and isomerization
is obtained by a detailed study of the formation of the isomeric
products 18 and 19. When the reaction conditions are varied,
the product ratio can be varied. In this case, increasing the
concentration of reagent alkene and/or alkyne boosts the
proportion of 18 over 19 (Table 2). This indicates that once
titananorbornene 49 is generated (Scheme 14), rapid isomer-
ization to 50 occurs. The subsequent rates of isomerization to
51 and displacement of 18 by olefin and/or alkyne are
comparable. The observed products can only be generated via
the endo-isomer 49, in which the phenyl substituent is oriented
away from the metal coordination sphere. Neither the exo-
isomer 52 nor the alternative regioisomer 53 can lead to the
observed products. Further mechanistic insight is given by
reacting ButCtCH with styrene-d8 in the presence of 2. In
this case, a higher proportion of the isomer 18* (Table 2)
indicates that a primary kinetic isotope effect is present for the
isomerization. Analysis of the 1H NMR spectra of these labeled
compounds shows that the two deuterium atoms migrating to
form 19* do so on the same face of the 1,3-cyclohexadiene
ring, i.e., they are mutually cis, consistent with the proposed
mechanism. This is concluded by the observation that in 19*
Experimental Section
All reactions were carried out under N2 or in Vacuo either in a
Vacuum Atmosphere Dri-Lab or by Standard Schlenk techniques.
Solvents were dried by distillation over Na/benzophenone under N2.
The synthesis of compounds 1, 2,10 3, 13,11a and [Ti(OC6H3Ph2-2,6)2-
Cl2]27 have been previously reported. The compound 3,9-dodecadiyne
was purchased from Lancaster Synthesis, Inc., and dried over 4 Å
molecular sieves. All other reagents were purchased from Aldrich
Chemical Company and dried with 4 Å molecular sieves prior to use.
1H and 13C NMR spectra were recorded using Varian Associates 200
or 500 MHz spectrometers and a General Electric QE-300-MHz
spectrometer. Gas chromatographic analyses were performed with a
Hewlett Packard model 5890 Series II gas chromatograph using a
capillary column (HP-1, cross-linked silicone gum; 25 m × 0.2 mm ×
0.33 µm film thickness) with a flame ionization detector. TLC
separations were performed with Kieselgel 60 F254 25 Folien 20 cm ×
20 cm, 2 mm thickness, preparative scale TLC plates. Mass spectral
data was acquired through Purdue in-house facilities. Molecular
mechanics calculations were performed with MacroModel V4.528
(MM3*) with full conformational searching. Due to the similarity of

7692 J. Am. Chem. Soc., Vol. 119, No. 33, 1997
Johnson et al.
the experimental procedures only representative examples are given.
Full experimental details are present in the Supporting Information.
Synthesis of cis-1,2,5,6-Tetraethyl-1,3-cyclohexadiene (cis-7). A
sample of [Ti(OC6H3Ph2-2,6)2(C4Et4)] (1, 0.1 g, 0.14 mmol) was
dissolved in 3-hexyne (3 mL, 26 mmol), and the reaction mixture was
stirred rapidly under one atmosphere of ethylene for 2 h. Excess
3-hexyne and ethylene were removed under vacuum, and the cis-7 (1.25
g, 6.5 mmol, 50%) was isolated by preparative TLC. HRMS: calcd
for C14H24 192.1878, found 192.1878. 1H NMR (C6D6, 30 °C): δ 5.77
3.81 (CHPh of 16); 5.67 (br s, olefinic proton of 16); 5.71 (br s, olefinic
ring proton of 15); 6.09 (s, olefinic proton of 17). Selected 13C NMR
(C6D6, 30 °C): δ 40.6, 42.6 (C5, C6 of 15); 45.5, 47.2 (C5, C6 of 16);
38.8, 43.1 (C5, C6 of 17). GC/MS analysis of the reaction mixture
yielded: MS(EI) of 15 268 (M+, 32%), 239 (93), 211 (100), 195 (8),
183 (38), 165 (12), 155 (30), 105 (17), 91 (11), 77 (8); MS(EI) of 16
268 (M+, 29%), 239 (81), 211 (100), 195 (5), 183 (42), 165 (12), 155
(38), 105 (8), 91 (13), 77 (7); MS(EI) of 17 268 (M+, 22%), 239 (100),
211 (59), 195 (4), 183 (26), 165 (10), 155 (26), 105 (15), 91 (50), 77
(11).
