Photoaddition reactions of 1,2-diketones with silyl ketene acetals. Formation of β-hydroxy-γ-ketoesters

Article abstract of DOI:10.1021/jo800473x

(Chemical Equation Presented) Photochemical reactions taking place between 1,2-diketones and silyl ketene acetals and their excited state reaction mechanisms have been explored. Irradiation of benzene, acetone, or acetonitrile solutions containing 1,2-diketones and silyl ketene acetals is observed to promote formation of 1,4-dioxenes, resulting from [4 + 2]-cycloaddition, oxetanes, arising by Paterno-Buchi processes, and β-hydroxy-γ- ketoesters, generated by SET-promoted Claisen-type condensation. These competitive pathways leading from the excited states of the 1,2-diketones to these products are influenced by solvent polarity and the nature of the silyl ketene acetal and 1,2-diketone. The Claisen-type condensation process, following an SET desilylation pathway and predominating when the photoreactions are carried out in the polar solvent acetonitrile, represents an efficient method to prepare a variety of diversely substituted β-hydoxy-γ-ketoesters.

Full text of DOI:10.1021/jo800473x

Photoaddition Reactions of 1,2-Diketones with Silyl Ketene Acetals.
Formation of ꢀ-Hydroxy-γ-ketoesters
Dae Won Cho,† Hyang-Yeol Lee,† Sun Wha Oh,‡ Jung Hei Choi,† Hea Jung Park,†
Patrick S. Mariano,*,§ and Ung Chan Yoon*,†
Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National UniVersity,
Busan 609-735, Korea, Basic Science Research Institute, Pukyong National UniVersity,
Busan, 608-737, Korea, and Department of Chemistry and Chemical Biology, UniVersity of New Mexico,
Albuquerque, New Mexico 87131
ucyoon@pusan.ac.kr; mariano@unm.edu
ReceiVed March 3, 2008
Photochemical reactions taking place between 1,2-diketones and silyl ketene acetals and their excited
state reaction mechanisms have been explored. Irradiation of benzene, acetone, or acetonitrile solutions
containing 1,2-diketones and silyl ketene acetals is observed to promote formation of 1,4-dioxenes, resulting
from [4 + 2]-cycloaddition, oxetanes, arising by Paterno-Buchi processes, and ꢀ-hydroxy-γ-ketoesters,
generated by SET-promoted Claisen-type condensation. These competitive pathways leading from the
excited states of the 1,2-diketones to these products are influenced by solvent polarity and the nature of
the silyl ketene acetal and 1,2-diketone. The Claisen-type condensation process, following an SET
desilylation pathway and predominating when the photoreactions are carried out in the polar solvent
acetonitrile, represents an efficient method to prepare a variety of diversely substituted ꢀ-hydoxy-γ-ketoesters.
Introduction
lytic fragmentation processes such as deprotonation.2 Conse-
quently, cation radical desilylation serves as an efficient and
regioselective method to generate carbon-centered radical
intermediates in carbon-carbon bond forming processes
Mechanistic pathways involving sequential single electron
transfer (SET) desilylation are now well documented in pho-
toreactions of electron acceptors and R-trialkylsilyl-substituted
electron donors.1 Owing to its high rate, silophile-assisted
desilylation of R-trialkylsilyl cation radicals normally takes place
much more rapidly than other possible cation radical R-hetero-
(2) (a) Zhang, X. M.; Yeh, S. R.; Hong, S.; Freccero, M.; Albini, A.; Falvey,
D. F.; Mariano, P. S. J. Am. Chem. Soc. 1994, 116, 4211. (b) Su, Z.; Falvey,
D. F.; Yoon, U. C.; Oh, S. W.; Mariano, P. S. J. Am. Chem. Soc. 1998, 120,
10676. (c) Yoshida, J.; Murata, T.; Isoe, S. Tetrahedron Lett. 1986, 27, 3373.
(d) Yoshia, J.; Maekawa, T.; Murata, T.; Matsunaga, S.; Isoe, S. J. Am. Chem.
Soc. 1990, 112, 1962. (e) Oelgemoller, M.; Griesbeck, A. G. J. Photochem.
Photobiol. C: Photochem. ReV. 2002, 3, 109. (f) Dinnocenzo, J. P.; Farid, S.;
Goodman, J. L.; Gould, I. R.; Todd, W. R.; Mattes, S. L. J. Am. Chem. Soc.
1989, 111, 8973. (g) Todd, W. R.; Dinnocenzo, J. P.; Farid, S.; Goodman, J. L.;
Gould, I. R. J. Am. Chem. Soc. 1991, 113, 3601. (h) de Lijser, P. H. J.; Snelgrove,
D. W.; Dinnocenzo, J. P. J. Am. Chem. Soc. 2001, 123, 9698.
* To whom correspondence should be addressed. Telephone: +82-51-510-
2241. Fax: +82-51-516-7421.
† Pusan National University.
‡ Pukyong National University.
§ University of New Mexico.
(1) (a) Yoon, U. C.; Mariano, P. S. Acc. Chem. Res. 1992, 25, 233. (b) Yoon,
U. C.; Mariano, P. S. Acc. Chem. Res. 2001, 34, 523. (c) Yoon, U. C.; Mariano,
P. S. Bull. Korean Chem. Soc. 2006, 27, 1099.
10.1021/jo800473x CCC: $40.75
Published on Web 05/22/2008
2008 American Chemical Society
J. Org. Chem. 2008, 73, 4539–4547 4539

Cho et al.
SCHEME 1
SCHEME 2
(Scheme 1).1–7 Numerous examples of SET photochemical
reactions promoted in this manner are found in the excited
state chemistry of iminium salts,3 cyanoarenes,4 conjugated
enones,5 ortho-quinones,6 and phthalimides.7
In recent studies, we explored photochemical reactions of
aromatic carbonyl compounds and silyl ketene acetals8 and
showed that versatile C-C bond forming processes take
place.9–11 The results of this effort demonstrated that several
types of reaction pathways can be followed (Scheme 2). In these
processes, SET from silyl ketene acetal electron donors to
excited states of aromatic carbonyl acceptors, which generates
ion radical intermediates I, effectively competes with other
SCHEME 3
(3) (a) Brumfield, M. A.; Quillen, S. L.; Yoon, U. C.; Mariano, P. S. J. Am.
Chem. Soc. 1984, 106, 6855. (b) Ohga, K.; Yoon, U. C.; Mariano, P. S. J. Org.
Chem. 1984, 49, 213.
(4) Brumfield, M. A.; Yoon, U. C.; Hasegawa, E.; Mariano, P. S. J. Org.
Chem. 1988, 53, 5435.
(5) (a) Yoon, Y. C.; Kim, J. U.; Hasegawa, E.; Mariano, P. S. J. Am. Chem.
Soc. 1987, 109, 4421. (b) Hasegawa, E.; Wu, X.; Mariano, P. S.; Yoon, U. C.;
Kim, J. U. J. Am. Chem. Soc. 1988, 110, 8099.
(6) Yoon, U. C.; Kim, Y. C.; Choi, J. J.; Kim, D. U.; Mariano, P. S.; Cho,
I. S.; Jeon, Y. T. J. Org. Chem. 1992, 57, 1422.
(7) (a) Yoon, U. C.; Kim, H. J.; Mariano, P. S. Heterocycles 1989, 29, 1041.
(b) Yoon, U. C.; Cho, S. J.; Oh, J. H.; Lee, J. G.; Kang, K. T.; Mariano, P. S.
Bull. Korean Chem. Soc. 1991, 12, 241. (c) Yoon, U. C.; Oh, J. H.; Lee, S. J.;
Kim, D. U.; Lee, J. G.; Kang, K. T.; Mariano, P. S. Bull. Korean Chem. Soc.
1992, 13, 166. (d) Yoon, U. C.; Lee, S. J.; Lee, K. J.; Cho, S. J.; Lee, C. W.;
Mariano, P. S. Bull. Korean Chem. Soc. 1994, 15, 154. (e) Yoon, U. C.; Oh,
S. W.; Lee, C. W. Heterocycles. 1995, 41, 2665. (f) Yoon, U. C.; Kim, J. W.;
Ryu, J. Y.; Cho, S. J.; Oh, S. W.; Mariano, P. S. J. Photochem. Photobiol. A:
Chem. 1997, 106, 145. (g) Yoon, U. C.; Oh, S. W.; Lee, J. H.; Park, J. H.;
Kang, K. T.; Mariano, P. S. J. Org. Chem. 2001, 66, 939. (h) Takahashi, Y.;
Miyashi, T.; Yoon, U. C.; Oh, S. W.; Mancheno, M.; Su, Z.; Falvey, D. F.;
Mariano, P. S. J. Am. Chem. Soc. 1999, 121, 3926–3932. (i) Yoon, U. C.; Jin,
Y. X.; Oh, S. W.; Park, C. H.; Park, J. H.; Campana, C. F.; Cai, X.; Duesler,
E. N.; Mariano, P. S. J. Am. Chem. Soc. 2003, 125, 10664. (j) Yoon, U. C.;
Kwon, H. C.; Hyung, T. G.; Choi, K. H.; Oh, S. W.; Yang, S.; Zhao, Z.; Mariano,
P. S. J. Am. Chem. Soc. 2004, 126, 1110. (k) Yoon, U. C.; Jin, Y. X.; Oh, S. W.;
Cho, D. W.; Park, K. H.; Mariano, P. S. J. Photochem. Photobiol. A: Chem.
