Iridium-catalyzed carbonyl allylations by allylic alcohols with Tin(II) chloride

Article abstract of DOI:10.1055/s-2005-872255

Iridium complex [IrCl(cod)]₂ can function as a catalyst for the allylation of aldehydes and ketones by allylic alcohols upon addition of an equimolar amount of SnCl₂ in THF-H₂O; the reaction is carried out between room temperature and 50 °C to give the corresponding homoallylic alcohols. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2005-872255

LETTER
2251
Iridium-Catalyzed Carbonyl Allylations by Allylic Alcohols with Tin(II)
Chloride
I
ridium-Catalyzed
o
C
arbonyl
A
l
s
lylations hiro Masuyama,* Toshiya Chiyo, Yasuhiko Kurusu
Department of Chemistry, Faculty of Science and Technology, Sophia University, 7-1 Kioicho, Chiyoda-ku, Tokyo 102-8554, Japan
Fax +81(3)32383361; E-mail: y-masuya@sophia.ac.jp
Received 21 June 2005
tested a number of tin(II) halides, however, lower yields
Abstract: Iridium complex [IrCl(cod)]2 can function as a catalyst
resulted with SnF2 (68 h, 12%) and SnBr2 (67 h, 13%),
while no reaction occurred even after 47 hours with SnI2.
for the allylation of aldehydes and ketones by allylic alcohols upon
addition of an equimolar amount of SnCl2 in THF–H2O; the reaction
As a solvent, THF was found to be superior to other sol-
vents such as acetonitrile (44 h, 69%) and DMF (20 h,
79%).
is carried out between room temperature and 50 °C to give the cor-
responding homoallylic alcohols.
Key words: nucleophilic addition, carbonyl allylation, p-allyliridi-
um, tin(II) chloride, allylic alcohols
Table 1 Allylation of Benzaldehyde with 2-Propenol (1)a
[IrCl(cod)]2
SnCl2
OH
OH
Complexes of group IX elements, such as [RhCl(cod)]2,
can catalyze the carbonyl allylation by allylic alcohols
with SnCl2 in THF–H2O at 50 °C,1 similarly to palladium-
catalyzed carbonyl allylations.2 A disadvantage of the pal-
ladium(0) cycle is that two equivalents of SnCl2 are re-
quired for each equivalent of allylic alcohol.3–5 In
contrast, the reaction with rhodium(I) has been accom-
plished with one equivalent of SnCl2. Here SnCl2 acts as a
reducing agent to accomplish the umpolung of the usual
electrophilic p-allylrhodium(III) complex. It has been
reported that p-allyliridium(III) complexes of other group
IX elements can be prepared from iridium(I) complexes,
such as [IrCl(cod)]2 and allylic esters and can be used
for reactions with nucleophiles.6 Thus, we hoped that
[IrCl(cod)]2 would be active as a catalyst for carbonyl
allylation by allylic alcohols with SnCl2.
+
PhCHO
THF–H2O
r.t.
Ph
1
Entry
1
SnCl2
(mmol)
Ligandb
Time
(h)
Yield
(%)c
(mmol)
1
1.0
1.0
1.5
2.0
1.0
1.5
2.0
1.5
1.5
1.5
1.5
1.5
–
69
45
42
45
43
44
20
20
22
22
57
2
1.0
–
68
3
1.0
–
71
4
1.5
–
61
5
1.5
–
81 (13)d
84
6
1.5
–
7e
8e
9e
1.5
–
87
1.5
PPh3
dppe
dppb
58
The catalytic activity of [IrCl(cod)]2 with some ligands,
along with varying the stoichiometry of SnCl2, were in-
vestigated for the allylation of benzaldehyde with 2-pro-
1.5
79
penol (1) in THF–H2O at room temperature under a 10e
1.5
76
nitrogen atmosphere (Table 1). No allylation occurs with-
out the addition of either the iridium catalyst or SnCl2. The
11e
1.5
P(C6F5)3 22
70
a The allylation of benzaldehyde (1.0 mmol) was carried out with
[IrCl(cod)]2 (0.02 mmol) in THF (3 mL) and H2O (0.1 mL).
