Reusable scandium/ionic liquid catalyst system for sequential C-C and C-O bond formations between phenols and dienes with atom economy

Article abstract of DOI:10.1055/s-2007-990963

Mild, efficient, and atom economical sequential C-C/C-O bond formations between phenols and dienes using the reusable catalyst system, Sc(OTf) ₃-[bmim] [PF₆], have been developed to afford in good yields a variety of dihydrobenzopyran and dihydrobenzofuran ring systems, which are important motifs in both naturally occurring and biologically active compounds. In these reactions the ionic liquid acts as not only an efficient additive but also an immobilizing agent for facilitating catalyst recycling. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2007-990963

3050
LETTER
Reusable Scandium/Ionic Liquid Catalyst System for Sequential C–C and
C–O Bond Formations between Phenols and Dienes with Atom Economy
R
eusable Sca
n
o
dium/Ionic
L
iquid
W
Catalyst
S
yste
m
on Youn
Department of Chemistry, Pukyong National University, Busan 608737, Korea
Fax +82(51)6288147; E-mail: sowony@pknu.ac.kr
Received 7 September 2007
lar or ionic character can reside in ionic liquids, and thus
Abstract: Mild, efficient, and atom economical sequential C–C/C–
O bond formations between phenols and dienes using the reusable
catalyst system, Sc(OTf)3–[bmim][PF6], have been developed to af-
ford in good yields a variety of dihydrobenzopyran and dihydroben-
catalysts can easily be recovered from the reaction mix-
ture and then be reused. Herein we report the discovery of
a recyclable catalytic system, Sc(OTf)3–[bmim][PF6], for
zofuran ring systems, which are important motifs in both naturally the sequential addition/cyclization of phenols with dienes
occurring and biologically active compounds. In these reactions the
in an atom-economical manner.
ionic liquid acts as not only an efficient additive but also an immo-
bilizing agent for facilitating catalyst recycling.
MeO
MeO
cat.
Key words: heterocycles, bicyclic compounds, annulations, scan-
+
dium, ionic liquids
O
OH
1
Scheme 1 Sequential C–C/C–O bond-formation reaction of p-me-
thoxyphenol and isoprene
Dihydrobenzopyrans and dihydrobenzofurans are perva-
sive motifs in biologically active natural products and
pharmaceutical drug targets.1 The dihydrobenzofurans are
generally prepared in two steps from allyl aryl ethers by
the Claisen rearrangement followed by cyclization of the
resulting 2-allylphenols with strong acid.2,3 The dihy-
drobenzopyrans are constructed typically by intramolecu-
lar hydroarylation from arene-ene substrates4 or by
cycloaddition of o-quinonemethides generated from sali-
cylaldehydes and alcohols with alkenes using a protic acid
or Lewis acid.5 Recently, we reported mild, efficient, and
economical Ag(I)-catalyzed sequential C–C/C–O bond
formations between phenols and dienes (Scheme 1).6 In
view of green chemistry, atom-economical one-pot syn-
theses and the reuse of catalysts are preferable. Although
Ag(I)-catalyzed reaction is an atom-economical one-pot
reaction for the synthesis of dihydrobenzopyrans and di-
hydrobenzofurans, recovery and reuse of catalysts are not
yet possible. Therefore, we were interested in exploring
the possibility of the reuse of catalyst, and we reasoned
that the use of ionic liquids as reaction media might offer
a convenient solution to the catalyst recycling problem,
obviating the need for structural modification of cata-
lysts.7
In light of our recent success in Ag(I)-catalyzed sequential
C–C/C–O bond formations,6 we chose this catalyst system
in preliminary studies of annulation of phenols with
dienes in ionic liquid as a solvent. Disappointingly, treat-
ment of p-methoxyphenol and isoprene with 10 mol% of
AgOTf in a range of RTILs, [bmim][X] ([bmim] = 1-bu-
tyl-3-methylimidazolium, X = PF6, BF4, OTf) and
[emim][BF4] ([emim] = 1-ethyl-3-methylimidazolium),
afforded no desired products (Table 1, entries 1–4).
