Photoaddition reactions of acetylpyridines with silyl ketene acetals: SET vs [2 + 2]-cycloaddition pathways

Article abstract of DOI:10.1021/jo301961n

Photoaddition reactions of silyl ketene acetals with 2-, 3- and 4-acetylpyridine have been explored. The results show that the acetylpyridines react with an electron rich, dimethyl-substituted silyl ketene acetal via a pathway in which excited state singl

Full text of DOI:10.1021/jo301961n

Article
pubs.acs.org/joc
Photoaddition Reactions of Acetylpyridines with Silyl Ketene Acetals:
SET vs [2 + 2]-Cycloaddition Pathways
Hea Jung Park,† Ung Chan Yoon,*,† Hyang-Yeol Lee,‡ Dae Won Cho,§ Dae Won Cho,*,∥
and Patrick S. Mariano⊥
†Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan 609-735, Korea
‡Department of Biotechnology, Korea National University of Transportation, 61 Daehak-ro, Jeungpyung, Chungbuk 368-701, Korea
§Fraunhofer ISE Next Generation Solar Cell Research Center, Konkuk University, Seoul 143-701, Korea
∥Department of Chemistry, Yeungnam University, Gyeongsan, Gyeongbuk 712-749, Korea
⊥Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, United States
S
* Supporting Information
ABSTRACT: Photoaddition reactions of silyl ketene acetals
with 2-, 3- and 4-acetylpyridine have been explored. The
results show that the acetylpyridines react with an electron
rich, dimethyl-substituted silyl ketene acetal via a pathway in
which excited state single electron transfer (SET) takes place
to produce β-hydroxyesters in high yields. In contrast,
photochemical reactions of the acetylpyridines with an
electron deficient, nonmethyl-substituted silyl ketene acetal
generate oxetanes as major products, which arise via a route
involving excited state [2 + 2]-cycloaddition. In addition, an
increase in solvent polarity significantly enhances the relative
efficiencies of the SET processes versus [2 + 2]-cycloaddition reactions. Importantly, the carbonyl groups rather than the
pyridine moieties in the acetylpyridine substrates participate in both types of addition reactions. Finally, the results demonstrate
that photoinduced electron transfer (PET)-promoted chemical reactions between acetylpyridines and electron rich silyl ketene
acetals in polar solvent serve as useful methods to promote β-hydroxyester forming, Claisen or Mukaiyama condensation
reactions under mild conditions.
is the SET-promoted addition of allyltrimethylsilane (2) to the
1-pyrrolinium perchlorate (1) (Scheme 2).
Studies in this and related areas have shown that a number of
α-trialkylsilyl substituted electron donors, including benzylsi-
lanes,7,8 allylsilanes,9−11 silyl ketene acetals,12−14 and silyl enol
ethers,15,16 serve as substrates for a wide variety of synthetically
INTRODUCTION
■
Earlier investigations in the area of single electron transfer
(SET) photochemistry have led to the development of new
synthetic methodologies1−3 and to the elucidation of
mechanisms involved in novel excited state reactions.4 In one
phase of this work, we showed that sequential SET-desilylation
reactions of α-trialkylsilyl substituted electron donors serve as
highly efficient and regioselective methods to generate carbon-
centered free radicals.5 The high efficiencies of these reactions
are a consequence of the fact that trialkylsilyl transfer from α-
trialkylsilyl cation radicals, generated by SET oxidation, to
silophiles takes place more rapidly than other possible radical
cation fragmentation processes (Scheme 1).1−6 A pertinent
example of a photochemical reaction that follows this pathway
Scheme 2
Scheme 1
Received: September 14, 2012
Published: October 23, 2012
© 2012 American Chemical Society
10304
dx.doi.org/10.1021/jo301961n | J. Org. Chem. 2012, 77, 10304−10313

The Journal of Organic Chemistry
Article
important ground and excited state organic transformations. Of
special relevance to the studies described below are Lewis acid
catalyzed Claisen or Mukaiyama reactions of carbonyl
compounds with silyl ketene acetals and silyl enol ethers.12−16
Recently, we explored photoinduced Mukaiyama type addition
reactions that take place between aromatic carbonyl com-
pounds and silyl ketene acetals,14b N-methylphthalimide and
silyl enol ether,17 and 1,2-diketones and silyl ketene acetal.3b
The results of these efforts revealed that diverse excited state
photochemical reaction pathways are operable in these systems
and that competition between the pathways is governed by the
structural nature and redox properties of the excited state of the
carbonyl reactant and ground state of the α-trialkylsiloxy
substituted alkenes, along with solvent polarity.3b,5c,12a,c,14b,17
For instance, we observed that irradiation of solutions
containing aromatic carbonyl compounds 4 and silyl ketene
acetals 5 promotes two competitive excited state reactions that
lead to formation of 3-silyloxyoxetanes 6 and β-hydroxyesters
12 (Scheme 3). Oxetanes were formed in these processes
ion pairs 8,14b which undergo desilylation to furnish radical
pairs 9 or zwitterions 10 that are converted to the respective 2-
silyloxyoxetanes 11 or β-hydroxyesters 12. Interestingly, in
photoreactions of electron rich, dimethyl-substituted silyl
ketene acetals, the SET-desilylation process producing 11 and
12 predominated. In contrast, photochemical processes of
electron deficient, nonmethyl-substituted silyl ketene acetals
gave rise to the formation of 6 by way of [2 + 2]-cycloaddition.
In addition, when solvents of high polarity were employed, the
SET pathway was favored.3b,14b These observations show that
the relative efficiencies of the competitive SET vs [2 + 2]-
cycloaddition reactions are strongly governed by the oxidation
potentials of silyl ketene acetals and polarity of the
medium.5c,12c,3b,14b
Scheme 3
In a recent effort, described below, we explored photo-
chemical reactions occurring between silyl ketene acetals and
2-, 3- and 4-acetylpyridines (13−15) and silyl ketene acetals
16−18, along with those involving the model aryl-ketone
acetophenone (19).14b As a consequence of the presence of
carbonyl and pyridine moieties in 13−15, a manifold of
different SET-promoted reactions can take place. For example,
it is well-known that the ketones serve as electron acceptors in
photochemical C−C bond forming processes as well as
participants in Paterno−Buchi reactions that generate oxetanes.
In addition, pyridines, especially those possessing electron-
withdrawing groups (e.g., cyano) have been observed to
participate in both the SET and [2 + 2]-cycloaddition
reactions19,20 (Scheme 4). The results of the current studies
show that acetylpyridines react with an electron rich, dimethyl-
substituted silyl ketene acetal via a pathway promoted by
excited state SET that produces β-hydroxyesters in high yields.
In contrast, photochemical reactions of the acetylpyridines with
an electron deficient, nonmethyl-substituted silyl ketene acetal
generate oxetanes along with β-hydroxyesters as major
products, the former of which arise via a route involving [2 +
2]-cycloaddition. In addition, an increase in solvent polarity
significantly enhances the relative efficiencies of the SET vs [2
+ 2]-cycloaddition reactions. Importantly, the carbonyl groups
rather than the pyridine moieties in the acetylpyridine
through classical Paterno−Buchi type [2 + 2]-cycloadditions18
taking place between the triplet excited states of 4 and ground
state of 5. A competitive route involving SET from 5 (or silyl
enol ethers) to the triplet excited states of 4 generated radical
Scheme 4
10305
dx.doi.org/10.1021/jo301961n | J. Org. Chem. 2012, 77, 10304−10313

The Journal of Organic Chemistry
Article
Scheme 5
substrates participate in both of the observed addition
reactions.
of a benzene solution containing 13 and electron rich, silyl
ketene acetal 16 resulted in formation of a mixture of products
containing predominantly β-hydroxyester 23, which arises by a
sequential SET-desilylation pathway. Minor components of the
product mixture (23:20a,b = ca. 6:1) were the diasteromeric
oxetanes 20a and 20b, formed by a [2 + 2]-cycloaddition
process (Scheme 5 and Table 1). When more polar acetonitrile
was used as the solvent, the SET pathway became more
favorable, and as a result, β-hydroxyester 23 was produced
nearly exclusively (90%, 23:20a,b = ca. 23:1).
Irradiation of a benzene solution containing 13 and the
monomethyl substituted silyl ketene acetal 17 promoted
formation of near equal amounts of β-hydroxyester 24 and
oxetane 21, both as mixtures of diastereomers, along with the
pinacol-type dimer 26.21 Interestingly, photoreaction of 13 with
17 in acetonitrile generated 3:1 ratio of 24 and 21.
RESULTS AND DISCUSSION
■
Photochemical reactions were performed by using Pyrex
filtered-light (α > 290 nm) in benzene or acetonitrile solutions
containing acetylpyridines 13−15 (20 mM) and silyl ketene
acetals 16−18 (40 mM) for time periods that bring about 45−
100% conversion of the acetylpyridines. In each case, the
photolysate was concentrated and the residue was subjected to
silica gel chromatography to obtain the photoproducts.
