Rhodium-catalyzed arylzincation of terminal allenes providing allylzinc reagents and its application to versatile three-component coupling reaction

Article abstract of DOI:10.1021/ja102303s

Rhodium-catalyzed regioselective arylzincation of terminal allenes affords synthetically useful functionalized allylzinc reagents. The allylzinc reagents react with a variety of electrophiles such as acetonitrile, offering a more versatile three-component coupling reaction.

Full text of DOI:10.1021/ja102303s

Published on Web 06/17/2010
Rhodium-Catalyzed Arylzincation of Terminal Allenes Providing Allylzinc
Reagents and Its Application to Versatile Three-component Coupling Reaction
Yuji Yoshida,† Kei Murakami,† Hideki Yorimitsu,*,‡ and Koichiro Oshima*,†
Department of Material Chemistry, Graduate School of Engineering, Kyoto UniVersity, Kyoto-daigaku Katsura,
Nishikyo-ku, Kyoto 615-8510, Japan and Department of Chemistry, Graduate School of Science, Kyoto UniVersity,
Sakyo-ku, Kyoto 606-8502, Japan
Received March 18, 2010; E-mail: yori@kuchem.kyoto-u.ac.jp; oshima@orgrxn.mbox.media.kyoto-u.ac.jp
Table 1. Scope of Allenes and Arylzinc Reagentsa
Multicomponent reactions of allenes have been attracting in-
creasing attention owing to their inherent efficiency.1 Among them,
transition-metal-catalyzed three-component couplings involving
allenes, organometallics, and carbonyls provide diversity-oriented
synthesis of useful homoallylic alcohols.2-4 In most cases, the
couplings consist of (1) transmetalation from an organometallic
Entry
1, R
2, Ar
3, Yield (%)b
3a, 80
reagent to a transition metal, (2) carbometalation of allene, and (3)
nucleophilic attack of the resulting allylic transition metal to
carbonyl. However, the couplings still remain unsatisfactory despite
its importance: the electrophiles are limited to aldehydes and imines
because of the low reactivity of the allylic transition metal
intermediates.
1
2
3
4
5
6
7
8
9
1a, C10H21
2a, Ph
c
1a, C10H21
2a, Ph
3a, 84
1a, C10H21
2b, 4-BrC6H4
2c, 3-CF3C6H4
2d, 3-MeOC6H4
2e, 2-MeC6H4
2a, Ph
3b, 77
3c, 74
3d, 77
3e, Trace
3f, 81
1a, C10H21
1a, C10H21
1a, C10H21
1b, TBDMSO(CH2)2
1c, Ts(Bn)N(CH2)9
1d, CH2dCH(CH2)8
1e, Ph
2a, Ph
3g, 78
Here we report rhodium-catalyzed arylzincation5 of terminal
allenes (Scheme 1).6-9 The reaction represents a rare example of
carbometalation of allenes accompanying accumulation of allylic
metals in a reaction flask. The key is smooth transmetalation
between allylrhodium B and arylzinc species. The resulting allylzinc
reagents C are reactive enough to allylate a wider variety of
electrophiles, realizing a more versatile three-component coupling
reaction.
2a, Ph
3h, 67
d
e
2a, Ph
10
3i, 84
a The reaction was performed on a 0.3 mmol scale. b A small amount
of product 3′ was also obtained. The ratio of 3/3′ was 9/1 unless
otherwise noted. c The reaction was performed on a 3 mmol scale.
d Performed at 66 °C for 1.5 h. e The ratio of 3i/3i′ was 97/3.
Table 2. Reaction of Allylzinc Intermediates with Various Electrophilesa
Scheme 1. Proposed Mechanism for Arylzincation of Allenes
Treatment of 1,2-tridecadiene (1a) with a phenylzinc iodide ·LiCl
complex in THF10 in the presence of [RhCl(cod)]2 and PtBu3 at
room temperature for 3 h gave the corresponding arylated product
3a in high yields (Table 1, entries 1 and 2). The reaction with
4-bromophenylzinc reagent 2b also proceeded smoothly, leaving
the bromo group untouched (entry 3). Arylzinc reagents bearing
an electron-withdrawing or an electron-donating group were also
applicable (entries 4 and 5). However, bulky 2-methylphenylzinc
reagents 2e failed to react (entry 6). Phenylzincation of allene
1b-1d proceeded smoothly without loss of the siloxy, tosylamide,
and additional olefinic moieties (entries 7-9). The reaction of
1-phenyl-1,2-propadiene (1e) afforded the phenylated product 3i
in 84% yield (entry 10).
a Reaction conditions: 1 (0.5 mmol), 2 (0.5 mmol), electrophile (0.3
mmol). b The reaction was performed on a 3 mmol scale. c 9% of isomer
4d′ was contained. d 10% of isomer 4e′ was contained. e Reaction
conditions: 1 (0.3 mmol), 2 (0.45 mmol), CH3CN (0.9 mmol). f Reaction
conditions: 1 (0.3 mmol), 2 (0.45 mmol), CH3CN (1 mL, 18 mmol).
When acetonitrile was added to the allylzinc reagent C (1.7
equiv) derived from 1a and 2a, the corresponding ketone 4a was
obtained in 62% yield. Instead, a Barbier-type reaction by mixing
1a, 2a, and acetonitrile together under the rhodium catalysis
† Department of Material Chemistry, Graduate School of Engineering.
‡ Department of Chemistry, Graduate School of Science.
9
8878 J. AM. CHEM. SOC. 2010, 132, 8878–8879
10.1021/ja102303s  2010 American Chemical Society

C O M M U N I C A T I O N S
improved the yield of 4a up to 81% (Table 2). Barbier-type reactions
of C with imines proceeded diastereoselectively to yield homoal-
lylamines 4d and 4e. Aldehyde and ketone also participated in the
reaction, and homoallyl alcohols 4f and 4g were obtained in good
yields. Arylzinc reagents bearing an ester or a nitrile group were
also applicable to the reaction without the loss of the functional
groups by using excess amounts of acetonitrile.
arylzincation reactions gave stereodefined (5E,8E,11E)-11-phenyl-
8-(4-fluorophenyl)-5-(3-methoxyphenyl)-1,2,5,8,11-docosapen-
taene (9). It is noteworthy that no isomerization of the olefinic
moiety of 9 was observed despite the basic reaction conditions.
Acknowledgment. This work was supported by Grants-in-Aid
for Scientific Research and GCOE Research from JSPS. K.M.
acknowledges JSPS for financial support.
The high yield and isomer ratio of 4f suggest that the allylzinc
C, not allylrhodium B, is responsible for the allylation reaction.
An allylzinc reagent was prepared from 1-chloro-2-phenyl-2-
tridecene, zinc powder, and lithium chloride.11 Treatment of
2-methylbenzaldehyde with the allylzinc reagent afforded 4f
quantitatively in a diastereomeric ratio of 86:14. The ratio is very
similar to that in Table 2. In contrast, the reaction with an
allylrhodium reagent, derived from the allylzinc reagent and
[RhCl(PtBu3)], gave a rather complex mixture which includes the
major isomer of 4f exclusively in 42% yield.
Supporting Information Available: Experimental procedures and
compound characterization data. This material is available free of charge
via the Internet at http://pubs.acs.org.
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