Therefore, we made a conscious effort to develop a cata-
lytic system that would work in RTILs. Several metal salts
and complexes that were included in the screen in our pre-
vious works6 were examined in this reaction, and most of
them did not show the ability to produce the desired prod-
uct 1 (Table 1, entries 9–13). In contrast, when the reac-
tion was carried out in the presence of Sc(OTf)3 in
[bmim][PF6],9,10 1 was produced in 30% yield (Table 1,
entry 5). Since Sc(OTf)3 is only slightly soluble in the hy-
drophobic ionic liquid, [bmim][PF6], the hydrophilic ionic
liquid, [bmim][BF4], in which Sc(OTf)3 is highly solu-
ble,9b,11 was used as a solvent. However, lower conversion
was obtained (Table 1, entry 6). Interestingly, no reaction
occurred in other hydrophilic ionic liquids, such as
[bmim][OTf] and [emim][BF4] (Table 1, entries 7 and 8).
These results suggest that the catalytic activity of
Sc(OTf)3 was influenced by both the anions and the cat-
ions of ionic liquids in this reaction.12
In particular, air- and moisture-stable room temperature
ionic liquids (RTILs) consisting of 1,3-dialkylimidazoli-
um cations and various anions have attracted considerable
attention as eco-friendly reaction media for organic syn-
thesis in the last few years.8 They are immiscible with
some organic solvents, such as alkanes and ethers, and,
hence, can be used as nonaqueous, polar alternatives in bi-
phasic systems. In biphasic systems, catalysts having po-
The low conversion in [bmim][PF6] as a sole solvent can
be attributed to the low solubilities of phenols and dienes
in [bmim][PF6].13 To provide biphasic systems in which
catalyst recycling and separation of the products would be
easy, toluene was then introduced into the system. Sur-
prisingly, the use of toluene as a co-solvent increased the
SYNLETT 2007, No. 19, pp 3050–3054
x
x
.x
x
.2
0
0
7
Advanced online publication: 08.11.2007
DOI: 10.1055/s-2007-990963; Art ID: U08207ST
© Georg Thieme Verlag Stuttgart · New York

LETTER
Reusable Scandium/Ionic Liquid Catalyst System
3051
Table 1 Optimization Studies for the Reaction of p-Methoxyphenol and Isoprene Using RTILsa
Entry
1
Catalyst
AgOTf
Solvent (ratio)
Yield (%)b
[bmim][PF6]
–
2
AgOTf
[bmim][BF4]
–
3
AgOTf
[bmim][OTf]
–
4
AgOTf
[emim][BF4]
–
5
Sc(OTf)3
Sc(OTf)3
Sc(OTf)3
Sc(OTf)3
Cu(OTf)2
AgOTf–PPh3
[bmim][PF6]
30
20
trace
–
6
[bmim][BF4]
7
[bmim][OTf]
8
[emim][BF4]
9
[bmim][PF6]
–
c
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27j
[bmim][PF6]
–
d
AuCl–AgOTf–PPh3
RuCl3–AgOTfe
AgNO3
[bmim][PF6]
–
[bmim][PF6]
–
[bmim][PF6]
–
Sc(OTf)3
Sc(OTf)3
Sc(OTf)3
Sc(OTf)3
Sc(OTf)3
Sc(OTf)3
Sc(OTf)3
Sc(OTf)3
Sc(OTf)3
Sc(OTf)3
Sc(OTf)3
–
[bmim][PF6]–toluene (1:1)
[bmim][PF6]–toluene (1:4)
[bmim][PF6]–THF (1:4)
[bmim][PF6]–1,4-dioxane (1:4)
[bmim][PF6]–MeCN (1:4)
[bmim][PF6]–CH2Cl2 (1:4)
[bmim][PF6]–DCE (1:4)
[bmim][PF6]–toluene (1:10)f
[bmim][PF6]–toluene (1:20)g
[bmim][PF6]–toluene (1:50)h
[bmim][PF6]–toluene (1:100)i
[bmim][PF6]–toluene (1:100)i
toluene
50
55
–
7
25
20
30
60
60
63
67
–
Sc(OTf)3
Sc(OTf)3
40
70
[bmim][PF6]–toluene (1:100)i
a Reaction conditions: p-MeOC6H4OH (1 equiv), isoprene (1 equiv), catalyst (10 mol%), solvent (0.1 M), 60 °C, 24 h.
b Determined by 1H NMR using trichloroethylene as internal standard.
c Performed with AgOTf (10 mol%) and PPh3 (10 mol%).
d Performed with AuCl (10 mol%), AgOTf (10 mol%), and PPh3 (10 mol%).
e Performed with RuCl3 (10 mol%) and AgOTf (20 mol%).
f The amount of [bmim][PF6] was about 400 mol% of the amount of p-MeOC6H4OH.