Photochemistry of 2-Acetylpyridine (13). As can be
seen by viewing the results (Scheme 5 and Table 1), irradiation
Table 1. Photoreactions of 2-Acetylpyridine (13) and Silyl
a
Ketene Acetals 16−18
In contrast to the photoreaction of 13 with 16, reaction with
the relatively electron poor, nonmethyl substituted, silyl ketene
acetal 18 in benzene yielded the diastereomeric oxetanes 22a
and 22b (36%), β-hydroxyester 25 (14%), and α-alkoxyacetate
27 as the major product (50%). On the basis of the proposal
that ester 27 arose by hydrolytic ring-opening of oxetanes 22, it
appears that excited state reaction of 13 with 18 predominantly
follows a [2 + 2]-cycloaddition pathway. Although the yield of
25 increased, the [2 + 2]-cycloaddition process was still favored
when acetonitrile was employed as the solvent. Another
observation is that, compared to the photoreactions occurring
between 13 and acetals 16 and 17, photoreaction between 13
and 18 required a longer time to bring about high conversion
reaction
%
b
reactants
solvent
time (h) conversion
product (% yield)
13 + 16 Benzene
13 + 16 CH3CN
13 + 17 Benzene
2.5
2.5
4
100
100
77
20a (7), 20b (6), 23 (75)
20a (2), 20b (2), 23 (90)
21a (10), 21b (20), 24a
(12), 24b (22), 26 (trace)
13 + 17 CH3CN
13 + 18 Benzene
13 + 18 CH3CN
4.5
16
16
96
94
82
21a (6), 21b (14), 24a (13),
24b (49), 26 (2)
22a (36), 22b (trace), 25
(14), 27 (50)
22a (23), 22b (10), 25 (23),
27 (15)
a
b
Concentrations of reactants, 13/16−18 are 20/40 (mM). Yields are
based on consumed 13.
1
(82−94%). In addition, it is important to note that careful H
NMR analysis of product mixtures generated in the reactions
Scheme 6
10306
dx.doi.org/10.1021/jo301961n | J. Org. Chem. 2012, 77, 10304−10313

The Journal of Organic Chemistry
Article
described failed to reveal the presence of substances that would
have been generated by reactions of the pyridine moieties in 13
as exemplified by those depicted in Scheme 4.
(29%). On the basis of the plausible assumption that
oxacyclobutanone 35 results from hydrolysis of 30, the product
profiles show that [2 + 2]-cycloaddition reactions of 3-
acetylpyridine, which occur in competition with those
promoted by SET, become more competitive when the silyl
ketene acetals are less electron rich and less polar benzene is
utilized as solvent. The substrate and solvent dependent
differences in preferred reaction pathways are also reflected in
reaction quantum efficiencies, which are qualitatively echoed in
irradiation time vs percent conversion data given in Table 2.
Photochemistry of 4-Acetylpyridine (15). Irradiation of
4-acetylpyridine (15) in benzene and acetonitrile solutions
containing 16−18 led to formation of product mixtures
containing the corresponding β-hydroxyesters 39−41, oxetanes
36−38 and, in certain cases, the pyridylethanol 42 and α-alkoxy
acetate 43 (Table 3, Scheme 7). In a manner that is similar to
The results described above show that photochemical
reactions of 13 with silyl ketene acetals 16−18 generate β-
hydroxyesters as well as oxetanes in ratios that depend on the
degree of methyl substitution on the acetals and the polarity of
the solvent. The relative yields of β-hydroxyesters and oxetanes
appear to be governed by the relative efficiencies of competitive
SET-desilylation vs [2 + 2]-cycloaddition open to the reactive
triplet excited state of 2-acetylpyridine, which are controlled by
both the electron donating abilities (i.e., oxidation potentials)
of the silyl ketene acetals and solvent stabilization of radical ion
intermediates. For example, when the electron rich acetal 16
with a relatively low oxidation potential (0.90 V vs SCE)12c is
the substrate and the more polar acetonitrile is the solvent, SET
from 16 to excited 13 takes place rapidly to form a radical ion
pair (ΔGSET ca. −0.26 V)22 Desilylation of the radical cation of
the silyl ketene acetal then occurs to form the radical pair
precursor of the β-hydroxyester product 21. However, classical
Paterno−Buchi [2 + 2]-cycloaddition reaction of the ketone
moiety in the excited state of 13 predominates when the SET is
slow because of the higher oxidation potentials (ca. 1.28 V vs
SCE, ΔGSET ca. 0.12 V)12c,22,23 of less methyl substituted silyl
ketene acetals (e.g., 18) and less solvent stabilization of the
resulting ion radicals. It is important to note that the patterns
observed for reactions of 13 with 16−18 match well trends
seen in previous studies with a number of substrates.3b,14b,17
Photochemistry of 3-Acetylpyridine (14). The results
arising from studies of the photoreactions of 3-acetylpyridine
(14) with 16−18, summarized in Scheme 6 and Table 2,
Table 3. Photoreactions of 4-Acetylpyridine (15) and Silyl
a
Ketene Acetals 16−18
reaction
%
b
reactants
solvent
time (h) conversion
product (% yield)
15 + 16 Benzene
15 + 16 CH3CN
15 + 17 Benzene
15 + 17 CH3CN
15 + 18 Benzene
15 + 18 CH3CN
3.5
6
79
78
64
63
96
89
36a (7), 36b (7), 39 (68),
42 (12)
36a (trace), 36b (trace), 39
(82), 42 (4)
4.5
4
37a (30), 37b (4), 40a (10),
40b (33),42 (8)
37a (14), 37b (trace), 40a
(24), 40b (48), 42 (8)
16
16
38a (25), 38b (4), 41 (17),
43 (52)
38a (21), 38b (2), 41 (26),
43 (37)
a
b
Table 2. Photoreactions of 3-Acetylpyridine (14) and Silyl
Ketene Acetals 16−18
Concentrations of reactants, 15/16−18 are 20/40 (mM). Yields are
based on consumed 15.
a
reaction
%
b
those of the 2- and 3-acetylpyridine analogues, photoreaction of
15 with 16 yielded β-hydroxyester 39, diastereomeric oxetanes
36, and alcohol 42 in relative yields that depend upon the
solvent used (39:36a,b = 5:1 in benzene and >80:1 in
acetonitrile). In addition, nearly equal amounts of 40 and 37
were produced in the photoreaction of 15 with 17 in benzene,
whereas the process in acetonitrile formed 40 and 37 in a 5:1
ratio. In both of these cases, alcohol 42 was a minor product.
Moreover, irradiation of benzene and acetonitrile solutions of
15 containing 18 led to generation of 38 and 43 as major
products along with minor amounts of 41. Finally, as is
observed with the other pyridine derivatives, a correlation
appears to exist between the nature of the major reaction
pathway followed by 15 and the irradiation time vs percent
conversion (i.e., longer times lower conversions for reactions in
which the [2 + 2]-cycloaddition process becomes more
predominate).
Comparison of Photoreaction of the Acetylpyridines
vs the Nonheterocyclic Analogue Acetophenone. A
comparison of the photochemical reaction profile of the
nonheterocyclic analogue acetophenone (19) with those of
the acetylpyridines was made to determine if differences exist in
the relative contributions of the SET vs [2 + 2]-cycloaddition
reaction pathways. The results of photoreactions of 19 with
16−18, observed in our previous study,14b are displayed
Scheme 8 and Table 4. Unfortunately, because of the fact that
different conditions (e.g., reactant concentrations and photo-
chemical apparatus) were employed in the earlier study, it is
reactants
solvent
time (h) conversion
product (% yield)
14 + 16 Benzene
14 + 16 CH3CN
14 + 17 Benzene
14 + 17 CH3CN
14 + 18 Benzene
14 + 18 CH3CN
7
90
60
71
45
93
81
28a (6), 28b (6), 31 (77),
34 (9)
7
28a (trace), 28b (trace), 31
(92), 34 (trace)
8.5
8.5
15
15
29a (22), 29b (trace), 32a
(7), 32b (23), 34 (8)
29a (11), 29b (6), 32a (26),
32b (55), 34 (trace)
30a (22), 30b (trace), 33
(29), 35 (50)
30a (12), 30b (trace), 33
(41), 35 (35)
a
b
Concentrations of reactants, 14/16−18 are 20/40 (mM). Yields are
based on consumed 14.
parallel those of the reactions of 13 with the same acetals.
Specifically, irradiation of a benzene solution containing 14 and
16 produced β-hyroxyester 31 predominantly (77%) along with
lesser amounts of the diastereomeric oxetanes 28 (12%) and
dimer 3424 (9%). Exclusive formation of 31 (92%) was
observed to take place when an acetonitrile solution of 14 and
16 was irradiated. Reaction of 14 with 17 in benzene
competitively generated diasteromeric β-hydroxyesters 32
(30%) and diasteromeric oxetanes 29a,b (22%, trace), and
the yield of 32 was dramatically enhanced (81%) when
acetonitrile was the solvent. Lastly, irradiation of a benzene
solution of 14 containing 18 generated of oxetane 30a,b (22%,
trace), oxacyclobutanone 35 (50%) and β-hydroxyester 33
10307
dx.doi.org/10.1021/jo301961n | J. Org. Chem. 2012, 77, 10304−10313

The Journal of Organic Chemistry
Article
Scheme 7
Scheme 8
Table 4. Photoreactions of Acetophenone (19) and Silyl
Ketene Acetals 16−18
Table 5. Reduction Potentials and Triplet Excited State
Energies of Acetylpyridines 13−15 and Acetophenone 19
a
reaction
%
triplet energy (kcal/mol)
b
reactants
solvent
time (h) conversion
product (% yield)
a
b
ketone
E1/2 (V)
hydrocarbon
alcohol
19 + 16 Benzene
19 + 16 CH3CN
19 + 17 Benzene
19 + 17 CH3CN
33
16
14
12
77
44a (11), 44b (7), 47 (64),
50 (3)
19
13
14
15
−2.09
−1.91
−1.94
−1.86
73.6
70.0
71.1
74.1
70.9
73.0
70.3
100
47
44a (5), 44b (6), 47 (83),
50 (5)
45a (21), 45b (34), 48a
(15), 48b (25)
69.5
a
b
Methylcyclohexane/isopentane (4:1). Ethanol/methanol (4:1).