2002, 150, 77. (l) Wang, R.; Zhao, Z.; Mariano, P. S.; Choi, K. H.; Kim, S. H.;
Yoon, U. C. J. Photochem. Photobiol. A: Chem. 2005, 175, 232. (m) Sung,
N. K.; Cho, D. W.; Choi, J. H.; Choi, K, W.; Yoon, U. C.; Maeda, H.; Mariano,
P. S. J. Org. Chem. 2007, 72, 8831. (n) Cho, D. W.; Choi, J. H.; Oh, S. W.;
Quan, C.; Yoon, U. C.; Wang, R.; Yang, S.; Mariano, P. S. J. Am. Chem. Soc.
2008, 130, 2276.
decay processes. The ion radical pairs react further to form
radical pairs III or zwitterions IV which are then converted to
the respective ꢀ-hydroxyester V and oxetane VI products. In
competition, the excited aromatic carbonyl compound can couple
with the silyl ketene acetal in a classical Paterno-Buchi manner
to produce oxetane II.
When ground state and excited state redox properties and
solvent polarities are taken into account, photoreactions of
1,2-diketones12,13 with silyl ketene acetals are expected to follow
three major routes involving (1) SET induced or direct [4 +
2]-cycloaddition to generate dioxenes,12b,14 (2) classical
Paterno-Buchi [2 + 2]-cycloaddition to form oxetanes,15 and
(3) sequential SET desilylation to produce ꢀ-hydroxy-γ-ke-
(8) Yoon, U. C.; Kim, M. J.; Moon, J. J.; Oh, S. W.; Kim, H. J.; Mariano,
P. S. Bull. Korean Chem. Soc. 2002, 23, 1218.
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1992, 114, 10271. (b) Mikami, K.; Matsumoto, S.; Ishida, A.; Takamuku, S.;
Suenobu, T.; Fuduzumi, S. J. Am. Chem. Soc. 1995, 117, 11134. (c) Totten,
G. E.; Wenke, G.; Rhodes, Y. E. Synth. Commun. 1985, 15, 291. (d) Bhattacharya,
A.; DiMichele, L. M.; Dolling, U. H.; Grabowski, E. J. J.; Grenda, V. J. J. Org.
Chem. 1989, 54, 6118. (e) Odenkirk, W.; Whelan, J.; Bosnich, B. Tetrahedron
Lett. 1992, 33, 5729.
(12) (a) Burkoth, T. L.; Ullman, E. F. Tetrahedron Lett. 1970, 11, 145. (b)
Gream, G. E.; Mular, M.; Paice, J. C. Tetrahedron Lett. 1970, 11, 3479.
(13) (a) Maruyama, K.; Ono, K.; Osugi, J. Bull. Chem. Soc. Jpn. 1972, 45,
847.
(11) (a) Mizuno, K.; Takahashi, N.; Nishiyama, T.; Inoue, H. Tetrahedron
Lett. 1995, 41, 7463. (b) Rotzoll, S.; Ullah, E.; Go¨rls, H.; Fischer, C.; Langer,
P. Tetrahedron 2007, 63, 2647. (c) Hinkle, R.; Lian, Y.; Litvinas, N. D.; Jenkins,
A. T.; Burnette, D. C. Tetrahedron 2005, 61, 11679. (d) Maslak, V.; Matovic´,
R.; Saicˇic´, R. N. Tetrahedron 2004, 60, 8957.
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Rubin, M. B.; Neuwirth-Weiss, Z. Chem. Commun. 1968, 24, 1607.
4540 J. Org. Chem. Vol. 73, No. 12, 2008

Photoaddition Reactions of 1,2-Diketones
TABLE 1. Photoreactions of 1,2-Diketones 1-3 and Silyl Ketene Acetals 6-8a
reaction time
(h)
conversion
entry
reactant
solvent
(%)
product (% yield)b
9 (19), 10 (7), 11 (49)
9 (2), 10 (12), 11 (58), 12 (4)
9 (trace), 10 (7), 11 (77), 12 (7)
13a (6), 13b (5), 14a (28), 14b (28), 15 (3)
15 (42)
1
2
3
4
5
6
7
8
1 + 6
1 + 6
1 + 6
1 + 7
1 + 8
1 + 8
2 + 6
2 + 6
2 + 6
2 + 7
2 + 7
2 + 8
2 + 8
3 + 6
3 + 6
3 + 6
3 + 7
3 + 8
benzene
acetone
CH3CN
CH3CN
CH3CN
benzene
benzene
acetone
CH3CN
acetone
CH3CN
acetone
CH3CN
benzene
acetone
CH3CN
CH3CN
CH3CN
4
3.5
2
89
93
93
66
77
81
48
47
85
80
81
80
53
80
71
80
54
87
6
18
11
8.5
5
5.5
16
4
16
10
3
16 (18), 15 (42)
17 (30), 18 (trace), 19 (trace), 12 (trace)
17 (trace), 18 (6), 19 (81), 12 (3)
17 (trace), 18 (6), 19 (55), 12 (7)
20a (4), 20b (4), 21a (12), 21b (12), 22 (12), 23 (23)
20a (8), 20b (6), 21a (28), 21b (19), 22 (5)
22 (23), 23 (25)
9
10
11
12
13
14
15
16
17
18
22 (27)
24 (41), 25 (25), 12 (trace)
24 (trace), 25 (71), 12 (trace)
24 (trace), 25 (76), 12 (21)
26 (61), 27 (5)
5
4
9
14.5
28 (23), 27 (40), 29 (19)
a Concentrations of reactants, [1,2-diketone compound]/[silyl ketene acetal], are 8.9/17.9 mM. b Yields are based on consumed 1,2-diketones.
SCHEME 4
SCHEME 5
SCHEME 6
toesters or oxetanes8 (Scheme 3). In the effort described below,
we investigated photoinduced reactions of 1,2-diketones 1-5
with silyl ketene acetals 6-8 and observed that competing
excited state reaction pathways are followed that lead to the
generation of product distributions which are dependent on the
nature of 1,2-diketone electron acceptors, silyl ketene acetal
electron donors, and the polarity of the solvent.
Results and Discussion
Photochemical reactions were performed by irradiation with
uranium glass filtered light (λ > 330 nm) of benzene, acetone,
or acetonitrile solutions of the 1,2-diketones 1-5 (9 mM) and
the silyl ketene acetals 6 and 7 (18 mM) for time periods that
bring about 47-93% conversion of the 1,2-diketones. In each
case, the crude photoreaction mixtures were subjected to silica
gel chromatography to obtain pure products.
(15) (a) Arnold, D. R. In AdVances in Photochemistry; Noyes, W. A.,
Hammond, G. S., Pitts, J. N., Eds.; Interscience Publishers: New York, 1968;
Vol. 6. (b) Jones, G. In Organic Photochemistry; Padwa, A., Ed.; Marcel Dekker:
New York, 1981; Vol. 5, Chapter 1.
Photochemistry of 1,2-Diketones 1-3. The products/yields
arising from photoreactions of aromatic 1,2-diketones 1-3
with silyl ketene acetals 6 and 7 are displayed in Table 1 and
J. Org. Chem. Vol. 73, No. 12, 2008 4541

Cho et al.
SCHEME 7
Schemes 4–6. Irradiation of a benzene solution of acenaph-
thenequinone (1) and dimethyl-substituted silyl ketene acetal 6
results in the formation of a mixture of products composed of
the ꢀ-silyloxy- and ꢀ-hydroxy-γ-ketoester, 10 and 11, and
dioxene 9 in a ca. 3:1 ratio of 10 + 11:9 (Scheme 4 and Table
1, entry 1). When photoreaction of 1 with 6 is conducted in the
more polar solvents acetone or acetonitrile, ketoesters 10 and
11 are produced nearly exclusively along with minor amounts
of the dimer 12 (entries 2 and 3).
