S. Kobayashi et al. / Journal of Organometallic Chemistry 624 (2001) 392–394
393
Table 1
Effect of the conditioning of the scandium catalyst a
Table 2
a,b
Effect of scandium salts (Sc(OSO2CnF2n+1 3
)
Time
Condition (i),
yield (%) b,c
Condition (ii),
yield (%) b,c
Condition (iii),
yield (%) b,c
Time
n=1,
n=2,
n=4,
n=6,
n=8,
yield (%) yield (%) yield (%) yield (%) yield (%)
10 min
30 min
1 h
0
0
0
4
7
38
54
60
48
76
91
94
10 min 52
30 mm 80
45
76
87
92
48
76
91
94
23
54
77
87
4
21
38
69
1 h
3 h
88
92
3 h
a See text.
a Yield into 3 (and 4)-methyl-1-acetylcyclohex-3-ene was deter-
mined by GC analysis. See also text.
b Yield into 3 (and 4)-methyl-1-acetylcyclohex-3-ene was deter-
mined by GC analysis.
b Ratio of isomers was not determined.
c Ratio of isomers was not determined.
Fig. 1.
Fig. 2.
,
proved to 94% using dry Sc(OSO2C4F9)3 with MS 5 A
(condition (iii)). These results suggested that water in-
terferes with the Diels–Alder reaction. It is noteworthy
that this suppressive effect of water is contrary to that
in most rare earth metal triflate-catalyzed reactions,
which proceed smoothly in the presence of water [3].
We then examined the length of perfluoroalkyl chains
of scandium salts1 in the model Diels–Alder reaction
(Table 2, Fig. 2). All reactions were carried out using 5
the longer perfluoroalkyl groups induce high Lewis
acidity of the scandium.
Several examples of the Diels–Alder reactions using
Sc(OSO2C4F9)3 as a catalyst are shown in Table 3.
3-Acyl-1,3-oxazolidin-2-one, MVK, and maleic anhy-
dride smoothly reacted with dienes such as cyclopenta-
diene, 1,3-cyclohexadiene, and isoprene to afford the
corresponding Diels–Alder adducts in high yields with
high diastereoselectivity. It is noted that less reactive
dimethyl fumarate and dimethyl acetylenedicarboxylate
reacted with cyclopentadiene to afford the desired
Diels–Alder adducts in high yields, respectively.
A typical experimental procedure is described for the
reaction of MVK with isoprene: to a suspension of
Sc(OSO2C4F9)3 (62.2 mg, 0.066 mmol), naphthalene
,
mol% of scandium salts with MS 5 A. Scandium triflate
(Sc(OTf)3), scandium pentafluoroethanesulfonate
(Sc(OSO2C2F5)3), and scandium nonafluorobutanesul-
fonate (Sc(OSO2C4F9)3) worked well to afford the de-
sired Diels–Alder adduct in excellent yields in 1 h.
Almost the same activity was observed among these
three scandium salts. On the other hand, a slight de-
crease of the activity was observed when scandium
tridecafluorohexanesulfonate (Sc(OSO2C6F13)3) was
used, and less activity was obtained using scandium
,
(82.6 mg, 0.644 mmol; internal standard), and MS 5 A
(100 mg) in dichloromethane (3 ml) were added MVK
(93.4 mg, 1.33 mmol) and isoprene (385 ml, 3.85 mmol).
After the mixture was stirred at −20°C for 3 h,
NaHCO3 aq. was added to quench the reaction. After a
usual work-up, the yield and stereoselectivity were de-
termined by GC analysis.
heptadecafluorooctanesulfonate
(Sc(OSO2C8F17)3.
Longer perfluoroalkanesulfonates gave lower yields
probably due to bulkiness of the counter anions albeit
In summary, Diels–Alder reactions proceeded
smoothly in the presence of a catalytic amount of
scandium perfluoroalkanesulfonate. Contrary to other
rare earth-catalyzed reactions, water interfered with the
reactions, and the desired adducts were most effectively
1 We used five scandium catalysts, Sc(OTf)3, Sc(OSO2C2F5)3,
Sc(OSO2C4F9)3, Sc(OSO2C6F13)3, Sc(OSO2C8F17)3, which were read-
ily prepared from Sc2O3 and the corresponding acids (TfOH,
C2F5SO3H, C4F9SO3H, C6F13SO3H) or ScCl3 and the corresponding
acid (C8F17SO3H).
Kobayashi, Shu
