Palladium-catalyzed carbocyclization/silastannylation and distannylation of bis(allenes) [12]

Full text of DOI:10.1021/ja001597l

J. Am. Chem. Soc. 2000, 122, 11529-11530
11529
Scheme 1
Palladium-Catalyzed Carbocyclization/
Silastannylation and Distannylation of Bis(allenes)
Suk-Ku Kang,*,† Tae-Gon Baik,† Alexander N. Kulak,†
Young-Hwan Ha,† Yoongho Lim,‡ and Joongmin Park‡
Department of Chemistry and
BK-21 School of Molecular Science
Sungkyunkwan UniVersity, Suwon 440-746, Korea
Department of Applied Biology and Chemistry
Konkuk UniVersity, Seoul 143-701, Korea
treated with Bu3SnSnBu3 (2b) in the presence of Pd(PPh3)4 (5
mol %) in THF at reflux for 3 h or (π-allyl)2Pd2Cl2 (5 mol %)
at room temperature for 3 h, the cyclization proceeded smoothly
to yield the cis-fused distannane 4a (entry 2). The cis stereo-
chemistry was deduced by the chemical shift (δ 2.93) of the two
ReceiVed May 10, 2000
1
symmetrical protons in the H NMR spectrum at ring junction
and the numbers of carbon-13 in 13C NMR for the symmetric
structure of 4a. To assign and determine the cis stereochemistry
for distannyl compound 4a more clearly, the cyclized distannane
4a was converted into the alkynyl compound 7 via iodostannane
6 (Scheme 2). The cis relationship was confirmed by the
examination of two-dimensional 1H NMR proton homodecoupling
experiments for compound 7 by the coupling constant (J ) 9.0
Hz) for the two protons at ring junction (see Supporting
Information). It is noteworthy that this result is in contrast to the
palladium-catalyzed carbocyclization of bis(dienes) with distan-
nane Bu3SnSnBu3 to give trans compound at ring junction reported
by Obora et al.2c As indirect additional evidence for the formation
of the cis-product 4a, the reaction of bis(allene) 1a with distannane
2b at reflux for a prolonged period (12 h) gave the cis-fused
bicyclic diene 5a in 58% yield resulting from intramolecular
palladium-catalyzed homocoupling of the intermediate distannyl
compound 4a (entry 3).8 The exact mechanism of the palladium-
catalyzed additions and cyclizations of allenes with two different
substrates Bu3SnSiMe3 and Bu3SnSnBu3 for the striking reversal
of stereochemistry in the cyclization remains to be elucidated.
Our explanation for the formation of the trans product 3a with
Bu3SnSiMe3 and the cis product 4a with Bu3SnSnBu3 is as follows
based on the addition of 2a and 2b with allenes worked by
Mitchell et al.3,9 We believe that Bu3SnPdSiMe3 species are
generated via oxidative addition and then add to the allene moiety
and the trimethylsilyl group is attached irreversibly to the central
carbon of the allene and the tributyltin on the Pd metal to
form σ-allylpalladium complex A or π-allylpalladium complex
which undergoes further reaction with the tethered another allenyl
group. Intermediate A′ must be favored over A in the cyclization
to form the trans product 3a probably due to the steric hindrance
of the neighboring trimethylsilyl group. The key to this prediction
of steric hindrance of the Me3Si group compared to Bu3Sn is the
shorter Si-C bond length and thus a larger effective size.3 On
the other hand in the case of Bu3SnSnBu3 at first the intermediate
cis-bis(allene)Pd(SnBu3)2 (B) is formed and/or the chelated
σ-allylpalladium complex B′ is formed probably reversibly. The
fast carbocyclization of cis-bis(allene)Pd(SnBu3)2 directly or
through B′ would give the vinylpalladium complex C′, which
then yields cis compound 4a by reductive elimination and/or cis-
bicyclic diene 5a through σ-bond metathesis as a kinetically
The transition metal-catalyzed intramolecular carbocyclization
of enyne, diynes, and bis(dienes) is a versatile method for the
construction of ring systems because this method offers a simple
entry from acyclic substrates to cyclic compounds.1 Along this
line, the palladium-catalyzed addition-cyclization reaction of
tethered diynes, enynes, or bis(dienes) with reagents having Sn-
Si, Sn-Sn, and B-Sn σ-bonds etc. is particularly useful because
the resulting heteroatom-containing cyclic compounds allow
further numerous synthetic transformations.2 To the best of our
knowledge, however, the transition metal-catalyzed cyclization
of bis(allenes) has not been known.3-5 Here we wish to report
carbocyclization via silastannylation and distannylation of bis-
(allenes) to form five-membered-ring systems with these Group-
14 atom compounds involving silylstannanes, distannanes, and
tributyltin hydride catalyzed by palladium complexes as illustrated
in Scheme 1.