g The amount of [bmim][PF6] was about 200 mol% of the amount of p-MeOC6H4OH.
h The amount of [bmim][PF6] was about 100 mol% of the amount of p-MeOC6H4OH.
i The amount of [bmim][PF6] was about 50 mol% of the amount of p-MeOC6H4OH.
j Performed with isoprene (2 equiv) in the presence of Sc(OTf)3 (20 mol%).
yields of 1. Various organic solvents were examined, and products (Table 1, entries 14, 15 and 21–24). The most
toluene appeared preferable (Table 1, entries 15–20). It dramatic improvement was observed when the ratio of
was also found that decreasing the amounts of [bmim][PF6] and toluene was 1:100, in which case the
[bmim][PF6] led to gradually better yields of annulated amount of [bmim][PF6] was less than 50 mol% of the
Synlett 2007, No. 19, 3050–3054 © Thieme Stuttgart · New York

3052
S. W. Youn
LETTER
Table 2 Sc–IL-Catalyzed Reaction of ROH with Isoprenea
(continued)
amount of p-methoxyphenol (Table 1, entry 24). Control
experiments employing only either Sc(OTf)3 or
[bmim][PF6] as the sole catalyst in toluene gave lower or
no conversions, respectively (Table 1, entries 25 and 26).
These results mean that [bmim][PF6] plays a role as an ad-
ditive to enhance either the catalytic activity of Sc(OTf)3
or the nucleophilicity of phenol14 and itself is not respon-
sible for the product formation.
Entry ROH
Product
Yield
(%)b
7
7
8
92
O
O
O
O
O
OH
8c
88 (8/9
OH
With the optimized conditions in hand, we set out to ex-
plore the scope of this coupling process.15 As shown in
Table 2, a variety of phenols underwent tandem addition/
cyclization in the presence of Sc(OTf)3 and [bmim][PF6]
to form the corresponding dihydrobenzopyrans in compa-
rable or better yields than in the previously reported meth-
od.6 The yields remained moderate to high with both
electron-donating and electron-withdrawing substituents
on the phenol ring. However, it is likely that the more
electron-rich substrates work better in this reaction system
than in the Ag(I)-catalyzed reaction system because high-
ly electron-rich substrates, such as di- or trimethoxyphe-
nol and resorcinol derivatives, did not react in the latter
system (Table 2, entries 5–10). Our attention then turned
to the synthesis of bicyclic compounds. To examine the
possibility of double cyclization, we used resorcinol de-
rivatives as substrates in this coupling process. We were
delighted to find that the reactions using four equivalents
of isoprene in the presence of Sc(OTf)3 and [bmim][PF6]
proceeded smoothly to afford the corresponding bicyclic
products 8–10 in good yields (Table 2, entries 8 and 9).
= 3:2)e
O
OH
O
9
O
O
O
O
9c
10
91
OH
OH
10
11
12
99
(100)f,g
(100)f,h
O
OH
11d
52
OH
O
Table 2 Sc–IL-Catalyzed Reaction of ROH with Isoprenea
a Reaction conditions: ROH (1 equiv), isoprene (2 equiv), Sc(OTf)3
(20 mol%), [bmim][PF6] (0.5 equiv), toluene (0.1 M), 60 °C, 24 h, un-
less otherwise noted.
Entry ROH
Product
Yield
(%)b
b Isolated yields.
c Performed with isoprene (4 equiv).
d Reaction time: 48 h.
1
2
1
55
MeO
Et
MeO
e The ratio of two isomers was determined by 1H NMR.
f Determined by 1H NMR using trichloroethylene as internal standard.
g Second cycle.
OH
O
h Third cycle.
2
65
Et
OH
O
Finally, this reaction system allowed easy recovery and
recycling of the catalyst, with three consecutive runs pro-
viding similar results. After completion of the reaction,
the ionic liquid phase containing Sc(OTf)3 was recovered
by simple decantation of the toluene phase containing
products/substrates, and then reused. Second and third
runs using recovered Sc(OTf)3-containing [bmim][PF6] in
the same reaction of 2-naphthol with isoprene yielded
amounts of 11 as high as in the first cycle (Table 2, entry
10).
