Gated Migration for Enantioselective Synthesis of Palladium Allyls Using a PdHBr Synthon

Article abstract of DOI:10.1021/om990267a

The synthesis of enantiomerically pure palladium cyclic allyl complexes is accomplished by reaction of PdHBr with several chiral cyclic terpenes. The strategy used involves a 100% stereoselective Pd-migration from an attached chain to the ring through a chiral carbon ( gated migration ). PdHBr species are produced by β-H elimination in the benzylic moiety of [Pd₂(μBr)₂(η³-PfCH₂CHPh) ₂] (1, Pf = C₆F₅). The allylic complexes prepared are transformed by carbonylation reactions into chiral unsaturated methyl esters.

Full text of DOI:10.1021/om990267a

Organometallics 1999, 18, 3359-3363
3359
“Ga ted Migr a tion ” for En a n tioselective Syn th esis of
P a lla d iu m Allyls Usin g a “P d HBr ” Syn th on
Ana C. Albe´niz, Pablo Espinet,* Yong-Shou Lin, and Blanca Mart´ın-Ruiz
Departamento de Quı´mica Inorga´nica, Facultad de Ciencias, Universidad de Valladolid,
47005 Valladolid, Spain
Received April 14, 1999
The synthesis of enantiomerically pure palladium cyclic allyl complexes is accomplished
by reaction of “PdHBr” with several chiral cyclic terpenes. The strategy used involves a
100% stereoselective Pd-migration from an attached chain to the ring through a chiral carbon
(“gated migration”). “PdHBr” species are produced by â-H elimination in the benzylic moiety
of [Pd2(µ-Br)2(η3-PfCH2CHPh)2] (1, Pf ) C6F5). The allylic complexes prepared are transformed
by carbonylation reactions into chiral unsaturated methyl esters.
Ch a r t 1
In tr od u ction
Palladium allyls can be synthesized in a variety of
ways.1 Subsequent palladium elimination using selec-
tive transformations affords functionalized alkenes, and
it is the final step in the Pd-mediated allylic substitu-
tion.2 Optically active organic derivatives can also be
obtained from enantiomerically pure Pd-allyls, since the
Pd-allyl bond can be cleaved in a stereoselective way.2-4
The strategies reported for the few enantioselective
syntheses of Pd-allyls are the following: (a) face selec-
tion in the coordination of a prochiral alkene, assisted
by another stereocenter in the molecule;5,6 (b) trans-
metalation of an optically active allylic silane to Pd(II);7
and (c) oxidative addition of an optically active allylic
acetate to Pd(0).8
In this paper we describe a new approach that makes
use of the stereoselective palladium migration to a ring
from an external hydrocarbon chain. We have used some
cyclic terpenes with exo- and endocyclic double bonds
(Chart 1). Cyclic allyls can be obtained from these dienes
by addition of a Pd-R moiety to the exocyclic double
bond and Pd-migration to reach the endocyclic double
bond. Pd-migration is a stereoselective process and
occurs via syn-Pd-H eliminations and readditions.5,9
Thus, the palladium must necessarily enter the cycle
from the same face where the H atom is in the carbon
bearing the chain (gated Pd-migration). This imposes
100% face selection in the formation of the palladium
allyl.
Since Pd-R addition to the exocyclic double bond does
not discriminate the enantiofaces of the double bond,
we used Pd-H instead of Pd-R to avoid the formation
of an exocyclic asymmetric carbon and the correspond-
ing diastereomeric mixture. Addition of Pd-H creates
a nonchiral isopropyl substituent and, after Pd-migra-
tion, an enantiomerically pure allyl complex.