Photolysis of 1,2-diketone 1 and monomethyl silyl ketene
acetal 7 in acetonitrile leads to formation of the ketoesters 13
and 14 as mixtures of diastereomers, along with pinacol-type
dimer 156 (Table 1, entry 4). Interestingly, 15 is the sole product
generated when an acetonitrile solution of 1 and the unsubsti-
tuted silyl ketene acetal 8 is irradiated (Table 1, entry 5). In
contrast, photoreaction of a benzene solution of 1 and 8 forms
dioxene 16 and dimer 15 (Table 1, entry 6).
Irradiation of a benzene solution of phenanthrenequinone 2
with dimethyl silyl ketene acetal 6 brings about nearly exclusive
formation of the [4 + 2]-cycloadditon product16,17 17, albeit in
low yield (Scheme 5 and Table 1, entry 7). When the higher
polarity solvents acetone and acetonitrile are used for this
photoreaction, products arising via sequential SET desilylation
(i.e., ketoesters 18 and 19) are generated predominantly in high
yield (entries 8 and 9). Reactions of phenanthrenequinone 2 with
the monomethyl silyl ketene acetal 7 in acetone and acetonitrile
also yield the corresponding ketoesters 20 and 21 as mixtures
of diastereomers along with 9,10-dihydroxyphenanthrene 2216
and the acetone adduct 23 (only in acetone) as minor products
(entries 10 and 11). Solvent-assisted 1,2-addition takes place
in several photochemical reaction of 1,2-diketones.13 Finally,
22 and 23 are the only substances formed when solutions of 2
and the unsubstituted ketene acetal 8 in either acetone or
acetonitrile are irradiated (entries 12 and 13).
An analysis of the results presented thus far shows that the
classical Paterno-Buchi-type [2 + 2]-cycloaddition reaction to
form oxetanes does not take place in the photoreactions of
diketones 1 and 2. In addition, the relative efficiencies of
processes promoted by desilylation versus [4 + 2]-cycloaddition
of the ion radical pairs generated by SET are highly dependent
on the polarity of the solvent. Last, the yields of the ꢀ-hydroxy
and ꢀ-silyloxy ketoesters formed by SET desilylation pathways
vary depending on the degree of methyl substitution in the silyl
ketene acetals.9a,18 The observations summarized above can be
rationalized on the basis of solvent and substituent effects on
the nature and reactivity of ion radical pairs that serve as
intermediates in these reactions. For example, radical ion pairs
generated by photoinduced SET in less polar benzene do not
readily undergo desilylation. In addition, close association
required for stabilization of the ion radical components in this
nonpolar solvent (i.e., formation of contact ion pairs) likely
enhances [4 + 2]-cyloaddition. Enhanced solvent polarity leads
to stabilization/separation of the ion radical species, thus
facilitating silophile-assisted desilylation to form radical pairs
that couple to produce ketoester products.
diketones. Previous studies have shown that irradiation of 3
promotes homolytic cleavage of the central carbon-carbon bond
to generate benzoyl radicals, which ultimately react to form
benzoic acid, benzaldehyde, and benzoin.13,19 Indeed, irradiation
of a benzene solution of benzil in the presence of the dimethyl-
substituted silyl ketene acetal 6 gives rise to production of a
ca. 1.6:1 mixture of 1,4-dioxene 24 and the ꢀ-ketoester 2520
(Scheme 6 and Table 1, entry 14), the latter of which likely
arises by a pathway involving coupling between radicals that
are generated by R-cleavage of the 1,2-diketone and sequential
SET desilylation.
In the photoreactions of 3 with ketene acetal 6 in acetone
and acetonitrile (Table 1, entries 15 and 16), formation of 25
prevails over other processes. Likewise, irradiation of an
acetonitrile solution of 3 and monomethyl-substituted ketene
acetal 7 (entry 17) gives rise to 2621 and benzoic acid 27,
exclusively. Finally, photoreaction of 3 with the unsubstituted
acetal 8 in acetonitrile leads to production of 27, 28,22 and 2923
(entry 18). The high yield (40%) of benzoic acid formed in this
process is caused by a reduction in the rate of SET from the
less electron-rich alkene 8 in contrast to homolytic cleavage of
the excited state of benzil (Scheme 7).
Photochemistry of 1,2-Diketones 4 and 5. The products/
yields arising from photoreactions of aromatic 1,2-diketones 4
and 5 with silyl ketene acetals 6-8 are displayed in Table 2
and Schemes 8 and 9. Photoreactions of 2,3-butanedione 4 with
silyl ketene acetals 6-8 give rise to different types of products
as compared with those produced from diketones 1-3. For
example, regardless of the solvent used, photoreaction of 4 with
dimethyl ketene acetal 6 leads to predominant formation of
ketoesters 30 and 31, arising by way of sequential SET
desilylation pathways, along with the dimer 12 as a minor
product (Scheme 8 and Table 2, entries 1-3). However,
irradiation of an acetonitrile solution of 4 containing acetal 7
leads to generation of not only the ketoesters 32 and 33 but
also the Paterno-Buchi-type [2 + 2]-adduct 34 (entry 4).
The photochemical behavior of benzil 3 in the presence of
silyl ketene acetals differs markedly from that of other 1,2-
(19) (a) Bunbury, D. L.; Wang, C. T. Can. J. Chem. 1968, 46, 1473. (b)
Inoue, H.; Takido, S.; Somemiya, T.; Nomura, Y. Tetrahedron Lett. 1973, 14,
2755.
(16) Moriconi, E.; Wallenberger, F. T.; O’Connor, W. F. J. Org. Chem. 1959,
24, 86.
(20) Cantrell, T. S.; Allen, A. C. J. Org. Chem. 1989, 54, 135.
(21) Royals, E. E.; Turpin, D. G. J. Am. Chem. Soc. 1954, 76, 5452.
(22) Sakurai, H.; Shirahata, A.; Hosomi, A. Tetrahedron Lett. 1980, 21, 1967.
(23) Shinkai, S.; Tsuji, H.; Hara, Y.; Manabe, O. Bull. Chem. Soc. Jpn. 1981,
54, 631.
(17) Lichtenthaler, F. W.; Weimer, T.; Immel, S. Tetrahedron: Asymmetry
2004, 15, 2703.
(18) Oh, S. W.; Kim, J. Y.; Cho, D. W.; Choi, J. H.; Yoon, U. C. Bull.
Korean Chem. Soc. 2007, 28, 629.
4542 J. Org. Chem. Vol. 73, No. 12, 2008

Photoaddition Reactions of 1,2-Diketones
TABLE 2. Photoreactions of 1,2-Diketone Compounds 4 and 5 and Silyl Ketene Acetals 6-8a
reaction time
(h)
conversion
(%)
entry
reactant
solvent
product (% yield)b
30 (52), 31 (15), 12 (trace)
30 (53), 31 (15), 12 (7)
30 (54), 31 (17), 12 (7)
32 (46), 33 (4), 34 (12)
35a (37), 35b (19)
36 (12), 37 (44), 38a (19), 38b (6), 39 (8)
36 (23), 37 (53), 12 (9)
36 (22), 37 (51), 12 (9)
1
2
3
4
5
6
7
8
9
10
4 + 6
4 + 6
4 + 6
4 + 7
4 + 8
5 + 6
5 + 6
5 + 6
5 + 7
5 + 8
benzene
acetone
CH3CN
CH3CN
CH3CN
benzene
acetone
CH3CN
CH3CN
CH3CN
2.5
2
2
2.5
2.5
2
2
1.5
2
72
70
73
73
73
88
86
79
80
53
40a (14), 40b (9), 41a (30), 41b (18), 42 (10)
43 (33), 44 (12)
5
a Concentrations of reactants, [1,2-diketone compound]/[silyl ketene acetal], are 8.9/17.9 mM. b Yields are based on consumed 1,2-diketones.
SCHEME 8
SCHEME 9
SCHEME 10
Photoreaction of 4 with the unsubstituted acetal 8 in acetonitrile
produces the Paterno-Buchi-type oxetane 35 exclusively
(entry 5).