72
45a (8), 45b (16), 48a
(19), 48b (24), 50 (16)
19 + 18 Benzene
19 + 18 CH3CN
16
20
65
49
46a (21), 46b (32), 49 (22)
reactions of 13−15 with 16−18 is that both the SET and [2 +
2]-cycloaddition processes take place at the ketone carbonyl
rather than pyridine ring center. The highly regioselective
nature of these excited state processes is somewhat surprising
because electron withdrawing group substituted pyridines were
known to participate in [2 + 2]-cycloaddition and SET-
promoted reactions, which occur in the pyridine ring centers
(Scheme 4).19,20 One possible reason for the high selectivity of
photochemical reactions of acetylpyridines could be associated
with the magnitudes of charge coefficients in the n−π triplet
excited states of these substrates (T1), which could govern the
sites of energetically most favored interactions with 16−18. To
gain information about this proposal, density functional theory
(DFT) calculations using a B3LYP hybrid exchange correlation
function employing 6-31G** (for ground states (S0) and anion
radicals of acetylpyridines) and CIS (for triplet states of
acetylpyridines T1) were carried out. The results, depicted in
Table 6, show that charge coefficients of 13−15 are both
heavily localized on the ketone carbonyl moieties, while a large
extent of charge coefficients are located on C2 and C6 in
pyridine ring (Table 7). If in fact [2 + 2]-photocyloaddition
46a (16), 46b (30), 49 (25)
a
b
Concentrations of reactants, 19/16−18 are 36/72 (mM). Yields are
based on consumed 19.
not possible to make a qualitative estimate of the relative
quantum efficiencies of the photoreactions of 13−15 with those
of 19. However, a comparison of the product composition data
shows that approximately the same ratios of oxetane and β-
hydroxyester products are generated in photoreactions of the
acetals with both 19 and 13−15 in benzene and acetonitrile.
This observation is interesting in light of the fact that the 13−
15 and 19 have nearly equivalent triplet excited state energies
and ground state reduction potentials (E1/2) (Table 5) (i.e.,
nearly equivalent triplet excited state reduction potentials).22
Thus, the propensity of the triplet excited state of 19 and 13−
15 to accept an electron from 16−18 appears to be the singular
most important factor governing the nature of the reaction
pathways followed in these processes.
Selectivity for Reactions at the Ketone Rather than
Pyridine Ring Center. An interesting feature of photo-
10308
dx.doi.org/10.1021/jo301961n | J. Org. Chem. 2012, 77, 10304−10313

The Journal of Organic Chemistry
Article
Table 6. Calculated Charge Coefficients of Ground States (S0), Triplet Excited States (T1) and Anion Radicals of the
Acetylpyridines 13−15
2-acetylpyridine (13)
3-acetylpyridine (14)
4-acetylpyridine (15)
atom
S0
T1
radical anion
S0
T1
radical anion
S0
T1
radical anion
N
−0.490
0.210
0.043
0.048
0.010
0.198
0.399
0.031
−0.450
−0.562
0.167
−0.553
0.182
−0.439
0.169
0.034
0.069
0.003
0.212
0.393
0.012
−0.450
−0.512
0.279
−0.483
0.046
−0.420
0.185
−0.502
0.242
−0.532
0.074
C2
C3
C4
C5
C6
C7
C8
O
0.077
−0.058
−0.069
−0.150
0.097
−0.098
0.094
0.057
−0.009
0.067
0.033
−0.103
0.080
0.030
−0.069
−0.082
0.024
−0.054
0.033
−0.101
0.263
−0.015
0.253
−0.009
0.185
−0.103
0.074
0.242
0.319
0.303
0.292
0.282
0.402
0.297
0.292
0.107
−0.134
−0.616
0.094
−0.157
−0.618
0.013
0.094
−0.154
−0.609
−0.391
−0.387
−0.440
−0.385
pressure mercury lamp surrounded by a Pyrex glass filter in a water-
cooled quartz immersion well surrounded by the solution being
irradiated. The photolysis solutions were purged with nitrogen before
and during irradiations. The photolyzates were concentrated under
reduced pressure giving residues, which were subjected to silica gel
column chromatography. High resolution (HRMS) mass spectra were
obtained by use of quadrupole mass analyzer, electron impact
ionization unless otherwise noted. All starting materials used in the
photoreactions were derived from commercial sources. All new
compounds described were isolated as oils in >90% purity (by NMR
analysis) unless noted otherwise.
Irradiation of 2-Acetylpyridine (13) and 1-Methoxy-2-
methyl-1-(trimethylsilyloxy)propene (16). In Benzene. A 150
mL solution of 13 (364 mg, 3.00 mmol) and 16 (1.04 g, 6.00 mmol)
was irradiated for 2.5 h (ca. 100% conversion of 13). Concentration of
photolysate gave a residue, which was subjected to silica gel column
chromatography (ethyl acetate:n-hexane = 1:3) giving 20 (20a, 62 mg,
7% and 20b, 53 mg, 6%) and 502 mg (75%) of 23.
Table 7. Calculated Charge Coefficients of the Ground State
(S0) and Excited State (S1, T1) of Pyridine
charge coefficient
atom
S0
S1
T1
N
−0.428
0.094
−0.584
0.314
−0.471
0.247
C2
C3
C4
C5
C6
−0.093
−0.058
−0.093
0.094
−0.056
−0.068
−0.056
0.314
−0.001
−0.020
−0.001
0.247
reactions are governed by interactions between the ground
state of silyl ketene acetals 16−18 and triplet states of the
acetylpyridines 13−15 (T1) and if odd electron densities in the
acetylpyridine radical anions, which are reflected in charge
densities, control the regioselectivity of radical coupling steps in
the SET-promoted processes, the DFT and CIS calculation
results are in accord with the regioselectivities in both types of
photochemical reactions observed to take place between these
substrates.
In Acetonitrile. A 150 mL solution of 13 (100 mg, 0.83 mmol) and
16 (290 mg, 1.65 mmol) was irradiated for 2.5 h (ca. 100% conversion
of 13). Workup and column chromatography (ethyl acetate:n-hexane
= 1:3) gave 20 (20a, 5 mg, 2% and 20b, 5 mg, 2%) and 166 mg (90%)
of 23.
20a (liq). 1H NMR (CDCl3) −0.10 (s, 9H), 1.31 and 1.50 (s, 6H),
1.78 (s, 3H), 3.47 (s, 3H), 7.09 (m, 1H), 7.64 (m, 2H), 8.54 (d, 1H, J
= 4.7 Hz); 13C NMR (CDCl3) 1.0, 24.3, 25.1, 25.9, 52.0, 89.8, 93.3,
103.2, 120.1, 121.2, 135.6, 148.1, 163.6; MS (CI) m/z (rel. intensity)
296 (M+ + H, 1), 280 (M+−CH3, 7), 264 (M+ − OCH3, 3), 222 (M+-
SiMe3, 25), 206 (M+ − OSiMe3, 3), 194 (8), 174 (100), 132 (16), 105
(16), 73 (37); HRMS (CI) m/z 296.1684 (M + H, C15H26NO3Si
requires 296.1682).
CONCLUSION
■
The combined results arising from our previous studies and
those described above demonstrate that photoaddition
reactions of acetylpyridines 13−15 with silyl ketene acetals
16−18 serve as a highly efficient and extremely mild methods
for the preparation of β-hydroxyesters. In contrast to typical
Claisen or Mukaiyama reactions that are used for this purpose,
the photochemical processes are promoted using mild
conditions that do not require the presence of strong acids or
bases and, as a result, are environmentally benign. The β-
hydroxyester forming reactions, following a sequential SET-
desilylation pathway, take place with high levels of chemo-
selectivity when the electron rich silyl ketene acetals and
relatively polar solvents are used.
1
20b (liq). H NMR (CDCl3) 0.25 (s, 9H), 1.43 and 1.49 (s, 6H),
1.77 (s, 3H), 2.80 (s, 3H), 7.11 (m, 1H), 7.66 (t, 1H, J = 8.0 Hz), 7.82
(d, 1H, J = 8.0 Hz), 8.52 (d, 1H, J = 4.8 Hz); 13C NMR (CDCl3) 1.4,
24.3, 24.5, 26.7, 51.4, 90.3, 92.9, 103.2, 121.4, 121.6, 135.8, 147.9,
163.0; MS (CI) m/z (rel. intensity) 296 (M+ + H, 5), 280 (M+ − CH3,
3), 264 (M+ − OCH3, 3), 222 (M+-SiMe3, 32), 206 (M+ − OSiMe3,
6), 194 (13), 174 (100), 132 (25), 105 (41), 73 (82); HRMS (CI) m/
z 296.1667 (M + H, C15H26NO3Si requires 296.1682).