Most of the hydridopalladium complexes available
contain phosphines as coligands and lack of easily
available coordination sites on the metal that are
necessary for reaction with the diene.10 However, it has
been reported that some reactive, “in situ” generated,
palladium hydrides react with dienes.5,11-13 The hydrido
moieties in these examples are formed by â-H elimina-
tion from palladium alkyls, which in turn require the
use of toxic organomercury derivatives in their syn-
theses.5,12-14 We have described before a palladium
benzylic derivative [Pd2(µ-Br)2(η3-PfCH2CHPh)2] (1, Pf
) C6F5), prepared without the use of toxic organome-
tallic derivatives, which is slightly soluble in chlorinated
solvents and decomposes slowly by â-H elimination to
give a palladium hydride.15 In the presence of the dienes
collected in Chart 1, the hydride generated from 1 reacts
* Corresponding author. E-mail: espinet@qi.uva.es.
(1) (a) Davies, J . A. In Comprehensive Organometallic Chemistry:
A Review of the Literature 1982-1994; Abel, E. W., Stone, F. G. A.,
Wilkinson, G., Eds.; Pergamon Press: Oxford, 1995; Vol 9, p 328. (b)
Maitlis, P. M.; Espinet, P.; Russell, M. J . H. In Comprehensive
Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W.,
Eds.; Pergamon Press: Oxford, 1982; Vol. 6, p 385.
(2) (a) Heck, R. F. Palladium Reagents in Organic Syntheses;
Academic Press: London, 1985. (b) Tsuji, J . Palladium Reagents and
Catalysis; Wiley: Chichester, 1995. (c) Malleron, J .-L.; Fiaud, J .-C.;
Legros, J .-Y. Handbook of Palladium-Catalyzed Organic Reactions;
Academic Press: London, 1997.
(3) Hayashi, T.; Yamamoto, A.; Iwata, T.; Ito, Y. J . Chem. Soc.,
Chem. Commun. 1997, 398-399.
(9) Parra-Hale, M.; Rettig, M. F.; Wing, R. M. Organometallics 1983,
2, 1013-1017.
(4) Keinan, E.; Roth, Z. J . Org. Chem. 1983, 48, 1769-1772.
(5) Larock, R. C.; Song, H.; Kim, S.; J acobson, R. A. J . Chem. Soc.,
Chem. Commun. 1987, 834-836.
(10) A recent review is available: Grushin, V. V. Chem. Rev. 1996,
96, 2011-2033.
(11) Mabbott, D. J .; Maitlis, P. M. J . Chem. Soc., Dalton Trans. 1976,
2156-2160.
(12) Stakem, F. G.; Heck, R. F. J . Org. Chem. 1980, 45, 3584-
3593.
(13) Larock, R. C.; Takagi, K. J . Org. Chem. 1984, 49, 2071-2705.
(14) Hosokawa, T.; Calvo, C.; Lee, H. B.; Mailtlis, P. M. J . Am. Chem.
Soc. 1973, 95, 4914-4923.
(6) Trost, B. M.; Strege, P. E.; Weber, L.; Fullerton, T. J .; Dietsche,
T. J . J . Am. Chem. Soc. 1978, 100, 3407-3415.
(7) Hayashi, T.; Konishi, M.; Kumada, M. J . Chem. Soc., Chem.
Commun. 1983, 736-737.
(8) Hayashi, T.; Hagihara, T.; Konishi, M.; Kumada, M. J . Am.
Chem. Soc. 1983, 105, 7767-7768.
10.1021/om990267a CCC: $18.00 © 1999 American Chemical Society
Publication on Web 07/23/1999

3360 Organometallics, Vol. 18, No. 17, 1999
Albe´niz et al.
Ch a r t 2
a trans arrangement of Pd and Me. The allyl 3 could be
isolated by crystallization from n-hexane (67% isolated
yield) and fully identified by 1H NMR, 2D 1H-1H
correlation, and elemental analyses.
The reaction of 1 with (1R)-(+)-trans-isolimonene (eq
2) gave 5 as the major product (85% of the mixture after
efficiently to give enantiomerically pure Pd-allyls in
good yields. These complexes can be stereoselectively
functionalized, and one of these transformations along
with the syntheses of the allylic complexes is described
here.