Observations made in studies of the photoreactions of the
aryl-alkyl-substituted diketone, 1-phenyl-1,2-propanedione 5,
with silyl ketene acetals 6-8 show that sequential SET
desilylation pathways take place highly efficiently and regiose-
lectively. Accordingly, irradiation of 5 in a benzene solution
containing 6 leads to the formation of aryl carbonyl function-
alized adducts, 36 and 37, and alkyl carbonyl functionalized
adducts, 38 and 39 (Scheme 9 and Table 2, entry 6). Photore-
actions of 5 with 6 in acetone and acetonitrile as well as that of
5 with 7 in acetonitrile proceed in a similar manner, giving only
the aryl carbonyl functionalized products along with dimers 1224
or 42 (entries 7-9). Also, the aryl carbonyl functionalized
(24) (a) Suzuki, Y.; Katoh, H.; Ishii, Y.; Hidai, M. J. Mol. Catal. A 1995,
95, 129. (b) Kondo, H.; Kageyama, A.; Yamaguchi, Y.; Haga, M. A.; Kirchner,
K.; Nagashima, H. Bull. Chem. Soc. Jpn. 2001, 74, 1927.
J. Org. Chem. Vol. 73, No. 12, 2008 4543

Cho et al.
gave a residue which was subjected to silica gel column chroma-
tography (ethyl acetate:n-hexane ) 1:5) giving 86 mg (19%) of 9,
32 mg (7%) of 10, and 177 mg (49%) of 11.
Acetone: A solution of acenaphthenequinone 1 (260 mg, 1.43
mmol) and silyl ketene acetal 6 (500 mg, 2.87 mmol) in 160 mL
of acetone was irradiated for 3.5 h (ca. 93% conversion of 1).
Workup and silica gel column chromatography (ethyl acetate:n-
hexane ) 1:5) gave 9 mg (2%) of 9, 57 mg (12%) of 10, 219 mg
(58%) of 11, and 5 mg (4%) of 12.24
adduct 43 is the major product formed in reaction of 5 with
ketene acetal 8 in acetonitrile (entry 10).
Several conclusions can be drawn from the results shown in
Table 2. First, the ratios of products arising by SET desilylation
versus Paterno-Buchi pathways are largely dependent on the
nature of the silyl ketene acetal donor. Similar trends have been
noted in previous reports describing photoreaction of silyl enol
ethers with aromatic carbonyl compounds.18 Second, 1,4-
dioxene products resulting by [4 + 2]-cycloadditions are not
produced in photoreactions of the dimethyl- or methylphenyl-
substituted diketones 4 and 5 with silyl ketene acetals 6-8.
Third, the exclusive production of ꢀ-hydroxy and ꢀ-silyloxy
ketoesters and oxetanes, produced by sequential SET desilylation
routes in reactions of 5 with 6 and 7, clearly demonstrates that
alkyl-aryl substituents are the major factors responsible for
governing the excited state reaction pathways. Finally, products
formed in photoreactions of 4 and 5 with the dimethyl-
substituted ketene acetal 6 do not reflect significant effects of
solvent polarity.
Acetonitrile: A solution of acenaphthenequinone 1 (260 mg, 1.43
mmol) and silyl ketene acetal 6 (500 mg, 2.87 mmol) in 160 mL
of acetonitrile was irradiated for 2 h (ca. 93% conversion of 1).
Workup and silica gel column chromatography (ethyl acetate:n-
hexane ) 1:5) gave trace of 9, 33 mg (7%) of 10, 291 mg (77%)
of 11, and 9 mg (7%) of 12.
9: 1H NMR (CDCl3) δ 0.32 (s, 9H), 1.41 and 1.54 (s, 3H), 3.39
(s, 3H), 7.38-7.46 (m, 4H), 7.58-7.64 (m, 2H); 13C NMR (CDCl3)
δ 1.9, 21.6, 22.3, 48.7, 79.9, 111.7, 117.8, 119.5, 125.9, 126.4,
127.2, 127.3, 121.6, 127.1, 130.9, 131.2, 132.7, 136.2; HRMS is
not measured due to the decomposition.
1
10: H NMR (CDCl3) δ -0.22 (s, 9H), 1.42 and 1.47 (s, 3H),
On the basis of an analysis of the photoproduct distributions
presented above and results arising from our recent studies of
related reactions of monoketones,8,18 it is possible to propose a
plausible general mechanistic pathway for photochemical reac-
tions of 1,2-diketones 1-5 with the silyl ketene acetals 6 and
7 (Scheme 10). SET and classical photochemical [2 + 2]-cy-
cloaddtion compete for deactivation of the diketone excited
states by the silyl ketene acetal. These respective processes
generate ion radical pairs VII and oxetanes VIII. Desilylation
of VII produces radical pairs XI, which undergo coupling to
form ketoester products XIV. Alternatively, radical and/or ionic
coupling of ion radical pairs VII produces biradicals X or
zwitterionic intermediates IX, which are the precursors of the
respective 1,4-dioxenes XIII and oxetanes XII, the latter of
which should easily convert to ketoesters XIV. The observations
made in photoreactions of acyclic 1,2-diketones 4 and 5 that
1,4-dioxene products by [4 + 2]-cycloadditions are not produced
and the product formations are not significantly affected by
solvent polarity are understandable considering predominant
existence of acyclic 1,2-diketone radical anions in the solutions
with more favorable anti-conformations XV which do not lead
to formation of [4 + 2]-cycloaddition products.
3.13 (s, 3H), 7.61-7.76 (m, 3H), 7.86-7.90 (m, 2H), 8.05-8.09
(m, 1H); 13C NMR (CDCl3) δ 1.0, 20.4, 20.9, 51.1, 51.7, 83.3,
120.6, 122.2, 125.4, 128.1, 128.2, 130.9, 130.3, 132.6, 139.1, 140.7,
175.0, 203.8; IR (KBr) 1730 (CdO); HRMS (EI) m/z 356.1441
(M+, C20H24O4Si requires 356.1444).
1
11: mp 93-95 °C; H NMR (CDCl3) δ 0.89 and 1.51 (s, 3H),
3.81 (s, 3H), 5.49 (s, 1H), 7.62-7.71 (m, 3H), 7.84-7.91 (m, 2H),
8.05-8.09 (m, 1H); 13C NMR (CDCl3) δ 20.2, 21.0, 47.3, 52.4,
82.6, 121.4, 121.5, 125.6, 128.1, 128.4, 130.5, 130.5, 131.4, 137.4,
142.2, 177.3, 204.4; IR (KBr) 3600-3200 (br, OH), 1730 and 1710
(CdO); HRMS (EI) m/z 284.1037 (M+, C17H16O4 requires 284.1049).
1
12: known compound, H NMR (CDCl3) δ 1.22 (s, 12H), 3.65
(s, 6H); 13C NMR (CDCl3) δ 21.9, 47.5, 51.7, 176.5.
Irradiation of Acenaphthenequinone (1) and 1-(Methoxy)-
1-(trimethylsilyloxy)propene (7). A solution of acenaphthene-
quinone 1 (260 mg, 1.43 mmol) and silyl ketene acetal 7 (460 mg,
2.87 mmol) in 160 mL of acetonitrile was irradiated for 6 h (ca.
66% conversion of 1). Concentration of photolysate gave a residue
which was subjected to silica gel column chromatography (ethyl
acetate:n-hexane ) 1:5), giving diastereomeric adducts 13 (13a,
19 mg, 6% and 13b, 16 mg, 5%), diastereomeric photoadducts 14
(14a, 71 mg, 28% and 14b, 71 mg, 28%), and 5 mg (3%) of 15.16
1
13a: H NMR (CDCl3) δ -0.23 (s, 9H), 1.58 (d, 3H, J ) 7.1
Hz), 3.07 (s, 3H), 3.45 (q, 1H, J ) 7.1 Hz), 7.62-7.77 (m, 3H),
7.87-7.99 (m, 2H), 8.07-8.11 (m, 1H); 13C NMR (CDCl3) δ 1.2,
11.0, 47.9, 51.1, 81.1, 121.3, 121.9, 125.7, 128.1, 128.3, 131.4,
130.5, 131.9, 138.4, 141.3, 172.4, 203.9; IR (KBr) 1740 (CdO);
HRMS (EI) m/z 342.1291 (M+, C19H22O4Si requires 342.1287).
1
13b: H NMR (CDCl3) δ 0.26 (s, 9H), 0.90 (d, 3H, J ) 7.2
Hz), 3.44 (q, 1H, J ) 7.2 Hz), 3.59 (s, 3H), 7.65-7.77 (m, 3H),
7.89-7.99 (m, 2H), 8.11-8.15 (m, 1H); 13C NMR (CDCl3) δ 1.2,
12.2, 48.0, 51.4, 81.7, 121.4, 123.2, 125.5, 128.0, 128.6, 121.8,
130.5, 131.5, 137.9, 141.9, 174.2, 203.8; IR (KBr) 1730 (CdO);
HRMS (EI) m/z 342.1296 (M+, C19H22O4Si requires 342.1287).