When bis(allene) 1a6 reacted with (trimethylsilyl)tributylstan-
nane (2a) in the presence of a catalytic amount of (Ph3P)4Pd (5
mol %) in refluxing THF for 3 h, the cyclization proceeded
smoothly to afford the trans-fused cyclized product 3a in 78%
yield. The use of (π-allyl)2Pd2Cl2 (5 mol %) at room temperature
in THF for 3 h afforded the same product 3a in 76% yield (entry
1 in Table 1). The trans stereochemistry of the cyclized product
3a was unambiguously confirmed by the coupling constant (J )
13.3 Hz) of the two protons (δ 2.79 and 2.97 ppm) at ring juncture
1
in the H NMR spectrum.7 However, when bis(allene) 1a was
* Address correspondence to this author. E-mail: skkang@chem.skku.ac.kr
† Sungkyunkwan University.
‡ Konkuk University.
(1) (a) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles
and Applications of Organotransition Metal Chemistry; University Science
Books: Mill Valley, CA, 1987. (b) Trost, B. M.; Krische, M. J. Synlett 1988,
1-16. (c) Negishi, E.; Coperet, C.; Ma. S.; Liou, S.-Y.; Liu, F. Chem. ReV.
1996, 96, 365-393. (d) Ojima, I.; Tzamarioudak, M.; Li, Z.; Donovan, R. J.
Chem. ReV. 1996, 96, 635-662.
(2) For the silastannylation, distannylation, and silaboration of diynes,
enynes, or bis(dienes) in cyclization, see: (a) Onozawa, S-y.; Hatanaka, Y.;
Choi, N.; Tanaka, M. Organometallics 1997, 16, 5389-5391. (b) Onozawa,
S-y.; Hatanaka, Y.; Tanaka, M. J. Chem. Soc., Chem. Commun. 1997, 1229-
1230. (c) Obora, Y.; Tsuji, Y.; Kakehi, T.; Kobayashi, M.; Shinkai, Y.; Ebihara,
M.; Kawamura, T. J. Chem. Soc., Perkin Trans. 1 1995, 599-608.
(3) Mitchell et al. studied the systematic and pioneering work on the
palladium-catalyzed silastannylation and distannylation of the allenes and it
is notable that the addition of hexa(n-butyl)distannane to allenes is reversible
and that of trimethylsilyltributylstannane is irreversible and the trimethylsilyl
group exclusively goes to the central position of the allenes. For the
silastannylation and distannylation of allenes, see: Mitchell, T. N.; Schneider,
U. J. Organomet. Chem. 1991, 407, 319-327.
(4) The palladium-catalyzed dimerization of allene followed by cyclization
is known; see: (a) Hegedus, L. S.; Kambe, N.; Tamaru, R.; Woodgate, P. D.
Organometallics 1983, 2, 1658-1661. (b) Hegedus, L. S.; Kambe, N.; Ishii,
Y.; Mori, A. J. Org. Chem. 1980, 50, 2240-2243. (c) It is well-known that
palladium complex catalyzes dimerization and addition of propa-1, 2-diene
in the presence of amines to give 2-methylene-3-methyl-3-butene-1-ylamines.
See: Coulson, D. R. J. Org. Chem. 1973, 38, 1483-1490.
(7) The proton signals of doublet of doublet of doublet because of
neighboring protons (J ) 13.3, 12.1, and 7.8 Hz), which have two trans and
one cis relationships, confirm the trans configuration (see Supporting
Information).
(8) In our hands, the reaction of bis(allene) (1a) without using hexa(n-
butyl)distannane in the presence of Pd(Ph3P)4 under the same conditions did
not give the bicyclic diene 5a, which mechanistically eliminate [2+2]
cyclization. The product 4a isolated was subjected to reaction in the presence
of Pd(PPh3)4 (5 mol %) in THF at reflux for 8 h to afford 5a.
