Exploration of photochemical reactions of N-trimethylsilylmethyl- substituted uracil, pyridone, and pyrrolidone derivatives

Article abstract of DOI:10.1039/c0pp00372g

Photochemical reactions of N-trimethylsilylmethyl-substituted uracil, pyridone and pyrrolidone derivatives were carried out to determine if silicone containing substituents have an impact on excited state reaction profiles. The results show that ultraviolet irradiation of N-trimethylsilylmethyl substituted uracils in the presence of substituted alkenes leads to efficient formation of both dimeric and cross [2+2]-cycloaddition products. Qualitatively similar observations were made in a study of the photochemistry of N- trimethylsilylmethyl-2-pyridone. The combined results demonstrate that [2+2]-photocycloaddition is a more efficient excited state reaction pathway for the uracil and pyridone substrates as compared to other processes, such as ylide-forming trimethylsilyl group C-to-O migration. Finally, photoreactions of N-trimethylsilylmethyl-2-pyrrolidone in solutions containing dipolarophiles, such as methyl acrylate, lead to the formation of the desilylation product, N-methyl-2-pyrrolidone by way of a simple, non-ylide generating, protodesilylation process. In addition, observations were made which show that orbital symmetry allowed photocycloreversion reactions of dimeric uracil derivatives, involving cyclobutane ring splitting, to take place. These processes, which lead to the formation of monomeric uracils, appear to be stimulated by the presence of electron donor groups on the cyclobutane ring, a likely result of a new SET promoted cyclobutane ring cleavage pathway. In the cases of N-trimethylsilylmethyl-substituted cyclobutane derivatives that possess phthalimide groups, highly efficient excited state cleavage of the cyclobutane moiety occurs to produce uracil derivatives and corresponding vinyl phthalimide. The Royal Society of Chemistry and Owner Societies 2011.

Full text of DOI:10.1039/c0pp00372g

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PAPER
Exploration of photochemical reactions of N-trimethylsilylmethyl-substituted
uracil, pyridone, and pyrrolidone derivatives†
Dae Won Cho,a,d Chan Woo Lee,b Jong Gu Park,a Sun Wha Oh,c Nam Kyoung Sung,a Hea Jung Park,a
Kyung Mok Kim,a Patrick S. Mariano*d and Ung Chan Yoon*a
Received 10th December 2010, Accepted 10th March 2011
DOI: 10.1039/c0pp00372g
Photochemical reactions of N-trimethylsilylmethyl-substituted uracil, pyridone and pyrrolidone
derivatives were carried out to determine if silicone containing substituents have an impact on excited
state reaction profiles. The results show that ultraviolet irradiation of N-trimethylsilylmethyl substituted
uracils in the presence of substituted alkenes leads to efficient formation of both dimeric and cross
[2+2]-cycloaddition products. Qualitatively similar observations were made in a study of the
photochemistry of N-trimethylsilylmethyl-2-pyridone. The combined results demonstrate that
[2+2]-photocycloaddition is a more efficient excited state reaction pathway for the uracil and pyridone
substrates as compared to other processes, such as ylide-forming trimethylsilyl group C-to-O migration.
Finally, photoreactions of N-trimethylsilylmethyl-2-pyrrolidone in solutions containing dipolarophiles,
such as methyl acrylate, lead to the formation of the desilylation product, N-methyl-2-pyrrolidone by
way of a simple, non-ylide generating, protodesilylation process. In addition, observations were made
which show that orbital symmetry allowed photocycloreversion reactions of dimeric uracil derivatives,
involving cyclobutane ring splitting, to take place. These processes, which lead to the formation of
monomeric uracils, appear to be stimulated by the presence of electron donor groups on the
cyclobutane ring, a likely result of a new SET promoted cyclobutane ring cleavage pathway. In the cases
of N-trimethylsilylmethyl-substituted cyclobutane derivatives that possess phthalimide groups, highly
efficient excited state cleavage of the cyclobutane moiety occurs to produce uracil derivatives and
corresponding vinyl phthalimide.
1. Introduction
Silicon containing organic compounds serve as key substrates in
synthetically useful chemical reactions.1 In addition, substances
that possess trialkylsilyl substitution at sites adjacent to electron
donor centers undergo ready oxidation to generate silicon stabi-
lized cation radical intermediates II (Scheme 1), which participate
in fast nucleophile-assisted desilylation reactions that produce
neutral, carbon-centered radicals III.2–7
Scheme 1
reactions of phthalimide acceptor- a-trimethylsilyl electron donor
systems.13–15 In this work,2–7 we have shown that phthalimides (1,
Scheme 2) containing tethered a-silyl electron donors undergo
intramolecular, photoinduced SET to form zwitterionic biradicals
2 that, through intrachain SET, generate silicon-stabilized 1,w-
zwitterionic biradicals 3. Silophile induced a-desilylation at the
cation radical centers in 3 results in the production of 1,w-
biradicals 4 that undergo C–C bond formation to form cyclic
products 5. By using this mechanistic analysis as a guide,
SET promoted photoreactions of diverse types of phthalimide
substrates have been devised for the preparation of a variety of
N-heterocyclic and macrocyclic systems.
From the time of the early pioneering studies by Kanaoka8–10
and Coyle11,12 of the single electron transfer (SET) photochemistry
of N-alkylphthalimides, efforts in our laboratories have focused on
developing the preparative potential of inter- and intra-molecular
aDepartment of Chemistry and Chemistry Institute for Functional Materials,
Pusan National University, Busan, 609-735, Korea
bDepartment of Chemistry, Hanyang University, Seoul, 133-791, Korea
cBasic Science Research Institute, Pukyong National University, Busan, 608-
735, Korea
dDepartment of Chemistry and Chemical Biology, University of New
Mexico, Albuquerque, New Mexico, 87131, USA. E-mail: ucyoon@pusan.
ac.kr, mariano@unm.edu
In these investigations, we observed that irradiation of N-
trimethylsilylmethylphthalimide 6 (Y = SiMe3) promotes an
excited state reaction involving sequential intramolecular SET-
C-to-O trimethylsilyl group migration to form the azomethine
† Electronic supplementary information (ESI) available: 1H and 13C NMR
spectra. See DOI: 10.1039/c0pp00372g
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with trimethylsilylmethyl iodide promoted by NaH in anhy-
drous DMF. This process gives both the mono- and bis-
trimethylsilylmethyl- substituted uracils 10 (40%) and 11 (35%),
respectively (Scheme 4).
Scheme 2
Scheme 4
ylide 7 (Scheme 3). Interestingly, this type of process, involving an
analogous C-to-O hydrogen migration, does not take place with
N-alkylphthalimide analogs 6 (Y = H).13–15
Direct irradiation (Vycor, l > 220 nm) of 10 in deoxygenated
MeCN leads to efficient production of the syn-[2+2] dimer 12
(70%) as the major product (Scheme 5 and 6). Similarly, irradiation
of 11 under the same conditions gives rise to a mixture of
the syn- and anti-diastereomeric cycloadducts 13 and 14 (77%).
