Cobalt(II) Chloride. Aluminium Promoted Allylation of Aldehydes with Allylic Halides

Article abstract of DOI:10.1039/a704607c

In the presence of cobalt(II) chloride-metallic aluminium, allylic halides react with aldehydes at room temperature in tetrahydrofuran-water to afford the corresponding alcohols in high yields.

Full text of DOI:10.1039/a704607c

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202 J. CHEM. RESEARCH (S), 1998
J. Chem. Research (S),
1998, 202±203$
Cobalt(II) Chloride. Aluminium Promoted Allylation
of Aldehydes with Allylic Halides$
Rahat H. Khan* and Turga S. R. Prasada Rao
Indian Institute of Petroleum, Dehradun-248 005, India
In the presence of cobalt(II) chloride±metallic aluminium, allylic halides react with aldehydes at room temperature in
tetrahydrofuran±water to afford the corresponding alcohols in high yields.
The addition of allylic metal compounds to aldehydes and
ketones to yield homoallylic alcohols is a useful transform-
ation in organic synthesis and consequently has received
considerable attention in recent years.1 The reaction is syn-
thetically analogous to the aldol condensation but allows
for the subsequent introduction of a variety of alternative
functional groups by manipulation of the alkene moiety.2
Like the aldol reaction, addition can be achieved with high
levels of regio- and stero-selectivity by judicious choice of
substrates and reaction conditions.3 Recently it was reported
that cobalt(II) chloride4,5 in acetonitrile eciently catalyses
the coupling of acetic anhydride with various aldehydes to
the corresponding 1,2-diones and acylation of alcohols and
amines with acetic anhydride. Herein we report our ®ndings
that Barbier-type allylation of aldehydes with allylic halides
can be easily e€ected in aqueous6 THF using CoCl2±
metallic aluminium.
Scheme 1
aromatic and aliphatic aldehydes reacted smoothly to a€ord
3 in good yields.
The use of CoCl2 is essential in this reaction; viz.
hardly any expected product was obtained using a Co±Al
system in THF±H2O. CoCl2 did not promote the allylation
in the absence of Al and the action of Al alone gave
none of the desired products. Although details of the inter-
mediate species of this reaction are not yet known, we
The overall reaction is shown in Scheme 1. Allylic
bromide, unlike allylic chloride, gave the expected adduct 3
in good yield. When an a,b-unsaturated aldehyde was used,
the 1,2-addition product 3f was obtained selectively. Both
Table 1 Synthesis of homoallylic alcohols 3a±h by allylation of aldehydes in THF±H2O and CoCl2±Al
bp/8C (mmHg)
Compound 3
R1
R2
Yield (%)a
Found
Reported
a
b
c
d
e
f
H
H
H
H
H
H
Me
H
Ph
95
82
70
85
70
80
84
30b
105±110 (2)
140 (2)
125±130 (2)
99±101 (2)
115 (2)
110±111 (2)
95±98 (2)
108±110 (2)
71 (0.757)
102±103 (0.337)
85±89 (0.337)
Oil8
pClC6H4
pMeOC6H4
C6H4[CH2]2
Me[CH2]7
MeCH1CH
Ph
Oil9
Oil10
g
h
118 (2011
)
Ph
71 (0.757)
aIsolated yields of the allylation products and based on the amount of 2. bWhen CH21CHCH2Cl is used.
Table 2 Spectral data for homoallylic alcohols 3a±h
1
ꢀ
max/cm
(CCl4)a
a
‡
Compound 3 OH C1C
dH
m/z (M )a
a
b
c
d
e
f
3500 1640
3500 1645
3500 1640
3450 1650
3400 1640
3450 1640
3500 1642
2.15±2.45 (m,2 H), 4.7 (t, 1 H), 5.15±6.25 (m, 3 H), 7.1 (s, 5 H)
2.30±2.51 (m, 2 H), 4.8 (t, 1 H), 5.25±6.25 (m, 2 H), 7.15±7.35 (m, 4 H)
2.15±2.51 (m, 2 H), 3.8 (s, 3 H), 4.75 (t, 1 H) 4.95±6.10 (m, 3 H), 7.05±7.30 (m, 4 H)
1.5±2.8 (m, 6 H), 3.9 (m, 1 H), 4.95±6.15 (m, 3 H), 7.15 (s, 5 H)
0.95 (t, 3 H), 2.15±2.75 (m, 18 H), 3.95 (m, 1 H) 5.05±5.95 (m, 3 H)
1.73 (d, 3 H), 2.32 (m, 2 H), 4.14 (m, 1 H), 5.15±5.93 (m, 5 H)
0.85 (d, 3 H), 1.75±1.95 (m, 1 H), 4.75 (d, 1 H), 5.05±6.15 (m, 3 H), 7.15 (m, 5 H)
148
182, 184
178
176
170
112
162
g
a 1H NMR and IR spectra of all compounds were in agreement with those previously reported.9,10,12±14 IR spectra were recorded on a
Perkin Elmer 237B spectrometer, 1H NMR spectra were recorded in CDCl3 using a Varian EM 360L NMR spectrometer with Me4Si as
internal standard and mass spectra were recorded on a Finnigan 3200 mass spectrometer.
assume that an allyl cobalt addition product is formed
through the oxidative addition of an allyl halide to Co
generated by the reduction of CoCl2 with Al in the presence
of water.
*To receive any correspondence.
$This is a Short Paper as de®ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1998, Issue 1]; there is there-
fore no corresponding material in J. Chem. Research (M).

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J. CHEM. RESEARCH (S), 1998 203
5 For other catalytic reactions of cobalt(II) chloride see: J. Marquet
and M. Moreno-Manas, Chem. Lett., 1981, 173; H. Matsuda
and H. Kanai, Chem. Lett. 1981, 395; J. Iqbal, B. Bhatia and
N. K. Nayyar, Chem. Rev., 1994 94, 519; M. Mukhopadhyay
and J. Iqbal, J. Org. Chem., 1997, 62, 1843.
Experimental
Typical Experimental Procedure.ÐTo a mixture of commercial
grade aluminium powder (4.8 mmol) and CoCl2 (2.4 mmol) was
added THF (5 ml) and H2O (1 ml) A mixture of aldehyde 2
(2.0 mmol) and the allylic halide 1 (2.4 mmol) was then added and
the resultant mixture stirred at room temperature for 10±20 h.
Progress of the reaction was monitored by TLC. The solution was
then poured into water (50 mL) and extracted with dichloromethane
(3Â 25 mL). The combined organic extracts were dried (anhy.
Na2SO4) and the solvent was removed in vacuo. The crude product
3 was puri®ed by Kugelrohr distillation or ¯ash chromatography or
preparative thin layer chromatography to give the corresponding
homoallylic alcohol. The results are summarized in Tables 1 and 2.
6 Other similar allylation of carbonyl compounds in aqueous
a Borbier-type reaction:
media has been reported to be
J. Nokami, I. Otera, T. Sudo and R. Okawara, Organometallics,
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Received, 1st July 1997; Accepted, 8th December 1997
Paper E/7/04607C
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