1
23 (liq). H NMR (CDCl3) 1.17 and 1.19 (s, 3H), 1.64 (s, 3H),
3.58 (s, 3H), 5.50 (s, 1H), 7.18 (t, 1H, J = 6.1 Hz), 7.34 (d, 1H, J = 8.1
Hz), 7.66 (t, 1H, J = 7.6 Hz), 8.49 (d, 2H, J = 4.8 Hz); 13C NMR
(CDCl3) 21.2, 21.6, 23.4, 50.9, 51.5, 76.4, 120.9, 122.1, 136.0, 146.9,
162.4, 177.1; IR (neat) 3100−3500 (br, OH stretching), 1730 (CO
stretching); MS (CI) m/z (rel. intensity) 224 (M+ + H, 5), 192 (M+ −
OCH3, 4), 176 (2), 146 (6), 123 (92), 122 (M+ − C(CH3)2CO2CH3,
100), 104 (22), 79 (23); HRMS (CI) m/z 224.1288 (M + H,
C12H18NO3 requires 224.1287).
EXPERIMENTAL SECTION
■
1
General Procedure. H and 13C NMR (200 MHz) spectra were
recorded on CDCl3 solutions, and chemical shifts are reported in parts
1
per million relative to CHCl3 peak (7.24 ppm for H NMR and 77.0
ppm for 13C NMR) as an internal standard. IR spectral bands are
reported in cm−1. Preparative photochemical reactions were conducted
with an apparatus consisting of a 450 W Hanovia medium vapor
10309
dx.doi.org/10.1021/jo301961n | J. Org. Chem. 2012, 77, 10304−10313

The Journal of Organic Chemistry
Article
Irradiation of 2-Acetylpyridine (13) and 1-Methoxy-1-
(trimethylsilyloxy)propene (17). In Benzene. A 150 mL solution
of 13 (357 mg, 2.85 mmol) and 17 (1.13 g, 7.10 mmol) was irradiated
for 4 h (ca. 77% conversion of 13). Workup and column
chromatography (ethyl acetate:n-hexane = 1:3) giving 21 (21a, 62
mg, 10% and 21b, 124 mg, 20%), 24 (24a, 55 mg, 12% and 24b, 101
mg, 22%) and trace of 26.21
SiMe3, 7), 146 (74), 99 (44), 73 (100); HRMS (EI) m/z 267.1267
(C13H21NO3Si requires 267.1291).
25 (liq). 1H NMR (CDCl3) 1.54 (s, 3H), 2.82 (d, 1H, J = 15.8 Hz),
3.19 (d, 1H, J = 15.8 Hz), 3.58 (s, 3H), 4.94 (s, 1H), 7.16 (t, 1H, J =
6.2 Hz), 7.64 (m, 2H), 8.48 (d, 1H, J = 4.8 Hz); 13C NMR (CDCl3)
29.2, 45.4, 51.5, 73.6, 119.2, 121.9, 136.8, 147.9, 164.9, 172.9; IR
(neat) 3100−3600 (br, OH stretching), 1730 (CO stretching); MS
(EI) m/z (rel. intensity) 195 (M+, 5), 180 (M+ − CH3, 67), 148 (66),
136 (77), 122 (M+ − CH2CO2CH3, 100), 106 (67), 79 (97), 51 (47);
HRMS (EI) m/z 180.0671 (M+ − CH3, C9H10NO3 requires
180.0666).
In Acetonitrile. A 150 mL solution of 13 (372 mg, 3.10 mmol) and
17 (1.08 g, 6.89 mmol) was irradiated for 4.5 h (ca. 96% conversion of
13). Workup and column chromatography (ethyl acetate:n-hexane =
1:3) gave 21 (21a, 50 mg, 6% and 21b, 118 mg, 14%), 24 (24a, 82 mg,
13% and 24b, 305 mg, 49%) and 14 mg (2%) of 26.
1
27 (liq). H NMR (CDCl3) 1.45 (d, 3H, J = 6.6 Hz), 3.64 (s, 3H),
1
21a (liq). H NMR (CDCl3) −0.19 (s, 9H), 1.31 (d, 3H, J = 6.2
3.97 (d of d, 2H, J = 16.5 Hz), 4.64 (q, 1H, J = 6.6 Hz), 7.18 (m, 1H),
7.45 (d, 1H, J = 7.8 Hz), 7.67 (t, 1H, J = 5.9 Hz), 8.52 (d, 1H, J = 4.1
Hz); 13C NMR (CDCl3) 21.9, 51.6, 66.1, 79.4, 120.0, 122.5 136.9,
148.7, 161.8, 170.4; IR (neat) 1770 (CO stretching); MS (EI) m/z
(rel. intensity) 195 (M+, 0.1), 180 (M+ − CH3, 2), 149 (7), 136 (17),
122 (M+ − CH2CO2CH3, 77), 107 (100), 106 (M+ − OCH2CO2CH3,
97), 78 (48), 59 (27), 50 (19); HRMS (EI) m/z 195.0871
(C10H13NO3 requires 195.0895).
Irradiation of 3-Acetylpyridine (14) and 1-Methoxy-2-
methyl-1-(trimethylsilyloxy)propene (16). In Benzene. A 150
mL solution of 14 (364 mg, 3.00 mmol) and 16 (1.04 g, 6.00 mmol)
was irradiated for 7 h (ca. 90% conversion of 14). Workup and column
chromatography (ethyl acetate:n-hexane = 1:3) giving 28 (28a, 47 mg,
6% and 28b, 47 mg, 6%), 471 mg (77%) of 31 and 59 mg (9%) of
34.24
Hz), 1.78 (s, 3H), 3.34 (s, 3H), 4.91 (q, 1H, J = 6.3 Hz), 7.13 (t, 1H, J
= 5.6 Hz), 7.67 (m, 2H), 8.53 (d, 1H, J = 4.8 Hz); 13C NMR (CDCl3)
1.0, 16.9, 22.2, 51.1, 83.1, 94.5, 102.7, 121.5, 121.7, 135.6, 148.1, 162.4;
MS (EI) m/z (rel. intensity) 281 (M+, 0.1), 266 (M+ − CH3, 2), 250
(M+ − OCH3, 1), 222 (19), 208 (M+-SiMe3, 5), 192 (M+ − OSiMe3,
4), 179 (17), 160 (100), 132 (16), 100 (58), 81 (53), 73 (82), 59
(72); HRMS (EI) m/z 281.1475 (C14H23NO3Si requires 281.1448).
21b (liq). 1H NMR (CDCl3) 0.20 (s, 9H), 1.41 (d, 3H, J = 6.4 Hz),
1.81 (s, 3H), 2.63 (s, 3H), 4.90 (q, 1H, J = 6.4 Hz), 7.17 (t, 1H, J = 4.9
Hz), 7.71 (t, 1H, J = 7.4 Hz), 7.85 (d, 1H, J = 8.0 Hz), 8.55 (d, 1H, J =
4.8 Hz); 13C NMR (CDCl3) 1.1, 15.8, 22.5, 49.9, 85.5, 94.9, 100.8,
122.5, 122.6, 136.0, 148.0, 161.9; MS (EI) m/z (rel. intensity) 281
(M+, 1), 266 (M+ − CH3, 0.6), 222 (21), 208 (M+-SiMe3, 4), 192 (M+
− OSiMe3, 5), 160 (100), 132 (15), 100 (62), 73 (96), 59 (73);
HRMS (EI) m/z 281.1463 (C14H23NO3Si requires 281.1448).
24a (liq). 1H NMR (CDCl3) 0.94 (d, 3H, J = 7.1 Hz), 1.56 (s, 3H),
3.06 (q, 1H, J = 7.2 Hz), 3.69 (s, 3H), 4.75 (s, 1H), 7.17 (t, 1H, J = 4.9
Hz), 7.51 (d, 1H, J = 7.9 Hz), 7.69 (t, 1H, J = 5.9 Hz), 8.51 (d, 1H, J =
4.8 Hz); 13C NMR (CDCl3) 12.4, 27.4, 48.8, 51.6, 75.0, 119.7, 121.9,
136.6, 147.9, 163.4, 176.4; IR (neat) 3100−3600 (br, OH stretching),
1730 (CO stretching); MS (EI) m/z (rel. intensity) 209 (M+, 0.4),
194 (M+ − CH3, 5), 162 (M+ − CO2CH3, 8), 122 (100), 102 (21), 77
(24), 56 (11); HRMS (EI) m/z 209.1039 (C11H15NO3 requires
209.1053).
In Acetonitrile. A 150 mL solution of 14 (364 mg, 3.00 mmol) and
16 (1.04 g, 6.00 mmol) was irradiated for 7 h (ca. 60% conversion of
14). Workup and column chromatography (ethyl acetate:n-hexane =
1:3) gave 28 (28a, trace and 28b, trace), 372 mg (92%) of 31 and
trace of 34.
28a (liq). 1H NMR (CDCl3) −0.03 (s, 9H), 1.25 and 1.48 (s, 6H),
1.66 (s, 3H), 3.45 (s, 3H), 7.25 (m, 1H), 7.70 (m, 1H), 8.46 (d, 1H, J
= 3.2 Hz), 8.57 (s, 1H); 13C NMR (CDCl3) 1.2, 24.8, 26.0, 26.6, 51.6,
89.7, 91.0, 102.9, 122.4 133.1 147.5, 147.6, 139.9; MS (CI) m/z (rel.
intensity) 296 (M+ + H, 2), 280 (M+ − CH3, 1), 237 (12), 222 (M+-
SiMe3, 4), 194 (24), 174 (83), 133 (55), 105 (29), 73 (100); HRMS
(CI) m/z 296.1675 (M + H, C15H26NO3Si requires 296.1682).