3c
4d
3
4
60
53
O
OH
Cl
Cl
OH
O
OMe
5
6
5
6
73
85
OMe
MeO
OH
OH
MeO
O
Subsequently, the reaction was examined on a range of
dienes (Table 3). Both cyclic and acyclic dienes partici-
pated in the Sc–IL-catalyzed C–C/C–O bond formations,
allowing the preparation of dihydrobenzopyrans and di-
hydrobenzofurans. Good yields were obtained for all cas-
es. With the exception of 2,3-dimethyl-1,3-butadiene, all
1-substituted 1,3-dienes gave the corresponding dihy-
OMe
OMe
MeO
MeO
MeO
MeO
O
Synlett 2007, No. 19, 3050–3054 © Thieme Stuttgart · New York

LETTER
Reusable Scandium/Ionic Liquid Catalyst System
3053
drobenzofurans as the sole products. Both 16 and 17 could
be obtained in better yields than in Ag(I)-catalyzed reac-
tion (Table 3, entries 3 and 4).6 Regioselectivity of Sc–IL-
catalyzed reaction presented herein parallels the regiose-
lectivity observed for Ag(I)-catalyzed reaction of phenols
with dienes, which suggests that C–C/C–O bond forma-
tion occurs by a similar mechanism in those reactions.
Acknowledgment
This work was supported by the Korea Research Foundation Grant
funded by the Korean Government (MOEHRD, Basic Research
Promotion Fund, KRF-2006-331-C00168).
References and Notes
(1) (a) Bioactive Compounds from Natural Sources; Tringali,
C., Ed.; Taylor & Francis: New York, 2001. (b) The
Chemistry of Heterocyclic Compounds, Vol. 36; Ellis, G. P.;
Lockhart, I. M., Eds.; John Wiley-Interscience: New York,
1981.
(2) (a) Nichols, D. E.; Hoffman, A. J.; Oberlender, R. A.; Riggs,
R. A. J. Med. Chem. 1986, 29, 302. (b) Harwood, L. M.
J. Chem. Soc., Chem. Commun. 1983, 530.
Table 3 Sc–IL-Catalyzed Reaction of 2-Naphthol with Dienesa
Entry Diene
1c
Product
Yield (%)b
13
98 (13/14 =
40:60)d
(3) (a) For Ir-catalyzed tandem Claisen rearrangement and
intramolecular hydroaryloxylation of allyl aryl ethers, see:
Grant, V. H.; Liu, B. Tetrahedron Lett. 2005, 46, 1237; and
references therein. (b) For transition-metal-catalyzed
cyclization of 2-allylphenols, see: Hori, K.; Kitagawa, H.;
Miyoshi, A.; Ohta, T.; Furukawa, I. Chem. Lett. 1998, 1083.
(4) Youn, S. W.; Pastine, S. J.; Sames, D. Org. Lett. 2004, 6,
581.
(5) Yadav, J. S.; Reddy, B. V. S.; Parisse, C.; Carvalho, P.; Rao,
T. P. Tetrahedron Lett. 2002, 43, 2999; and references
therein.
(6) Youn, S. W.; Eom, J. I. J. Org. Chem. 2006, 71, 6705.
(7) For one-pot synthesis of dihydrobenzopyrans by the
reactions of phenols with dienes using Amberlyst 15 as a
reusable catalyst, see: Cichewicz, R. H.; Kenyon, V. A.;
Whitman, S.; Morales, N. M.; Arguello, J. F.; Holman, T. R.;
Crews, P. J. Am. Chem. Soc. 2004, 126, 14910; and
references therein.
(8) For recent reviews on ionic liquids, see: (a) Afonso, C. A.
M.; Branco, L. C.; Candeias, N. R.; Gois, P. M. P.;
Lourenço, N. M. T.; Mateus, N. M. M.; Rosa, J. N. Chem.
Commun. 2007, 2669. (b) Pârvulescu, V. I.; Hardacre, C.
Chem. Rev. 2007, 107, 2615. (c) Binnemans, K. Chem. Rev.
2007, 107, 2592. (d) Imperato, G.; König, B.; Chiappe, C.
Eur. J. Org. Chem. 2007, 1049. (e) Song, C. E.; Yoon, M.
Y.; Choi, D. S. Bull. Korean Chem. Soc. 2005, 26, 1321.
(f) Dupont, J.; de Souza, R. F.; Suarez, P. A. Z. Chem. Rev.
2002, 102, 3667. (g) Sheldon, R. Chem. Commun. 2001,
2399. (h) Wasserscheid, P.; Keim, W. Angew. Chem. Int. Ed.
2000, 39, 3772. (i) Welton, T. Chem. Rev. 1999, 99, 2071.