Photoreactions of 10 in MeCN containing methyl acrylate (0.1
M) and vinyl acetate (10–20 mM) produce the respective crossed
[2+2] cycloaddition products 15 (63%), and 16 and 17 (68%). The
photoreaction of bis-trimethylsilylmethyl uracil 11 in MeCN in
the presence of vinyl acetate also generates the corresponding
cycloadducts 18 and 19 (63%). Assignment of regiochemistry and
stereochemistry to cycloadducts 12–19 was made on the basis of
their characteristic 1H- and 13C-NMR properties and comparisons
with those of closely related 1,3-dimethyluracil derived photo-
Scheme 3
Since other conjugated imides and amides that contain N-
silylmethyl substitution are transformed to their corresponding
azomethine ylides by photoinduced C-to-O silyl migration,13–17
it is possible that this novel reaction is a general excited state
process. Another general excited state process involves excited
state [2+2] cycloaddition.14,18–21 An interesting feature related to
[2+2]-cycloaddition reactions, which generate strained cyclobu-
tane ring systems, is the orbital topology allowed,22–23 and the
photoinduced cycloreversion reaction, which cleaves the four-
membered ring to produce a pair of olefins. The importance
of this reaction is exemplified by the biologically interesting
cleavage of photogenerated pyrimidine dimers in DNA.24–30 It
is known that UV induced damage of DNA is caused, in part,
by cyclobutane formation through [2+2]-cycloaddition between
proximal pyrimidine chromophores. To reverse this damage, en-
zymes, dubbed photolyases,28–31 have evolved to promote electron
transfer processes to generate cyclobutane radical cation or anion
intermediates, which undergo cyclobutane ring splitting.24–27,32–35
Our continuing interest in this area stimulated an exploration
for photoreactions of substrates that contain structures and substi-
tution patterns that enable the operation of SET promoted, ylide
forming silyl migration and other general excited state processes.
Below, we describe the results of a photochemical investigation
of N-trimethylsilylmethyl-uracils and N-trimethylsilylmethyl-2-
pyridone substances that are capable of participating in a compet-
itive excited state [2+2]-cycloaddition and SET promoted C-to-O
silyl migration reactions.
1
cycloadducts 21–26 (Scheme 6).36–37 Interestingly, the H-NMR
spectrum of the symmetric dimer 12 contains an AB quartet
(3.45 and 4.06 ppm) that corresponds to CH2SiMe3 protons,
which are apparently rendered non-equivalent as a consequence
of restricted rotation about the N–C bond This phenomenon
is a likely result of steric effects caused by the location of the
2. Results and discussion
Photoreaction of the N-trimethylsilylmethyl-uracils 10 and 11
These studies began with the preparation of the N-trimethyl-
silylmethyl-uracils 10 and 11 via reaction of uracil (9)
Scheme 5
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Scheme 6
Scheme 7
CH2SiMe3 groups in the crowded environment of the syn-tricyclic
1
ring system. This behavior is also seen in the H-NMR spectra
of structurally similar substances (see supporting information†).
For instance, dimer 13 which has two different kinds of methylene
protons associated with the two sets of CH2SiMe3 groups, has
a spectrum in which one set of methylene protons appear as a
singlet at 3.28 ppm as a consequence of their chemical equivalence
and another set of CH2SiMe3 protons that resonate as an AB
quartet.
At the outset of this effort, we anticipated that incorporation
of N-silylmethyl moieties in place of N-methyl groups on the
uracil ring system would enable the operation of excited state SET-
promoted C-to-O silyl migration leading to the formation of tran-
sient azomethine ylides 27 (Scheme 7), as occurs in the case with
other conjugated imides (e.g., N-trimethylsilylmethylphthalimide
6 (Y = SiMe3)13,15 and N-trimethylsilylmethylmaleimide 3016).
However, as is demonstrated by the results outlined above,
irradiation of the N-trimethylsilylmethyl substituted uracils
10 and 11 fails to produce ylide intermediate 27, which
would have participated in ready dipolar cycloaddition reac-
tions with the olefinic dipolarophiles to form pyrrolizidines
28. Instead, [2+2]-cycloaddition occurs selectively in the ex-
cited states of these substrates to produce photodimers 12–14
and 15–19.
Photoreactions of N-trimethylsilylmethyl-2-pyridone (33) and
N-trimethylsilylmethy-2-pyrrolidinone (34)
Photochemical reactions of N-trimethylsilylmethyl-2-pyridione
(33),17 prepared by reaction of trimethylsilymethyl iodide with
2-hydroxypyridine, in MeCN solutions containing either methyl
acrylate or acrylonitrile take place in a qualitatively similar
manner to those of the N-trimethylsilylmethyl uracils 10 and 11.
In contrast to the results of its thermal reaction,17 irradiation
of an MeCN solution of 33 containing methyl acrylate induces
production of the crossed [2+2] cycloadducts 35 (15%) and
36 (46%), along with eight-member ring dienamide 40 (3%)
(Scheme 8). The latter substance arises by way of cyclobutane
ring formation through [2+2]-cycloaddition of the acrylate ester
across the C1–C2 positions of the 2-pyridone ring system followed
by cyclohexadiene-to-hexatriene like electrocyclic ring opening.
In addition, irradiation of 33 in MeCN solutions containing
acrylonitrile leads to the formation of a similar product spectrum
including 37 (62%) and 41 (29%). Assignments of photoproduct
structures and stereochemistry of 35–37 and 40–41 are mainly
based upon comparisons of their spectroscopic data with those of
previously characterized photoproducts previously generated in
Scheme 8
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Scheme 11
investigation of factors governing the efficiencies of electron trans-
fer promoted cycloreversion reactions of cyclobutane containing
dimers of uracil and related substances could provide interesting
information about DNA photorepair.
To evaluate the role, if any, played by the N-trimethylsilylmethyl
group in photochemical cycloreversion reactions of the [2+2]-
cycloadducts, photoreactions of the syn-uracil dimers 12 and 13 in
MeCN were carried out. Irradiation (Vycor) of the photodimer 12
and 13 gives rise to cycloreversion to produce the respective uracils
10 and 11 in high yields (Scheme 12). When uranium grass filtered
light (l > 330 nm) is used along with the SET-photosensitizer
9,10-dicyanoanthracene (the light absorbing species), the tetra-
trimethylsilylmethyl substituted uracil dimer 13 reacts to generate
uracil 11. On the other hand, as expected uranium glass filtered
light irradiation of 13 without the SET-photosensitizer induces no
cycloreversion reaction to give 11.
Scheme 9
closely related reactions of N-methyl-2-pyridone with alkenes38–40
(Scheme 9).
As part of an investigation exploring novel routes for the
synthesis of retronecine derivatives (42, Scheme 10), Vedejs and
his co-workers observed that azomethine ylide 44 formation
takes place when N-[(trimethylsilyl)methyl] pyrrolidinone 34 is
sequentially treated with methyl triflate and CsF.41–42 The ylide
44, formed in this manner, was trapped with methyl acrylate to
generate the pyrrolizidine product 42 (Scheme 10).
In contrast to this chemistry, the photoreaction of 34, induced
by irradiation of a MeCN solution containing methyl acrylate (0.1
M) and LiCl, does not form a dipolar cycloadduct 46 (Scheme 11)
via an intermediate ylide. Instead, this process only generates
the desilylation product N-methylpyrrolidinone (45) in a 77%
yield (Scheme 11). Although the desilylation process observed to
place in this reaction is reminiscent of other photoreactions in
which azomethine ylides serve as intermediates,13 the absence of a
dipolarophile-trapping product, such as 46, suggests that C-to-O
silyl migration does not occur in the excited state of 34.
The results described above show that excited state photochemi-
cal processes involving C-to-O silyl migration, which are observed
in diverse N-trimethylsilylmethyl substituted conjugated imides
and amides,13,15,16 do not compete with [2+2] photocycloaddition
processes in similarly substituted uracils and 2-pyridones and with
desilylation of 2-pyrrolidinones.
Scheme 12
Another set of substrates explored in this effort contain
the diverse heteroatom substituted, 1,3-dimethyluracil based-
cyclobutanes 25,36–37 49 and 50. As shown in Scheme 6, acetoxy-
substituted dimethyluracil [2+2]-cycloadduct 25 can be prepared
by using a well known procedure.17 Hydrolysis of the acetate
ester moiety in 25 using methanolic sodium hydroxide forms the
alcohol 47, which undergoes a reaction with methanesulfonyl
chloride in the presence of triethylamine to form the mesylate
48 (Scheme 13). The mesylate can be used to introduce various
heteroatom containing side chains to the uracil [2+2]-adduct, as
exemplified by the amine group in 49 and thioether in 50.