24b (liq). 1H NMR (CDCl3) 1.24 (d, 3H, J = 7.3 Hz), 1.45 (s, 3H),
3.20 (q, 1H, J = 7.3 Hz), 3.44 (s, 3H), 4.76 (s, 1H), 7.10 (t, 1H, J = 4.8
Hz), 7.53 (d, 1H, J = 6.8 Hz), 7.62 (t, 1H, J = 7.3 Hz), 8.44 (d, 1H, J =
5.1 Hz); 13C NMR (CDCl3) 11.9, 25.5, 47.7, 51.3, 75.3, 119.5, 121.7,
136.5, 147.5, 165.2, 176.5; IR (neat) 3100−3500 (br, OH stretching),
1730 (CO stretching); MS (EI) m/z (rel. intensity) 209 (M+, 0.3),
162 (M+ − CO2CH3, 5), 194 (M+ − CH3, 3), 178 (M+ − OCH3, 5),
149 (7), 122 (100), 99 (14), 78 (22); HRMS (EI) m/z 209.1053
(C11H15NO3 requires 209.1053).
Irradiation of 2-Acetylpyridine (13) and 1-Methoxy-1-
(trimethylsilyloxy)ethene (18). In Benzene. A 150 mL solution
of 13 (374 mg, 3.10 mmol) and 18 (1.00 g, 7.00 mmol) was irradiated
for 16 h (ca. 94% conversion of 13). Workup and column
chromatography (ethyl acetate:CH2Cl2:n-hexane = 1:1:6) giving 22
(22a, 280 mg, 36% and 22b, trace), 81 mg (14%) of 25 and 284 mg
(50%) of 27.
1
28b (liq). H NMR (CDCl3) 0.28 (s, 9H), 1.39 and 1.46 (s, 6H),
1.66 (s, 3H), 2.92 (s, 3H), 7.24 (t, 1H, J = 4.8 Hz), 7.81 (d, 1H, J = 8.1
Hz), 8.48 (d, 1H, J = 1.8 Hz), 8.66 (s, 1H); 13C NMR (CDCl3) 1.6,
24.3, 26.3, 26.4, 51.3, 89.9, 90.3, 103.0, 122.5 133.7 147.7, 147.9,
139.3; MS (EI) m/z (rel. intensity) 295 (M+, 0.3), 280 (M+ − CH3,
2), 237 (12), 222 (M+-SiMe3, 5), 194 (22), 174 (71), 133 (35), 73
(100); HRMS (EI) m/z 295.1613 (C15H25NO3Si requires 295.1605).
1
31 (liq). H NMR (CDCl3) 1.13 and 1.15 (s, 3H), 1.61 (s, 3H),
3.69 (s, 3H), 4.60 (s, 1H), 7.24 (m, 1H), 7.80 (d, 1H, J = 8.1 Hz), 8.48
(d, 1H, J = 4.8 Hz), 8.66 (s, 1H); 13C NMR (CDCl3) 21.3, 21.4, 24.7,
50.0, 51.9, 75.8, 122.1, 134.7, 139.1, 147.7, 148.2, 178.0; IR (neat)
3100−3500 (br, OH stretching), 1710 (CO stretching); MS (CI)
m/z (rel. intensity) 224 (M+ + H, 3), 176 (0.5), 146 (0.5), 122 (M+ −
C(CH3)2CO2CH3, 100), 106 (12), 87 (10); HRMS (CI) m/z
224.1287 (M + H, C12H18NO3 requires 224.1287).
Irradiation of 3-Acetylpyridine (14) and 1-Methoxy-1-
(trimethylsilyloxy)propene (17). In Benzene. A 150 mL solution
of 14 (363 mg, 3.00 mmol) and 17 (1.00 g, 6.30 mmol) was irradiated
for 8.5 h (ca. 71% conversion of 14). Workup and column
chromatography (ethyl acetate:CHCl3:n-hexane = 1:1:5) giving 29
(29a, 132 mg, 22% and 29b, trace), 32 (32a, 32 mg, 7% and 32b, 102
mg, 23%) and 42 mg (8%) of 34.
In Acetonitrile. A 150 mL solution of 13 (375 mg, 3.10 mmol) and
18 (1.00 g, 7.00 mmol) was irradiated for 16 h (ca. 82% conversion of
13). Workup and column chromatography (ethyl acetate:CH2Cl2:n-
hexane = 1:1:3) gave 22 (22a, 156 mg, 23% and 22b, 67 mg, 10%),
112 mg (23%) of 25 and 74 mg (15%) of 27.
1
22a (liq). H NMR (CDCl3) −0.11 (s, 9H), 1.80 (s, 3H), 3.37 (s,
3H), 4.52 (d, 1H, J = 6.6 Hz), 4.67 (d, 1H, J = 7.0 Hz), 7.15 (m, 1H),
7.68 (m, 2H), 8.58 (d, 1H, J = 4.7 Hz); 13C NMR (CDCl3) 0.7, 21.9,
50.9, 79.0, 98.1, 101.0, 120.3, 121.5, 135.7, 148.4, 161.9; MS (CI) m/z
(rel. intensity) 268 (M+ + H, 11), 252 (M+ − CH3, 13), 194 (M+-
SiMe3, 41), 179 (59), 146 (100), 131 (65), 104 (90), 89 (82), 74 (98);
HRMS (CI) m/z 268.1378 (M + H, C13H22NO3Si requires 268.1368).
In Acetonitrile. A 150 mL solution of 14 (368 mg, 3.10 mmol) and
17 (1.00 g, 6.26 mmol) was irradiated for 8.5 h (ca. 45% conversion of
14). Workup and column chromatography (ethyl acetate:CHCl3:n-
hexane = 1:1:5) gave 29 (29a, 42 mg, 11% and 29b, 23 mg, 6%), 32
(32a, 76 mg, 26% and 32b, 162 mg, 55%) and trace of 34.
1
22b (liq). H NMR (CDCl3) 0.19 (s, 9H), 1.83 (s, 3H), 2.79 (s,
1
3H), 4.61 (d, 1H, J = 6.8 Hz), 4.70 (d, 1H, J = 6.7 Hz), 7.18 (m, 1H),
7.75 (m, 2H), 8.56 (d, 1H, J = 5.9 Hz); 13C NMR (CDCl3) 1.0, 22.3,
50.1, 79.6, 97.6, 101.2, 121.6, 122.0, 136.1, 148.2, 161.3; MS (EI) m/z
(rel. intensity) 267 (M+, 2), 252 (M+ − CH3, 1), 222 (9), 194 (M+-
29a (liq). H NMR (CDCl3) −0.18 (s, 9H), 1.34 (d, 3H, J = 6.2
Hz), 1.76 (s, 3H), 3.33 (s, 3H), 4.93 (q, 1H, J = 6.3 Hz), 7.27 (t, 1H, J
= 6.7 Hz), 7.78 (d, 1H, J = 6.3 Hz), 8.50 (d, 1H, J = 6.4 Hz), 8.65 (s,
1H); 13C NMR (CDCl3) 1.0, 16.6, 22.9, 51.2, 82.7, 92.0, 102.9, 122.5,
10310
dx.doi.org/10.1021/jo301961n | J. Org. Chem. 2012, 77, 10304−10313

The Journal of Organic Chemistry
Article
134.5, 138.3, 148.2, 148.3; MS (CI) m/z (rel. intensity) 282 (M+ + 1,
0.6), 266 (M+ − CH3, 5), 224 (31), 194 (59), 192 (M+ − OSiMe3, 3),
160 (100), 133 (66), 105 (38), 74 (95), 56 (97); HRMS (CI) m/z
282.1526 (M + H, C14H24NO3Si requires 282.1525).
stretching); MS (CI) m/z (rel. intensity) 164 (M+ + H, 1), 149 (M+ +
1 − CH3, 10), 135 (6), 122 (100), 106 (98), 78 (29), 50 (19); HRMS
(CI) m/z 164.0732 (C9H10NO2 requires 164.0712).
Irradiation of 4-Acetylpyridine (15) and 1-Methoxy-2-
methyl-1-(trimethylsilyloxy)propene (16). In Benzene. A 150
mL solution of 15 (363 mg, 3.00 mmol) and 16 (1.04 g, 6.00 mmol)
was irradiated for 3.5 h (ca. 79% conversion of 15). Workup and
column chromatography (ethyl acetate:n-hexane = 1:3) giving 36
(36a, 50 mg, 7% and 36b, 50 mg, 7%), 359 mg (68%) of 39 and 34 mg
(12%) of 42.19,25
In Acetonitrile. A 150 mL solution of 15 (364 mg, 3.00 mmol) and
16 (1.04 g, 6.00 mmol) was irradiated for 6 h (ca. 78% conversion of
15). Workup and column chromatography (ethyl acetate:n-hexane =
1:3) gave 36 (36a, trace and 36b, trace), 430 mg (82%) of 39 and 5
mg (4%) of 42.