(9) For recent related examples of Sc(OTf)3-catalyzed reactions
in ionic liquids, see the following. For hydroarylations:
(a) Song, C. E.; Jung, D.; Choung, S. Y.; Roh, E. J.; Lee, S.
Angew. Chem. Int. Ed. 2004, 43, 6183. (b) Song, C. E.;
Shim, W. H.; Roh, E. J.; Choi, J. H. Chem. Commun. 2000,
1695. (c) For Claisen rearrangement/cyclization: Zulfiqar,
F.; Kitazume, T. Green Chem. 2000, 2, 296. (d) For Diels–
Alder reactions: Song, C. E.; Shim, W. H.; Roh, E. J.; Lee,
S.; Choi, J. H. Chem. Commun. 2001, 1122. (e) For C–C
bond-forming reactions, see: Gu, Y.; Ogawa, C.; Kobayashi,
J.; Mori, Y.; Kobayashi, S. Angew. Chem. Int. Ed. 2006, 45,
7217.
O
14
15
O
O
O
O
2c
3e
4e
95 (syn/anti =
83:17)d
16
17
92 (syn/anti =
64:36)d
91 (only syn)
a Reaction conditions: 2-naphthol (1 equiv), diene (2 equiv), Sc(OTf)3
(20 mol%), [bmim][PF6] (0.5 equiv), toluene (0.1 M), 18–24 h.
b Isolated yields.
c Performed at 60 °C.
d The ratio of two isomers was determined by 1H NMR.
e Performed at 100 °C.
In summary, we have developed mild and efficient Sc–IL-
catalyzed sequential C–C/C–O bond formations between
phenols and dienes. In these reactions, an ionic liquid
plays an important role as not only an efficient additive
but also an immobilizing agent for facilitating catalyst re-
cycling. Electron-rich substrates are more beneficial than
electron-deficient substrates, and both cyclic and acyclic
dienes could be applied. Because of the simple procedure,
easy recovery and reuse of this new catalytic system,
Sc(OTf)3–[bmim][PF6], this one-pot reaction represents a
greener and more attractive means for the facile and atom
economical construction of dihydrobenzopyran and dihy-
drobenzofuran ring systems, which are important motifs
in both naturally occurring and biologically active com-
pounds.
(10) For dimerization and telomerization of 1,3-butadiene in
ionic liquids, see: (a) Silva, S. M.; Suarez, P. A. Z.; de
Souza, R. F.; Dupont, J. Polym. Bull. (Berlin) 1998, 40, 401.
(b) Dullius, J. E. L.; Suarez, P. A. Z.; Einloft, S.; de Souza,
R. F.; Dupont, J.; Fischer, J.; Cian, A. D. Organometallics
1998, 17, 815.
(11) Yadav, J. S.; Reddy, B. V. S.; Gayathri, K. U.; Prasad, A. R.
Synthesis 2002, 2537.
Synlett 2007, No. 19, 3050–3054 © Thieme Stuttgart · New York

3054
S. W. Youn
LETTER
(12) (a) For effect of the structures of ionic liquids on their
physical-chemical properties, see: Hu, Y.-F.; Xu, C.-M.
Chem. Rev. 2007, in press. (b) For effects of the anions, see:
refs. 9b and 8c and references therein. (c) For effects of the
alkyl chain lengths of the cations, see: Williams, D. B. G.;
Ajam, M.; Ranwell, A. Organometallics 2006, 25, 3088; and
ref. 9c.
(13) For miscibility of organic compounds in [bmim][PF6], see:
Blanchard, L. A.; Breunecke, J. F. Ind. Eng. Chem. Res.
2001, 40, 287; and ref. 8f.
102.4, 155.0, 158.5, 159.3. HRMS (EI): m/z [M]+ calcd for
C13H18O3: 222.1256; found: 222.1255.
5,6,7-Trimethoxy-2,2-dimethylchroman (6):
Colorless oil (EtOAc–n-hexane, 1:20). 1H NMR (400 MHz,
CDCl3): d = 1.31 (s, 6 H), 1.74 (t, J = 6.8 Hz, 2 H), 2.63 (t,
J = 6.8 Hz, 2 H), 3.78 (s, 3 H), 3.80 (s, 3 H), 3.88 (s, 3 H),
6.16 (s, 1 H). 13C NMR (100 MHz, CDCl3): d = 17.0, 26.6,
32.3, 55.7, 60.5, 61.0, 74.0, 96.5, 106.6, 135.3, 149.9, 151.3,
152.3. HRMS (EI): m/z [M]+ calcd for C14H20O4: 252.1362;
found: 252.1364.