3
4
(dd, JH-H ) 9.5 Hz, JH-H ) 2.9 Hz, 1H, CHCHCEt); 5.43 (br dd,
4
3JH-H < 2 Hz, JH-H ) 1.8 Hz, 1H, CHCHCHEt); 0.8-2.5 (m, 22H,
The reaction can also be catalyzed by 13. See Table 1.
CH2Me, CH2Me, CHEt). 13C NMR (C6D6, 30 °C): δ 139.8, 131.4
(C1, C2); 129.8, 128.6 (C3, C4); 42.1, 41.4 (C5, C6); 26.4, 24.4, 24.1,
19.3 (CH2CH3); 15.8, 14.5, 13.0, 12.4 (CH2CH3). Photolysis of cis-7
in pentane produced (Z,Z,E)-4,5-diethyl-3,5,7-decatriene (37). 1H NMR
Characterization of Products from [2 + 2 + 2] Cycloaddition of
1
3,3-Dimethyl-1-butyne with Styrene. Spectroscopic data for 18. H
4
NMR (C6D6, 30 °C): δ 6.56 (m, JH-H ) 1.4 Hz, 1H, CButCHCPh);
3
2
5.72 (dd, JH-H ) 3.5 Hz, 1H, CButCHCH(But)); 2.51 (dd, JH-H
)
)
3
4
16.3 Hz, 3JH-H ) 8.7 Hz, 1H, CPhCHe(Ha)CH(But)); 2.42 (m, 3JH-H
(C6D6, 30 °C): δ 5.33 (tt, JH-H ) 7.1 Hz, JH-H ) 1.3 Hz, 1H,
CH2CHCEt); 6.02 (d, 3JH-H ) 10.7 Hz, 1H, CEtCHCH); 6.28 (dd, trans-
13.2 Hz, 4JH-H ) 1.7 Hz, 1H, CPhCHe(Ha)CH(But)); 7.0-7.6 (m, 5H,
Ph); 1.14 (s, 9H, CC(CH3)3); 0.91 (s, 9H, CHC(CH3)3). 13C NMR
(C6D6, 30 °C): δ 146.1 (C1); 122.2 (C2); 138.0 (C3); 119.2 (C4); 45.0
(C5); 28.0 (C6); 34.6 (CC(CH3)3); 33.8 (CHC(CH3)3); 29.6 (CC(CH3)3);
27.8 (CHC(CH3)3; 143.0 (ipso); 129.2, 127.6, 126.1 (CPh) MS(CI):
269 ((M + H)+, 100.0%), 211 (2.3), 210 (1.5). Photolysis of 18 in
pentane produced (Z,E)-7,7-dimethyl-2-phenyl-4-tert-butyl-1,3,5-octa-
riene (47). 1H NMR (C6D6, 30 °C): δ 6.31 (br s, 1H, CPhCH); 5.75
(d, trans-3JH-H ) 16.1 Hz, 1H, CH(But)CH); 5.51 (d, 1H, CHCH(But));
5.47 (m, 1H) 5.24 (t, 1H) (gem-2J ) 1.6 Hz, CH(H)CPh); 7.0-7.7 (m,
5H, aromatics); 1.14 (s, 9H, CC(CH3)3); 0.81 (s, 9H, CHC(CH3)3.
Spectroscopic data for 19. 1H NMR (C6D6, 30 °C): δ 6.26 (m, 4JH-H
3JH-H ) 15.1 Hz, J ) 1.4 Hz, 1H, CHCHCHEt); 5.65 (dt, JH-H
)
4
3
6.6 Hz, 1H, CH2CHCH); 0.5-2.8 (m, 20H, CH2Me, CH2Me). 13C
NMR (C6D6, 30 °C): δ 142.2, 140.5 (C4, C5); 134.8, 129.9, 128.6,
126.3 (C3, C6, C7, C8); 29.7, 29.6, 26.4, 22.9 (CH2Me); 13.0, 13.1,
14.2, 14.5 (CH2Me).