29b (liq). 1H NMR (CDCl3) 0.21 (s, 9H), 1.42 (d, 3H, J = 6.2 Hz),
1.77 (s, 3H), 2.60 (s, 3H), 4.89 (q, 1H, J = 6.2 Hz), 7.17 (t, 1H, J = 4.9
Hz), 7.71 (t, 1H, J = 7.4 Hz), 7.85 (d, 1H, J = 8.0 Hz), 8.55 (d, 1H, J =
4.8 Hz); 13C NMR (CDCl3) 1.1, 15.8, 22.5, 49.9, 85.5, 94.9, 100.8,
122.5, 136.0, 138.3, 148.0, 148.1; MS (EI) m/z (rel. intensity) 281
(M+, 1), 266 (M+ − CH3, 0.6), 222 (21), 208 (M+-SiMe3, 4), 192 (M+
− OSiMe3, 5), 160 (100), 132 (15), 100 (62), 73 (96), 59 (73);
HRMS (EI) m/z 281.1463 (C14H23NO3Si requires 281.1448).
32a (liq). 1H NMR (CDCl3) 0.97 (d, 3H, J = 7.0 Hz), 1.58 (s, 3H),
2.85 (q, 1H, J = 7.0 Hz), 3.77 (s, 3H), 4.75 (s, 1H), 7.28 (t, 1H, J = 4.8
Hz), 7.81 (d, 1H, J = 6.1 Hz), 8.51 (d, 1H, J = 4.8 Hz), 8.65 (s, 1H);
13C NMR (CDCl3) 12.7, 29.6, 49.1, 52.0, 73.3, 123.0, 133.0, 140.5,
36a (liq). 1H NMR (CDCl3) −0.01 (s, 9H), 1.25 and 1.47 (s, 6H),
1.62 (s, 3H), 3.45 (s, 3H), 7.29 (d, 2H, J = 6.0 Hz), 8.54 (d, 2H, J =
5.8 Hz); 13C NMR (CDCl3) 1.1, 24.7, 26.0, 26.1, 51.6, 89.8, 91.6,
102.8, 120.7, 148.9, 153.6; MS (CI) m/z (rel. intensity) 295 (M+, 0.1),
280 (M+ − CH3, 2), 237 (8), 222 (M+-SiMe3, 4), 194 (24), 174 (52),
133 (29), 106 (13), 73 (100); HRMS (EI) m/z 295.1595
(C15H25NO3Si requires 295.1605).
146.8, 148.0, 177.1; IR (neat) 3100−3300 (br, OH stretching), 1730
(CO stretching); MS (CI) m/z (rel. intensity) 210 (M+ + H, 5),
194 (M+ − CH3, 40), 162 (M+ − CO2CH3, 21), 122 (100), 106 (17),
88 (65), 57 (48); HRMS (CI) m/z 210.1131(M + H, C11H16NO3
requires 210.1130).
32b (liq). 1H NMR (CDCl3) 1.34 (d, 3H, J = 7.3 Hz), 1.48 (s, 3H),
3.01 (q, 1H, J = 7.2 Hz), 3.49 (s, 3H), 7.20 (q, 1H, J = 4.1 Hz), 7.75
(d, 1H, J = 7.7 Hz), 8.40 (d, 1H, J = 2.9 Hz), 8.59 (s, 1H); 13C NMR
(CDCl3) 12.2, 26.4, 48.4, 51.7, 73.5, 122.9, 132.7, 142.8, 146.5, 147.8,
176.5; IR (neat) 3100−3400 (br, OH stretching), 1730 (CO
stretching); MS (CI) m/z (rel. intensity) 210 (M+ + H, 16), 194 (M+
− CH3, 5), 178 (M+ − OCH3, 11), 162 (M+ − CO2CH3, 8), 149 (8),
122 (100), 106 (74), 88 (66), 78 (59), 57 (52); HRMS (CI) m/z
210.1130 (C11H16NO3 requires 210.1130).
1
36b (liq). H NMR (CDCl3) 0.30 (s, 9H), 1.38 and 1.45 (s, 6H),
1.60 (s, 3H), 2.98 (s, 3H), 7.36 (d, 1H, J = 6.2 Hz), 8.48 (d, 2H, J =
5.8 Hz); 13C NMR (CDCl3) 1.6, 24.3, 26.3, 51.5, 90.4, 90.5, 103.1,
121.2, 149.0, 153.1; MS (CI) m/z (rel. intensity) 295 (M+, 0.3), 280
(M+ − CH3, 2), 237 (12), 222 (M+-SiMe3, 5), 194 (22), 174 (71), 133
(35), 73 (100); HRMS (CI) m/z 296.1680 (M + H, C15H26NO3Si
requires 296.1682).
1
39 (liq). H NMR (CDCl3) 1.13 and 1.17 (s, 6H), 1.58 (s, 3H),
3.67 (s, 3H), 4.64 (s, 1H), 7.34 (d, 2H, J = 6.2 Hz), 8.52 (d, 1H, J =
4.8 Hz); 13C NMR (CDCl3) 21.3, 24.3, 49.8, 51.8, 76.2, 122.1, 148.5,
153.0, 177.6; IR (neat) 3100−3500 (br, OH stretching), 1710 (CO
stretching); MS (CI) m/z (rel. intensity) 224 (M+ + H, 7), 206 (M+−
OH, 1), 176 (1), 122 (M+ − C(CH3)2CO2CH3, 100), 102 (42), 87
(14); HRMS (CI) m/z 224.1283 (M + H, C12H18NO3 requires
224.1287).
Irradiation of 4-Acetylpyridine (15) and 1-Methoxy-1-
(trimethylsilyloxy)propene (17). In Benzene. A 150 mL solution
of 15 (373 mg, 3.10 mmol) and 17 (1.20 g, 7.50 mmol) was irradiated
for 4.5 h (ca. 64% conversion of 15). Workup and column
chromatography (ethyl acetate:CH2Cl2:n-hexane = 1:1:5) giving 37
(37a, 168 mg, 30% and 37b, 21 mg, 4%), 40 (40a, 41 mg, 10% and
40b, 137 mg, 33%) and 20 mg (8%) of 42.
Irradiation of 3-Acetylpyridine (14) and 1-Methoxy-1-
(trimethylsilyloxy)ethene (18). In Benzene. A 150 mL solution
of 14 (372 mg, 3.10 mmol) and 18 (1.00 g, 7.00 mmol) was irradiated
for 16 h (ca. 93% conversion of 14). Workup and column
chromatography (ethyl acetate:CHCl3:n-hexane = 1:1:5) giving 30
(30a, 172 mg, 22% and 30b, trace), 164 mg (29%) of 33 and 238 mg
(50%) of 35.
In Acetonitrile. A 150 mL solution of 14 (380 mg, 3.14 mmol) and
18 (1.00 g, 7.00 mmol) was irradiated for 16 h (ca. 81% conversion of
14). Workup and column chromatography (ethyl acetate:CHCl3:n-
hexane = 1:1:5) gave 30 (30a, 80 mg, 12% and 30b, trace), 195 mg
(41%) of 33 and 146 mg (35%) of 35.
1
30a (liq). H NMR (CDCl3) −0.11 (s, 9H), 1.71 (s, 3H), 3.36 (s,
3H), 4.49 (d, 1H, J = 7.0 Hz), 4.63 (d, 1H, J = 7.0 Hz), 7.26 (t, 1H, J =
6.6 Hz), 7.70 (d, 1H, J = 8.1 Hz), 8.45 (d, 1H, J = 4.8 Hz), 8.58 (s,
1H); 13C NMR (CDCl3) 0.7, 23.9, 50.5, 78.7, 95.9, 100.5, 122.6, 133.3,
138.3, 147.4, 147.9; MS (CI) m/z (rel. intensity) 268 (M+ + H, 11),
252 (M+ − CH3, 13), 194 (M+-SiMe3, 41), 179 (59), 146 (100), 131
(65), 104 (90), 89 (82), 74 (98); HRMS (CI) m/z 268.1378 (M + H,
C13H22NO3Si requires 268.1369).
In Acetonitrile. A 150 mL solution of 15 (373 mg, 3.10 mmol) and
17 (1.00 g, 6.26 mmol) was irradiated for 4 h (ca. 63% conversion of
15). Workup and column chromatography (ethyl acetate:CH2Cl2:n-
hexane = 1:1:5) gave 37 (37a, 77 mg, 14% and 37b, trace), 40 (40a,
97 mg, 24% and 40b, 198 mg, 48%) and 21 mg (8%) of 42.
1
37a (liq). H NMR (CDCl3) −0.15 (s, 9H), 1.31 (d, 3H, J = 6.3
1
Hz), 1.70 (s, 3H), 3.34 (s, 3H), 4.91 (q, 1H, J = 6.4 Hz), 7.33 (d, 2H, J
= 6.2 Hz), 8.57 (d, 2H, J = 6.1 Hz); 13C NMR (CDCl3) 1.0, 16.7, 22.8,
51.1, 82.9, 92.5, 102.6, 121.4, 149.0, 151.8; MS (EI) m/z (rel.
intensity) 281 (M+, 0.1), 266 (M+ − CH3, 0.7), 250 (M+ − OCH3,
2.0), 224 (27), 192 (M+ − OSiMe3, 2), 160 (99), 133 (57), 105 (70),
74 (100), 60 (93); HRMS (EI) m/z 281.1447 (C14H23NO3Si requires
281.1448).
