1
312
Y. Masaki et al.
LETTER
a
Table 2 Cleavage Reactions of Ethylene Acetals and THP Ethers
Catalyzed by Monomeric and Polymeric Dicyanoketene Acetals in
Aqueous Mediab
Table 2 indicated that the reactions catalyzed by the poly-
mer 3 proceeded much more smoothly in water (entries 3,
6
, 11, 17, and 23) than the reactions by the molecular cat-
Entry Substrate
Catalyst Reaction
Media
Time
(h)
Product
Yield(%)
(Recovered SM %)
alysts 1 and 2, by which almost no reaction took place (en-
tries 1, 2; 4, 5; 7, 9; 13, 15; and 19, 21) and that in aqueous
1
DCKEA
water
20
20
20
trace (SM 88)
trace (SM 83)
34 (SM 45)
O
CH CN (CH CN/H O = 9/1) the molecular catalysts 1
(1)
3 3 2
O
O
H
2
Monomer water
and 2 worked to afford the desired ketone 15 and alcohols
n-C9H19
(2)
n-C H
9
19
H
3
Polymer
water
1
7, 19, though sluggishly or rather moderately (entries 8,
(
10)
(11)
(3)
1
0; 14, 16; and 20, 22).
4
5
6
7
(1)
(2)
(3)
(1)
water
water
water
20
O
trace (SM 74)
no react
93
O
O
20
20
With t-butyldimethylsilyl ethers 20 and 22 shown in Table
, appreciable or remarkable acceleration of desilylation
Ph
Ph
(
12)
(13)
3
water
20
20
10 (SM 65)
to give alcohols 21 and 23 was observed by the polymeric
catalyst 3 in aqueous CH CN (CH CN/H O = 1/1) ( en-
8
9
(1) CH3CN/H2O
(2)
water
(2) CH CN/H O
O
38 (SM 48)
trace (SM 79)
O
O
2
0
3
3
2
1
0
20
20
20
60 (SM 18)
tries 5, 9) compared with the monomeric ones 1 and 2 (en-
tries 3, 4; and 7, 8), although almost no reaction occurred
in water even by the polymer 3 (entries 2, 6).
3
2
(14)
(15)
1
1
(3)
water
88
73
1
2
(3) CH3CN/H2O
(1)
water
(1) CH3CN/H2O
(2)
water
(2) CH3CN/H2O
1
1
1
3
4
5
12
12
12
trace (SM 88)
11 (SM 73)
no react
O-THP
(16)
OH
(17)
Ph
Ph
Ph
a
Table 3 Cleavage Reactions of Silyl Ethers of Alcohols Catalyzed
8 (SM 85)
41 (SM 54)
34 (SM 52)
1
1
6
7
12
12
12
by Monomeric and Polymeric Dicyanoketene Acetals in Aqueous
Media
(3)
water
(3) CH3CN/H2O
water
1
8
Entry
Substrate
Catalyst
Reaction
Media
Product
Yield (%)
(Recovered SM)
1
2
9
0
(1)
(1) CH3CN/H2O
Ph O-THP (2)
water
(18)
(2) CH3CN/H2O
(3)
water
(3) CH3CN/H2O
12
trace (SM 92)
12
12
27 (SM 67)
no react
1
DCKEA (1)
polymer (3)
no react
2
2
2
2
1
2
3
4
OH
(19)
n-C12H25
water
12
28 (SM 65)
40 (SM 47)
63 (SM 26)
2
3
trace (SM 95)
trace (SM 92)
O
12
12
(1)
Si(Me)2t-Bu
CH
3
CN/H
1 /1 )
2
O
4
monomer (2)
(
n-C12H25 OH trace (SM 96)
(20)
aThe reaction was carried out at room temperature using 0.2 equiv of
5
(3)
(21)
23 (SM 69)
a catalyst.
6
7
Me
n-C6H13
(3)
(1)
water
trace (SM 91)
b
The reaction media employed were water and a mixed solvent sy-
stem of acetonitrile/water (9/1).
O
trace (SM 95)
trace (SM 92)
Me
n-C6H13
8
9
(2)
CH
3
CN/H
1 /1 )
2
O
Si(Me)2t-Bu
22)
(
OH
(
(3)
(23)
98
aThe reaction was carried out at room temperature for 10 h using 0.2
tively (entries 1, 2), while a 59% yield of styrene glycol 5 equiv of a catalyst.
was obtained with a 34% recovery of the acetonide 4 by
using the polymeric DCKA 3 as a catalyst (entry 3). Anal-
In every run, more than 90% of the catalyst 1, 2, or 3 was
ogous results with higher efficiency of the polymeric
DCKA 3 for acetonides 6 and 8 of hexane-1,2-diol 7 and
cyclohexane-1,2-diol 9 were obtained and shown in en-
tries 7, 8, 9 and 13, 14, 15.
recovered intact after the reactions described. Particularly,
the polymer-supported catalyst 3 was easily recovered af-
ter the reactions by simple filtration and washing with
EtOAc and could be reused several times for the reactions
without any loss of the catalytic activity (Table 4).
Encouraged by the results, we were intrigued to carry out
the reaction in water as a sole solvent. Results for the re-
action under the same conditions except for water as a sol-
vent were shown also in Table 1. Reaction of styrene
derivative 4 was found to proceed more smoothly by us-
ing polymeric DCKA 3 as a catalyst to give a high yield
In conclusion, polymeric functionalization of dicy-
anoketene acetal moiety as a -acid gave rise to a remark-
able acceleration of deprotecting reactions of acetals and
silyl ethers in water. Although the mechanisms for the ex-
cellent polymer effect observed are not clear, interactions
associated with hydrophilicity of the products and lipo-
philicity of the substrates and catalysts are thought to play
an important role: In the aqueous medium, the lipophilic
substrates such as acetals and monomeric catalysts 1 and
(
(
94%) of styrene glycol 5 than the case in aqueous CH CN
entries 3, 6), and molecular DCKAs 1 and 2 were ineffec-
3
tive as a catalyst (entries 4, 5). With the polymer 3, appre-
ciable improvements of the yields of the products 7 and 9
were observed for the acetonides 6 and 8 (entries 9, 12 and
2
are likely to form clusters which appear difficult to react
1
5, 18).
each other. When the polymer 3 exists, the lipophilic sub-
strates are easy to access molecularly to pores and the sur-
face of the polymer 3 where the lipophilic active DCKA
groups are arrayed in suitable distances for the reaction,
and hydrophilic products upon generation are apt to leave
the site and diffuse in water phase. Investigation in line
with the concept is currently under way in our laboratory.
Deprotecting reactions were tested for other acetals such
as ethylene acetals 10, 12, and 14 of an aldehyde 11 and
ketones 13 and 15, respectively, and tetrahydropyranyl
(
THP) ethers 16 and 18 of primary alcohol 17 and a sec-
ondary alcohol 19, respectively, in water and/or aqueous
CH CN (CH CN/H O = 9/1). The results summarized in
3
3
2
Synlett 2001, No. 8, 1311–1313 ISSN 0936-5214 © Thieme Stuttgart · New York