Characterization of trans-1,2,3,5,6-Pentaethyl-1,3-cyclohexadiene
(trans-4) and Photoproduct (39). HRMS: calcd for C16H28 220.2191,
3
found 220.2191. 1H NMR (C6D6, 30 °C): δ 5.44 (br d, JH-H ) 6.5
Hz, 4JH-H ) 1.0 Hz, 1H, CEtCHCHEt); 0.85-2.45 (m, 27H, CH2Me,
CH2Me, CHEt); 13C NMR C6D6: 138.4, 138.0, 131.0 (C1-3); 122.9
(C-4); 44.2, 38.1 (C5, C6); 26.4, 26.1, 25.8, 24.2, 20.5 (CH2CH3); 15.6,
14.3, 13.9, 12.6, 12.3 (CH2CH3). Photolysis of trans-4 in pentane
produced (Z,Z,Z)-4,5,6-triethyl-3,5,7-decatriene (39). 1H NMR (C6D6,
30 °C): δ 6.05 (d, cis-3JH-H ) 11.8 Hz, 1H, CEtCHCH); 5.23 (m, 2H,
CH2CHCEt, CH2CHCH); 0.8-2.5 (m, 25H, CH2Me, CH2Me).
) 1.6 Hz, 1H, CButCH); 6.04 (m, 1H, CH(But)CH); 2.20 (dd, 2JH-H
)
3
3
14.8 Hz, JH-H ) 7.0 Hz, CButCHe(Ha)); 2.01 (m, JH-H ) 15.0 Hz,
CButCHa(He)); 2.1-2.2 (m, 1H, CH2CH(But)); 7.0-7.6 (m, 5H,
aromatics); 1.10 (s, 9H, CC(CH3)3); 0.93 (s, 9H, CHC(CH3)3. 13C NMR
(C6D6, 30 °C): δ 138.5 (C1); 118.0 (C2); 150.9 (C3); 124.2 (C4); 46.6
(C5); 25.4 (C6); 36.2 (CC(CH3)3); 33.4 (CHC(CH3)3); 29.1 (CC(CH3)3);
27.9 (CHC(CH3)3); 142.7 (ipso); 129.2, 127.5, 126.7 (Ph). MS(CI):
277 ((M + H+), 100.0%), 218 (1.9), 217 (3.2), 276 (11.6). Photolysis
of 18 in pentane produced (Z,E)-7,7-dimethyl-4-phenyl-2-tert-butyl-
1,3,5-octatriene (48). 1H NMR (C6D6, 30 °C): δ 6.37 (br s, 1H,
CButCHCPh); 6.46 (d, trans-3JH-H ) 16.2 Hz, 1H, CPhCHCH(But));
5.56 (d, H, CH(But)CH), 4.88 (d, 1H), 4.69 (t, 1H) (gem-2JH-H ) 1.5
Hz, (H(H)CBut); 7.0-7.7 (m, 5H, aromatics); 0.99, 0.80 (s, 18H,
CC(CH2)3).
Characterization of cis-1,2,3,5,6-Pentaethyl-1,3-cyclohexadiene
(cis-4) and Photoproducts. 1H NMR (C6D6, 30 °C): δ 5.22 (m, 3JH-H
) 1.8 Hz, 1H, CEtCHCEtH); 0.9-2.6 (m, 27H, CH2Me, CH2Me,
CHEt). 13C NMR (C6D6, 30 °C): δ 142,0, 139.6, 133.0 (C1-3); 125.2
(C4); 41.9, 41.7 (C5, C6); 27.3, 25.9, 24.6, 20.7, 19.1 (CH2Me); 16.0,
15.7, 14.2, 13.3, 12.5 (CH2Me). Photolysis of cis-4 in pentane produced
(Z,Z,E)-4,5,6-triethyl-3,5,8-decatriene (38). 1H NMR (C6D6, 30 °C):
δ 5.33 (tt, 3JH-H ) 7.1 Hz, 3JH-H ) 1.3 Hz, 1H, CH2CHCEt); 6.43 (dt,
trans-3JH-H ) 15.9 Hz, 4JH-H ) 1.5 Hz, 1H, CH(Et)CHCEt); 5.68 (dt,
3JH-H ) 6.5 Hz, 1H, CH2CHCH); 0.9-2.8 (m, 25H, CH2Me, CH2Me).