Irradiation (uranium) of cyclobutanes 25, 49 and 50 in MeCN
solutions containing DCA were carried out, while monitoring the
formation of 1,3-dimethyl-uracil 20 as a function of irradiation
time. The results arising from monitoring these reactions are
compiled in Table 1. Irradiation of solutions containing DCA
and cyclobutanes 25, 49 and 50 promotes efficient formation
Photocycloreversion reactions of the [2+2] cycloadducts
As described above, photochemically induced cycloreversion of
cyclobutane ring containing dimeric uracil derivatives is a biolog-
ically relevant process, owing to its relationship to the action of
photolyases that catalyze the cleavage of cyclobutane pyrimidine
dimers formed by the photoinduced [2+2]-cycloaddition between
adjacent pyrimidine bases within DNA sequences. The excited
state processes that repair photodamaged DNA are believed to
proceed through SET pathways.24–35 Thus, we believed that an
Scheme 10
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Scheme 13
Scheme 14
Table 1 Photocycloreversion reactions of cyclobutane derivatives 25, 49
and 50 to form 20a
thioether (E1/2(+) ca. 1.4 V vs. SCE) substrates begin with SET
from the heteroatom centers in 49 and 50 to the DCA singlet
excited state (E1/2S1(-) ca. 2.8 V vs. SCE) (Scheme 14). This is
followed by cyclobutane ring cleavage, back electron transfer to
the DCA anion radical and 1,4-biradical fragmentation. Owing
to the excessively large oxidation potential of the acetoxy moiety
(E1/2(+) > 2.5 V vs. SCE), either a different, less efficient, non-SET
mechanistic route operates in the cycloreversion reaction of 25 or
the initial rate of SET from 25 to DCA is slow compared with the
decay of the DCA singlet excited state.
Yields of 20 (presence of DCA)
Irradiation time (h)
25
49
50
1
3
4
6
—
5
10
30
50
70
90
100
—
60
80
90
100
—
10
—
a Irradiation of photoreactant (2 mM) containing DCA (4 mM) was carried
out.
Photochemistry of phthalimide substituted cyclobutanes
The N-trimethylsilylmethyl-substituted cyclobutane tethered ph-
thalimides 55–57 were synthesized via routes starting with the
cyclobutanes 16 and 18–19. Treatment of these substances with
methanolic sodium hydroxide affords the corresponding alcohols
58–60, which undergo sequential O-mesylation and N-alkylation
with potassium phthalimide to produce the respective cyclobutyl
ring linked phthalimides 55–57 (Scheme 15).
Reactions of 55–57 in MeCN solutions induced by 1 h irradia-
tion with Vycor filtered light (100% reactant conversions) yield the
trimethylsilylmethyl group containing uracils 10 and 11 along with
N-vinylphthalimide 64 (Scheme 16). In addition, 15 h irradiation
(uranium) of MeCN solutions of 55 and 57, containing DCA
of 20. While amine and thioether substituted substrates 49 and
50 are completely converted to 20 during a 4–6 h, irradiation
period, only 50% of the acetoxy derivative 25 is transformed to
20 after 10 h of irradiation. The different photoreversion reaction
efficiencies reflected by the percent conversion vs. irradiation time
data correlates with oxidation potentials of pendent heteroatom
electron donor groups that are linked to the cyclobutane rings in
25, 49 and 50. Based on the inverse relationship that exists between
the rates of excited state electron transfer and oxidation potentials
of donors,43–48 it appears that the mechanistic pathways followed
in cycloreversion of the amine (E1/2(+) ca. 0.6 V vs. SCE) and
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Scheme 15
4. Experimental
General Procedure
1H- and 13C-NMR spectra were recorded using CDCl3 solutions
unless otherwise noted and chemical shifts are reported in parts
per million relative to CHCl3 (1H-NMR 7.24 ppm and 13C-NMR
77.0 ppm) 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 pressure
mercury lamp surrounded by a Vycor, Pyrex or Uranium glass
filter in a water-cooled quartz immersion well immersed in the
solution being irradiated. Photolysis solutions were purged with
nitrogen before and during irradiation. The photolysates were
concentrated in vacuo giving residues which were subjected to
silica gel column chromatography. High resolution (HRMS) mass
spectra were obtained by using electron impact ionization unless
otherwise noted. All new compounds described are isolated as oils
in >90% purity (by NMR analysis) unless noted otherwise.
Scheme 16
(0.5 mM) and methyl acrylate (20 mM) DCA, brings about clean
formation of 10, 11 and 64.
3. Conclusions
In this investigation, the photochemical reactivity of a diverse
variety of N-trimethylsilylmethyl substituted uracil, 2-pyridone
and 2-pyrrolidone derivatives has been explored. Although the
excited states of the N-trimethylsilylmethyl containing substrates
do not undergo sequential SET - C-to-O silyl migration processes,
they do participate in efficient [2+2]-cycloaddition leading to
cyclobutane containing products. Orbital topology allowed
photocycloreversion reactions of uracil derived cyclobutanes,
promoted by direct irradiation, resulted in efficient formation of
the corresponding uracils. A novel finding in this effort is that
the DCA-photosensitized SET reactions of amine and thioether
containing uracil [2+2] cycloadducts take place efficiently by
way of an interesting SET promoted pathway to form uracil and
alkenes. Finally, in the cases of N-trimethylsilylmethyl substituted
uracil cyclobutylphthalimides, highly efficient excited state cy-
cloreversion takes place to generate uracil and N-vinylphthalimide
upon either direct or SET photosensitized irradia-
tion.
Preparation of N-trimethylsilylmethyl substituted uracils 10 and 11
A solution of uracil (9) (4.7 g, 42 mmol) in anhydrous DMF
(50 mL) containing NaH (2 g, 83 mmol) was stirred at 0 ◦C
for 2 h. Trimethylsilylmethyl iodide (10 g, 47 mmol) was added
dropwise and the resulting solution was stirred for 10 h at
◦
110 C. Concentration of solution in vacuo gave a residue which
was diluted with CHCl3 and washed with water. The organic layer
was dried, filtered and concentrated in vacuo to afford a residue
which was subjected to silica gel chromatography (1 : 4 EtOAc–
hexane) to afford 10 (3.3 g, 40%) and 11 (4.1 g, 35%).
10: 1H-NMR 0.12 (s, 9H, SiMe3), 3.32 (s, 2H, CH2SiMe3), 5.67
(d, 1H, J = 7.8 Hz, COCH), 7.08 (d, 1H, J = 7.8 Hz, NCH);
13C-NMR -2.3 (SiMe3), 40.3 (CH2SiMe3), 101.6 (COCH), 145.0
(NCH), 151.0 and 164.2 (CO); IR (KBr) 1690 (amide), 1450
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(C C); LRMS (EI) m/z (rel. intensity) 198 (M+, 36), 183 (100), 73
(11); HRMS (EI) m/z 198.0761 (C8H14N2O2 Si1 requires 198.0825).
11: H-NMR 0.04 (s, 9H, SiMe3), 0.08 (s, 9H, SiMe3), 3.33 (s,
2H, CH2SiMe3), 3.50 (s, 2H, CH2SiMe3), 5.67 (d, 1H, J = 7.8 Hz,
COCH), 7.02 (d, 1H, J = 7.8 Hz, NCH); 13C-NMR -2.2 and
-1.6 (SiMe3), 32.4 (s, 2H, CH2SiMe3), 41.3 (CH2SiMe3), 100.5
(COCH), 141.6 (NCH), 151.2 and 162.8 (CO); IR (KBr) 1690
(amide), 1450 (C C); LRMS (EI) m/z (rel. intensity) 284 (M+,
32), 269 (100), 243 (8), 183 (7), 167 (6), 99 (5); HRMS (EI) m/z
284.1379 (C12H24N2O2Si2 requires 284.1376).
