Novel and highly regio- and stereoselective nickel-catalyzed homoallylation of benzaldehyde with 1,3-dienes [10]

Full text of DOI:10.1021/ja973847c

J. Am. Chem. Soc. 1998, 120, 4033-4034
4033
Table 1, when a mixture of isoprene (1b, 4 mmol), benzaldehyde
(1 mmol), Ni(acac)2 (0.1 mmol), and Et3B (2.4 mmol) in dry THF
(5 mL) was stirred at room temperature under nitrogen for 35 h,
3-methyl-1-phenyl-4-pentenol (2b) was obtained in a 90% isolated
yield.8 The use of 2.4 mmol of Et3B seems to be essential; with
1.2 mmol, the reaction is not completed (80% isolated yield of
2b based on 70% conversion after 71 h). In the absence of Et3B,
the reaction provides neither 2b nor the oligomers of 1b as
monitored by GLC and TLC.
Novel and Highly Regio- and Stereoselective
Nickel-Catalyzed Homoallylation of Benzaldehyde
with 1,3-Dienes
Masanari Kimura, Akihiro Ezoe, Kazufumi Shibata, and
Yoshinao Tamaru*
Department of Applied Chemistry
Faculty of Engineering, Nagasaki UniVersity
1-14 Bunnkyo, Nagasaki 852-8521, Japan
The reaction is remarkable in many respects. First, 1b reacts
with benzaldehyde exclusively at the C1 position of the diene
moiety with an exclusive delivery of hydrogen at C2. No other
products that might stem from the C-C bond formation at C4
and the hydrogen delivery to the other allylically related positions
were detected.9 Thus, the reaction formally corresponds to a
reductive coupling of the C1-C2 double bond of 1b and the CdO
double bond of benzaldehyde, whereby Et3B serves as a reducing
agent. Second, the reaction exhibits high 1,3-diastereoselectivity,
providing 1,3-anti-2b in preference to 1,3-syn-2b (15:1) (see
Figure 1 for selected NMR data).10,11 1,3-Dienes with a similar
substitution pattern, e.g., 1c and 1f (runs 3 and 7), show higher
1,3-asymmetric induction than 1b, giving rise to 1,3-anti-2c and
1,3-anti-2f as single diastereomers, respectively. Third, the
selective and high yield formation of a 1:1 adduct of diene and
aldehyde is surprising in light of the propensity of nickel
complexes to promote oligomerization of simple dienes.1,4 In fact,
it has been reported that nickel catalyzes or promotes the coupling
reaction of isoprene and aldehyde (or ketone) to furnish homoallyl
alcohols as a mixture of 1:1, 2:1, and 3:1 adducts, each of which
consists of many possible regio- and stereoisomers.12
ReceiVed NoVember 10, 1997
Organonickel complexes are distinctive in their nucleophilic
reactivity from organometal complexes of the other group 10
elements.1 By virtue of this characteristic, many efficient nickel-
catalyzed or -promoted C-C bond formation reactions have been
developed.2,3 Among these, allylation of carbonyls and alkyl and
allyl halides with π-allylnickels has proved to be particularly
useful and has been utilized widely for the synthesis of natural
and unnatural products.4,5 Unfortunately, however, this methodol-
ogy requires a stoichiometric amount of nickel.
Recently, a useful version of catalytic addition of π-allylnickel
to aldehyde has been developed, which promotes the cyclization
of ω-dienyl aldehydes to 2-[(E)-1-propenyl]cycloalkanols (eq 1).6
2-Allylcycloalkanols may be obtained selectively by employing
a stoichiometric amount of “Ni-H” complexes generated under
sophisticated conditions (eq 1).7
1,3-Pentadiene (1d) exhibited a different reaction feature (run
4), where both termini of the diene moiety took part in the
reaction, providing 3a (C1 addition product) as a major product
together with 2d (C4 addition product, as a 5.2:1 diastereomeric
mixture). Judging from the exclusive formation of 1,3-anti-2e
(C4 addition product) from 3-methyl-1,3-pentadiene (1e, run 5),
however, the C3 methyl group is apparently more influential than
the C4 methyl group in controlling the regioselectivity. In this
regard, both methyl groups of 1g are properly arranged to
cooperatively promote the C1 addition reaction (run 8). Indeed,
the expected isomer, 1,3-anti-2g, was obtained exclusively.
Together with these, the selective reaction of 1h at the terminus
carrying an electron-withdrawing group (run 9) suggests that the
butadiene terminus bearing higher electron density undergoes an
addition reaction to aldehyde in a nucleophilic fashion. Under
the usual reaction conditions, styrene and 2,5-dimethyl-2,4-
hexadiene were unreactive and cyclic dienes (1,3-cyclohexadiene
and 1,3-cyclooctadiene) reacted slowly to provide intractable
mixtures of addition products in low yields.