Resu lts a n d Discu ssion
Complex [Pd2(µ-Br)2(η3-PfCH2CHPh)2] (1, Pf ) C6F5)
suspended in chloroform or dichloromethane, where it
is sparingly soluble, slowly gets in solution and decom-
poses at room temperature via Pd-(â-H) elimination to
(E)-PhCHdCHPf (2) and a hydrido-containing pal-
ladium species. In the absence of other ligands, this
species, which can be represented as the mixed dimer
depicted in Chart 2, undergoes an interesting H-transfer
that has been described in detail elsewhere.15
When a suspension of 1 in CDCl3 decomposed in the
presence of (R)-(+)-limonene, selective insertion of the
exocyclic double bond into the Pd-H bond of the
smoothly generated “PdHBr” was observed (eq 1). The
chromatographic separation of 2 and excess diene, based
on integration of H NMR signals). A minor product,
1
4cis (3%), and several other unidentified Pd-allyls (12%)
were formed. The latter might be the result of the
reaction with dienes formed by isomerization of (1R)-
(+)-trans-isolimonene. 4cis is the result of Pd-H addi-
tion to the endocyclic double bond, the cis arrangement
being imposed by the stereoselective gated Pd-migra-
tion. Although 5 is very soluble, it could be isolated as
a pure solid by crystallization in n-hexane (28% yield).
The conformations assigned to 3 and 5 are based on
the analysis of coupling constants and comparison with
previous data reported for η3-cyclohexenylpalladium
derivatives.17 Compound 3 adopts a pseudo boat con-
3
formation, as shown by the 3J values found: J 4-5
)
3
3
5.4 Hz, J 5-6 ) 5.8 Hz, and J 5-6′ ) 3.2 Hz. However,
the observed coupling constants for 5 (3J 5-6′ ) 11.7 Hz,
3J 5′-6′ ) 5.7 Hz) suggest a pseudo chair conformation.
In both cases it seems that the preferred conformation
accommodates the isopropyl or methyl group bound to
C4 in the equatorial position (eqs 1 and 2), as it has been
observed in the X-ray stuctures of other substituted
cyclic Pd-allyls.18
The reaction of 1 with (R)-(-)-carvone is summarized
in eq 3. The insertion of the exocyclic double bond into
Pd atom migrates along the hydrocarbon chain to reach
the second double bond and forms an η3-allylpalladium
complex (3). The entrance to the ring via an asymmetric
tertiary carbon (C4) determines a cis arrangement of Pd
and H4 (gated Pd-migration). Thus the migration of
palladium creates 3 as a single enantiomer. The crude
product of the reaction (after chromatographic separa-
tion of 2 and an excess of limonene) was analyzed by
1H NMR and contained 3 (96% of the mixture), 4tr a n s
(ca. 2%), and traces of unidentified products. Compound
3 arises from Pd-H addition to the external double bond
followed by gated Pd-migration.16 4tr a n s is formed by
Pd-H addition to the endocyclic double bond followed
by gated migration to the exocyclic one, this imposing
the Pd-H bond generated from complex 1, followed by
gated Pd-migration, afforded the allylic derivative 6.
Compound 7 was also formed in a ratio 6:7 ) 9:1. The
products in the reaction mixture could be separated by
column chromatography, and 6 could be crystallized as
a yellow solid in 50% yield.
(15) Albe´niz, A. C.; Espinet, P.; Lin, Y.-S. Organometallics 1997,
16, 4030-4032.
(16) We did not observe any symmetrical Pd-allyl coming from Pd-
migration along the longer way in the ring. It seems that Pd-H
elimination of one of the H atoms in the allylic position leading to an
intermediate conjugated diene is much more favorable. This is
consistent with our previous results: Albe´niz, A. C.; Espinet, P.; Lin,
Y.-S. Organometallics 1995, 14, 2977-2986.
(17) A° kermark, B.; Oslob, J . D.; Norrby, P. O. Organometallics 1995,
14, 1688-1693.
(18) Grennberg, H.; Langer, V.; Ba¨ckvall, J .-E. J . Chem. Soc., Chem.
Commun. 1991, 1190-1192.