15: 1H-NMR 0.09 (s, 9H, SiMe3), 2.44 and 3.27 (two d,
2H, J = 15.5 Hz, two diastereotopic CH2TMS), 2.40–2.48 (m,
2H, CHCH2), 3.24–3.32 (m, 2H, COCHCH2 and CHCO2CH3),
3.72 (s, 3H, CO2CH3), 4.12 (t, 1H, J = 8.5 Hz, NCH), 8.55
(s, 1H, NH); 13C-NMR -1.1 (SiMe3), 24.9 (CHCH2), 36.3
(CHCO), 37.8 (CHCO2CH3), 46.2 (CH2SiMe3), 52.7 (CO2CH3),
55.8 (NCH), 152.6 (CONCH2SiMe3), and 172. 1 (CO2CH3),
173.1 (NHCO); IR (KBr) 1690 (amide); LRMS (EI) m/z (rel.
intensity) 284 (M+, 19), 269 (85), 225 (42), 198 (29), 183 (100), 73
(56), 55 (29); HRMS (EI) m/z 284.1187 (C12H20N2O4Si requires
284.1192).
1
Irradiation of N-trimethylsilylmethyl uracil derivatives 10 and 11;
formation of photodimers 12 and 13–14
Irradiation of trimethylsilylmethyl uracil derivatives (10–11) in the
presence of vinyl acetate; formation of [2+2] photoadducts 16–19
Independent solutions of uracils 10 (300 mg, 1.5 mmol), 11
(300 mg, 1.0 mmol) in MeCN (200 mL) were irradiated by
using Vycor glass filtered light for 1 h (100% conversion). The
photolysates were concentrated in vacuo to give residues which
were subjected to silica gel chromatography (1 : 1 EtOAc–hexane)
to afford 12 (415 mg, 70%) from 10, and 13 (210 mg, 37%) and 14
(227 mg, 40%) from 11.
Independent solutions of the uracils 10 (300 mg, 1.5 mmol) and 11
(300 mg, 1.5 mmol) in MeCN (150 mL) containing vinyl acetate
(260 mg, 3 mmol for 10, 170 mg, 2 mmol for 11) were irradiated by
using Vycor filtered light for 1 h (93% conversion of 10) and 100%
conversion of 11). The photolysates were concentrated in vacuo to
give residues which were subjected to silica gel chromatography
(1 : 1 EtOAc–hexane) to afford 16 (180 mg, 45%) and 17 (90 mg,
23%) from 10, and 18 (150 mg, 40%) and 19 (85 mg, 23%) from
11.
1
12: H-NMR 0.07 (s, 18H, SiMe3), 2.37 and 3.16 (two d, 2H,
J = 15.1 Hz, two diastereotopic CH2TMS), 2.52 (s, 2H, NH), 3.45
(d, 4H, J = 8.4 Hz, COCH), 4.06 (d, 4H, J = 8.4 Hz, NCH); 13C-
NMR (DMSO) -0.9 (SiMe3), 38.4 (CHCO), 40.4 (CH2SiMe3),
60.5 (NCH), 151.3 and 169.9 (amide, NCO); IR (KBr) 1694
(amide, NCO); LRMS (EI) m/z (rel. intensity) 396 (M+, 5), 381
(52), 271 (550), 183 (100), 73 (32); HRMS (EI) m/z 396.1644
(C16H28N4O4Si2 requires 396.1649).
1
16: H-NMR 0.04 (s, 9H, SiMe3), 2.01 (s, 3H, CH3CO), 2.43
and 3.21 (two d, 2H, J = 15.0 Hz, two diastereotopic CH2TMS),
2.55–2.67 (m, 2H, CHCH2), 3.18– 3.30 (m, 1H, COCH), 3.78–
3.86 (m, 1H, NCH), 4.95–5.08 (m, 1H, CHOCOCH3), 9.01
(s, 1H, NH); 13C-NMR -1.7 (SiMe3), 20.5 (CH3CO), 29.4
(CHCH2), 31.8 (CH2SiMe3), 38.1 (CHCO), 59.1 (NCH), 73.3
(CHOCOCH3), 151.3 (CONCH2SiMe3), 169.3 (COCH3), 171.2
(NHCO); IR (KBr) 1690 (amide); LRMS (EI) m/z (rel. intensity)
284 (M+, 1.3), 269 (40), 198 (50), 183 (100), 169 (15), 74
(89), 62 (25); HRMS (EI) m/z 284.1195 (C12H20N2O4Si requires
284.1192).
17: 1H-NMR 0.02 (s, 9H, SiMe3), 1.99 (s, 3H, OCOCH3), 2.20
and 3.23 (two d, 2H, J = 15.4 Hz, two diastereotopic CH2TMS),
2.65–2.75 (m, 2H, CHCH2), 3.25–3.31 (m, 1H, COCH), 3.96–
4.04 (m, 1H, NCH), 5.15–5.25 (m, 1H, CHOCOCH3), 8.83 (s, 1H,
NH); 13C-NMR -1.7 (SiMe3), 20.5 (CH3CO), 29.8 (CHCH2), 36.8
(CH2SiMe3), 37.9 (CHCO), 55.0 (NCH), 72.0 (CHOCOCH3),
151.3 (CONCH2SiMe3), 171.7 (COCH3), 171.6 (NHCO); IR
(KBr) 1690 (amide); LRMS (EI) m/z (rel. intensity) 284 (M+, 1.3),
269 (40), 198 (50), 183 (100), 169 (15), 74 (89), 62 (25); HRMS (EI)
m/z 284.1195 (C12H20N2O4Si requires 284.1192).
1
13: H-NMR 0.02 (s, 18H, SiMe3), 0.09 (S, 18H, SiMe3), 2.16
and 3.34 (two d, 4H, J = 15.1 Hz, two diastereotopic CH2TMS),
3.28 (s, 4H, CH2SiMe3), 3.69–3.73 (m, 2H, COCH), 3.92–3.97 (m,
2H, NCH); 13C-NMR -2.0 (SiMe3), 1.1 (SiMe3), 33.6 (CHCO),
40.0 (CH2SiMe3), 40.6 (CH2SiMe3), 55.7 (NCH), 152.9 and 165.5
(amide, NCO); IR (KBr) 1694 (amide, NCO); LRMS (EI) m/z
(rel. intensity) 568 (M+, 0.2), 553 (16), 357 (42), 283 (37), 269
(99), 73 (100); HRMS (EI) m/z 568.2751 (C24H48N4O4Si4 requires
568.2753).
14: 1H-NMR (CDCl3) 0.05 (s, 9H, SiMe3), 0.07 (s, 9H, SiMe3),
0.08 (s, 9H, SiMe3), 0.10 (s, 9H, SiMe3), 2.26 and 3.48 (two d, 2H,
J = 15.2 Hz, two diastereotopic CH2TMS), 3.36 and 3.49 (two
d, 2H, J = 15.2 Hz, two diastereotopic CH2TMS), 3.54 (d, 2H,
J = 8.2 Hz, COCH), 3.75 (d, 2H, J = 8.2 Hz, NCH); 13C-NMR
-1.0 (SiMe3), -1.1 (SiMe3), 33.2 CHCO), 40.0 (CH2SiMe3), 40.9
(CH2SiMe3), 60.5 (NCH), 151.8, and 168.0 (amide, NCO); LRMS
m/z (rel, intensity) 568 (M+,0.8), 553 (14), 551 (30), 355 (56),
283 (47), 269 (100), 73(34); HRMS m/z 568.2781 (C24H48N4O4Si4
requires 568.2753).