14: (1:1 mixture of two diastereomers based on 1H NMR
Importantly, the relative importance of these excited state
reaction pathways is controlled by nature of the diketone, ketene
acetal, and solvent. The results of this study demonstrate that
photoinduced SET desilylation pathways predominate in pho-
tochemical reactions of the diketones when electron-rich silyl
ketene acetals and highly polar solvents are employed. More-
over, the process can be used as an efficient methodology for
the generation of highly substituted Claisen condensation type
products.
1
integration) H NMR (CDCl3) of 14a δ 1.03 (d, 3H, J ) 7.1 Hz),
3.20 (q, 1H, J ) 7.2 Hz), 3.80 (s, 3H), 7.64-7.78 (m, 3H),
7.90-8.00 (m, 2H), 8.12-8.16 (m, 1H); 13C NMR (CDCl3) δ 12.3,
44.9, 52.2, 80.3, 122.0, 122.2, 125.7, 128.2, 128.7, 132.2, 130.7,
131.2, 137.2, 142.2, 174.4, 203.7; IR (KBr) 3600-3200 (br, OH),
1730 (CdO); HRMS (EI) m/z 270.0889 (M+, C16H14O4 requires
1
270.0892). H NMR (CDCl3) of 14b δ 1.10 (d, 3H, J ) 7.3 Hz),
Experimental Section
3.28 (q, 1H, J ) 7.2 Hz), 3.64 (s, 3H), 7.64-7.78 (m, 3H),
7.90-8.00 (m, 2H), 8.11-8.15 (m, 1H); 13C NMR (CDCl3) δ 11.2,
45.3, 52.1, 80.2, 122.6, 122.0, 125.7, 128.3, 128.7, 131.8, 130.6,
131.2, 138.1, 142.0, 175.5, 204.1; IR (KBr) 3600-3200 (br, OH),
1730 (CdO); HRMS (EI) m/z 270.0889 (M+, C16H14O4 requires
270.0892).
Irradiation of Acenaphthenequinone (1) and 1-(Methoxy)-
2-methyl-1-(trimethylsilyloxy)propene (6). Benzene: A solution
of acenaphthenequinone 1 (260 mg, 1.43 mmol) and silyl ketene
acetal 6 (500 mg, 2.87 mmol) in 160 mL of benzene was irradiated
for 4 h (ca. 89% conversion of 1). Concentration of photolysate
4544 J. Org. Chem. Vol. 73, No. 12, 2008

Photoaddition Reactions of 1,2-Diketones
1
15: known compound, H NMR (DMSO-d6) δ 7.05-7.20 (m,
Acetone: A solution of phenanthrenequinone 2 (298 mg, 1.43
mmol) and silyl ketene acetal 7 (460 mg, 2.87 mmol) in 160 mL
of acetone was irradiated for 16 h (ca. 80% conversion of 2).
Workup and silica gel column chromatography (ethyl acetate:n-
hexane ) 1:5) gave diastereomeric adducts 20 (20a, 17 mg, 4%
and 20b, 17 mg, 4%) and 21 (21a, 41 mg, 28% and 21b, 41 mg,
19%), 29 mg (12%) of 22, and 70 mg (23%) of 23.
2H), 7.40-7.55 (m, 2H), 7.65-7.80 (m, 4H), 7.90-8.00 (m, 1H),
8.15-8.25 (m, 2H, aromatic); 13C NMR (DMSO-d6) δ 82.8, 121.6,
123.6, 126.2, 128.8, 130.8, 132.1, 132.2, 137.9, 142.3, 203.3; IR
(KBr) 3400 (OH).
Irradiation of Acenaphthenequinone (1) and 1-(Methoxy)-
1-(trimethylsilyloxy)ethene (8). Benzene: A solution of acenaph-
thenequinone 1 (260 mg, 1.43 mmol) and silyl ketene acetal 8 (420
mg, 2.87 mmol) in 160 mL of benzene was irradiated for 11 h (ca.
81% conversion of 1). Concentration of photolysate gave a residue
which was subjected to silica gel column chromatography (ethyl
acetate:n-hexane ) 1:5) giving 66 mg (18%) of 16 and 176 mg
(42%) of 15.
1
20: H NMR (CDCl3) of 20a δ 0.14 (s, 9H), 1.02 (d, 3H, J )
7.0 Hz), 2.87 (q, 1H, J ) 7.0 Hz), 3.28 (s, 3H), 7.35-7.45 (m,
3H), 7.56-7.70 (m, 2H), 7.82-7.94 (m, 3H); 13C NMR (CDCl3)
δ 1.9, 11.9, 51.0, 51.1, 84.0, 123.0, 124.0, 127.0, 127.3, 128.4,
128.5, 134.5, 135.0, 130.0, 130.2, 137.2, 140.1, 172.0, 201.2; IR
(KBr) 1740 and 1710 (CdO); HRMS (EI) m/z 368.1435 (M+,
1
Acetonitrile: A solution of acenaphthenequinone 1 (260 mg, 1.43
mmol) and silyl ketene acetal 8 (420 mg, 2.87 mmol) in 160 mL
of acetonitrile was irradiated for 18 h (ca. 77% conversion of 1).
Workup and silica gel column chromatography (ethyl acetate:n-
hexane ) 1:5) gave 99 mg (49%) of 15.
C21H24O4Si requires 368.1444). H NMR (CDCl3) of 20b δ 0.14
(s, 9H), 1.00 (d, 3H, J ) 7.0 Hz), 2.90 (q, 1H, J ) 7.0 Hz), 3.49
(s, 3H), 7.36-7.47 (m, 3H), 7.60-7.68 (m, 2H), 7.78-7.90 (m,
3H); 13C NMR (CDCl3) δ 2.0, 11.1, 50.9, 51.2, 84.7, 122.7, 124.3,
127.5, 127.7, 128.3, 128.5, 134.1, 134.5, 130.3, 131.1, 136.3, 139.7,
172.0, 202.4; IR (KBr) 1740 and 1710 (CdO); HRMS (EI) m/z
368.1443 (M+, C21H24O4Si requires 368.1444).
1
16: H NMR (CDCl3) δ 0.32 (s, 9H), 3.45 (s, 3H), 3.94 and
4.30 (two d, 1H, J ) 10.7 Hz), 7.42-7.59 (m, 4H), 7.63-7.67 (m,
2H); 13C NMR (CDCl3) δ 1.2, 29.7, 48.6, 70.2, 118.5, 119.6, 126.4,
126.5, 127.2, 108.2, 127.1, 127.4, 128.7; HRMS (EI) m/z 328.1139
(M+, C18H20O4Si requires 328.1131).
1
21: H NMR (CDCl3) of 21a (mp 95-97 °C) δ 1.10 (d, 3H, J
) 7.0 Hz), 2.86 (q, 1H, J ) 7.0 Hz), 3.56 (s, 3H), 4.21 (s, 1H),
7.37-7.47 (m, 3H), 7.64-7.92 (m, 5H); 13C NMR (CDCl3) δ 11.2,
49.7, 51.5, 80.4, 123.0, 124.5, 127.5, 127.8, 128.4, 128.6, 128.7,
134.8, 129.3, 129.8, 136.9, 137.4, 172.6, 203.1; IR (KBr) 3600-3200
(br, OH), 1730 and 1700 (CdO); HRMS (EI) m/z 296.1053 (M+,
C18H16O4 requires 296.1049). 1H NMR (CDCl3) of 21b (mp 83-85
°C) δ 1.00 (d, 3H, J ) 7.1 Hz), 2.89 (q, 1H, J ) 7.1 Hz), 3.40 (s,
3H), 4.39 (s, 1H), 7.34-7.48 (m, 3H), 7.63-7.97 (m, 5H); 13C
NMR (CDCl3) δ 11.9, 50.7, 51.5, 79.7, 123.3, 124.1, 126.8, 127.3,
128.6, 128.8, 129.5, 135.2, 129.4, 129.9, 137.7, 138.0, 172.4, 202.0;
IR (KBr) 3600-3200 (br, OH), 1730 and 1700 (CdO); HRMS
(EI) m/z 296.1046 (M+, C18H16O4 requires 296.1049).
Irradiation of Phenanthrenequinone (2) and Silyl Ketene
Acetal (6). Benzene: A solution of phenanthrenequinone 2 (298
mg, 1.43 mmol) and silyl ketene acetal 6 (500 mg, 2.87 mmol) in
160 mL of benzene was irradiated for 8.5 h (ca. 48% conversion
of 2). Concentration of photolysate gave a residue which was
subjected to silica gel column chromatography (ethyl acetate:n-
hexane ) 1:5) giving 79 mg (30%) of 17, trace of 18, 12, and 19.