Gated Migration
Organometallics, Vol. 18, No. 17, 1999 3361
Sch em e 1
Ch a r t 3
Sch em e 2
7 is the tautomeric form of the cyclohexadienone
expected to be formed in the palladium migration
process (eq 4). Pd-migration is generally very efficient,
and Pd-H readdition occurs faster than decoordination
of the diene. However the stabilization associated with
aromatization may be the driving force that promotes
the decoordination of the dienone at that point.
The carbonylation of η3-allylpalladium complexes to
give ester derivatives is highly regio- and stereoselec-
tive.19,20 Thus, 3 or 5 reacted with CO and NaOMe to
yield the enantiomerically pure methyl esters (1S,6S)-8
(94%) or (1R,6R)-9 (90%), respectively, each of them
having two chiral centers with fixed configurations
(Scheme 1). This means that CO insertion has occurred
preferably into the less substituted Pd-C external
allylic bond, C3. Subsequent attack by MeO- on the
intermediate acyl formed gives the final ester with
retention of the stereochemistry of the Pd-allyl deriva-
tive. Their 1H NMR spectra reveal the presence of a
regioisomeric methyl ester (6% in the reaction of 3 and
10% for 5). These minor regioisomers were not com-
The carbonylation of complex 6 is much less selective.
In the presence of CO, 6 decomposes through several
competitive pathways. The ester derivative (1R,6R)-10
is formed stereoselectively but accounts for only 20% of
the final reaction mixture. CO insertion into the less
substituted Pd-C bond of a transient palladium σ-allyl
seems to be slower in this case, and two other processes
compete: â-H elimination and reductive elimination of
an allylic bromide (Scheme 2). â-H elimination is favored
since it gives the stable phenol derivative 7 (15%). The
Pd-H species generated undergo H-transfer between
Pd atoms to give cyclic monoolefins 11 (5%) and 12
(10%).15 An allylic alcohol 13 (16%, mixture of diaste-
reoisomers) is also found. 13 could be formed in the basic
reaction medium by nucleophillic substitution of Br in
the allylic bromide formed by reductive elimination from
the starting allyl complex (Scheme 2). Some unreacted
Pd-complex (10%) and other unidentified compounds are
also found. Ester 10 can be isolated by careful chro-
matographic separation of the reaction mixture.
1
pletely identified due to severe overlap of their H NMR
signals with the major derivatives. However, the pres-
ence of AB systems in the olefinic region in either case
is consistent with a 1,2-disubstituted cyclic double bond,
as expected from carbonylation at the most substi-
tuted allylic carbon in each of the starting allylic
complexes, C1.
The conformational assignments of 8 and 9 were
3
made by measurement of J H-H coupling constants
(Chart 3). These show the axial-trans arrangement of
3
H1 and H6 for (1S,6S)-8 (3J 1-6 ) 8.6 Hz; J 5′-6 ) 4.5
The conversion of the Pd allyls synthesized into
enantiomerically pure organic derivatives can be achieved
if a selective reaction (i.e., carbonylation) is chosen. This
works very well for our derivatives except when linked
to a thermodynamically favored process, i.e., enol tau-
tomerization in the synthesis and reactions of 6; in this
Hz; 3J 5-6 ) 11 Hz) and an equatorial-axial-cis arrange-
ment of H1 and H6 for (1R,6R)-9 (3J 1-6 ) 5 Hz; 3J 5′-6
)
3
3.4 Hz; J 5-6 ) 13.6 Hz).21
(19) Colquhoun, H. M.; Thompson, D. J .; Twigg, M. V. Carbonyla-
tion: Direct Synthesis of Carbonyl Compounds; Plenum Press: New
York, 1991.
(20) Albe´niz, A. C.; Espinet, P.; Lin, Y.-S. Tetrahedron 1998, 54,
13851-13866.
(21) Trost, B. M.; Schmuff, N. R. J . Am. Chem. Soc. 1985, 107, 396-
405.

3362 Organometallics, Vol. 18, No. 17, 1999
Albe´niz et al.