13C NMR (C6D6, 30 °C): δ 140.9, 138.8, 135.2 (C4-6); 130.0, 129.7,
128.9 (C3, C7, C8); 30.1, 26.8, 24.7, 23.0, 23.1 (CH2Me). A secondary
photoproduct (Z)-5,7-diethyl-3,4,6-decatriene was observed upon ex-
Reaction of 3,3-dimethyl-1-butyne with styrene-d8 produced 18* and
19*. Spectroscopic data for 18*. 1H NMR (C6D6, 30 °C): δ 6.53 (d,
4JH-H ) 1.4 Hz, 1H, (CPhCH); 5.69 (d, 1H, CD(But)CH); 1.14 (s, 9H,
CC(CH3)3); 0.90 (s, 9H, CDC(CH3)3. 13C NMR (C6D6, 30 °C): δ 146.1
(C1); 122.1 (C2); 137.8 (C3); 119.1 (C4); 44.2 (t, C5); 28.0 (C6); 34.6
(CC(CH3)3); 33.7 (CDC(CH3)3); 29.6 (CCC(CH3)3); 27.8 (CDC(CH3)3).
MS(CI): 277 {(M + H)+, 100.0%}, 218 (1.9), 217 (3.2), 276 (11.6).
Spectroscopic data for 19*. 1H NMR (C6D6, 30 °C): δ 6.22 (d, 4JH-H
) 2.3 Hz, 1H, CH); 2.02 (s, 1H, CD(H)); 1.10 (s, 9H, CC(CH3)3; 0.93
(s, 9H, CDC(CH3)3. 13C NMR (C6D6, 30 °C): δ 121.5 (C2); 150.0
(C3); 36.1 (CC(CH3)3); 33.3 (CDC(CH3)3); 29.1 (CC(CH3)3); 27.9
(CDC(CH3)3); 142.5 (ipso). MS(CI): 277 ((M + H)+, 100.00%), 276
(15.7), 218 (1.3).
3
tended irradiation. 1H NMR (C6D6, 30 °C): δ 5.15 (tt, JH-H ) 6.4
5
Hz, JH-H ) 3.3 Hz, 1H, CH2CHC); 0.5-2.8 (m, 22H, CH2Me, CH2-
CH2Me). 13C NMR C6D6: 201.7 (C4); 92.6 (C3); 107.4 (C5); 137.0,
134.5 (C7, C8); 36.0, 26.5, 25.0, 24.4, 23.5, 22.8 (CH2).
Characterization of Products from [2 + 2 + 2] Cycloaddition of
3,3-Dimethyl-1-butyne with Ethylene. Spectroscopic data for 2,6-
di-tert-butyl-1,3-cyclohexadiene 10. 1H NMR (C6D6, 30 °C): δ 5.61
(m, 4JH-H ) 1.2 Hz, 1H, CH(But)CHCBut); 6.08 (dq, 3JH-H ) 9.8 Hz,
4
3
1H, CHCHCBut); 5.82 (dt, JH-H ) 1.2 Hz, JH-H ) 4.1 Hz, 1H,
CH2CHCH); 1.9-2.8 (m, 3H, CBut(H)CH2); 1.08 (s, 9H, CC(CH3)3);
0.88 (s, 9H, CHC(CH3)3). 13C NMR (C6D6, 30 °C): δ 44.4 (C5); 34.4
(CC(CH3)3); 33.4 (CHC(CH3)3); 29.3 (CC(CH3)3); 27.7 (CHC(CH3)3);
24.5 (C6); 127.5, 125.4, 121.5, 119.3 (C1-4). MS(EI) of 10: 192
(M+, 0.8%), 134 (2.2), 120 (0.8), 119 (12.2), 105 (1.7), 91 (3.1), 79
(1.1), 77 (1.3), 58 (2.6), 57 (100). MS(EI) of 11: 192 (M+, 0.7%),
134 (0.8), 119 (4.3), 105 (1.4), 91 (2.1), 79 (0.9), 77 (1.1), 58 (2.2), 57
(100). MS(EI) of 9: 192 (M+, 1.3%), 119 (9.9), 105 (1.5), 91 (3.2),
79 (1.1), 77 (1.3), 58 (1.6), 57 (100).
The reaction can also be catalyzed by 13. See Table 1.
