K. Shibata et al. / Journal of Organometallic Chemistry 624 (2001) 348–353
349
(2)
E-selectivity. No (Z)-3 isomers were detected. Further-
more, 1-substituted 9-phenylnona-3,7-dien-1-ols, the
type of compounds obtained as the major side products
(
3)
in the reaction of Me Zn–1,3-butadiene–aldehydes [4],
2
Here we would like to report that the three-compo-
nent connection reactions of Ph–1,3-butadiene–alde-
hydes and Ph–isoprene–aldehydes proceed nicely and
furnish (E)-5-phenyl-3-penten-1-ols (3) and (E)-3-
methyl-5-phenyl-3-penten-1-ols (5), respectively, in high
yields and with excellent stereoselectivity under the
catalysis of a nickel complex.
were not formed.
For the reaction with isoprene, on the other hand,
the phenylation of aldehydes turned out to be a very
serious problem, especially for the reactions with reac-
tive aldehydes (benzaldehyde and alkyl aldehydes that
do not possess substituents at the a-position) (runs 5
and 6, Table 2). In these cases, the expected products 5a
and 5b were produced only as the minor products. An
We expected that the three-component connection
reaction of Ph Zn–dienes–aldehydes would be rather
2
attempt to minimise 6a by adding slowly the Ph Zn
solution into the solution of benzaldehyde, isoprene,
problematic, since, as compared with Me Zn, Ph Zn is
2
2
2
so reactive that it might possibly react with aldehydes
without incorporating dienes as the reaction partner [6].
Accordingly, we undertook preliminary experiments for
and Ni(acac) over 1 h was unsuccessful, and 5a and 6a
2
were obtained in 38 and 39% yields, respectively. For
the reaction with less reactive secondary and tertiary
alkyl aldehydes, the expected products 5c and 5d were
obtained in moderate yields (runs 7 and 8).
In order to circumvent the competitive phenylation
of aldehydes, we next examined Ph B as the phenylat-
the reaction of Ph Zn with benzaldehyde in the absence
2
and in the presence of a nickel catalyst (Table 1). In
fact, Ph Zn reacted rather slowly with benzaldehyde at
2
room temperature (runs 1 and 2). However, in the
presence of 10 mol% of Ni(acac) [acac=acetylaceto-
3
2
ing agent, since our preliminary study indicated that
nate], it underwent facile reaction. The reaction was
complete within 20 min at room temperature and pro-
vided benzhydrol in a quantitative yield (run 3).
Despite these somewhat discouraging preliminary re-
sults, to our pleasant surprise, the three-component
connection reaction did proceed nicely for the reaction
with 1,3-butadiene and aldehydes (runs 1–4, Table 2).
Except for the reaction with dihydrocinnamaldehyde
Ph B was unreactive toward benzaldehyde even in the
3
presence of nickel catalysts (runs 4–6, Table 1).
Although Ni(acac) served nicely as the catalyst for
the connection reaction of Me B–isoprene–aldehydes
2
3
(
Eq. (3)) [5], it turned out to be completely ineffective
for the version of Ph B–isoprene–aldehydes and no 5
formed at all. In sharp contrast to this, Ni(cod) [cod=
cyclooctadiene] promoted the reaction effectively (Table
3). In the presence of 10 mol% of Ni(cod) , the reaction
3
2
(
run 2, Table 2), the direct phenylation of aldehydes
presented little difficulty and the expected products 3
were obtained in reasonable yields and with excellent
2
proceeded smoothly at room temperature and furnished
Table 1
a
Reaction of Ph Zn and Ph B with benzaldehyde in the presence and in the absence of nickel catalysts
2
3
Run
Phenylating agent
Nickel catalyst
Reaction time (h)
Benzhydrol (% yield) b
1
2
3
4
5
6
Ph Zn
None
None
Ni(acac)2
None
Ni(acac)2
Ni(cod)2
5
0.3
0.3
36
10
10
81
65
96
0
0
2
Ph Zn
2
Ph Zn
2
c
Ph B
3
c
Ph B
3
c
Ph B
3
0
a
A mixture of benzaldehyde (1 mmol), Ph Zn (1.2 mmol), and a nickel catalyst (0.1 mmol, if indicated) in dry THF (5 ml) was stirred at room
2
temperature under N .
2
b
Yields refer to the isolated yields of benzhydrol by means of column chromatography over silica gel.
No formation of benzhydrol was confirmed by means of TLC and GPLC.
c