MeCH(Me)-), 2.01 (ddd, J ) 15.8, 5.9, 2.3 Hz, 1H, H6), 1.58
(m, J ) 12.5, 5.7, 2.3 Hz, 1H, H5′), 1.38 (ddd, J ) 15.8, 11.7,
5.7 Hz, 1H, H6′), 1.20 (b, 4H, Me, H,4 AB3 system), 1.19 (d, J
) 6.8 Hz, 3H, MeCH(Me)-), 1.18 (d, J ) 6.8 Hz, 3H, MeCH-
(Me)-). [RD]20 ) -45.4 (c ) 28 mg/mL in CHCl3).
case we found â-H elimination and decoordination
detrimental for our purposes. Otherwise the desired
route is faster than other possibly competing processes.
Con clu sion s
4cis:
1H NMR (300 MHz, δ, CDCl3), 3.75 (s, 1H, H1syn), 3.21
(s, 1H, H1anti), 2.02 (s, 3H, Me2), 1.2-2.4 (m, 9H, H,4 H,5 H,6
H,7 H8)*, 0.83 (d, J ) 6.3 Hz, 3H, Me6). *: overlapped with
other signals.
The results obtained show that the selective Pd-
migration produces an efficient face selection provided
there is a tertiary carbon in a cycle connecting a reactive
center inside and outside the cycle (a “gate”). For the
dienes used in this work we observe that, when the Pd
atom enters the cycle, an optically active Pd-cyclic allyl
is formed (complexes 3, 5, and 6); on the other hand
when Pd exits the cycle, the configuration of the tertiary
carbon (the “gate”) also brings about the steroselective
formation of an exocyclic allyl (complexes 4). The
addition of “PdHBr” is produced preferentially in the
less substituted double bond, and the allyl is formed in
the position of the most substituted olefin; in the
examples given this affords, as expected, an endocyclic
palladium allyl.
Syn th esis of 6. To a suspension of 1 (0.640 g, 0.7 mmol) in
CH2Cl2 (30 mL) was added (R)-(-)-carvone (0.44 mL, 2.8
mmol). The mixture was stirred for 26 h, and the solution was
filtered through activated carbon and evaporated to dryness.
The residue was chromatographed through silica (neutral),
eluting with n-hexane first (2), then n-hexane/ethyl acetate )
9:1 (7 and excess diene), and finally n-hexane/ethyl acetate )
1:1 (6). The last batch was evaporated to dryness, and the
residue was triturated with Et2O and then cooled. The yellow
solid (6) obtained was filtered, washed with Et2O, and air-dried
(0.24 g, 50% yield).
6: Anal. Calcd for C20H30O2Br2Pd2: C, 35.58; H, 4.47.
1
Found: C, 36.07; H, 4.53. H NMR (300 MHz, δ, CDCl3), 5.73
(d, J ) 6.7 Hz, 1H, H2), 5.07 (d, J ) 6.7 Hz, 1H, H3), 2.48 (m,
2H, H,4 H5), 1.75 (m, 1H, H7), 1.64 (s, 3H, Me1), 1.56 (m, 1H,
H5′), 0.89 (d, J ) 6.6 Hz, 3H, Me7), 0.86 (d, J ) 6.7 Hz, 3H,
Me7′). [RD]20) -205.48 (c ) 12.2 mg/mL in CHCl3).
Exp er im en ta l Section
1
Gen er a l Com m en ts. 19F, H, and 13C NMR spectra were
7: 1H NMR (300 MHz, δ, CDCl3), 7.03 (d, J ) 7.7 Hz, 1H,
H3), 6.72 (dd, J ) 7.7, 1.7 Hz, 1H, H4), 6.66 (d, J ) 1.7 Hz, 1H,
H6), 4.63 (s, 1H, OH), 2.82 (sep, J ) 6.9 Hz, 1H, H7), 2.21 (s,
3H, Me2), 1.22 (d, J ) 6.9 Hz, 6H, Me7); MS(EI) m/z (relative
intensity), 150 (M+, 42), 135 (100), 115 (12), 107 (56), 91 (39),
77 (23), 67 (8), 53 (12), 51 (9).
recorded on Bruker AC-300 and ARX-300 instruments. Chemi-
cal shifts are reported in δ units (parts per million, ppm)
downfield from Me4Si for 1H and from CFCl3 for 19F. Carbon
and hydrogen analyses were carried out on a Perkin-Elmer
2400 CHN elemental analyzer. Organic products were ana-
lyzed using a HP-5890 gas chromatographer connected to a
HP-5988 mass spectrometer at an ionizing voltage of 70 eV
using a quadrupole analyzer. Relative rotations were deter-
mined with a Perkin-Elmer 241 polarimeter in CHCl3 solution.