18: H-NMR 0.04 (s, 9H, SiMe3), 0.08 (s, 9H, SiMe3), 2.06 (s,
3H, COCH3), 2.14–2.30 (m, 2H, CHCH2), 2.57–2.69 (m, 1H,
CHOCOCH3), 2.51 and 3.26 (two d, 2H, J = 15.3 Hz, two
diastereotopic CH2TMS), 3.33 and 3.44 (two d, 2H, J = 15.3 Hz,
two diastereotopic CH2TMS), 3.75–3.83 (m, 1H, COCH), 4.95–
5.05 (m, 1H, NCH); 13C-NMR -1.6 (SiMe3), 20.8 (COCH3), 29.2
(CHCH2), 30.0 (CH2SiMe3), 32.0 (CH2SiMe3), 40.2 (CHCO),
59.1 (NCH), 74.2 (CHOCOCH3), 151.8 (CONCH2SiMe3), 169.2
(COCH3), 169.5 (NHCO); IR (KBr) 1690 (amide); IR (KBr) 1690
(amide); LRMS (EI) m/z (rel. intensity) 370 (M+, 3.6), 355 (51),
327 (5), 283 (67), 269 (100), 210 (11), 183 (8), 73 (18); HRMS (EI)
m/z 370.1732 (C16H32N2O4Si2 requires 370.1744).
Irradiation of trimetylsilylmethyl uracil 10 in the presence of
methyl acrylate; formation of [2+2] photoadduct 15
A solution of uracil 10 (300 mg, 1.5 mmol) in MeCN (150 mL)
containing methyl acrylate (1.4 g, 15 mmol) was irradiated by
using Vycor glass filtered light for 1 h (100% conversion). The
photolysate was concentrated in vacuo to give a residue which was
subjected to silica gel chromatography (1 : 1 EtOAc–hexane) to
afford 15 (268 mg, 63%).
1
19: H-NMR 0.08 (s, 9H, SiMe3), 0.09 (s, 9H, SiMe3), 1.94
(s, 3H, COCH3), 2.25 and 3.24 (two d, 2H, J = 15.3 Hz, two
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diastereotopic CH2TMS), 2.46–2.59 (m, 2H, CHCH2), 2.68–2.85
(m, 1H, CHOCOCH3), 3.33 and 3.46 (two d, 2H, J = 15.3 Hz,
two diastereotopic CH2TMS), 3.95–4.02 (m, 1H, COCH), 5.20–
5.30 (m, 1H, NCH); 13C-NMR -1.6 (SiMe3), 20.8 (COCH3), 30.3
(CHCH2), 32.0 (CH2SiMe3), 32.4 (CH2SiMe3), 39.7 (CHCO),
57.8 (NCH), 73.7 (CHOCOCH3), 151.9 (CONCH2SiMe3), 169.5
(COCH3), 169.9 (NHCO); IR (KBr) 1690 (amide); LRMS (EI)
m/z (rel. intensity) 370 (M+, 2), 355 (47), 327 (3), 283 (66),
269 (100), 210 (7), 183 (4), 73 (11); HRMS (EI) m/z 370.1732
(C16H32N2O4Si2 requires 370.1744).
Pyrex filtered light for 17 h (80% conversion). The photolysate
was concentrated in vacuo to give a residue which was subjected to
silica gel chromatography (ether) to afford 37 (320 mg, 62%) and
41 (150 mg, 29%).
37: 1H-NMR 0.00 (s, 9H), 2.63–2.73 (m, 2H, CH2), 2.96 (AB q,
2H, J = 15.0 Hz, CH2SiMe3), 3.21–3.27 (m, 1H, CHCN), 3.33–
3.43 (m, 2H, CH2CHCN), 4.93–4.96 (m, 1H, CHCO), 6.04–6.07
(m, 1H, CH CHN), 7.10 (m, 1H, CH CHN); 13C-NNR -2.1
(SiMe3), 27.2, 35.7 and 36.9 (CH), 30.7 and 38.4 (CH2), 101.3 and
132.6 (CH, alkenyl), 118.8 (CN), 165.5 (C O); IR (KBr) 3050
and 2235 (CN stretching), 1640 (C O stretching).
41: 1H-NMR 0.07 (s, 9H, SiMe3), 2.87–2.90 (m, 2H, CH2),
2.99 (AB q, 2H, J = 15.0 Hz, CH2SiMe3), 4.50 (t, 1H, J =
4.8 Hz, CHCN), 5.57–5.70 (m, 3H), 5.82 (d, 1H, J = 4.6 Hz,
NCH CH); 13C-NMR -2.0 (SiMe3), 32.7 (CH), 33.4 and 39.9
(CH2), 117.5 (CN), 111.9, 122.1, 128.1 and 128.8 (CH, alkenyl),
164.8 (C O); IR (KBr) 3050 and 2250 (CN stretching), 1660
(C O stretching).
Irradiation of N-trimethylsilylmethyl-2-pyridone 33 in the presence
of methyl acrylate; formation of 35, 36 and 40
A solution of pyridone 33 (500 mg, 3 mmol) in MeCN (200 mL)
containing methyl acrylate (2.5 mL, 28 mmol) was irradiated
by using Pyrex filtered light for 11 h (86% conversion). The
photolysate was concentrated in vacuo to give a residue which
was subjected to silica gel chromatography (ether) to afford 35
(90 mg, 15%), 36 (270 mg, 46%) and 40 (20 mg, 3%).
Irradiation of N-trimethylsilylmethyl-2-pyrrolidone 34
35: 1H-NMR -0.01 (s, 9H, SiMe3), 2.40–2.49 (m, 1H,
CHCH2), 2.59–2.67 (m, 1H, CHCH2), 2.72 (q, 2H, J = 7.5 Hz,
CH2SiMe3), 3.13–3.20 (m, 1H, CH(CO2CH3)), 3.49–3.60 (m,
1H, CHCH(CO2CH3)), 3.61 (s, 3H, CH3), 3.77–3.83 (m, 1H,
CHNCO), 5.83–5.86 (m, 1H, COCH CH), 6.17–6.28 (m, 1H,
COCH CH); 13C-NMR -1.6 (SiMe3), 32.4 (CH2), 37.3 (SiCH3),
37.4 (CH3), 39.1, 51.6 and 51.7 (CH), 125.7 and 135.5 (CH,
alkenyl), 161.2 and 171.3 (C O).
A solution of pyrrolidone 34 (200 mg, 1 mmol) in MeCN (100 mL)
containing methyl acrylate (1 g, 12 mmol) was irradiated by using
Vycor filtered light for 17 h (70% conversion). The photolysate
was concentrated in vacuo to give a residue which was subjected
to silica gel chromatography (1 : 5 EtOAc–hexane) to afford 45
(62 mg, 77%).
36: 1H-NMR -0.07 (s, 9H), 2.34–2.41 (m, 1H, CHCH2), 2.61–
2.74 (m, 1H, CHCH2), 2.86 (AB q, 2H, J = 7.6 Hz, CH2SiMe3),
3.03–3.12 (m, 1H, CHCO2CH3), 3.27–3.37 (m, 1H, COCH),
3.54 (s, 3H, CH3), 4.61–4.65 (m, 1H, CHCH(CO2CH3)), 5.79–
5.81 (m, 1H, CH CHN), 7.12 (m, 1H, CH CHN); 13C-NMR
-2.1 (SiMe3), 28.3 and 38.2 (CH2), 34.4 (CH), 37.5 (CH3),
41.8 and 51.2 (CH), 102.0 and 131.6 (CH, alkenyl), 166.9 and
171.9 (C O).
Irradiation of uracil photodimers 12 and 13; formation of uracil
monomer 10 and 11
Independent solutions of uracil dimers 12 (100 mg, 0.3 mmol) and
13 (100 mg, 0.2 mmol) in MeCN (200 mL) were irradiated by using
Vycor filtered light for 1 h (100% conversion). The photolysates
were concentrated in vacuo to give residues which were subjected
to silica gel chromatography (1 : 1 EtOAc–hexane) to afford 10
(74 mg, 75%) and 11 (77 mg, 80%) respectively.