Characterization of Products from [2 + 2 + 2] Cycloaddition of
Trimethylsilylacetylene with Styrene. Anal. Calcd for C28H28Si2:
C, 71.92; H, 9.39. Found: C, 71.45; H, 9.71. The slow isomerization
of 20 to 21 was observed by 1H NMR upon thermolysis of the reaction
mixture at 95 °C. Attempts at separation by TLC was frustrated by
extensive aromatization. Spectroscopic data for 20. 1H NMR (C6D6,
30 °C): δ 6.59 (m, 3JH-H ) 3.2 Hz, 1H, C(H)PhCH); 6.27 (d, 4JH-H
)
)
Characterization of Products from [2 + 2 + 2] Cycloaddition of
3-Hexyne with Styrene. Anal. Calcd for C20H28: C, 89.49; H, 10.51.
Found: C, 89.85; H, 10.62. Attempts to separate the reaction mixture
by chromatographic methods led to extensive aromatization. 1H NMR
of the reaction mixture (C6D6, 30 °C): δ 7.0-7.5 (aromatics, all three
isomers); 0.5-2.9 (aliphatic and Et group protons of all three isomers);
1.0 Hz, 1H, CSiMe3CHCSiMe3); 3.40 (ddd, 3JH-H ) 14.8 Hz, 3JH-H
4
2
8.1 Hz, JH-H ) 1.9 Hz, 1H, CHPh); 2.43 (dd, JH-H ) 16.5 Hz, 1H,
4
CHeHa); 2.28 (m, JH-H ) 2.3 Hz, 1H, CHaHe); 7.0-7.6 (m, 5H,
aromatics); 0.167, 0.098 (s, 18H, CSiMe3). 13C NMR (C6D6, 30 °C):
δ 134.1 (C2); 141.0 (C4); 41.5 (C5); 34.1 (C6); -1.10, -1.20 (CSi-
(CH3)3). Spectroscopic data for 21. 1H NMR (C6D6, 30 °C): δ 6.47
4
3
3
(d, JH-H ) 2.6 Hz, JH-H ) 2.3 Hz, 1H, CPhCH); 6.23 (d, JH-H
5.6 Hz, 1H, CHSiMe3CH); 2.85 (ddd, JH-H ) 16.3 Hz, JH-H ) 9.9
)
(28) Mohamadi, F.; Richards, N. G. J.; Guida, W. C.; Liskamp, R.;
Lipton, M.; Caulfield, C.; Chang, G.; Hendrickson, T.; Still, W. C. J.
Comput. Chem. 1990, 11, 440.
2
3
3
Hz, CHaHe); 2.53 (dd, JH-H ) 4.0 Hz, 1H, CHeHa); 1.74 (ddd, 1H,

Cycloaddition Reactions Catalyzed by Ti Compounds
J. Am. Chem. Soc., Vol. 119, No. 33, 1997 7693
CHSiMe3); 7.0-7.6 (m, 5H, aromatics); 0.195 (s, 9H, CSiMe3); 0.00
(s, 9H, CHSiMe3). 13C NMR (C6D6, 30 °C): δ 137.1 (C1); 139.6 (C2);
124.3 (C4); 28.2 (C5); 26.8 (C6); -0.90 (CSi(CH3)3); -1.45 (CHSi-
(CH3)3).
(CH2Me); 19.8, 23.8, 23.9, 24.2, 24.8, 25.1 (CH2Me,C7-10); 29.5 (C-
3); 36.3 (C-4); 126.2, 128.7, 129.5, 137.5 (Ph); 140.5, 140.7 (C1, C6).
Characterization of cis-2-Benzyl-1,4-diethyl-1,2,5,6,7,8-hexahy-
dronaphthalene (cis-34). 1H NMR (C6D6, 30 °C): δ 5.24 (br s, 1H,
CH); 6.9-7.4 (m, 5H, aromatics); 0.7-3.1 (m, 20H, CH2Me, CH2
CH2Me). 13C NMR (C6D6, 30 °C): δ 13.6, 14.1 (CH3); 19.7, 31.7
(CH2CH3); 37.8 (PhCH2); 23.8, 24.2, 25.7, 25.9 (C5, C6, C7, C8); 40.8
(C1); 44.2 (C2). The photolysis of cis-34 in pentane initially produced
The reaction can also be catalyzed by 13. See Table 1.