Here, we disclose that Ni(acac)2 (acac ) acetylacetonato) in
combination with triethylborane nicely catalyzes the homoally-
lation of benzaldehyde with 1,3-dienes to provide 1-phenyl-4-
pentenols 2 in excellent yields and with pronounced regio- and
stereoselectivities (eq 2). For example, as exemplified in run 2,
2
(1) Davies, S. G. Organotransition Metal Chemistry: Application to Organic
Synthesis; Pergamon: Oxford, 1982; Chapter 6.
(2) Ni-catalyzed 1,2-addition to aldehydes: Oblinger, E.; Montgomery, J.
J. Am. Chem. Soc. 1997, 119, 9065-9066.
(3) Ni-catalyzed 1,4-addition to enones: Ikeda, S.; Mori, N.; Sato, Y. J.
Am. Chem. Soc. 1997, 119, 4779-4780. Montgomery, J.; Oblinger, E.;
Savchenko, A. V. Ibid. 1997, 119, 4911-4920. Montgomery, J.; Savchenko,
A. V. Ibid. 1996, 118, 2099-2100. Ikeda, S.; Kondo, K.; Sato, Y. J. Org.
Chem. 1996, 61, 8248-8255. Ikeda, S.; Yamamoto, H.; Kondo, K.; Sato, Y.
Organometallics 1995, 14, 5015-5016. Ikeda, S.; Sato, Y. J. Am. Chem. Soc.
1994, 116, 5975-5976. Grisso, B. A.; Johnson, J. R.; Mackenzie, P. B. Ibid.
1992, 114, 5160-5165. Johnson, J. R.; Tully, P. S.; Mackenzie, P. B.; Sabat,
M. Ibid. 1991, 113, 6172-6177.
(4) Semmelhack, M. F. In Organic Reactions; Wiley: New York, 1972;
Vol. 19, Chapter 2.
(5) Hegedus, L. S.; Varaprath, S. Organometallics 1982, 1, 259-263.
Semmelhack, M. F.; Wu, E. S. C. J. Am. Chem. Soc. 1976, 98, 3384-3386.
Hegedus, L. S.; Wagner, S. D.; Waterman, W. E. L.; Siirala-Hansen, K. J.
Org. Chem. 1975, 40, 593-598.
(8) The same reaction, using Ni(cod)2 (cod ) cyclooctadiene) (0.1 mmol)
in place of Ni(acac)2 (0.1 mmol), proceeded much faster and provided 2b in
a 88% isolated yield within 3 h at room temperature.
(9) ZrCp2(isoprene) reacts with ketones to provide C1 homoallylation
products of isoprene: Yasuda, H.; Tatsumi, K.; Nakamura, A. Acc. Chem.
Res. 1985, 18, 120-126. Erker, G.; Engel, K.; Atwood, J. L.; Hunter, W. E.;
Angew. Chem., Int. Ed. Engl. 1983, 22, 494-495. Erker, G.; Dorf, U. Ibid.
1983, 22, 777-778.
(10) The ratio of diastereomers was determined by combination of GLC,
1H NMR (400 MHz), and/or 13C NMR (100 MHz).
(11) The stereochemistry of 2 was determined unequivocally on the basis
of 1H and 13C NMR spectra of cyclic compounds 5-7 (Figure 1), derived
from 2 by chemical transformations: 5 (cis:trans ) 5:1) in 30% overall yield
from 2b (1,3-anti:syn ) 15:1) via (1) BH3 in THF, (2) H2O2/NaOH, and (3)
TsCl/pyridine; 6 (syn:anti ) 5.3:1) in a 58% overall yield from 2e (1,2-syn:
anti ) 13:1) and syn-6 in 42% overall yield from 2i via (1) O3 in CH2CH2
and (2) H2O2/H2SO4 in AcOH; 7a in 70% overall yield from 2h via (1) LiAlH4
in THF and (2) Me2C(OMe)2/TsOH; 7b in 70% overall yield from 2j via (1)
Bu4NF in THF and (2) Me2C(OMe)2/TsOH. The stereochemistry of 2c, 2f,
and 2g was tentatively assigned by analogy with that of 2b and 2j.
(12) Baker, R.; Crimmin, M. J. J. Chem. Soc., Perkin Trans. 1 1979, 1264-
1267. Akutagawa, S. Bull. Chem. Soc. Jpn. 1976, 49, 3646-3648.
(6) Sato, Y.; Saito, N.; Mori, M. Tetrahedron Lett. 1997, 38, 3931-3934.
Sato, Y.; Takimoto, M.; Hayashi, K.; Katsuhara, T.; Tagaki, K.; Mori, M. J.
Am. Chem. Soc. 1994, 116, 9771-9772. For transition-metal-catalyzed
intermolecular allylation of aldehydes with dienes, see: Kitayama, K.; Tsuji,
H.; Uozumi, Y.; Hayashi, T. Tetrahedron Lett. 1996, 37, 4169-4172. Gao,
Y.; Urabe, H.; Sato, F. J. Org. Chem. 1994, 59, 5521-5523. Kobayashi, S.;
Nishio, K. Ibid. 1994, 59, 6620-6628.