All solvents were dried and distilled before use by standard
methods. (R)-(+)-Limonene, (1R)-(+)-isolimonene, and (R)-
(-)-carvone were commercially available (Aldrich and Fluka).
[Pd2(µ-Br)2(η3-PfCH2CHPh)2] (1) was prepared as previously
reported.15
Syn th esis of th e η3-Allylp a lla d iu m Der iva tives. Syn -
t h esis of 3. To a suspension of 1 (0.300 g, 0.328 mmol) in
CH2Cl2 (20 mL) was added (R)-(+)-limonene (0.213 mL, 1.311
mmol). After 2 days the small amount of metallic palladium
formed was eliminated by filtration through activated carbon.
The yellow solution was evaporated, and the residue was
fractionated by column chromatography (silica, neutral), elut-
ing first with n-hexane and then with ether. The latter fraction
was evaporated to dryness, n-hexane was added to the residue,
and the mixture was cooled. A yellow solid 3 crystallized (0.142
g, 67% yield).
P r ep a r a tion of (1S,6S)-8. A solution of 3 (0.040 g, 0.062
mmol) in CH2Cl2 (6 mL) was mixed with another of NaOMe
(0.020 g, 0.372 mmol) in MeOH (4 mL). CO was bubbled
through the mixture for 15 min. Metallic palladium precipi-
tated, which was filtered through Celite. The resulting solution
was evaporated to dryness using a water pump to avoid losing
volatiles. The residue was extracted with ether. Solvent
evaporation gave a colorless oil (83% yield), which was a
mixture of (1R,6S)-8 and an unidentified methyl ester in a
ratio of 16:1.
1
(1S,6S)-8: H NMR (300 MHz, δ, CDCl3), 5.25 (m, J ) 2.3,
0.8 Hz, 1H, H2), 3.68 (s, 3H, COOMe), 3.04 (m, J ) 8.6, 2.3
Hz, 1H, H1), 1.90-2.05 (m, 2H, H,4 H4′), 1.78 (m, J ) 11, 8.6,
4.5, 2.5 Hz, 1H, H6), 1.72 (m, 1H, H5′), 1.67 (m, W1/2 ) 4.5 Hz,
3H, Me), 1.62 (m, J ) 6.8, 6.7, 2.5 Hz,1H, (Me)CHMe), 1.30
(m, J ) 13, 11, 6 Hz, 1H, H5), 0.92 (d, J ) 6.7 Hz, 3H, (Me)-
CHMe), 0.82 (d, J ) 6.8 Hz, 3H, (Me)CHMe); MS(EI) m/z
(relative intensity), 196 (M+, 6), 137 (36), 95 (32), 93 (44), 81
(100), 79 (29), 41 (24). [RD]20 ) -106.3 (94% purity, c ) 5.1
mg/mL in CHCl3).
3: Anal. Calcd for C20H34Br2Pd2: C 37.12, H 5.30. Found:
C 37.20, H 5.24. 1H NMR (300 MHz, δ, CDCl3), 5.30 (d, J )
6.5 Hz, 1H, H2), 4.89 (d, J ) 6.5 Hz, 1H, H3), 2.08 (ddd, J )
19.6, 11.2, 5.8 Hz, 1H, H6), 1.87 (dt, J ) 10.0, 5.4 Hz, 1H, H4),
1.79 (ddd, J ) 19.6, 5.0, 3.2 Hz, 1H, H6′), 1.64 (m, 2H, H,5 (Me)-
CHMe), 1.60 (s, 3H, Me), 0.92 (d, J ) 6.8 Hz, 3H, (Me)CHMe),
0.89 (d, J ) 6.8 Hz, 3H, (Me)CHMe), 0.77 (m, J ) 11.2, 10.0,
5.0 Hz, 1H, H5′); [RD]20 ) +130.3 (c ) 10 mg/mL in CHCl3).
P r ep a r a tion of (1R,6R)-9. It was prepared as described
for 6, using allylpalladium complex 5 as starting material.
