T. Hino et al. / Tetrahedron Letters 47 (2006) 1429–1432
1431
tra of catalysts 1 and 2 indicated that these catalysts
clearly had fullerene moiety and that these absorption
patterns of catalysts 1 and 2 were similar to that of
C60 (solid state) itself (see Supplementary data).
tions of phenol 13 was hard to take place, compared
with the similar case in CDCl3.
1
In conclusion, various types of solvent-free O2-photo-
oxygenations were demonstrated to proceed under vis-
ible-light irradiation by using catalysts 1 and 2 prepared
by conjugating C60 to amino-functional silica gels. Addi-
tionally in some cases, the catalyst efficiency of 1 was
higher than that of 2. The detailed investigations are
now in progress and the results will be reported
elsewhere.
The visible-light induced photooxygenations of several
substrates were carried out by using catalysts 1 and 2
in the solid-solution system or in the solvent-free system
(Table 1).14 The Diels–Alder photooxygenation of
cyclohexadiene 3 in the presence of catalysts 1 and 2
in CDCl3 gave the corresponding product 4, in which
the yield in the case with catalyst 1was higher than that
with catalyst 2, presumably due to the distinct amount
of C60 between these catalysts. Meanwhile, the solvent-
free photooxygenations of substrate 3 quantitatively
proceeded with catalyst 1 and even with catalyst 2 for
the same reaction time (60 min) to the cases in CDCl3.
In addition, the reaction smoothly underwent even by
using catalyst 1 recycled more than 50 times and also
took place even with a halogen lamp equipped with a fil-
ter, cutting radiation below 380 nm. Thus, these results
imply that the present catalyst efficiently mediated a vis-
ible-light induced photooxygenation even in the solvent-
free system, and then similar reactions with various sub-
strates were also performed as shown in Table 1.
Acknowledgments
This work was financially supported by Kurita Water
and Environment Foundation.
Supplementary data
The UV–vis data and the photographs of catalysts 1 and
2 and C60 are available. Supplementary data associated
with this article can be found, in the online version, at
The solvent-free photooxygenations of a-terpinene 5
also smoothly proceeded by use of catalysts 1 and 2 to
yield the oxygenated product (6), and the reaction effi-
ciencies were also similar to the case in CDCl3. The
ene reaction of substrate 7 also readily took place,
although the solvent-free reactions using catalysts 1
and 2 needed prolonged reaction time to quantitatively
convert to product 8, compared with the reaction in
CDCl3 (2 h vs 60 min). Interestingly, the solvent-free
ene reactions of methylcyclohexene 9 both with catalysts
1 and 2 quantatively underwent for 60 min, although the
reaction rate of photooxygenation of compound 9 with
RB in the solution system is known to be extremely
lower than that of compound 7 [(krel of 9)/(krel of 7) =
0.0041].15 In addition, the total yields of endocyclic
products 10a and 10c were higher than the case in solu-
tion, and it strongly implied that the intermediate giving
10a and 10c, perepoxide b, might be rather preferred in
the solvent-free system to the intermediate giving 10b,
perepoxide a, probably due to more restricted molecular
movement of the substrate in the solid-phase reaction
field, compared with that in solution phase. Incidentally,
in the similar reactions with RB and MB in solution the
ratios of endo- and exo-cyclic products are 56:44 and
57:43, respectively.16 The photooxygenation of citronel-
lol (11), which is known to be industrially useful process
for production of a fragrance, ‘Rose Oxide’, was also
carried out in the present solvent-free systems by using
catalysts 1 and 2. As a result, the reaction also
proceeded along with the similar production ratios of
products 12a and 12b to the result of a common photo-
oxygenation with RB in solution system.17 Additionally,
in the reaction using catalyst 2, the total yield of prod-
ucts 12a–b was 50% even in the reaction for 12 h. The
oxidations of phenol 13 and sulfide 15 also proceeded
in the solid-solution system as well as in the solvent-free
system to give products 14 and 16, although the reac-
References and notes
1. Anastas, P. T.; Warner, J. C. Green Chemistry. Theory and
Practice; Oxford University Press, 1998.
2. Clennan, E. L.; Pace, A. Tetrahedron 2005, 61, 6665.
3. Singlet Oxygen; Frimer, A. A., Ed.; CRC Press: Boca
Raton, 1985; Vol. I.
4. Rabek, J. F. 1O2 Oxidation of Polymers and their
Stabilization. In Singlet O2; Frimer, A. A., Ed.; Polymers
and Biomolecules; CRC Press: Boca Raton, FL, 1985;
Vol. IV, p 36.
5. (a) Fullerenes: Chemistry, Physics, and Technology;
Kadish, K. M., Ruoff, R. S., Eds.; John Wiley and Sons:
New York, 2000; (b) Takaguchi, Y.; Yanagimoto, Y.;
Fujima, S.; Tsuboi, S. Chem. Lett. 2004, 33, 1142; (c)
Anderson, J. L.; An, Y.-Z.; Rubin, Y.; Foote, C. S. J. Am.
Chem. Soc. 1994, 116, 9763; (d) Orfanopoulos, M.;
Kambourakis, S. Tetrahedron Lett. 1994, 35, 1945; (e)
Tokumaru, H.; Nakamura, E. J. Org. Chem. 1994, 59,
1135; (f) Aborgast, J. W.; Darmanyan, A. P.; Foote, C. S.;
Rubin, Y.; Diederich, F. N.; Alvarez, M. M.; Anz, S. J.;
Whetten, R. L. J. Phys. Chem. 1991, 95, 11; (g) Arbogast,
J. W.; Foote, C. S. J. Am. Chem. Soc. 1991, 113, 8886; (h)
Hung, R. R.; Grabowski, J. J. J. Phys. Chem. 1991, 95,
6073.
6. (a) Blossey, E. C.; Neckers, D. C.; Thayer, A. L.; Schaap,
A. P. J. Am. Chem. Soc. 1973, 95, 5820; (b) Madhavan, D.;
Pitchumani, K. Tetrahedron 2001, 57, 8391; (c) Soggiu, N.;
Cardy, H.; Jiwan, J. L. H.; Leray, I.; Soumillon, J. P.;
Lacombe, S. J. Photochem. Photobiol. 1999, 124, 1; (d) Li,
X.; Ramamurthy, V. Tetrahedron Lett. 1996, 37, 5235; (e)
Zhou, W.; Clennan, E. L. J. Am. Chem. Soc. 1999, 121,
2915.
7. Latassa, D.; Enger, O.; Thilgen, C.; Habicher, T.; Offer-
manns, H.; Diederich, F. J. Mater. Chem. 2002, 12, 1993.
8. Our reaction system was distinctly different from that of
Latassa’s reaction system. As described in the text,
Latassa et al. reported photooxydation of sulfides under
irradiation with a mercury lamp in MeOH by use of
fullerene linking polysiloxane beads (DeloxanÒ DAP