Acetone: A solution of phenanthrenequinone 2 (298 mg, 1.43
mmol) and silyl ketene acetal 6 (500 mg, 2.87 mmol) in 160 mL
of acetone was irradiated for 5 h (ca. 47% conversion of 2). Workup
and silica gel column chromatography (ethyl acetate:n-hexane )
1:5) gave trace of 17, 15 mg (6%) of 18, 169 mg (81%) of 19, and
2 mg (3%) of 12.
1
22: known compound, mp 245-250 °C; H NMR (CDCl3) δ
7.78-7.84 (m, 8H), 8.26-8.36 (m, 8H); 13C NMR (CDCl3) δ 127.2,
134.1, 183.1; IR (KBr) 3600-3200 (br, OH), 1710 (CdO); HRMS
(EI) m/z 210.0673 (M+, C14H10O2 requires 210.0681).
Acetonitrile: A solution of phenanthrenequinone 2 (298 mg, 1.43
mmol) and silyl ketene acetal 6 (500 mg, 2.87 mmol) in 160 mL
of acetonitrile was irradiated for 5.5 h (ca. 85% conversion of 2).
Workup and silica gel column chromatography (ethyl acetate:n-
hexane ) 1:5) gave trace of 17, 28 mg (6%) of 18, 207 mg (55%)
of 19, and 9 mg (7%) of 12.
23: 1H NMR (CDCl3) δ 2.09 (s, 3H), 2.80 and 3.00 (two d, 2H,
J ) 14.5 Hz), 7.38-7.48 (m, 3H), 7.69-7.96 (m, 5H); 13C NMR
(CDCl3) δ 32.1, 55.6, 78.3, 123.1, 124.4, 125.9, 127.6, 128.6, 128.7,
129.3, 134.8, 128.9, 139.4, 136.7, 139.4, 202.9, 206.0; IR (KBr)
3600-3200 (br, OH), 1710 (CdO); HRMS (EI) m/z 266.0933 (M+,
C17H14O3 requires 266.0943).
1
17: mp 115-117 °C; H NMR (CDCl3) δ 0.40 (s, 9H), 1.41
Irradiation of Phenanthrenequinone (2) and Silyl Ketene
Acetal (8). Acetonitrile: A solution of phenanthrenequinone 2 (298
mg, 1.43 mmol) and silyl ketene acetal 8 (420 mg, 2.87 mmol) in
160 mL of acetonitrile was irradiated for 10 h (ca. 53% conversion
of 2). Concentration of photolysate gave a residue which was
subjected to silica gel column chromatography (ethyl acetate:n-
hexane ) 1:5) giving 43 mg (27%) of 22.
Acetone: A solution of phenanthrenequinone 2 (298 mg, 1.43
mmol) and silyl ketene acetal 8 (420 mg, 2.87 mmol) in 160 mL
of acetone was irradiated for 16 h (ca. 80% conversion of 2).
Workup and silica gel column chromatography (ethyl acetate:n-
hexane ) 1:5) gave 37 mg (4%) of 22 50 mg (25%) of 23.
Irradiation of Benzil (3) and Silyl Ketene Acetal (6). Benzene:
A solution of benzil 3 (300 mg, 1.43 mmol) and silyl ketene acetal
6 (500 mg, 2.87 mmol) in 160 mL of benzene was irradiated for
3 h (ca. 80% conversion of 3). Concentration of photolysate gave
a residue which was subjected to silica gel column chromatography
(ethyl acetate:n-hexane ) 1:10) giving 180 mg (41%) of 24, 59
mg (25%) of 25,20 and trace of 12.
and 1.65 (s, 3H), 3.37 (s, 3H), 7.57-7.66 (m, 4H), 8.15-8.29 (m,
2H), 8.61-8.67 (m, 2H); 13C NMR (CDCl3) δ 2.0, 21.9, 22.3, 48.8,
78.0, 110.5, 119.9, 121.4, 122.3, 122.7, 124.6, 125.2, 126.6, 126.8,
125.8, 126.5, 126.7, 127.1, 129.9, 132.2; HRMS (EI) m/z 382.1605
(M+, C22H26O4Si requires 382.1600).
1
18: H NMR (CDCl3) δ 0.10 (s, 9H), 1.03 and 1.13 (s, 3H),
3.24 (s, 3H), 7.36-7.40 (m, 3H), 7.60-7.68 (m, 2H), 7.84-7.89
(m, 3H); 13C NMR (CDCl3) δ 1.8, 20.8, 21.9, 51.3, 53.3, 86.2,
122.6, 123.5, 127.3, 127.8, 128.4, 128.6, 129.0, 134.3, 131.6, 131.7,
137.6, 138.8, 174.4, 201.9; IR (KBr) 1730 and 1700 (CdO); HRMS
(EI) m/z 382.1593 (M+, C22H26O4Si requires 382.1600).
1
19: mp 90-92 °C; H NMR (CDCl3) δ 0.96 and 1.20 (s, 3H),
3.39 (s, 3H), 4.47 (s, 1H), 7.37-7.44 (m, 3H), 7.67-7.91 (m, 5H);
13C NMR (CDCl3) δ 20.5, 21.5, 51.6, 52.8, 81.4, 122.7, 123.5,
127.0, 128.0, 128.4, 128.7, 128.9, 135.0, 130.3, 131.2, 136.1, 138.2,
174.5, 202.8; IR (KBr) 3600-3200 (br, OH), 1730 and 1680
(CdO); HRMS (EI) m/z 310.1207 (M+, C19H18O4 requires 310.1205).
Irradiation of Phenanthrenequinone (2) and Silyl Ketene
Acetal (7). Acetonitrile: A solution of phenanthrenequinone 2 (298
mg, 1.43 mmol) and silyl ketene acetal 7 (460 mg, 2.87 mmol) in
160 mL of acetonitrile was irradiated for 4 h (ca. 81% conversion
of 2). Concentration of photolysate gave a residue which was
subjected to silica gel column chromatography (ethyl acetate:n-
hexane ) 1:5) giving diastereomeric adducts 20 (20a, 34 mg, 8%
and 20b, 26 mg, 6%), diastereomeric photoadducts 21 (21a, 96
mg, 28% and 21b, 65 mg, 19%), and 12 mg (5%) of 22.17
Acetone: A solution of benzil 3 (300 mg, 1.43 mmol) and silyl
ketene acetal 6 (500 mg, 2.87 mmol) in 160 mL of acetone was
irradiated for 5 h (ca. 71% conversion of 3). Workup and silica gel
column chromatography (ethyl acetate:n-hexane ) 1:10) gave trace
of 24, 148 mg (71%) of 25, and trace of 12.
Acetonitrile: A solution of benzil 3 (300 mg, 1.43 mmol) and
silyl ketene acetal 6 (500 mg, 2.87 mmol) in 160 mL of acetonitrile
J. Org. Chem. Vol. 73, No. 12, 2008 4545

Cho et al.
was irradiated for 4 h (ca. 80% conversion of 3). Workup and silica
gel column chromatography (ethyl acetate:n-hexane ) 1:10) gave
trace of 24, 179 mg (76%) of 25, and 92 mg (21%) of 12.
34: 1H NMR (CDCl3) δ 0.17 (s, 9H), 1.33 (d, 3H, J ) 7.3 Hz),
1.47 (d, 3H), 2.26 (s, 3H), 3.31 (s, 3H), 4.81 (q, 1H, J ) 6.4 Hz);
13C NMR (CDCl3) δ 1.4, 16.8, 19.1, 27.0, 51.3, 84.1, 96.5, 102.1,
211.2; IR (KBr) 1750 (CdO); HRMS (EI) m/z 246.1293 (M+,
C11H22O4Si requires 246.1287).
1
24: H NMR (CDCl3) δ 0.26 (s, 9H), 1.41 and 1.49 (s, 3H),
3.53 (s, 3H), 7.16-7.27 (m, 10H); 13C NMR (CDCl3) δ 1.9, 21.2,
22.0, 48.7, 77.0, 110.4, 127.7, 128.1, 128.3, 128.4, 129.0, 129.8,
130.9, 133.5, 135.0, 135.3; HRMS (EI) m/z 384.1749 (M+,
C22H28O4Si requires 384.1757).
Irradiation of 2,3-Butanedione (4) and Silyl Ketene Acetal
(8). A solution of 2,3-butanedione 4 (123 mg, 1.43 mmol) and silyl
ketene acetal 8 (420 mg, 2.87 mmol) in 160 mL of acetonitrile
was irradiated for 2.5 h (ca. 73% conversion of 4). Concentration
of photolysate gave a residue which was subjected to silica gel
column chromatography (ethyl acetate:n-hexane ) 1:15) giving
diastereomeric photoadducts 35 (35a, 83 mg, 37% and 35b, 43 mg,
19%).