b Based on phosphorus (4 mol%).
optimum reaction conditions employed equimolar
amounts of 1 and SnCl2 in THF (2 mL) and H2O (0.1 mL)
(Table 1, entry 7);7 under these conditions the homoallylic
c Isolated yields.8
alcohol was isolated after 20 hours in 87% yield. The al-
lylation proceeded without H2O, however, after a reaction
time of 43 hours a low yield of homoallylic alcohol result-
ed (Table 1, entry 5). We also studied the effect of adding
a ligand (entries 8–11); although the yields were lower,
the character of the ligand did not have a significant ef-
fect. Under optimum conditions (Table 1, entry 7)
[IrCl(cod)]2 exhibited higher catalytic activity than either
IrCl(CO)(PPh3)2 (89 h, 88%) or IrCl3 (7 d, 0%). We also
d The figure in parentheses is the yield without H2O.
e The reaction was carried out in THF (2 mL) and H2O (0.1 mL).
Having optimized the reaction conditions, we subjected a
range of aldehydes to the allylation (Table 2). Aromatic
aldehydes bearing an electron-withdrawing or electron-
donating group (Table 2, entries 1 and 2), an a,b-unsatur-
ated aldehyde (Table 2, entry 3), and aliphatic aldehydes
(Table 2, entries 4–7) were employed. This iridium cata-
lytic system can also be utilized for the allylation of ke-
tones with 1 (2.0 mmol) and SnCl2 (2.0 mmol) at 50 °C,
this is in contrast to the poor applicability of the rhodium
catalytic system to ketones (Table 2, entries 8–11).1
SYNLETT 2005, No. 14, pp 2251–2253
0
2
.0
9
.2
0
0
5
Advanced online publication: 29.07.2005
DOI: 10.1055/s-2005-872255; Art ID: U19005ST
© Georg Thieme Verlag Stuttgart · New York

2252
Y. Masuyama et al.
LETTER
Table 2 Iridium-Catalyzed Carbonyl Allylation with 1
Table 3 Iridium-Catalyzed Carbonyl Allylation with 3 or 4
[IrCl(cod)]2
SnCl2
[IrCl(cod)]2
SnCl2
OH
OH
R1
R2
OH
R1
R2
OH
OH
+
+
R2
R1
R
RCHO
THF–H2O
50 °C
THF–H2O
r.t.
R
O
1
2
3: R1 = H, R2 = Me
4: R1 = Me, R2 = H
5a
5b
Entry R1
R2
H
Time (h)
17
2; Yield (%)a
Entry
1
R
3 or 4 Time
Yield
(%)a
5a/5b
1
2
4-ClC6H4
91
80
65
67
53
61
55
46
48
41
59
(h)
(5b; syn/anti)b
4-CH3C6H4
PhCH=CH
PhCH2CH2
H
24
Ph
3
3
3
3
3
3
4
4
4
4
4
4
47
74
78
72
59
41
49
70
80
72
62
46
50
7:93
(41:59)
3
H
44
2
4-ClC6H4
4-CH3C6H4
PhCH2CH2
C6H13
45
48
48
66
74
49
45
49
47
68
69
5:95
4
H
48
(30:70)
5
CH2=CH(CH2)8
C6H13
H
47
3
2:98
(40:60)
6
H
45
4
2:98
7
c-C6H11
Ph
H
45
(49:51)
8
CH3
CH3
89
5
9:91
9b
10b
11b
C6H13
49
(40:60)
-(CH2)4-
-(CH2)5-
44
6
c-C6H11
Ph
67:33
(39:61)
46
7
8:92
a Isolated yields.8
b The reaction was carried out at 50 °C.