Characterization of 1,3,5-Tris(trimethylsilyl)-1,3-cyclohexadiene
(23). The 1H NMR spectrum of 23 obtained was essentially identical
to that previously reported.17b 1H NMR (C6D6, 30 °C): δ 2.44 (ddd,
2JH-H ) 16.5 Hz, 3JH-H ) 9.5 Hz, 4JH-H ) 2.5 Hz, 1H, CHa(He)); 2.24
3
triene 40. 1H NMR (C6D6, 30 °C): δ 3.38 (d, JH-H ) 6.7 Hz, 2H,
3
3
PhCH2); 5.81 (dt, trans-3JH-H ) 15.8 Hz, 1H, PhCH2CH); 6.53 (dt,
1H, CHCH); 5.2-5.3 (m, 1H, CH3CH2CH); 6.9-7.4 (m, 5H, aromat-
ics); 0.7-3.1 (m, 20H, CH2Me, CH2CH2Me). Continued photolysis
(dd, JH-H ) 4.0 Hz, 1H, CHe(Ha)); 1.62(ddd, JH-H ) 5.6 Hz, 1H,
CH(SiMe3)); 6.25 (d, 1H, CSiMe3(H)CH); 6.34 (d, 1H
CSiMe3CHCSiMe3); 0.03(s, 9H, CHSiMe3); 0.14, 0.12 (s, 18H,
CSiMe3).
3
produced allene 42. 1H NMR (C6D6, 30 °C): δ 3.32 (d, JH-H ) 6.9
Hz, 2H, PhCH2); 5.31 (tt, trans-3JH-H ) 3.3 Hz, PhCH2CH); 1.07 (t,
Characterization of Products from [2 + 2 + 2] Cycloaddition of
3,9-Dodecadiyne with Ethylene. Spectroscopic data for 26. 1H NMR
(C6D6, 30 °C): δ 5.36 (br m, 1H, CH). Selected 13C NMR (C6D6, 30
°C): δ 40.8 (C4), 13.0, 14.3 (Me). Spectroscopic data for 27. 1H
NMR (C6D6, 30 °C): δ 5.55 (dd, 3JH-H ) 9.5 Hz, 3JH-H ) 2.9 Hz, 1H,
CH(Et)CH); 5.82 (dd, 1H, CEtCH). Selected 13C NMR (C6D6, 30
°C): δ 39.5, 44.5 (C4, C10), 12.8, 14.7 (Me). Spectroscopic data for
3
3JH-H ) 7.4 Hz, 3H, CCH2CH3); 0.93 (t, JH-H ) 7.4 Hz, 3H,
CH2CH2CH3); 7.0-7.4 (m, 5H, aromatics); 0.6-2.8 (m, 22H, CH2-
Me, CH2, CH2Me). Selected 13C NMR (C6D6, 30 °C): δ 202.1, 91.0,
109.0. MS(EI): 280 (M+, 5.4%), 189 (53.7), 161 (12.7), 119 (14.8),
105 (13.8), 91 (100). MS(CI): 281 ((M + H)+, 100.0%), 280 (17.6),
279 (39.4), 189 (10.9).
4
28. 1H NMR (C6D6, 30 °C): δ 5.74 (m, JH-H ) 2.4 Hz, 1H, CH).