Irradiation of Benzil (3) and Silyl Ketene Acetal (7). A solution
of benzil 3 (300 mg, 1.43 mmol) and silyl ketene acetal 7 (460
mg, 2.87 mmol) in 160 mL of benzene was irradiated for 9 h (ca.
54% conversion of 3). Concentration of photolysate gave a residue
which was subjected to silica gel column chromatography (ethyl
acetate:n-hexane ) 1:10) giving 90 mg (61%) of 2621 and 5 mg
(5%) of 27.
35: (2:1 mixture of two diastereomers based on 1H NMR
1
integration) H NMR of major diastereomer 35a (CDCl3) δ 0.16
Irradiation of Benzil (3) and Silyl Ketene Acetal (8). A solution
of benzil 3 (300 mg, 1.43 mmol) and silyl ketene acetal 8 (420
mg, 2.87 mmol) in 160 mL of benzene was irradiated for 14.5 h
(ca. 87% conversion of 3). Concentration of photolysate gave a
residue which was subjected to silica gel column chromatography
(ethyl acetate:n-hexane ) 1:10) giving 51 mg (23%) of 28,22 61
mg (40%) of 27, and 34 mg (19%) of 29.23
(s, 9H), 1.50 (s, 3H), 2.28 (s, 3H), 3.29 (s, 3H), 4.51 (d, 1H, J )
6.8 Hz), 4.60 (q, 1H, J ) 6.8 Hz); 13C NMR (CDCl3) δ 0.7, 18.5,
26.2, 50.8, 79.7, 99.9, 100.5, 209.5; HRMS (EI) m/z 232.1143 (M+,
1
C10H20O4Si requires 232.1131). H NMR of minor diastereomer
35b (CDCl3) δ 0.21 (s, 9H), 1.44 (s, 3H), 2.31 (s, 3H), 3.21 (s,
3H), 4.52 (d, 1H, J ) 7.0 Hz), 4.65 (q, 1H, J ) 7.0 Hz); 13C NMR
(CDCl3) δ 1.0, 19.2, 26.6, 50.4, 79.0, 99.0, 99.8, 210.2; HRMS
(EI) m/z 232.1143 (M+, C10H20O4Si requires 232.1131).
Irradiation of 1-Phenyl-1,2-propanedione (5) and Silyl Ketene
Acetal (6). Benzene: A solution of 1-phenyl-1,2-propanedione 5
(232 mg, 1.43 mmol) and silyl ketene acetal 6 (500 mg, 2.87 mmol)
in 160 mL of benzene was irradiated for 2 h (ca. 88% conversion
of 5). Concentration of photolysate gave a residue which was
subjected to silica gel column chromatography (ethyl acetate:n-
hexane ) 1:15) giving 49 mg (12%) of 36, 138 mg (44%) of 37,
diastereomeric photoadducts 38 (38a, 77 mg, 19% and 38b, 24 mg,
6%), and 24 mg (8%) of 39.
1
29: known compound, H NMR (CDCl3) δ 2.63 (s, 4H), 3.69
(s, 6H); 13C NMR (CDCl3) δ 28.8, 51.8, 172.7; IR (KBr) 1740
(CdO); HRMS (EI) m/z 146.0572 (M+, C6H10O4 requires 146.0579).
Irradiation of 2,3-Butanedione (4) and Silyl Ketene Acetal
(6). Benzene: A solution of 2,3-butanedione 4 (123 mg, 1.43 mmol)
and silyl ketene acetal 6 (500 mg, 2.87 mmol) in 160 mL of benzene
was irradiated for 2.5 h (ca. 72% conversion of 4). Concentration
of photolysate gave a residue which was subjected to silica gel
column chromatography (ethyl acetate:n-hexane ) 1:15) giving 101
mg (52%) of 30, 40 mg (15%) of 31, and trace of 12.
Acetone: A solution of 2,3-butanedione 4 (123 mg, 1.43 mmol)
and silyl ketene acetal 6 (500 mg, 2.87 mmol) in 160 mL of acetone
was irradiated for 2 h (ca. 70% conversion of 4). Workup and silica
gel column chromatography (ethyl acetate:n-hexane ) 1:15) gave
100 mg (53%) of 30, 39 mg (15%) of 31, and 14 mg (7%) of 12.
Acetonitrile: A solution of 2,3-butanedione 4 (123 mg, 1.43
mmol) and silyl ketene acetal 6 (500 mg, 2.87 mmol) in 160 mL
of acetonitrile was irradiated for 2 h (ca. 73% conversion of 4).
Workup and silica gel column chromatography (ethyl acetate:n-
hexane ) 1:15) gave 106 mg (54%) of 30, 46 mg (17%) of 31,
and 15 mg (7%) of 12.
Acetone: A solution of 1-phenyl-1,2-propanedione 5 (232 mg,
1.43 mmol) and silyl ketene acetal 6 (500 mg, 2.87 mmol) in 160
mL of acetone was irradiated for 2 h (ca. 86% conversion of 5).
Workup and silica gel column chromatography (ethyl acetate:n-
hexane ) 1:15) gave 91 mg (23%) of 36, 163 mg (53%) of 37,
and 22 mg (9%) of 12.
Acetonitrile: A solution of 1-phenyl-1,2-propanedione 5 (123
mg, 1.43 mmol) and silyl ketene acetal 6 (500 mg, 2.87 mmol) in
160 mL of acetonitrile was irradiated for 1.5 h (ca. 79% conversion
of 5). Workup and silica gel column chromatography (ethyl acetate:
n-hexane ) 1:15) gave 80 mg (22%) of 36, 144 mg (51%) of 37,
and 2 mg (9%) of 12.
30: 1H NMR (CDCl3) δ 1.25 (s, 3H), 1.31 (s, 6H), 2.25 (s, 3H),
3.69 (s, 3H), 4.40 (s, 1H); 13C NMR (CDCl3) δ 20.0, 21.7, 21.8,
25.8, 48.6, 52.2, 81.7, 178.7, 212.0; IR (KBr) 3600-3200 (br, OH),
1710 (CdO); HRMS (EI) m/z 188.1040 (M+, C9H16O4 requires
188.1049).
36: 1H NMR (CDCl3) δ 0.21 (s, 9H), 1.15 (s, 3H), 1.19 (s, 3H),
2.19 (s, 3H), 3.64 (s, 3H), 7.33-7.37 (m, 5H); 13C NMR (CDCl3)
δ 2.7, 22.6, 23.5, 28.4, 51.2, 51.6, 89.8, 127.4, 127.6, 127.8, 138.9,
176.6, 208.1; IR (KBr) 1730 and 1720 (CdO); HRMS (EI) m/z
322.1590 (M+, C17H26O4Si requires 322.1600).
31: 1H NMR (CDCl3) δ 0.16 (s, 9H), 1.18 (s, 6H), 1.40 (s, 3H),
2.18 (s, 3H), 3.64 (s, 3H); 13C NMR (CDCl3) δ 2.3, 20.8, 21.3,
21.8, 27.5, 51.0, 51.7, 85.5, 175.7, 213.8; IR (KBr) 1720 (CdO);
HRMS (EI) m/z 260.1433 (M+, C12H24O4Si requires 260.1444).
Irradiation of 2,3-Butanedione (4) and Silyl Ketene Acetal
(7). A solution of 2,3-butanedione 4 (123 mg, 1.43 mmol) and silyl
ketene acetal 7 (460 mg, 2.87 mmol) in 160 mL of acetonitrile
was irradiated for 2.5 h (ca. 73% conversion of 4). Concentration
of photolysate gave a residue which was subjected to silica gel
column chromatography (ethyl acetate:n-hexane ) 1:15) giving 118
mg (46%) of 32, 10 mg (4%) of 33, and 31 mg (12%) of 34.
32: 1H NMR (CDCl3) δ 1.21 (s, 3H), 1.27 (d, 3H, J ) 7.4 Hz),
2.30 (s, 3H), 3.04 (q, 1H, J ) 7.4 Hz), 3.64 (s, 3H), 4.07 (s, 1H);
13C NMR (CDCl3) δ 10.8, 22.2, 24.2, 44.9, 52.0, 79.6, 176.4, 213.3;
IR (KBr) 3600-3200 (br, OH), 1710 (CdO); HRMS (EI) m/z
174.0886 (M+, C8H14O4 requires 174.0892).