(46:54)
8
4-ClC6H4
4-CH3C6H4
PhCH2CH2
C6H13
5:95
(43:57)
9
8:92
Regio- and diastereoselectivity were investigated for the
iridium-catalyzed carbonyl allylation with 3-buten-2-ol
(3) and 2-buten-1-ol (4). The allylation of benzaldehyde
with 3 under optimum conditions for 1 was quite slow [5
(R = Ph), 93 h, 62%; 5a/5b, 1:99; 5b-syn/5b-anti, 20:80].
In addition, the reaction of 4 at room temperature is not
practical [5 (R = Ph), 47 h, 8%, 5a/5b, 15:85, 5b-syn/5b-
anti, 39:61]. The allylation of various aldehydes with 3
and 4 at 50 °C occurred at the allylic position substituted
by a methyl group except for cyclohexanecarboxalde-
hyde,9 while anti-diastereoselectivities were lower than
that of benzaldehyde at room temperature (Table 3).
(46:54)
10
11
12
1:99
(45:55)
8:92
(44:56)
c-C6H11
36:64
(37:63)
a Isolated yields.8
b The ratios were determined by 1H NMR spectroscopy.
A study of the reaction of 1 (1.0 mmol) with SnCl2 (1.2
mmol) in the presence of a catalytic amount of
[IrCl(cod)]2 (2 mol%) in THF-d8 (0.75 mL) at room tem-
perature without aldehyde or H2O in a sealed tube by
NMR spectroscopy (JEOL L-500) was undertaken. In
contrast to both the preparation of the 2-propenyltin spe-
cies in the palladium-catalyzed reaction3 and the prepara-
tion of propene in the rhodium-catalyzed reaction,1 diallyl
ether was found to form.10 A plausible mechanism for the
iridium-catalyzed carbonyl allylation is illustrated in
Scheme 1, based on both the g-regioselectivity which was
observed with both 3 and 4 and the NMR spectroscopic
studies. The detection of diallyl ether suggests the forma-
tion of a p-allyliridium complex A; the p-allyliridium
complex A, derived from 1 and [IrCl(cod)]2 with SnCl2,
can undergo further nucleophilic attack by 1.6 The g-regi-
oselectivity using both 3 and 4 suggests the formation of
a s-allyliridium complex B; the preparation of 5b from ei-
ther 3 or 4 can be demonstrated by: (1) the transformation
of an initial syn,anti-mixed 1-methyl-p-allyliridium com-
plex derived from 3 or 4 into a mixture of (E)- and (Z)-2-
butenyliridium complex C accompanied by the coordina-
tion of aldehydes; and then (2) the nucleophilic addition
of the 2-butenyl moiety at the g-position (Scheme 2).
In conclusion, [IrCl(cod)]2 is superior to [RhCl(cod)]2 as
a catalyst for carbonyl allylation, because not only alde-
hydes but also ketones can be applied to the iridium-cata-
lyzed allylation with 1. The p-allyliridium complex A,
derived from 1 with SnCl2 and the iridium catalyst, should
be an amphoteric allylating agent that can function either
as an electrophile in the absence of an aldehyde or as a nu-
cleophile in the presence of an aldehyde, unlike either
palladium3 or rhodium catalysts.1
Synlett 2005, No. 14, 2251–2253 © Thieme Stuttgart · New York

LETTER
Iridium-Catalyzed Carbonyl Allylations
2253
(4) Palladium-catalyzed carbonyl allylations need over two
equivalents of reducing agent for one equivalent of allylic
alcohol and/or aldehyde: (a) For triethylborane, see:
Kimura, M.; Tomizawa, T.; Horino, Y.; Tanaka, S.; Tamaru,
Y. Tetrahedron Lett. 2000, 41, 3627. (b) For indium iodide,
see: Araki, S.; Kamei, T.; Hirashita, T.; Yamamura, H.;
Kawai, M. Org. Lett. 2000, 2, 847. (c) For diethylzinc, see:
Kimura, M.; Shimizu, M.; Tanaka, S.; Tamaru, Y.
Tetrahedron 2005, 61, 3709.