1
40: H-NMR -0.01 (s, 9H, SiMe3), 2.80–2.82 (m, 2H, CH2),
3.13 (AB q, 2H, J = 7.4 Hz, CH2SiMe3), 3.65 (s, 3H, CH3), 4.33
and 4.35 (dd, 1H, J = 3.0 Hz, J = 4.8 Hz, CHCO2CH3), 5.54–5.58
(m, 1H, CH2CH CH), 5.64–5.69 (m, 1H, CH2CH CH), 5.73–
5.78 (m, 1H, NCH CH), 5.85 (d, 1H, J = 4.6 Hz, NCH CH);
13C-NMR -1.8 (SiMe3), 31.0 and 39.6 (CH2), 45.2 and 52.2
(CH), 118.9, 121.5, 128.9 and 135.5 (CH, alkenyl), 169.4 and
170.2 (C O).
Irradiation of photodimer 13 in the presence of DCA
A solution of dimer 13 (100 mg, 0.2 mmol) in MeCN (200
mL) containing DCA (15 mg, 0.1 mmol) was irradiated by
using uranium glass filtered light for 15 h (60% conversion). The
photolysate was concentrated in vacuo to give a residue which was
subjected to silica gel chromatography (1 : 1 EtOAc–hexane) to
afford 11 (49 mg, 85%).
Irradiation of N-trimethylsilylmethyl-2-pyridone 33 in the presence
of methyl acrylate and LiCl
A solution of pyridone 33 (400 mg, 2 mmol) in acetone (100 mL)
containing methyl acrylate (950 mg, 11 mmol) and LiCl (0.2 g, 0.4
mmol) was irradiated by using Pyrex filtered light for 16 h (75%
conversion). The photolysate was concentrated in vacuo to give a
residue which was subjected to silica gel chromatography (ether)
to afford 35 (86 mg, 20%), 36 (70 mg, 16%) and 40 (33 mg, 8%).
Preparation of uracil based cyclobutylalcohol 47
A solution of 25 (0.5 g, 2 mmol) in MeOH (20 mL) containing
0.1 M methanolic sodium hydroxide (0.9 mL) was stirred at room
temperature for 20 min. Concentration of solution in vacuo gave a
residue which was subjected to silica gel column chromatography
(EtOAc) to afford 47 (0.4 g, 97%).
47: 1H-NMR 2.01–2.21 and 2.44–2.56 (m, 2H, CH2), 3.03
(s, 3H, CHNCH3), 3.14 (s, 3H, CON(CH3)CO), 3.20–3.38 (m,
1H, COCHCH2), 3.60–3.70 (m, 1H, CHNCH3), 4.19–4.31 (m,
1H, CHOH); 13C-NMR 27.9 (CON(CH3)CO), 30.5 (CH2), 32.6
(COC), 34.6 (CHNCH3), 59.9 (NCH), 73.2 (CHOH), 152.5
Irradiation of N-trimethylsilylmethyl-2-pyridone 33 in the presence
of acrylonitrile; formation of 37 and 41
A solution of pyridone 33 (500 mg, 3 mmol) in MeCN (200 mL)
containing acrylonitrile (2 mL, 30 mmol) was irradiated by using
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(NCH3C( O)NCH3), 171.7 (N(CH3)COCH); IR (KBr) 3200–
Irradiation of uracil based cyclobutyl acetate 25 in the presence of
DCA
3600 cm-1 (br, OH stretching).
A solution of 25 (80 mg, 0.4 mmol) in MeCN (200 mL) containing
DCA (15 mg, 0.1 mmol) was irradiated by using uranium filtered
light for 10 h (50% conversion). The photolysate was concentrated
in vacuo to give a residue which was subjected to silica gel column
chromatography (EtOAc) to yield 20 (22 mg, 91%).
Preparation of uracil based cyclobutyl mesylate 48
A solution of alcohol 47 (1 g, 5.5 mmol) in CH2Cl2 (30 mL)
containing triethylamine (0.8 g, 8 mmol) was stirred for 30 min at
0 ◦C. MsCl (0.7 g, 6 mmol) was added dropwise and the resulting
solution was stirred for 1 h at 0 ◦C. Concentration of solution in
vacuo gave a residue which was diluted with CH2Cl2 and washed
with water. The organic layer was dried, filtered and concentrated
in vacuo to afford 48 (1.2 g, 80%).
Irradiation of uracil based cyclobutyl amine 49 in the presence of
DCA
◦
1
A solution of 49 (80 mg, 0.4 mmol) in MeCN (200 mL) containing
DCA (15 mg, 0.1 mmol) was irradiated by using uranium filtered
light for 4 h (100% conversion). The photolysate was concentrated
in vacuo to give a residue which was subjected to silica gel column
chromatography (EtOAc) to afford 20 (29 mg, 90%).
48: mp 112–113 C; H-NMR: 2.41–2.48 and 2.64–2.68 (m,
2H, CHCH2), 3.00 (s, 3H, OMs), 3.05 (s, 3H, CHNCH3), 3.06
(s, 3H, CON(CH3)CO), 3.32–3.35 (m, 1H, COCHCH2), 3.97–
1.02 (m, 1H, CHNCH3), 4.89–4.95 (m, 1H, -CHOMs); 13C-
NMR: 28.0 (CON(CH3)CO), 30.2 (CH2CHOMs), 31.3 (CHCH2),
34.9 (CHNCH3), 38.3 (SO2CH3), 58.1 (N(CH3)CHCHOMs), 77.2
(CHOMs), 152.1 (NCON), 169.9 (CON(CH3)CH); IR (KBr)
Irradiation of uracil based cyclobutyl thioether 50 in the presence
of DCA
1700 (C O stretching), 1375 (S O asymetric), 1175 (S
O
symmetric); LRMS (EI) m/z (rel. intensity) 262 (M+, 1), 183
(12), 162 (6), 141 (17), 140 (100); HRMS (EI) m/z 262.0622
(C9H14N2O5S requires 262.0623).
A solution of 50 (100 mg, 0.4 mmol) in MeCN (200 mL) containing
DCA (15 mg, 0.1 mmol) was irradiated by using uranium filtered
light for 6 h (100% conversion). The photolysate was concentrated
in vacuo to give a residue which was subjected to silica gel column
chromatography (EtOAc) to afford 20 (52 mg, 91%).
Preperation of uracil based cyclobutyl amine 49
A solution of NaH (0.1 g, 5 mmol) in dry DMF (15 mL)
◦
containing diethylamine (1.5 g, 21 mmol) was stirred at 0 C for
Preparation of uracil based cyclobutyl alcohols 58–60
30 min. Mesylate 48 (1.1 g, 4 mmol) in dry DMF (10 mL) was
added dropwise and the resulting solution was stirred for 24 h at
60 ◦C. Concentration of the solution in vacuo gave a residue which
was subjected to silica gel column chromatography (EtOAc) to
afford 49 (0.8 g, ◦78%).
A 5% methanolic NaOH 20 mL was added dropwise to respective
MeOH (30 mL) solutions of 16 (200 mg, 0.7 mmol), 18 (200 mg, 0.5
mmol) and 19 (200 mg, 0.5 mmol). These solutions were stirred at
0 ◦C for 30 min and concentrated in vacuo to give residues which
were diluted with CH3Cl and washed with water. The organic
layers were dried, filtered and concentrated in vacuo to afford
residues which were subjected to silica gel column chromatography
(1 : 2 EtOAc–hexane) to afford 58 (150 mg, 90%), 59 (150 mg, 85%)
and 60 (140 mg, 80%) respectively.
