COMMUNICATION
DOI: 10.1002/chem.201201138
Stereodefined Construction of Trisubstituted Alkenes by Direct Coupling
Reaction of Allylating Agents, Alkynes, and Organoboranes
Masahiro Fukushima, Daiki Takushima, Hideaki Satomura, Gen Onodera, and
Masanari Kimura*[a]
À
Stereodefined construction of C C multiple bonds
through carbometallation is among the most challenging
and significant synthetic strategies in organic and organome-
tallic chemistry.[1] In particular, alkenylboranes are valuable
and salient active species for the Suzuki–Miyaura cross-cou-
pling reaction, which affords tri- and tetrasubstituted al-
kenes as efficient functional materials.[2] Therefore, highly
regio- and stereocontrolled preparations of alkenylboranes
by means of hydroboration of alkynes and migration of
alkynylborates have been developed.[3]
undergo the multicomponent coupling reactions accompany-
ing dimerization of diene moieties to give cyclic alkanes and
heterocyclic compounds possessing dienyl and alkenyl side
chains in excellent regio- and stereoselectivities.
The scope and limitation for the initial reactions were de-
termined in the presence of
a catalytic amount of
[Pd(acac)2] and PPh3 at 508C under nitrogen atmosphere.
AHCTUNGTRENNUNG
The results of the coupling reaction of phenylacetylene with
phenyl-substituted allylating agents and Et3B are summar-
ized in Table 1.[7]
Previously, we have demonstrated the direct allylic activa-
tion of allyl alcohols, promoted by a combination of a Pd
catalyst and Et3B, to form a p-allylpalladium intermediate.[4]
This species serves as an allyl cation equivalent for a wide
variety of soft nucleophiles, facilitating electrophilic allyla-
tion (Tsuji–Trost reaction). In the absence of nucleophiles,
the p-allylpalladium species undergoes an allyl–ethyl ex-
change reaction; this provides allyl diethylborane as an
allyl-anion equivalent, which in turn reacts with aldehydes,
acetals, and aldimines to give homoallyl alcohols and homo-
allylamines (Umpolung of p allylpalladium).[5] Thus, the
combination of a Pd0 catalyst and Et3B works for the gener-
ation of both allyl cation and allyl anion equivalents directly
from allylic alcohols to achieve amphiphilic allylic alkyla-
tions.[6]
Herein, we report a similar reaction system by using trial-
kylboranes and allylic alcohols with terminal alkynes in the
presence of a Pd0 catalyst, which evoked a three-component
coupling reaction of alkyne, allyl, and alkyl groups to give
(E)-1-substituted 2-alkyl-1,4-pentadienes involving geminal
alkylation and allylation at the acetylenic terminal carbon
atom with high regio- and stereoselectivities. In this case, it
is notable that trialkylboranes serve as not only alkylating
components for the coupling reaction, but also promoters
for the oxidative addition of allylic alcohols toward Pd0 cata-
lyst forming p-allylpalladium intermediates. Moreover, we
disclose herein, that bis-dienes can act as allylating agents to
Table 1. Pd-catalyzed three-component coupling of phenylacetylene,
allylating agents, and triethylborane.[a]
Entry
Allylating agent X
t [h]
Yield 1a [%]
1
2
3
4
Cl
72
30
50
30
0
OAc
OCO2Me
OH
0[b]
62 [single]
81 [single]
[a] The reaction was performed in the presence of phenylacetylene
(1 mmol), allylating agent (2 mmol), [Pd(acac)2] (0.025 mmol), PPh3
AHCTUNGTRENNUNG
(0.05 mmol), and Et3B (2.4 mmol) in THF (0.5 mL) at 508C. [b] (1E,4Z)-
1,4-Diphenylhepta-1,4-diene (1a’) was obtained as a regioisomer in 41%
yield.
The reaction outcome depends on the type of leaving
group of the allylating agents. The stronger the basicity of
the leaving group, the higher the yield of the expected prod-
uct. Cinnamyl chloride inhibited the expected reaction, and
phenylacetylene was recovered quantitatively (Table 1,
entry 1). Cinnamyl acetate showed the electrophilic allyla-
tion at the b-carbon of alkynylborate to give 1,4-diphenyl-
hepta-1,4-diene 1a’, which has been previously reported by
Murakami group (Table 1, entry 2).[3i] Methyl carbonate
gave the desired three-component coupling product, 1-
phenyl-2-ethyl-1,4-pentadiene (1a) as a single isomer in rea-
sonable yield (Table 1, entry 3). The similar coupling reac-
tion proceeded smoothly by employment of cinnamyl alco-
hol as an allylating agent to give 1a in good yield with excel-
lent regio- and stereoselectivities (Table 1, entry 4).
[a] M. Fukushima, D. Takushima, H. Satomura, Dr. G. Onodera,
Prof. Dr. M. Kimura
Graduate School of Engineering, Nagasaki University
1-14 Bunkyo machi, Nagasaki 852-8521 (Japan)
Fax: (+81)95-819-2677
Allylation of phenylacetylene with a wide structural varie-
ty of substituted allylic alcohols and tributylborane was stud-
ied under similar conditions (Table 2). Crotyl alcohol and
Supporting information for this article is available on the WWW
Chem. Eur. J. 2012, 18, 8019 – 8023
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
8019