OH
IrI
SnCl2
H2O
+
O
R
1
SnCl2
H
IrIII
SnCl2OH
R
O
1
(5) For nickel-catalyzed carbonyl allylation with over two
equivalents of indium iodide and one equivalent of aldehyde,
see: Hirashita, T.; Kambe, S.; Tsuji, H.; Omori, H.; Araki, S.
J. Org. Chem. 2004, 69, 5054.
(6) Takeuchi, R. Synlett 2002, 1954; and references cited
therein.
B
IrIII
RCHO
SnCl2OH
A
(7) A typical procedure is as follows: To a solution of 1 (0.087
g, 1.5 mmol), benzaldehyde (0.11 g, 1.0 mmol), and SnCl2
(0.28 g, 1.5 mmol) in THF (2 mL) and H2O (0.1 mL) was
added [IrCl(cod)]2 (0.013 g, 0.02 mmol), and the solution
was stirred at r.t. for 20 h. The solution was diluted with
Et2O–CH2Cl2 (2:1; 120 mL), washed with aq 10% HCl
solution (20 mL), aq NaHCO3 solution (20 mL), H2O (20
mL), and brine (20 mL). The extracts were dried over anhyd
MgSO4. After evaporation of the solvent, column
chromatography (silica gel; hexane–EtOAc, 7:1), and then
HPLC (Japan Analytical Industry Co. Ltd., LC-908,
JAIGEL-2H; CHCl3) afforded 0.13 g (87%) of 1-phenyl-3-
buten-1-ol as a colorless oil.
(8) The structures and/or ratios were confirmed by comparison
of the IR and 1H NMR spectra with those of authentic
samples, see: (a) ref. 3 (b) Ito, A.; Kishida, M.; Kurusu, Y.;
Masuyama, Y. J. Org. Chem. 2000, 65, 494.
(9) Since the reactivity of cyclohexanecarboxaldehyde is low,
initially produced 5b may react with excess
cyclohexanecarboxaldehyde and isomerize to sterically
unhindered and thermodynamically stable 5a via a
homoallyloxycarbenium ion intermediate: (a) Nokami, J.;
Ohga, M.; Nakamoto, H.; Matsubara, T.; Hussain, I.;
Kataoka, K. J. Am. Chem. Soc. 2001, 123, 9168. (b) Ref. 1.
(10) 1H NMR (500 MHz): d = 3.93 (d, J = 6 Hz, 2 H), 5.09 (d,
J = 10 Hz, 1 H), 5.23 (d, J = 17 Hz, 1 H), 5.83–5.91 (m, 1 H);
13C NMR (125 MHz): d = 71.5, 116.0, 136.1.
Scheme 1
Ir cat.
OH
H
IrIII
SnCl2
3 or 4
R
γ-addition
RCHO
R
O
C
5b
Scheme 2
References
(1) Masuyama, Y.; Kaneko, Y.; Kurusu, Y. Tetrahedron Lett.
2004, 45, 8969.
(2) For reviews containing carbonyl allylations by allylic
alcohols via umpolung of p-allylpalladium, see:
(a) Masuyama, Y. J. Synth. Org. Chem., Jpn. 1992, 50, 202.
(b) Masuyama, Y. In Advances in Metal-Organic Chemistry,
Vol. 3; Liebeskind, L. S., Ed.; JAI Press: Greenwich CT,
1994, 255–303. (c) Tamaru, Y. In Perspectives in
Organopalladium Chemistry for the XXI Century; Tsuji, J.,
Ed.; Elsevier Science: Switzerland, 1999, 215–231.
(d) Tamaru, Y. In Handbook of Organopalladium Chemistry
for Organic Synthesis; Negishi, E., Ed.; Wiley: New York,
2002, 1917–1953.
(3) For the palladium-catalyzed carbonyl allylation by allylic
alcohols with SnCl2, see: Takahara, J. P.; Masuyama, Y.;
Kurusu, Y. J. Am. Chem. Soc. 1992, 114, 2577.
Synlett 2005, No. 14, 2251–2253 © Thieme Stuttgart · New York