49: mp 53–54 C; 1H-NMR: 1.00 (t, 6H, J = 7.1 Hz, CH2CH3),
2.12–2.19 and 2.27–2.34 (m, 2H, CH2CHN(CH2CH3)2), 2.59 (q,
4H, J = 7.4 Hz, CH2CH3), 3.06 (s, 3H, CHNCH3), 3.14–3.21 (m,
1H, COCHCH2), 3.23 (s, 3H, CON(CH3)CH), 3.28–3.37 (m, 1H,
CHN(CH2CH3)2), 3.65 (t, 1H, J = 7.6 Hz, CHNCH3); 13C-NMR:
11.1, 27.9, 33.1, 35.9, 42.6, 57.1, 65.1, 152.8, 172.2
1
58: H-NMR: 0.11 (s, 9H, SiMe3), 1.90 (br s, 1H, OH), 2.40
and 3.35 (two d, 2H, J = 15.2 Hz, two diastereotopic CH2TMS),
2.16–2.29 and 2.65–2.89 (m, 2H, CHCH2), 3.18–3.29 (m, 1H,
CHCO), 3.86–3.93 (m, 1H, NCH), 4.43–4.51 (br s, 1H, CHOH),
8.14 (br s, 1H, NH); 13C-NMR: -1.8 (SiMe3), 33.6 (CHCH2), 35.5
(CH2SiMe3), 38.4 (CHCO), 56.3 (NCH), 69.8 (CHOH), 152.7
(CHNCO), 172.0 (COCH); IR (KBr) 1690 (amide).
Preparation of uracil based cyclobutyl thioether 50
A solution of NaH (10 mg, 0.4 mmol) in THF (10 mL) containing
1-propanethiol (0.2 mL, 2 mmol) was stirred at 0 ◦C for 30 min.
Mesylate 48 (94 mg, 0.4 mmol) in dry THF (10 mL) was added
dropwise and the resulting solution was stirred for 24 h at
60 ◦C. Concentration of the solution in vacuo gave a residue which
was diluted with ether and washed with water. The organic layer
was dried over Na2SO4, filtered and concentrated in vacuo to afford
a residue which was subjected to silica gel column chromatography
(ether) to afford 50 (43 mg, 50%).
59: 1H-NMR: 0.02 (s, 9H, SiMe3), 0.09 (s, 9H, SiMe3), 1.90 (s,
1H, OH), 2.04–2.19 and 2.44–2.54 (m, 2H, CHCH2), 2.62 and
3.28 (two d, 2H, J = 15.2 Hz, two diastereotopic CH2TMS),
3.29 and 3.42 (two d, 2H, J = 15.2 Hz, two diastereotopic
CH2TMS), 3.57–3.66 (m, 2H, CHCO and NCH), 4.22–4.35
(m, 1H, CHOH); 13C-NMR: -1.7 (SiMe3), 31.2 (CHCH2), 32.7
(CH2SiMe3), 33.3 (CH2SiMe3), 40.2 (CHCO), 60.9 (NCH), 74.0
(CHOH), 152.3 (CONCH2SiMe3), 171.7 (COCH3); LRMS (EI)
m/z (rel. intensity) 328 (M+, 5), 311 (51), 284 (54), 269 (70), 256
(70), 195 (14), 73 (48); HRMS (EI) m/z 328.1630 (C14H28N2O3Si2
requires 328.1639).
1
50: H-NMR: 0.98 (t, 3H, J = 7.4 Hz, SCH2CH2CH3), 1.52–
1.62 (m, 2H, J = 7.2 Hz, SCH2CH2CH3), 2.15–2.22 and 2.56–
2.63 (m, 2H, CH2CHS), 2.51 (t, 2H, J = 7.2 Hz, SCH2CH2CH3),
3.05 (s, 3H, CHNCH3), 3.23 (s, 3H, CON(CH3)CO), 3.34–3.39
(m, 2H, COCH and CHS), 3.66–3.72 (m, 1H, N(CH3)CH); 13C-
NMR: 13.3 (CH2CH3), 23.8 (CH2CH3), 27.5 (CON(CH3)CO),
30.5 (CHCH2), 35.1 (COCH), 34.2 (COCH), 34.7 (CHNCH3),
35.0 (SCH2CH2), 40.0 (CHSCH2), 61.2 (NCH), 152.5 (NCH3CO),
172.0 (N(CH3)COCH).
1
60: H-NMR: 0.08 (s, 9H, SiMe3), 0.09 (s, 9H, SiMe3), 1.99–
2.14 and 2.80–2.92 (m, 2H, CHCH2), 2.44 and 3.26 (two d, 2H,
J = 15.2 Hz, two diastereotopic CH2TMS), 3.33 and 3.48 (two
d, 2H, J = 15.2 Hz, two diastereotopic CH2TMS), 3.78–3.83 (m,
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2H, CHCO and CHN), 4.39–4.47 (m, 1H, CHOH); 13C-NMR:
-1.7 (SiMe3), -1.6 (SiMe3), 31.2 (CHCH2), 30.7 (CHCH2), 34.5
(CH2SiMe3), 35.1 (CH2SiMe3), 39.4 (CHCO), 54.6 (NCH), 69.4
(CHOH), 154.0 (CONCH2SiMe3), 171.2 (COCH3); IR (KBr) 1690
(amide).
over Na2SO4, filtered and concentrated in vacuo to afford residues
which were subjected to silica gel column chromatography (1 : 3
EtOAc–hexane) to yield 55 (186 mg, 80%), 56 (71 mg, 65%) and
57 (65 mg, 60%) respectively.
1
55: H-NMR: 0.03 (s, 9H, SiMe3), 1.53 (s, 1H, NH), 2.23 and
3.26 (two d, 2H, J = 15.0 Hz, two diastereotopic CH2TMS),
2.48–2.59 and 3.39–3.49 (m, 2H, CHCH2), 2.93–3.09 (m, 1H,
COCH), 4.78–5.00 (m, 2H, NCH and CH2CHN(CO)2), 7.75–7.90
(m, 4H, aromatic); 13C-NMR: -1.8 (SiMe3), 26.7 (CHCH2), 33.2
(COCH), 37.9 (CH2SiMe3), 51.2 (NCH), 56.3 (CH2CHN(CO)2),
123.6, 131.3, and 134.5 (CH, aromatic), 151.6 (CHNCO), 167.7
(COCH), 171.3 (CO); IR (KBr) 1720 and 1690 (NCO); LRMS
(EI) m/z (rel. intensity) 371 (1.4), 356 (27), 246 (26), 198 (60), 183
(100), 173 (15), 73 (56); HRMS (EI) m/z 371.1299 (C22H32N3O4Si2
requires 371.1301).
Preparation of uracil based cyclobutyl mesylates 61–63
Independent solutions of 58 (200 mg, 0.8 mmol), 59 (200 mg, 0.6
mmol) and 60 (100 mg, 0.3 mmol) in CH2Cl2 (50 mL) containing
◦
triethylamine (2 g, 0.2 mmol) were stirred at 0 C for 1 h. MsCl
(131 mg, 0.9 mmol for 58–60) was added dropwise to each and
the resulting solutions were stirred at room temperature for 5 h
and concentrated in vacuo to give residues which were diluted
with ether and washed with water. The organic layers were dried
over Na2SO4, filtered and concentrated in vacuo to afford residues
which were subjected to silica gel column chromatography (1 : 3
EtOAc–hexane) to afford 61 (183 mg, 70%), 62 (194 mg, 70%) and
63 (80 mg, 65%) respectively.
1
56: H-NMR: 0.02 (s, 9H, SiMe3), 0.09 (s, 9H, SiMe3), 2.27
and 3.27 (two d, 2H, J = 15.2 Hz, two diastereotopic CH2TMS),
2.42–2.53 and 3.36–3.45 (m, 2H, CHCH2), 2.93–3.09 (m, 1H,
COCH), 3.40 and 3.52 (two d, 2H, J = 15.2 Hz, two diastereotopic
CH2TMS), 4.73–4.90 (m, 2H, NCH and CH2CHN(CO)2), 7.74–
7.80 (m, 4H, aromatic); 13C-NMR: -1.6 (SiMe3), -1.7 (SiMe3),
-1.6 (SiMe3), 27.6 (CHCH2), 32.4 (COCH), 33.3 (CH2SiMe3),
39.4 (CH2SiMe3), 51.3 (NCH), 54.7 (CH2CHN(CO)2), 151.8
(CHNCO), 167.8 (COCH), 170.3 (CO), 123.6, 131.5, and 134.5
(CH, aromatic); IR (KBr) 1780 and 1700 (NCO); LRMS (EI)
m/z (rel. intensity) 457 (M+, 1), 442 (40), 284 (100), 267 (35), 246
(1), 210 (11); HRMS (EI) m/z 457.1851 (C22H31N3O4Si2 requires
457.1853).