(9) An alternative mechanism proposed by one of the reviewers is as
follows. For the formation of the trans product 3a it is suggested that the
insertion of Bu3SnPdSiMe3 to the bis(allene) moiety forms the (1-Bu3Sn-vinyl)-
(allene)PdSiMe3 complex and the carbocyclization occurs after isomerization
to the more thermodynamically stable trans-π-allyl(allene)PdSiMe3 complex.
(5) In the Pd(0)-catalyzed intermolecular cyclization low yields are due to
dimerization of allenes; see: (a) Shier, G. D. J. Organomet. Chem. 1967, 10,
15-17. (b) Reference 4c.
(6) Bis(allene) 1a was readily prepared from p-toluenesulfonamide by
propargylation followed by Crabbe reaction (see Supporting Information).
10.1021/ja001597l CCC: $19.00 © 2000 American Chemical Society
Published on Web 11/03/2000

11530 J. Am. Chem. Soc., Vol. 122, No. 46, 2000
Communications to the Editor
Table 1. Palladium-Catalyzed Carbocyclization-Silastannylation
and Distannylation of Bis(allenes)
Scheme 2
Scheme 3
Scheme 4
in THF at room temperature for 12 h provided the bicyclic
compound 5a in 62% yield (entry 3).
Treatment of bis(allene) 1a with 2 equiv of nBu3SnH (2c) with
Pd(PPh3)4 (5 mol %) in THF at reflux for 12 h or (π-allyl)2Pd2-
Cl2 (5 mol %) in THF at room temperature for 12 h provided the
bicyclic diene 5a in 54 and 57% yield, respectively (entry 4 in
Table 1). It is notable that the use of 1 equiv of nBu3SnH resulted
in the formation of 5a in comparable yield. Moreover, the
formation of 5a can be realized by reacting a subcatalytic amount
of nBu3SnH (0.5 equiv, 25 mol %) under the same conditions in
49% yield. In considering a plausible mechanism for the formation
of the bicyclic diene 5a with a subcatalytic amount of nBu3SnH,
it is presumed that at first the intermediate cis-bis(allene)Pd(H)-
SnBu3 is formed followed by dehydrocoupling with nBu3SnH to
afford cis-bis(allene)Pd(SnBu3)2 or the formation of the intermedi-
ate B′ to afford the cyclized product 5a liberating Bu3SnSnBu3
(Scheme 4).10
We have applied this method to a variety of bis(allenes) 1b,
1c, 1d, and 1e and the results are summarized in Table 1.
In summary, we have demonstrated the first palladium-
catalyzed carbocyclization reaction of tethered bis(allene) sub-
strates with Group 14 atom compounds to form the substituted
five-membered rings.
a Method A: Pd(PPh3)4 (5 mol %), THF, reflux, 3 h. Method B:
(π-allyl)2Pd2Cl2 (5 mol %), THF, room temperature, 3 h. b Pd(PPh3)4
(5 mol %), THF, reflux, 12 h. c (π-allyl)2Pd2Cl2 (5 mol %), THF, room
temperature, 12 h. d A mixture of isomers.
Acknowledgment. Generous financial support from KOSEF-CMDS-
(Center for Molecular Design and Synthesis) is gratefully acknowledged.
controlled product. The oxidative insertion of Pd(0) into the Sn-C
bond in 4a followed by σ-bond metathesis with the Sn-C bond
also affords the bicyclic compound 5a with liberation of Bu3-
SnSnBu3. Alternatively, for the same substrate 1a the reaction
with distannane 2b in the presence of (π-allyl)2Pd2Cl2 (5 mol %)
Supporting Information Available: Typical experimental procedures
for the preparation of 1a and 3a-5a, spectroscopic and analytical data
for 1a, 3a-5a, 3b-5b, 3c-5b, 3d, 3e, 6, and 7, and X-ray crystal-
lographic data of 5a (PDF). This material is available free of charge via
the Internet at http://pubs.acs.org.
(10) Elimination of PdH2 from vinylpalladium complex has been reported
in the palladium-catalyzed addition of nBu3SnH to allenes. See: Ichinose,
Y.; Oshima, K.; Utimoto, K. Bull. Chem. Soc. Jpn. 1988, 61, 2693-2695.
JA001597L