37:
1H NMR (CDCl3) δ 1.13 and 1.21 (s, 3H), 2.09 (s, 3H),
3.76 (s, 3H), 5.58 (s, 1H), 7.36-7.37 (m, 5H); 13
C NMR (CDCl3)
δ 22.1, 22.6, 25.9, 47.6, 52.5, 86.2, 127.4, 127.6, 128.0, 135.7,
181.5, 209.6; IR (KBr) 3600-3200 (br, OH), 1720 and 1700
(CdO); HRMS (EI) m/z 250.1201 (M+, C14H18O4 requires 250.1205).
38: (3.2:1 mixture of two diastereomers based on 1H NMR
1
integration) H NMR of major diastereomer 38a (CDCl3) δ 0.25
(s, 9H), 0.83 (s, 3H), 1.23 (s, 3H), 2.22 (s, 3H), 3.42 (s, 3H),
7.27-7.34 (m, 3H), 7.49-7.50 (m, 2H); 13C NMR (CDCl3) δ 1.5,
19.7, 22.3, 26.7, 48.9, 54.5, 88.5, 115.5, 125.9, 127.4, 127.8, 137.1,
210.5; IR (KBr) 1720 (CdO); HRMS is not measured due to the
decomposition. 1H NMR of minor diastereomer 38b (CDCl3) δ 0.28
(s, 9H), 0.84 (s, 3H), 1.26 (s, 3H), 2.19 (s, 3H), 3.40 (s, 3H),
7.27-7.34 (m, 3H), 7.49-7.50 (m, 2H); 13C NMR (CDCl3) δ 1.4,
20.5, 22.2, 26.7, 49.4, 54.5, 88.5, 115.2, 126.0, 127.5, 127.7, 137.0,
209.7; IR (KBr) 1720 (CdO); HRMS is not measured due to the
decomposition.
33: 1H NMR (CDCl3) δ 0.14 (s, 9H), 1.14 (d, 3H, J ) 7.1 Hz),
1.33 (s, 3H), 2.23 (s, 3H), 2.99 (q, 1H, J ) 7.2 Hz), 3.60 (s, 3H);
13C NMR (CDCl3) δ 2.3, 10.8, 22.4, 27.0, 47.7, 51.5, 83.6, 173.3,
212.6; IR (KBr) 1720 (CdO); HRMS (EI) m/z 246.1283 (M+,
C11H22O4Si requires 246.1287).
39: 1H NMR (CDCl3) δ 1.33 (s, 3H), 1.38 (s, 3H), 1.51 (s, 3H),
3.70 (s, 3H), 4.98 (s, 1H), 7.40-7.47 (m, 3H), 8.12-8.17 (m, 2H);
13C NMR (CDCl3) δ 21.1, 21.8, 22.2, 48.7, 52.3, 83.2, 128.0, 130.0,
4546 J. Org. Chem. Vol. 73, No. 12, 2008

Photoaddition Reactions of 1,2-Diketones
132.2, 136.3, 180.5, 203.1; IR (KBr) 1730 and 1680 (CdO); HRMS
(EI) m/z 250.1198 (M+, C14H18O4 requires 250.1205).
δ 11.6, 24.4, 44.9, 52.3, 84.1, 125.2, 127.9, 128.6, 137.3, 178.7,
210.9; HRMS (EI) m/z 236.1048 (M+, C13H16O4 requires 236.1049).
1
42: known compound, H NMR δ 1.16 (d, 3H, J ) 6.7 Hz),
Irradiation of 1-Phenyl-1,2-propanedione (5) and Silyl Ketene
Acetal (7). A solution of 1-phenyl-1,2-propanedione 5 (232 mg,
1.43 mmol) and silyl ketene acetal 7 (460 mg, 2.87 mmol) in 160
mL of acetonitrile was irradiated for 2 h (ca. 80% conversion of
5). Concentration of photolysate gave a residue which was subjected
to silica gel column chromatography (ethyl acetate:n-hexane ) 1:15)
giving diastereomeric photoadduct 40 (40a, 49 mg, 14% and 40b,
32 mg, 9%), 41 (41a, 81 mg, 30% and 41b, 49 mg, 18%), and 20
mg (10%) of 42.25
2.81 (q, 2H, J ) 6.0 Hz), 3.67 (s, 3H); 13C NMR (CDCl3) δ 13.6,
41.6, 51.8, 175.6; IR (KBr) 1730.
Irradiation of 1-Phenyl-1,2-propanedione (5) and Silyl Ketene
Acetal (8). A solution of 1-phenyl-1,2-propanedione 5 (232 mg,
1.43 mmol) and silyl ketene acetal 8 (420 mg, 2.87 mmol) in 160
mL of acetonitrile was irradiated for 5 h (ca. 53% conversion of
5). Concentration of photolysate gave a residue which was subjected
to silica gel column chromatography (ethyl acetate:n-hexane ) 1:15)
giving 56 mg (33%) of 43 and 40 mg (12%) of 44.
40: (1.6:1 mixture of two diastereomers based on 1H NMR
43: 1H NMR (CDCl3) δ 2.16 (s, 3H), 2.82 (d, 1H, J ) 16.7 Hz),
3.41 (d, 1H, J ) 16.7 Hz), 5.15 (s, 1H), 7.33-7.50 (m, 5H); 13C
NMR (CDCl3) δ 24.0, 42.4, 52.1, 81.2, 124.9, 128.1, 128.7, 139.1,
173.5, 209.0; IR (KBr) 3600-3200 (br, OH), 1740 and 1710
(CdO); HRMS (EI) m/z 222.0887 (M+, C12H14O4 requires 222.0892).
1
integration) H NMR of major diastereomer 40a (CDCl3) δ 0.13
(s, 9H), 1.18 (d, 3H, J ) 7.1 Hz), 2.22 (s, 3H), 3.52 (q, 1H, J )
7.1 Hz), 3.56 (s, 3H), 7.33-7.36 (m, 5H); 13C NMR (CDCl3) δ
2.2, 13.5, 27.0, 47.5, 51.5, 87.1, 126.8, 128.0, 128.9, 139.7, 173.9,
209.4; IR (KBr) 1740 and 1720 (CdO); HRMS (EI) m/z 308.1444
1
44: mp 91-94 °C; H NMR (CDCl3) -0.07 (s, 9H), 2.27 (s,
1
(M+, C16H24O4Si requires 308.1444). H NMR of minor diastere-
3H), 7.31-7.33 (m, 6H), 7.46-7.49 (m, 4H); 13C NMR (CDCl3)
δ 2.4, 29.6, 91.1, 127.4, 128.1, 141.4, 207.4; HRMS (EI) m/z
442.2015 (M+, C24H34O4Si2 requires 442.1996).
omer 40b (CDCl3) δ 0.13 (s, 9H), 1.06 (d, 3H), 2.22 (s, 3H), 3.51
(q, 1H, J ) 7.1 Hz), 3.56 (s, 3H), 7.29-7.33 (m, 5H); 13C NMR
(CDCl3) δ 2.2, 13.5, 27.0, 47.3, 51.7, 87.1, 126.9, 128.2, 128.9,
139.9, 173.7, 209.8; IR (KBr) 1740 and 1720 (CdO); HRMS (EI)
m/z 308.1449 (M+, C16H24O4Si requires 308.1444).
Acknowledgment. This research was supported (for U.C.Y.)
by the Ministry of Information and Communication (MIC),
Korea under the Information Technology Research Center
(ITRC) support program supervised by the Institute of Informa-
tion Technology Assessment (IITA) and the National Science
Foundation (CHE-0550133, for P.S.M.).
1
41: H NMR of 41a δ 1.27 (d, 3H, J ) 7.1 Hz), 2.16 (s, 3H),
3.44 (s, 3H), 3.71 (q, 1H, J ) 7.0 Hz), 4.47 (s, 1H), 7.28-7.38
(m, 3H), 7.50-7.55 (m, 2H); 13C NMR (CDCl3) δ 13.1, 25.2, 45.6,
51.8, 83.9, 125.4, 128.0, 128.4, 140.2, 176.8, 208.3; HRMS (EI)
m/z 236.1065 (M+, C13H16O4 requires 236.1049). 1H NMR of 41b
δ 0.96 (d, 3H, J ) 7.5 Hz), 2.12 (s, 3H), 3.47 (q, 1H, J ) 7.0 Hz),
3.74 (s, 3H), 4.96 (s, 1H), 7.31-7.44 (m, 5H); 13C NMR (CDCl3)
Supporting Information Available: 1H NMR and 13C NMR
spectra are included. This material is available free of charge
via the Internet at http://pubs.acs.org.
(25) Ando, M.; Ibe, S.; Kagabu, S.; Nakagawa, T.; Asao, T.; Takase, K.
J. Chem. Soc. D 1970, 1538.
JO800473X
J. Org. Chem. Vol. 73, No. 12, 2008 4547