61: 1H-NMR: 0.11 (s, 9H, SiMe3), 2.36 and 3.37 (two d, 2H, J =
15.4 Hz, two diastereotopic CH2TMS), 2.46–2.55 and 2.76–2.80
(m, 2H, CHCH2), 3.05 (s, 3H, OMs), 3.30–3.39 (m, 1H, CHCO)
4.11–4.18 (m, 1H, NCH), 5.23–5.29 (m, 1H, CHOMs), 8.02 (br s,
1H, NH); 13C-NMR: -1.7 (SiMe3), 31.1 (OMs), 36.4 (CHCH2),
37.9 (COCH), 39.0 (CH2SiMe3), 55.3 (NCH), 76.1 (CHOMs),
152.0 (CHNCO), 170.7 (COCH); IR (KBr) 1700(C O), 1180
and 1361 (OMs, stretching); LRMS (EI) m/z (rel. intensity) 320
(4), 241 (28), 189 (51), 183 (100), 73 (41); HRMS (EI) m/z 320.0867
(C11H20N2O5SiS requires 320.0862).
1
57: H-NMR: 0.07 (s, 9H, SiMe3), 0.08 (s, 9H, SiMe3), 2.26
1
62: H-NMR: 0.04 (s, 9H, SiMe3), 0.10 (s, 9H, SiMe3), 2.41–
and 3.35 (two d, 2H, J = 15.3 Hz, two diastereotopic CH2TMS),
2.41–2.52 and 3.38–3.47 (m, 2H, CHCH2), 2.92–3.08 (m, 1H,
COCH), 3.38 and 3.51 (two d, 2H, J = 15.3 Hz, two diastereotopic
CH2TMS), 4.71–4.88 (m, 2H, NCH and CH2CHN(CO)2), 7.73–
7.88 (m, 4H, aromatic); 13C-NMR: -1.7 (SiMe3), -1.6 (SiMe3), 27.5
(CHCH2), 32.4 (COCH), 33.3 (CH2SiMe3), 39.4 (CH2SiMe3), 51.3
(NCH), 54.7 (CH2CHN(CO)2), 151.8 (CHNCO), 167.7 (COCH),
170.1 (CO), 123.6 and 134.4 (CH, aromatic); IR (KBr) 1780 and
1700 (C O stretching); LRMS (EI) m/z (rel. intensity) 457 (1.5),
442 (52), 284 (100), 267 (29), 246 (30), 210 (16); HRMS (EI) m/z
457.1834 (C22H31N3O4Si2 requires 457.1853).
2.50 and 2.63–2.74 (m, 2H, CHCH2) 2.58 and 3.34 (two d, 2H, J =
15.4 Hz, two diastereotopic CH2TMS), 3.02 (s, 3H, OMs), 3.24–
3.38 (m, 1H, COCH) 3.32 and 3.44 (two d, 2H, J = 15.4 Hz, two
diastereotopic CH2TMS), 3.92–4.00 (m, 1H, NCH), 4.85–4.96 (m,
1H, CHOMs); 13C-NMR: -1.7 (SiMe3), -1.6 (SiMe3), 30.5 (OMs),
31.5 (CHCH2), 32.5 (COCH), 38.5 (CH2SiMe3), 39.7 (CH2SiMe3),
58.2 (NCH), 77.6 (CHOMs), 151.7 (CHNCO), 169.1 (COCH); IR
(KBr) 1690 and 1660 (NCO); LRMS (EI) m/z (rel. intensity) 406
(6), 390 (94), 311 (69), 284 (80), 269 (95), 195 (27), 152 (11); HRMS
(EI) m/z 406.1417 (C15H30N2O5Si2S requires 406.1414).
63: 1H-NMR: 0.04 (s, 9H, SiMe3), 0.07 (s, 9H, SiMe3), 2.34 and
3.32 (two d, 2H, J = 15.4 Hz, two diastereotopic CH2TMS), 2.42–
2.49 and 2.77–2.92 (m, 2H, CHCH2), 2.98 (s, 3H, OMs), 3.35 and
3.43 (two d, 2H, J = 15.4 Hz, two diastereotopic CH2TMS), 3.27–
3.33 (m, 1H, CHCO), 4.05–4.12 (m, 1H, NCH), 5.15–5.21 (m, 1H,
CHOMs); 13C-NMR: -1.6 (SiMe3), 31.4 (OMs), 32.3 (CHCH2),
35.6 (COCH), 38.7 (CH2SiMe3), 39.2 (CH2SiMe3), 53.9 (NCH),
75.9 (CHOMs), 152.6 (CHNCO), 169.2 (COCH); IR (KBr) 1700
and 1660 (NCO); LRMS (EI) m/z (rel. intensity) 406 (6), 390 (94),
311 (69), 284 (80), 269 (95), 195 (27), 152 (11); HRMS (EI) m/z
406.1417 (C15H30N2O5Si2S requires 406.1414).
Irradiation of phthalimides 55–57
Independent solutions of 55 (100 mg, 0.3 mmol), 56 (100 mg, 0.2
mmol) and 57 (100 mg, 0.2 mmol) in MeCN (200 mL) containing
methyl acrylate (230 mL, 2.6 mmol) were irradiated by using
Vycor filtered light for 1 h (100% conversion in each case). The
photolysates were concentrated in vacuo to give residues which
were subjected to silica gel column chromatography (1 : 2 EtOAc–
hexane) to afford 10 (46 mg, 77%) and 64 (40 mg, 77%) from 55,
11 (48 mg, 85%) and 64 (30 mg, 85%) from 56, and 11 (51 mg,
90%) and 64 (29 mg, 85%) from 57.
Preparation of N-uracil based cyclobutyl phthalimides 55–57
Irradiation of phthalimides 55 and 57 in the presence of methyl
acrylate and DCA
Independent solutions of 61 (200 mg, 0.6 mmol), 62 (100 mg, 0.2
mmol) and 63 (100 mg, 0.2 mmol) in DMF (50 mL) containing
potassium phthalimde (11 g, 0.6 mmol) were stirred at 110 ◦C for
20 h and concentrated in vacuo giving residues which were diluted
with CH2Cl2 and washed with water. The organic layers were dried
Independent solutions of 55 (100 mg, 0.3 mmol) and 57 (100 mg,
0.2 mmol) in MeCN (150 mL) containing methyl acrylate (230 mL,
3 mmol) and DCA (15 mg, 0.1 mmol) were irradiated by using
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uranium filtered light for 15 h (20% conversion of 55 and
55% conversion of 57). The photolysates were concentrated in
vacuo to give residues which were subjected to silica gel column
chromatography (1 : 2 EtOAc–hexane) to afford 10 (11 mg, 90%)
and 64 (9 mg, 85%) from 55, and 11 (25 mg, 80%) and 64 (15 mg,
81%) from 57.
16 U. C. Yoon, S. J. Cho, Y.-Y. Lee, M. J. Mancheno and P. S. Mariano,
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Irradiation of MeCN (150 mL) solutions of 55 and 57 without
DCA did not give any products.
19 C. Pac and O. Ishitani, Electron-transfer organic and bioorganic
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Acknowledgements
This research was supported by (for UCY) National Research
Foundation of Korea Grant funded by the Korean Government
(KRF-2008-521-C00156) and (for PSM) the National Science
Foundation (CHE-0550133 to PSM).
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