Crude yield: 66%, a mixture of 9 and an unidentified methyl
ester in a 9:1 ratio.
(1R,6R)-9: 1H NMR (300 MHz, δ, CDCl3), 5.41 (m, J ) 3.6
Hz, 1H, H2), 3.67 (s, 3H, COOMe), 3.14 (m, J ) 5.0, 3.6 Hz,
1H, H1), 2.20 (sep., J ) 6.9 Hz, 1H, MeCH(Me)-), 2.05-2.15
(m, J ) 13.6, 5.0, 3.4 Hz, 1H, H6), 1.90-2.05 (m, J ) 18.4,
13.0, 6.2, 6.0, 2.0 Hz, 2H, H,4 H4′), 1.76 (m, J ) 16.0, 13.6, 6.2,
2.0 Hz, 1H, H5), 1.36 (m, J ) 16.0, 13.0, 6.0, 3.4 Hz, 1H, H5′),
1.01 (d, J ) 6.9 Hz, 6H, Me2CH-), 0.88 (d, J ) 7.0 Hz, 3H,
Me); MS(EI) m/z (relative intensity), 196 (M+, 4), 95(43), 93
(49), 81 (100), 79 (38), 43 (40), 41 (78). [RD]20 ) +56.4 (90%
purity, c ) 6.1 mg/mL in CHCl3).
Ca r bon yla tion of 6. CO was bubbled through a mixture
of complex 6 (0.04 g, 0.06 mmol) and NaOMe (0.019 g, 0.35
mmol) in CH2Cl2 (6 mL)/MeOH (4 mL). After 30 min, the black
suspension obtained was filtered through Celite and the
solvent was evaporated to dryness. The residue was extracted
4tr a n s
:
1H NMR (300 MHz, δ, CDCl3), 3.78 (s, 1H, H1syn),
3.25 (s, 1H, H1anti), 2.02 (s, 3H, Me2), 1.2-2.4 (m, 9H, H,4 H,5
H,6 H,7 H8)*, 0.80 (d, J ) 6.5 Hz, 3H, Me6). *: overlapped with
other signals.
Syn th esis of 5. It was prepared as described above for 3
but using (1R)-(+)-isolimonene instead of limonene. Crystal-
lization from n-hexane gave yellow solid 5 (28% yield).
5: Anal. Calcd for C20H34Br2Pd2: C, 37.12; H, 5.30. Found:
1
C, 37.22; H, 5.22. H NMR (300 MHz, δ, CDCl3), 5.25 (d, J )
7.0 Hz, 1H, H2), 4.74 (d, J ) 7.0 Hz, 1H, H3), 2.33 (m, J )
12.5, 11.7, 5.9 Hz, 1H, H5), 2.17 (sep., J ) 6.8 Hz, 1H,

Gated Migration
Organometallics, Vol. 18, No. 17, 1999 3363
with diethyl ether, and the resulting suspension was filtered.
The filtrate was evaporated to dryness, and the residue was
chromatographed using preparative TLC (silica sheets 0.25
mm thick) and a mixture of n-hexane/ethyl acetate, 7:1. The
following products were separated (percentages based on
integration of 1H signals in the residue before separation): 10
(20%, Rf ) 0.21), 7 (15%, Rf ) 0.29), 11 (5%, Rf ) 0.29) 12
(10%, Rf ) 0.39), 13 (mixture of diastereoisomers 131 and 132,
16%, Rf ) 0.04), unreacted 6 (10%, Rf ) 0.04).