Characterization of cis-2-n-Butyl-1,4-diethyl-1,2,5,6,7,8-hexahy-
dronaphthalene (cis-35). 1H NMR (C6D6, 30 °C): δ 5.22 (br s, 1H,
CH); 0.8-1.2 (overlapping triplets, 9H, CH3); 1.2-2.3 (m, 18H,
CH2CH). 13C NMR (C6D6, 30 °C): δ 13.7, 14.2, 14.8 (Me); 23.8,
24.2 (C6, C7); 25.7, 25.9 (C5, C8); 30.7, 19.4 (CH2CH3); 23.8, 31.6,
31.9 (CH2CH2CH2); 39.0, 44.5 (C1, C2). The primary photoproduct
of cis-35 in pentane is triene 43. HRMS: calcd. for C18H30 246.2348,
found 246.2351. 1H NMR (C6D6, 30 °C): δ 5.28 (td, 1H, CH3CH2CH);
6.49 (dt, 3JH-H ) 15.8 Hz, 1H, CH2CHCH); 5.71 (dt, 3JH-H ) 7.0 Hz,
1H, CH2CHCH); 0.7-2.9 (m, 19H, CH2Me, CH2, CH2Me). 13C NMR
(C6D6, 30 °C): 14.6, 14.8, 15.1 (CH3); 127.0, 130.9, 128.7 (CHd);
132.2, 137.4, 140.3 (Cd). MS(EI): 246 (M+, 32.2%), 217 (43.4), 190
(13.2), 189 (93.2), 162 (12.6), 161 (100.0), 14 (29.7), 145 (10.1), 133
(45.0), 131 (19.0), 119 (60.4), 117 (17.5), 77 (14.6), 67 (12.8), 57 (24.9),
55 (29.2). Continued photolysis produced allene 45. HRMS: calcd
for C18H30 246.2348, found 246.2351. 1H NMR (C6D6, 30 °C): δ 5.18
(tt, 3JH-H ) 6.8 Hz, 3JH-H ) 3.2 Hz, CH); 0.8-2.5 (m, 29H, CH2Me,
CH2, CH2Me). Selected 13C NMR (C6D6, 30 °C): δ 201.5, 91.3, 108.3.
130.0, 133.1. MS(EI): 246 (M+, 37.8%), 217 (52.8), 203 (18.8), 190
(14.6), 189 (100.0), 176 (15.1), 175 (14.0), 162 (12.8), 161 (97.5), 147
(40.7), 145 (11.3), 133 (45.7), 131 (19.7), 119 (66.7), 117 (22.3), 115
(11.5), 105 (38.9), 93 (15.8), 91 (69.1), 81 (12.8), 79 (26.0), 77 (20.6),
67 (18.8), 57 (29.5), 55 (41.8), 53 (11.9).
13C NMR (C6D6, 30 °C): δ 128.7 (C2, C3); 128.2 (C1, C4); 42.6 (C9,
C10); 28.7, 27.3 (CH2Me, C5, C8); 24.0 (C6, C7); 10.9 (Me).
Spectroscopic data for 29. 1H NMR (C6D6, 30 °C): δ 1.12 (m, 18H,
Me); 1.65 (m, 12H, CH2); 2.61 (m, 24H, CH2). 13C NMR (C6D6, 30
°C): δ 138.2, 138.0, 137.4, 135.8, 135.7, 133.2, 31.6, 30.3, 29.4, 27.6,
23.9, 22.7, 22.3, 22.2, 19.0, 16.5, 15.1, 14.7.
Characterization of Products from [2 + 2 + 2] Cycloaddition of
1,8-Bis(trimethylsilyl)-1,7-octadiyne with Ethylene. Analysis by GC/
MS showed three components with M+ ions of 278, each with a base
peak of 73 (SiMe3+). Spectroscopic data for 30. 1H NMR (C6D6, 30
°C): δ 5.97 (dd, J ) 6.9 Hz, J ) 3.0 Hz, 1H, CH); 0.05 (s, 9H), 0.22
(s, 9H, SiMe3). Spectroscopic data for 31. 1H NMR C6D6: 5.65 (dd,
3
4
3JH-H ) 9.5 Hz, JH-H ) 4.8 Hz, 1H, CHSiMe3H); 6.06 (dd, JH-H
)
2.4 Hz, 1H, CSiMe3CH); 0.02, (s, 9H), 0.17 (s, 9H, SiMe3). Spectro-
scopic data for 32. 1H NMR (C6D6, 30 °C): δ 5.57 (m, AA′XX′, 4JH-H
) 2.6 Hz, 2H, CH); 2.24 (m, 2H, CH); 1.6-2.1 (br m, 8H, CH2); 0.11
(s, 18H, SiMe3). 13C NMR C6D6: 125.4 (C1, C4); 123.7 (C2, C3);
36.6 (C9, C10); 32.1 (C5, C8); 24.3 (C6, C7); 0.00 (SiMe3).
The reaction can also be catalyzed by 13. See Table 1.
Characterization of cis-2-Phenyl-1,4-diethyl-1,2,5,6,7,8-hexahy-
dronaphthalene (cis-33). Anal. Calcd for C20H26: C, 90.16; H, 9.84.
