syn-Diastereoselective carbonyl allylation by 1- or 3-substituted prop-2-en-1-ols
with tin(ii) iodide and tetrabutylammonium iodide
Yoshiro Masuyama,* Takanori Ito, Kentaro Tachi, Akihiro Ito and Yasuhiko Kurusu
Department of Chemistry, Sophia University, 7-1 Kioicho, Chiyoda-ku, Tokyo 102-8554, Japan.
E-mail: y-masuya@hoffman.cc.sophia.ac.jp
Received (in Cambridge, UK) 22nd March 1999, Accepted 17th May 1999
1-Substituted or 3-substituted prop-2-en-1-ols cause syn-
diastereoselective carbonyl allylation with tin(ii) iodide and
tetrabutylammonium iodide via the formation of 3-substi-
tuted prop-2-enylpolyiodotins to produce syn-1,2-disub-
stituted but-3-en-1-ols.
Diastereoselective allylation of benzaldehyde (1 mmol) by
(E)-but-2-en-1-ol (3; R Me, RA H, 2 mmol) was
=
=
investigated with tin(ii) iodide (3 mmol) and TBAI (1 mmol) at
60 °C in various solvents containing a small amount of H2O;
DMI (19 h, 74%, syn+anti = 83+17) is superior to other
solvents (THF, 26 h, 74%, syn+anti = 83+17; DMF, 72 h, 18%,
syn+anti = 67+33; H2O, 72 h, 31%, syn+anti = 89+11; DMI
without H2O, 72 h, 25%, syn+anti = 71+29) for both reactivity
and diastereoselectivity. The results in the diastereoselective
carbonyl allylation by some 1- or 3-substituted prop-2-en-
1-ols† with SnI2, TBAI and NaI in DMI–H2O are summarized
in Table 2. Allylic alcohols bearing an aliphatic group at the a-
or g-position can be applied to the syn-diastereoselective
carbonyl allylation. In contrast, (E)-cinnamyl alcohol bearing
an aromatic group at the g-position exhibits anti-selectivity,
similar to the palladium-catalysed carbonyl allylation with
tin(ii) chloride.
Barbier-type carbonyl allylation is one of the most convenient
methods for the introduction of allylic functions.1 Allylic metal
reagents in the allylation reaction are generated in situ from
allylic halides, which are usually prepared from allylic alcohols
in advance. Thus, it should be an important aim to generate
allylic metal reagents from available and storable allylic
alcohols directly. We have already reported carbonyl allylations
by allylic alcohols with tin(ii) chloride, which need a catalytic
amount of palladium complexes such as PdCl2(PhCN)2,
Pd(PPh3)4 and so on.2 We here report that allylic alcohols serve
as carbonyl allylating agents without the palladium complexes
via the use of tin(ii) iodide and tetrabutylammonium iodide
(TBAI),3 and that the carbonyl allylation by 1- or 3-substituted
prop-2-en-1-ols with tin(ii) iodide and TBAI exhibits syn-
diastereoselectivity,4 in contrast to the palladium-catalysed
anti-diastereoselective carbonyl allylation by 3-substituted (E)-
prop-2-en-1-ols with tin(ii) chloride in 1,3-dimethylimidazoli-
din-2-one (DMI).5
Prop-2-en-1-ol (1) slowly caused allylation of benzaldehyde
without palladium catalysts in the presence of tin(ii) iodide,
TBAI and NaI under the same conditions (namely at room
temperature in DMI containing a small amount of H2O) which
gave the best results for the carbonyl allylation by allylic halides
with tin(ii) halides and tetrabutylammonium halides;4
15–20 °C, 166 h, 17% yield. When the temperature was raised
to 60 °C, prop-2-en-1-ol (1) was amenable to the allylation of
various aldehydes, as summarized in Table 1. Use of less than
2 equiv. of tin(ii) iodide with respect to benzaldehyde lowered
the yield (SnI2 (2 mmol), 60 °C, 66 h, 61%). Tin(ii) bromide
slowed down the allylation of benzaldehyde (72 h, 38%), and no
reaction occurred with tin(ii) chloride, under the same condi-
tions as those of the allylation with tin(ii) iodide.
The syn-diastereoselective carbonyl allylation by 1- or
3-substituted prop-2-en-1-ols, except (E)-cinnamyl alcohol,
with tin(ii) iodide and TBAI probably proceeds via (i) the
transformation of the prop-2-en-1-ol into 1-substituted 3-iodo-
prop-1-ene A, which is then converted into 3-substituted prop-
2-enylpolyiodotin B, and (ii) the formation of an acyclic
antiperiplanar transition state C between 3-substituted prop-
2-enylpolyiodotin B, in which the tin has no Lewis acidity, and
an aldehyde, as shown in Scheme 1.4‡ The tin in (E)-
cinnamylpolyiodotin, derived from (E)-cinnamyl alcohol with
tin(ii) iodide and TBAI, may have Lewis acidity owing to (s–
Table 2 Diastereoselective carbonyl allylation with SnI2, TBAI and NaIa
OH
OH
SnI2
R
R'
TBAI, NaI
R2CHO
R2
+
+
R2
DMI, H2O
60 °C
OH
R1
R1
4a
anti
3
4s
syn
Allylic alcohol
Product
Ratioc
Yieldb of 4 (%) 4s+4a
Table 1 Carbonyl allylation by 1 with SnI2, TBAI and NaIa
R
RA
t/h R1 R2
OH
SnI2, TBAI, NaI
OH
RCHO
+
Me
Me
Me
Me
Me
Me
Me
H
H
H
H
H
H
H
H
Me
Me
H
47 Me Ph
76
50
79
58
37
61
82+18
81+19
82+18
67+33
67+33
75+25
78+22
82+18
77+23
1+99d
70+30
DMI, H2O
60 °C
R
65 Me 4-MeC6H4
47 Me 4-ClC6H4
71 Me PhCH2CH2
72 Me c-C6H11
46 Me C6H13
1
2
R
t/h
Yieldb of 2 (%)
Ph
41
54
45
72
62
35
77
55
79
64
36
52
54
78 Me CH2NCH(CH2)8 56
4-MeC6H4
4-ClC6H4
PhCH2CH2
c-C6H11
C6H13
CH2NCH(CH2)8 46
91 Me Ph
87 Me C6H13
24 Ph Ph
48 Pr Ph
51
45
49
80
H
Ph
Pr
H
a
The allylation of aldehydes (1 mmol) by allylic alcohols (2 mmol) was
carried out with SnI2 (3 mmol), TBAI (0.25 mmol) and NaI (2.5 mmol) in
a
b
c
The allylation of aldehydes (1 mmol) by prop-2-en-1-ol (2 mmol) was
DMI (3 ml) and H2O (0.1 ml) at 60 °C. Isolated yields. The ratio was
determined by 1H NMR spectroscopy (JEOL GX-270 or L-500) and/or GC
(Capillary column PEG 20M 0.25 mm 3 30 m). d See ref. 5.
carried out with SnI2 (3 mmol), TBAI (0.25 mmol) and NaI (2.5 mmol) in
DMI (3 ml) and H2O (0.1 ml) at 60 °C. b Isolated yields.
Chem. Commun., 1999, 1261–1262
1261
Masuyama, Yoshiro