(14) Kim, D. W.; Hong, D. J.; Seo, J. W.; Kim, H. S.; Kim, H. K.;
Song, C. E.; Chi, D. Y. J. Org. Chem. 2004, 69, 3186.
(15) General Procedure for the Sc–IL-Catalyzed Reaction of
Phenols and Dienes and Catalyst Recycling: To a solution
of phenol and diene (2 equiv) in toluene (0.1 M) and
[bmim][PF6] (0.5 equiv) was added Sc(OTf)3 (20 mol%).
The resulting mixture was stirred at the reported temperature
for 18–48 h. The organic(toluene) layer was decanted to
leave the ionic liquid phase containing Sc(OTf)3 which was
washed with Et2O (3 ×) for extraction of the product. The
combined organic layer was concentrated and the residue
was purified by column chromatography on silica gel
(EtOAc–n-hexanes, 1:20–1:100) to give the corresponding
product.
2,2,8,8-Tetramethyl-3,4,9,10-tetrahydro-2H,8H-
pyrano[2,3-f]chromene (8) and 2,2,8,8-Tetramethyl-
3,4,7,8-tetrahydro-2H,6H-pyrano[3,2-g]chromene (9):
The mixture of isomers was obtained as a colorless oil
(8/9 = 3:2, EtOAc–n-hexane, 1:50). Signals corresponding
to 8: 1H NMR (400 MHz, CDCl3): d = 1.32 (s, 3 H), 1.33 (s,
3 H), 1.77 (m, 4 H), 2.62 (t, J = 6.8 Hz, 2 H), 2.70 (t, J = 6.8
Hz, 2 H), 6.34 (d, J = 8.5 Hz, 1 H), 6.80 (d, J = 8.2 Hz, 1 H).
13C NMR (100 MHz, CDCl3): d = 17.1, 22.0, 26.7, 27.1,
32.4, 32.9, 73.5, 73.9, 108.4, 109.5, 111.3, 127.0, 151.7,
152.8. Signals corresponding to 9: 1H NMR (400 MHz,
CDCl3): d = 1.32 (s, 6 H), 1.77 (m, 4 H), 2.69 (t, J = 6.8 Hz,
4 H), 6.24 (s, 1 H), 6.74 (s, 1 H). 13C NMR (100 MHz,
CDCl3): d = 21.8, 26.8, 33.1, 73.8, 104.7, 112.6, 129.3,
153.1. HRMS (EI): m/z [M]+ calcd for C16H22O2: 246.1620;
found: 246.1618.
The recovered ionic liquid layer remaining in the vessel was
reused without any pre-treatment. For the second cycle,
more reactants (phenol and diene) and toluene were added to
the recovered ionic liquid layer.
2,2,8,8,10-Pentamethyl-3,4,7,8-tetrahydro-2H,6H-
pyrano[3,2-g]chromene (10):
5,7-Dimethoxy-2,2-dimethylchroman (5):
White solid (EtOAc–n-hexane, 1:50). 1H NMR (400 MHz,
CDCl3): d = 1.33 (s, 12 H), 1.76 (t, J = 6.8 Hz, 4 H), 2.03 (s,
3 H), 2.70 (t, J = 6.8 Hz, 4 H), 6.62 (s, 1 H). 13C NMR (100
MHz, CDCl3): d = 8.0, 22.1, 27.1, 33.1, 73.5, 111.8, 113.0,
125.8, 150.7. HRMS (EI): m/z [M]+ calcd for C17H24O2:
260.1776; found: 260.1776.
Colorless oil (EtOAc–n-hexane, 1:20). 1H NMR (400 MHz,
CDCl3): d = 1.32 (s, 6 H), 1.75 (t, J = 6.8 Hz, 2 H), 2.57 (t,
J = 6.8 Hz, 2 H), 3.75 (s, 3 H), 3.78 (s, 3 H), 6.01 (d, J = 2.4
Hz, 1 H), 6.03 (d, J = 2.4 Hz, 1 H). 13C NMR (100 MHz,
CDCl3): d = 16.6, 26.6, 32.4, 55.2, 55.3, 74.2, 90.8, 93.5,
Synlett 2007, No. 19, 3050–3054 © Thieme Stuttgart · New York

Copyright of Synlett is the property of Georg Thieme Verlag Stuttgart and its content may not
be copied or emailed to multiple sites or posted to a listserv without the copyright holder's
express written permission. However, users may print, download, or email articles for
individual use.