Found: C, 89.98; H, 10.19. HRMS: calcd for C20H26 266.2035, found
3
266.2032. 1H NMR (C6D6, 30 °C): δ 0.71 (t, JH-H ) 7.5 Hz, 3H,
Characterization of cis-2-Phenyl-1,4-bis(trimethylsilyl)-1,2,5,6,7,8-
hexahydronaphthalene (cis-36). 1H NMR (C6D6, 30 °C): δ 5.87 (d,
3JH-H ) 5.1 Hz, 1H, CH); 2.98 (d, 3JH-H ) 5.04, 1H, CHSiMe3); 2.41
(t, 1H, CHPh); 7.0-7.5 (m, 5H, aromatics); 0.142 (s, 9H, CSiMe3);
-0.018 (s, 9H, CHSiMe3). 13C NMR (C6D6, 30 °C): δ 0.2, 1.2 (SiMe3);
24.1, 24.4, 31.8, 32.3 (C5-8); 37.6 (C1); 39.3 (C2); 123.3 (C3); 126.1,
126.7, 127.1, 130.4 (Ph); 124.8, 135.2, 144.2 (C4, C9, C10). MS(EI):
354 (M+, 1.4%), 281 (15.7), 73 (100.0). MS(CI): 355 ((M + H)+
44.4%), 354 (41.6), 353 (52.7), 337 (22.0); 323 (19.3), 282 (21.1); 28
(100.0), 265 (39.8).
CCH2(CH3)); 1.08 (t, 3JH-H ) 7.3 Hz, 3H, CHCH2CH3); 3.98 (m, 1H,
CHPh); 5.70 (br s, 1H; CH); 0.8-2.5 (m, 18H, CH2Me, CH2). 13C
NMR (C6D6, 30 °C): δ 13.1, 13.9, (CH3); 19.7, 31.3 (CH2CH3); 23.4,
23.9, 25.5, 25.6 (C5-8); 46.2 (C1); 47.6 (C2). MS(EI): 266 (M+,
23.0), 264 (59.8), 249 (12.4), 238 (10.5), 237 (100.0), 235 (41.1), 221
(10.5), 209 (25.3), 195 (13.3), 191 (10.2), 179 (25.4), 178 (18.0), 167
(38.8), 165 (22.6), 115 (11.7), 105 (14.9), 91 (42.8), 77 (14.2).
MS(CI): 275 ((M + H)+, 100.0%), 274 (28.4), 273 (18.1), 272 (14.6).
Use of styrene-d8 in the above procedure produces cis-33*. 1H NMR
3
(C6D6, 30 °C): δ 0.71 (t, JH-H ) 7.5 Hz, 3H, CCH2CH3); 1.08 (t,
3JH-H ) 7.4 Hz, 3H, CDCH2CH3); 0.8-2.5 (m, 18H, CH2Me, CH2).
13C NMR (C6D6, 30 °C): δ 13.5, 14.2 (CH3); 19.9, 31.5 (CH3CH2);
Acknowledgment. I.P.R. thanks the National Science Foun-
dation (Grant CHE-9321906) for research support.
1
23.7, 24.2, 25.7, 25.8 (C5-8) 45.6 (t, JD-C ) 19.2 Hz, C-1); 47.1 (t,
1JD-C ) 19.5 Hz, C-2). MS(EI): 274 (M+, 55.8), 246 (16.9), 245
(100.0), 217 (19.4), 176 (16.3), 175 (24.0), 98 (11.1), 97 (12.6).
MS(CI): 275 ((M + H)+, 100.0%), 274 (28.4), 273 (18.1), 272 (14.6).
The photolysis of cis-33 in pentane produced a product assigned as
2,5-diethyl-3-phenyltricyclo[4.4.0.02,4] deca-1(6)-ene (46). 1H NMR
(C6D6, 30 °C): δ 7.0-7.6 (m, 5H, aromatics); 0.6-3.0 (m, 21H,
CH2Me, CH2CH2Me, CH). 13C NMR (C6D6, 30 °C): δ 12.9, 14.3
Supporting Information Available: Figures of calculated
energies and full experimental procedures (7 pages). See any
current masthead page for ordering and Internet access
instructions.
JA970516R