30b (liq). H NMR (CDCl3) 0.23 (s, 9H), 1.78 (s, 3H), 2.80 (s,
3H), 4.63 (two d, 2H, J = 7.0 Hz and J = 11.0 Hz), 7.31 (m, 1H), 7.85
(d, 1H, J = 7.7 Hz), 8.51 (s, 1H), 8.68 (s, 1H); 13C NMR (CDCl3) 1.1,
23.9, 50.0, 79.1, 94.8, 101.3, 122.7, 134.2, 137.4, 147.7, 148.4; MS (EI)
m/z (rel. intensity) 267 (M+, 2), 252 (M+ − CH3, 1), 222 (9), 194
(M+-SiMe3, 7), 146 (74), 99 (44), 73 (100); HRMS (EI) m/z
267.1267 (C13H21NO3Si requires 267.1291).
37b (liq). 1H NMR (CDCl3) 0.22 (s, 9H), 1.42 (d, 3H, J = 6.2 Hz),
1.72 (s, 3H), 2.69 (s, 3H), 4.90 (q, 1H, J = 6.3 Hz), 7.45 (d, 2H, J =
5.9 Hz), 8.57 (d, 2H, J = 5.5 Hz); 13C NMR (CDCl3) 1.1, 15.5, 22.9,
49.6, 85.3, 92.3, 101.1, 121.6, 149.2, 151.2; MS (EI) m/z (rel.
intensity) 281 (M+, 0.1), 266 (M+ − CH3, 0.7), 250 (M+ − OCH3,
2.0), 224 (27), 192 (M+ − OSiMe3, 3), 160 (99), 133 (57), 105 (70),
74 (100), 60 (93); HRMS (EI) m/z 281.1447 (C14H23NO3Si requires
281.1448).
33 (liq). 1H NMR (CDCl3) 1.56 (s, 3H), 2.91 (q, 2H, J = 16.6 Hz),
3.62 (s, 3H), 4.58 (s, 1H), 7.29 (t, 1H, J = 4.8 Hz), 7.83 (d, 1H, J = 8.0
Hz), 8.49 (d, 1H, J = 4.7 Hz), 8.65 (s, 1H); 13C NMR (CDCl3) 30.3,
45.9, 51.8, 71.4, 123.1, 132.5, 146.2, 148.0, 142.1, 172.6; IR(neat)
3100−3400 (br, OH stretching), 1730 (CO stretching); MS (EI)
m/z (rel. intensity) 195 (M+, 2), 180 (M+ − CH3, 84), 148 (25), 136
(77), 122 (M+ − CH2CO2CH3, 100), 106 (88), 78 (51), 50 (30);
HRMS (EI) m/z 180.0675 (M+ − CH3, C9H10NO3 requires
180.0666).
40a (liq). 1H NMR (CDCl3) 0.96 (d, 3H, J = 7.2 Hz), 1.53 (s, 3H),
2.83 (q, 1H, J = 7.1 Hz), 3.78 (s, 3H), 3.98 (s, 1H), 7.35 (d, 2H, J =
6.2 Hz), 8.58 (d, 2H, J = 6.2 Hz); 13C NMR (CDCl3) 12.5, 29.0, 48.6,
51.9, 73.6, 120.1, 149.4, 154.3, 176.7; IR (neat) 3100−3500 (br, OH
stretching), 1730 (CO stretching); MS (EI) m/z (rel. intensity) 209
35 (liq). 1H NMR (CDCl3) 1.83 (s, 3H), 5.39 (d of d, 2H, J = 15.2
Hz), 7.33 (q, 1H, J = 4.2 Hz), 7.76 (d, 1H, J = 7.8 Hz), 8.60 (d, 1H, J
= 1.5 Hz), 8.74 (s, 1H); 13C NMR (CDCl3) 23.9, 86.9, 107.3, 123.4,
131.8, 134.3, 145.7, 149.5, 201.3 (CO); IR (neat) 1730 (CO
10311
dx.doi.org/10.1021/jo301961n | J. Org. Chem. 2012, 77, 10304−10313

The Journal of Organic Chemistry
Article
(M+, 0.8), 194 (M+ − CH3, 31), 162 (M+ − CO2CH3, 15), 122 (100),
105 (76), 88 (72), 57 (37); HRMS (CI) m/z 210.1131 (M + H,
C11H16NO3 requires 210.1130).
ACKNOWLEDGMENTS
■
This research was supported by Basic Science Research
Program through the National Research Foundation of Korea
(NRF) funded by the Ministry of Education, Science and
Technology (2012R1A1A1013201 for D.W.C.,
2012R1A1A2007158 for U.C.Y.).
40b (liq). 1H NMR (CDCl3) 1.35 (d, 3H, J = 7.3 Hz), 1.42 (s, 3H),
2.98 (q, 1H, J = 7.2 Hz), 3.47 (s, 3H), 4.25 (s, 1H), 7.33 (d, 2H, J =
6.3 Hz), 8.53 (d, 2H, J = 6.2 Hz); 13C NMR (CDCl3) 12.1, 26.0, 47.8,
51.6, 73.8, 119.9, 149.3, 156.5, 176.2; IR (neat) 3100−3400 (br, OH
stretching), 1730 (CO stretching); MS (EI) m/z (rel. intensity) 209
(M+, 5), 194 (M+ − CH3, 4), 162 (M+ − CO2CH3, 9), 122 (100), 106
(76), 88 (76), 88 (76), 61 (61); HRMS (EI) m/z 209.1052
(C11H15NO3 requires 209.1053).
REFERENCES
■
(1) (a) Cho, D. W.; Yoon, U. C.; Mariano, P. S. Acc. Chem. Res. 2011,
44, 204. (b) 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. (c) Yoon, U. C.; Oh, S. W.; Lee, C. W.
Heterocycles 1995, 41, 2665.
(2) (a) Wang, R.; Zhao, Z.; Mariano, P. S.; Choi, K. H.; Kim, S. H.;
Yoon, U. C. J. Photochem. Photobiol., A 2005, 175, 232. (b) Maeda, H.;
Tierney, D. L.; Mariano, P. S.; Cho, D. W.; Yoon, U. C. Tetrahedron
2008, 64 (22), 5268.
(3) (a) 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. (b) Cho,
D. W.; Lee, H.-Y.; Oh, S. W.; Choi, J. H.; Park, H. J.; Mariano, P. S.;
Yoon, U. C. J. Org. Chem. 2008, 73, 4539.
(4) (a) 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. (b) 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.
(c) Mattay, J.; Gersdorf, J.; Leismann, H.; Steenken, S. Angew. Chem.,
Int. Ed. 1984, 23, 249. (d) Mattay, J. Angew. Chem., Int. Ed. 1987, 26,
825. (e) Gersdorf, J.; Mattay, J.; Goerner, H. J. Am. Chem. Soc. 1987,
109, 1203. (f) Mattay, J. Synthesis 1989, 4, 233.
(5) (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) Abe,
M.; Shirodai, Y.; Nojima, M. J. Chem. Soc., Perkin Trans. 1 1998, 19,
3253.
(6) (a) Das, S.; Von Sonntag, C. Z. Naturforscher 1986, 416, 505.
(b) Powell, M. F.; Wu, J. C.; Bruice, T. C. J. Am. Chem. Soc. 1984, 106,
3850. (c) Sinha, A.; Bruice, T. C. J. Am. Chem. Soc. 1984, 106, 7291.
(d) Dinnocenzo, J. P.; Banach, T. E. J. Am. Chem. Soc. 1989, 111, 8646.
(e) Anne, A.; Hapiot, P.; Moiroux, J.; Neta, P.; Saveant, J. -M. J. Am.
Chem. Soc. 1992, 114, 4694. (f) Nicholas, A. M. D.; Arnold, D. R. Can.
J. Chem. 1982, 60, 2165.
(7) (a) Hirao, T.; Morimoto, C.; Takada, T.; Sakurai, H. Tetrahedron
2001, 57, 5073. (b) Maruyama, T.; Mizuno, Y.; Shimizu, I.; Suga, S.;
Yoshida, J. J. Am. Chem. Soc. 2007, 129, 1902.
(8) Cermenati, S.; Freccero, M.; Venturello, P.; Albini, A. J. Am.
Chem. Soc. 1995, 117, 7869.
(9) (a) Jervis, P. J.; Kariuki, B. M.; Cox, L. R. Tetrahedron Lett. 2008,
49, 2514. (b) Shindoh, N.; Tokuyama, H.; Takasu, K. Tetrahedron Lett.
2007, 48, 4749. (c) Huang, Y.; Moeller, K. D. Tetrahedron 2006, 62,
6536.
(10) (a) Asao, N.; Chan, C. S.; Takahashi, K.; Yamamoto, Y.
Tetrahedron 2005, 61, 11322. (b) Sarkar, T. K.; Hazra, A.;
Gangopadhyay, P.; Panda, N.; Slanina, Z.; Lin, C.-C.; Chen, H. -T.
Tetrahedron 2005, 61, 1155. (c) Fernandez-Rivas, C.; Mendez, M.;
Echavarren, A. M. J. Am. Chem. Soc. 2000, 122, 1221. (d) Huang, H.;
Panek, J. S. Org. Lett. 2003, 5, 1991.
(11) (a) Li, W.-D. Z.; Yang, J.-H. Org. Lett. 2004, 6, 1849.
(b) Beignet, J.; Tiernan, J.; Woo, C. H.; Kariuki, B. M.; Cox, L. R. J.
Org. Chem. 2004, 69, 9323. (c) Judd, W. R.; Ban, S.; Aube, J. J. Am.
Chem. Soc. 2006, 128, 13736. (d) Chabaud, L.; James, P.; Landais, Y.