(7) Sato, Y.; Takimoto, M.; Mori, M. Tetrahedron Lett. 1996, 37, 887-
890.
S0002-7863(97)03847-X CCC: $15.00 © 1998 American Chemical Society
Published on Web 04/14/1998

4034 J. Am. Chem. Soc., Vol. 120, No. 16, 1998
Communications to the Editor
Table 1. Nickel-Catalyzed Homoallylation of Benzaldehyde with
Acyclic 1,3-Dienes
Table 2. Nickel-Catalyzed Homoallylation of Benzaldehyde with
Dienes with Reduced Amounts of Ni(acac)2 and Dienesa
a A mixture of diene (indicated amount), benzaldehyde (1.0 mmol
for runs 1 and 4; 2 mmol for runs 2, 5, and 7-9; 5 mmol for runs 3
and 6), Ni(acac)2 (indicated amount), and Et3B (2.4 equiv) in dry THF
(5 mL for runs except for runs 3 and 6; 3 mL for runs 3 and 6) at room
temperature under N2.
(Z:E ) 6.9:1) provides 1,2-syn-2i with remarkably high stereo-
selectivity (run 10).
For convenience of experimental procedure, we routinely
applied 4 equiv of diene and 0.1 equiv of Ni(acac)2 relative to
benzaldehyde. The homoallylation, however, turned out to be
successful with reduced amounts of dienes and the catalyst (Table
2). The initial molar ratio of diene to benzaldehyde could be
minimized virtually to unity without serious deterioration of the
yields (runs 7 and 9, Table 2; see also run 6, Table 1). This
aspect is beneficial especially when dienes are expensive or
prepared with difficulty. Furthermore, the amount of the catalyst
could be reduced to as small as 1 mol % (runs 3 and 6, Table 2),
under which neither the yields nor the reaction rates discernibly
decreased.
a Reaction conditions: diene (4.0 mmol), benzaldehyde (1.0 mmol),
Ni(acac)2 (0.1 mmol), and Et3B (2.4 mmol, 1 M in hexane) in dry THF
(5 mL) at room temperature under N2. b All products were properly
1
characterized by H (400 MHz), 13C NMR (100 MHz), IR, HRMS,
and/or elemental analyses. The syn-anti mixture was not separated,
and their structures were assigned on the basis of mixtures (see ref 11
and Figure 1). c A mixture of Z:E ) 1.9:1 was used. d A reduced amount
of 1e (1.0 mmol) was used. e A mixture of Z:E ) 6.9:1 was used.
In conclusion, the Ni(acac)2-Et3B system allows us to obtain
the reductive coupling products 2 of benzaldehyde and acyclic
1,3-dienes of a wide structural variety. The utility of the reaction
may be apparent from (1) the usefulness of 2, which is obtained
in excellent yields and with high 1,2-, 1,3-, and 1,2,3-diastereo-
selectivities, (2) the mildness of the reaction conditions (room
temperature), (3) the ease of the experimental procedure, and (4)
the high catalytic turnover number over 80 (runs 3 and 6, Table
2). The low cost of the reagents [Ni(acac)2 and Et3B] and a 1:1
stoichiometry of the reaction partners (diene and benzaldehyde)
are important aspects from an economic point of view. This paper
demonstrates, for the first time, that Et3B plays an important role
as a reducing agent in maintaining the catalytic cycle for
transition-metal-catalyzed reductive coupling reactions. We are
now undertaking extensive study aimed at a catalytic asymmetric
synthesis of 2 and reactions with other electrophiles, such as
imines and allyic halides.
Figure 1. Selected NMR data diagnostic for structure determination: δ
in ppm [13C NMR (100 MHz, CDCl3)], J in Hz [1H NMR (400 MHz,
CDCl3)], and percent (%) increment in NOE.
Acknowledgment. This work was financially supported by Grant-
in-Aid for Scientific Research on Priority Area No. 08245104 from the
Ministry of Education, Science, Sports and Culture, of the Japanese
Government.
Interestingly, the ratio of 1,2-syn-2e to 1,2-anti-2e decreases
with a decrease in the initial molar ratio of 1e (a mixture of Z:E
) 1.9:1) to benzaldehyde (runs 5 and 6). This may be rationalized
by assuming that (1) (Z)-1e reacts faster than (E)-1e and (2) (Z)-
1e and (E)-1e selectively furnish 1,2-syn-2e and 1,2-anti-2e,
respectively. On this assumption, it may be explained that 1i
Supporting Information Available: Physical and spectral data of
2a-j, 3a, and 4 (5 pages, print/PDF). See any current masthead page
for ordering information and Web access instructions.
JA973847C