2.15-2 (m, 2H, H4′, H6′), 1.85 (m, 1H, H5), 1.76 (m, 3H, Me2),
0.9 (d, J ) 6.7 Hz, 6H, Me7); MS(EI) m/z (relative intensity),
152 (M+, 37), 109 (100), 91 (6), 70 (4), 56 (7).
131: 1H NMR (300 MHz, δ, CDCl3), 6.65 (q, J ) 1.6 Hz, 1H,
H3), 4.34 (m, J ) 9.3 Hz, 1H, H4), 2.45 (dd, J ) 16, 3.4 Hz, 1H
H6), 2.17 (m, 1H, H7), 2.08 (d, J ) 16 Hz, 1H, H6′), 1.97 (dt, J
) 9.3, 3.4 Hz, 1H, H5), 1.77 (m, 3H, Me2), 0.95 (d, J ) 7 Hz,
3H, Me7), 0.89 (d, J ) 7 Hz, 3H, Me7′); MS(EI) m/z (relative
intensity), 168 (M+, 48), 126 (48), 111 (44), 98 (100), 77 (10),
70 (46), 41 (30).
132: 1H NMR (300 MHz, δ, CDCl3), 6.77 (dc, J ) 6, 1.4 Hz,
1H, H3), 4.41 (m, 1H, H4), 2.4-2.6 (m, 1H, H6), 2.17 (m, 1H,
H7), 2.1 (m, 1H, H6′), 1.92 (dt, J ) 8, 2.9 Hz, 1H, H5), 1.79 (m,
3H, Me2), 1.02 (d, J ) 7 Hz, 6H, Me,7 Me7′); MS(EI) m/z
(relative intensity), 168 (M+, 48), 126 (48), 111 (44), 98 (100),
77 (10), 70 (46), 41 (30).
(1R,6R)-10: 1H NMR (300 MHz, δ, CDCl3), 6.53 (dc, J ) 3.0,
1.5 Hz, 1H, H3), 3.75 (s, 3H, OMe), 3.35 (ddc, J ) 9, 3.0, 2.1
Hz, 1H H4), 2.53 (dd, J ) 15.6, 3.7 Hz, 1H H6), 2.37 (m, J )
11.9, 9, 4.2, 3.7, Hz, 1H, H5), 2.2 (dd, J ) 15.6, 11.9 Hz, 1H,
H6′), 1.8 (m, J ) 2.1, 1.5 Hz, 3H, Me2), 1.73 (m, J ) 6.9, 4.2
Hz, 1H, H7), 0.93 (d, J ) 6.9 Hz, 3H, Me7), 0.88 (d, J ) 6.9 Hz,
3H, Me7′); MS(EI) m/z (relative intensity), 210 (M+, 55), 178
(11), 167 (61), 140 (57), 112 (100), 97 (37), 79 (53), 59 (33), 43
(25), 41 (23).
11: 1H NMR (300 MHz, δ, CDCl3), 5.82, 5.67 (2H, AB
system, J ) 10.5 Hz, H3, H4), 2.45 (m, 1H, H5), 2.0 (m, 1H,
H2), 1.72 (m, 1H, H7), 0.98 (d, J ) 6.7 Hz, 3H, Me2), 0.91 (d, J
) 6.8 Hz, 3H, Me7), 0.75 (d, J ) 6.6 Hz, 3H, Me7′); MS(EI) m/z
(relative intensity), 152 (M+, 25), 135 (4), 109 (100), 95 (10),
79 (9), 67 (2), 43 (8).
Ack n ow led gm en t. This work was supported by the
Direccio´n General de Investigacio´n Cient´ıfica y Te´cnica
(Project PB96-0363) and the J unta de Castilla y Leo´n
(Project VA 40-96). The Spanish Ministerio de Educa-
cio´n y Cultura is also acknowledged for fellowships to
B.M.-R. and Y.-S.L.
12: 1H NMR (300 MHz, δ, CDCl3), 6.75 (m, J ) 1.6 Hz, 1H,
H3), 2.53 (ddd, J ) 3.6, 2.5, 1.6, 1H, H6), 2.37 (m, 1H, H4),
OM990267A