Eur. J. Org. Chem. 2004, 15, 3173. (e) Huber, J. D.; Perl, N. R.;
Leighton, J. L. Angew. Chem., Int. Ed. 2008, 120, 3079.
(12) (a) Sato, T.; Wakahara, Y.; Otera, J.; Nozaki, H.; Fukuzumi, S. J.
Am. Chem. Soc. 1991, 113, 4028. (b) Fukuzumi, S.; Suenobu, T.;
Fujitsuka, M.; Ito, O.; Tonoi, T.; Matsumoto, S.; Miakmi, K. J.
Organomet. Chem. 1999, 574, 32. (c) Fukuzumi, S.; Fujita, M.; Otera,
J.; Fujita, Y. J. Am. Chem. Soc. 1992, 114, 10271. (d) Fukuzumi, S.;
Fujita, M. J. Org. Chem. 1993, 58, 5405.
Irradiation of 4-Acetylpyridine (15) and 1-Methoxy-1-
(trimethylsilyloxy)ethene (18). In Benzene. A 150 mL solution
of 15 (367 mg, 3.00 mmol) and 18 (1.00 g, 7.00 mmol) was irradiated
for 16 h (ca. 96% conversion of 15). Workup and column
chromatography (ethyl acetate:CHCl3:n-hexane = 1:1:5) giving 38
(38a, 193 mg, 25% and 38b, 32 mg, 4%), 292 mg (52%) of 41 and 285
mg (52%) of 43.
In Acetonitrile. A 150 mL solution of 15 (372 mg, 3.10 mmol) and
18 (1.00 g, 7.00 mmol) was irradiated for 16 h (ca. 89% conversion of
15). Workup and column chromatography (ethyl acetate:CHCl3:n-
hexane = 1:1:5) gave 38 (38a, 156 mg, 21% and 38b, 16 mg, 2%), 140
mg (26%) of 41 and 190 mg (37%) of 43.
1
38a (liq). H NMR (CDCl3) −0.11 (s, 9H), 1.66 (s, 3H), 3.35 (s,
3H), 4.47 (d, 1H, J = 7.0 Hz), 4.60 (d, 1H, J = 7.0 Hz), 7.28 (d, 2H, J
= 5.9 Hz), 8.57 (d, 2H, J = 4.8 Hz); 13C NMR (CDCl3) 0.6, 23.6, 50.4,
78.6, 96.4, 100.3, 120.6, 149.1, 151.8; MS (CI) m/z (rel. intensity) 268
(M+ + 1, 4), 252 (M+ − CH3, 13), 237 (47), 236 (M+ − OCH3, 16),
194 (M+-SiMe3, 48), 178 (M+ − OSiMe3, 59), 147 (59), 110 (79), 92
(84), 75 (97), 61 (100), 52 (74); HRMS (CI) m/z 268.1369 (M + H,
C13H22NO3Si requires 268.1369).
1
38b (liq). H NMR (CDCl3) 0.23 (s, 9H), 1.71 (s, 3H), 2.85 (s,
3H), 4.62 (s, 2H), 7.39 (d, 2H, J = 4.8 Hz), 8.59 (d, 2H, J = 5.1 Hz);
13C NMR(CDCl3) 1.2, 23.2, 50.2, 79.0, 95.4, 101.3, 121.1, 149.3,
151.0; MS (EI) m/z (rel. intensity) 267 (M+, 0.1), 252 (M+ − CH3,
3), 237 (6), 195 (M+-SiMe3, 56), 180 (26), 122 (80), 106 (100), 75
(70), 59 (74), 50 (90); HRMS (EI) m/z 267.1293 (C13H21NO3Si
requires 267.1291).
41 (liq). 1H NMR (CDCl3) 1.52 (s, 3H), 2.89 (q, 2H, J = 16.2 Hz),
3.62 (s, 3H), 4.54 (s, 1H), 7.35 (d, 2H, J = 6.2 Hz), 8.56 (d, 2H, J =
6.2 Hz); 13C NMR (CDCl3) 30.0, 45.4, 51.9, 72.0, 119.7, 149.8, 155.8,
172.6; IR(neat) 3100−3400 (br, OH stretching), 1730 (CO
stretching); MS (EI) m/z (rel. intensity) 195 (M+, 7), 180 (M+ −
CH3, 100), 148 (36), 122 (M+ − CH2CO2CH3, 64), 106 (68), 78
(50); HRMS (EI) m/z 195.0892 (C10H13NO3 requires 195.0896).
1
43 (liq). H NMR (CDCl3) 1.42 (d, 3H, J = 6.6 Hz), 3.66 (s, 3H),
3.93 (d of d, 2H, J = 16.4 Hz), 4.50 (q, 1H, J = 6.5 Hz), 7.20 (d, 2H, J
= 5.6 Hz), 8.51 (d, 2H, J = 4.4 Hz); 13C NMR (CDCl3) 23.3, 52.3,
67.2, 78.0, 123.1, 149.6, 155.8, 174.1; IR(neat) 1750 (CO
stretching); MS (EI) m/z (rel. intensity) 195 (M+, 2), 180 (M+ −
CH3, 8), 149 (15), 122 (M+ − CH2CO2CH3, 100), 106 (M+
−
OCH2CO2CH3, 93), 78 (16), 75 (20), 50 (13); HRMS (EI) m/z
180.0661 (M+ − CH3, C9H10NO3 requires 180.0666).
ASSOCIATED CONTENT
■
S
* Supporting Information
1H and 13C NMR spectra of all previously unidentified
compounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: ucyoon@pusan.ac.kr; dwcho00@yu.ac.kr.
Notes
The authors declare no competing financial interest.
10312
dx.doi.org/10.1021/jo301961n | J. Org. Chem. 2012, 77, 10304−10313

The Journal of Organic Chemistry
Article
(13) (a) Abe, M.; Ikeda, M.; Shirodai, Y.; Nojima, M. Tetrahedron
Lett. 1996, 37, 5901. (b) Mizuno, K.; Takahashi, N.; Nishiyama, T.;
Inoue, H. Tetrahedron Lett. 1995, 36, 7463. (c) Rotzoll, S.; Ullah, E.;
Fischer, C.; Michalik, D.; Spannenberg, A.; Langer, P. Tetrahedron
2006, 62, 12084.
(14) (a) Saha, N. N.; Desai, V. N.; Dhavale, D. D. Tetrahedron 2001,
57, 39. (b) 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.
(15) (a) Mukaiyama, T.; Banno, K.; Narasaka, K. J. Am. Chem. Soc.
1974, 96, 7503. (b) Mukaiyama, T. Org. React. 1982, 28, 203.
(c) Mukaiyama, T. Challenges in Synthetic Organic Chemistry; Oxford
University Press: New York, USA, 1990; pp 177−213. (d) Mukaiyama,
T.; Kobayashi, S.; Tamura, M.; Sagawa, Y. Chem. Lett. 1987, 3, 491.
(16) Giuseppone, N.; Van De Weghe, Pierre; Mellah, M.; Collin, J.
Tetrahedron 1998, 54, 13129.
(17) Oh, S. W.; Kim, J. Y.; Cho, D. W.; Choi, J. H.; Yoon, U. C. Bull.
Korean Chem. Soc. 2007, 28, 629.
(18) (a) Jones, G. In Organic Photochemistry; Padwa, A., Ed.; Marcel
Dekker: New York, 1981; Vol. 5, Chapter I. (b) Griesbeck, A. G.;
Fiege, M.; Bondock, S.; Gudipati, M. S. Org. Lett. 2002, 2, 3623.
(c) Adam, W.; Stegmann, V. R. Synthesis 2001, 8, 1203. (d) Buchi, G.;
̈
Inman, C. G.; Lipinsky, E. S. J. Am. Chem. Soc. 1954, 76, 4327.
(e) Bach, T. Synthesis 1998, 5, 683.
(19) Bernardi, R.; Caronna, T.; Morrocchi, S.; Vittimberga, B. M. J.
Chem. Soc., Perkin Trans. 2 1991, 22, 1411.
(20) (a) Sakamoto, M.; Yagi, T.; Mino, T.; Yamaguchi, K.; Fujita, T.
J. Am. Chem. Soc. 2000, 122, 8141. (b) Sakamoto, M.; Sano, T.; Fujita,
S.; Ando, M.; Yamaguchi, K.; Mino, T.; Fujita, T. J. Org. Chem. 2003,
68, 1447.
(21) Clerici, A.; Porta, O. J. Org. Chem. 1982, 47, 2852.
(22) (a) Loutfy, R. O.; Loutfy, R. O. Can. J. Chem. 1973, 51, 1169.
(b) Cowan, D. O.; Drisko, R. L. In Elements of Organic Photochemistry;
Plenum Press: New York, 1976; Chapter 5, pp 205−266. (c) The
ΔGSET was calculated according to Rehm−Weller equation, ΔGSET
Eox − Ered −ET*.
=
(23) Because of the structural similarity, oxidation potential (Eox) of
CH2C(OEt)OSiMe3 (ref 12c) was used.
(24) Allen, M. J. J. Org. Chem. 1950, 15, 435.
(25) Okano, T.; Matsuoka, M.; Konishi, H.; Kiji, J. Chem. Lett. 1987,
1, 181.
10313
dx.doi.org/10.1021/jo301961n | J. Org. Chem. 2012, 77, 10304−10313