The Reactivity of Thymine and Thymidine 5,6-Epoxides with Organometallic Reagents - A Route to Thymidine (6-4) Photoproduct Analogues

Article abstract of DOI:10.1021/acs.joc.6b00495

This report describes an efficient procedure for the generation and isolation of various thymine and thymidine 5,6-epoxides from the corresponding trans-5,6-bromohydrins by reaction with triethylamine. The quantitative isolation of the epoxides, accomplished by solvent precipitation of triethylamine hydrobromide, enabled their regiospecific ring-opening at C6 position by organometallic nucleophiles. The reaction was amenable to a broad range of alkyl, aryl, alkenyl, and alkynyl organomagnesium, -zinc, -aluminum, or -boron reagents, although the reactivity was strongly affected by the electronic effects of N3 protecting group. Additionally, the reaction featured excellent cis-diastereoselectivity providing access to C6-carbon-functionalized dihydrothymidine cis-alcohols, which are synthetic derivatives of UV-induced DNA lesions, namely, thymidine (6-4) photoproducts.

Full text of DOI:10.1021/acs.joc.6b00495

Article
pubs.acs.org/joc
The Reactivity of Thymine and Thymidine 5,6-Epoxides with
Organometallic Reagents − A Route to Thymidine (6-4)
Photoproduct Analogues
Pauli Wrigstedt,† Jari Kavakka,‡ Sami Heikkinen,‡ Martin Nieger,† Minna Raisanen,† and Timo Repo*,†
̈
̈
†
‡
Department of Chemistry, Laboratory of Inorganic Chemistry and Laboratory of Organic Chemistry, University of Helsinki, P.O.
Box 55, Helsinki FIN-00014, Finland
S
* Supporting Information
ABSTRACT: This report describes an efficient procedure for the generation and isolation of various thymine and thymidine 5,6-
epoxides from the corresponding trans-5,6-bromohydrins by reaction with triethylamine. The quantitative isolation of the
epoxides, accomplished by solvent precipitation of triethylamine hydrobromide, enabled their regiospecific ring-opening at C6
position by organometallic nucleophiles. The reaction was amenable to a broad range of alkyl, aryl, alkenyl, and alkynyl
organomagnesium, -zinc, -aluminum, or -boron reagents, although the reactivity was strongly affected by the electronic effects of
N3 protecting group. Additionally, the reaction featured excellent cis-diastereoselectivity providing access to C6-carbon-
functionalized dihydrothymidine cis-alcohols, which are synthetic derivatives of UV-induced DNA lesions, namely, thymidine (6-
4) photoproducts.
Scheme 1. Isolation of Pyrimidine 5,6-Epoxides Permits Their
Manipulation with Organometallic Nucleophiles
INTRODUCTION
■
Thymine nucleobase and nucleoside analogues have an
important role in the field of drug development1 and in the
studies of DNA strand breaking.2 Thymine glycol (5,6-
dihydroxy-5,6-dihydrothymine) and its deoxyribonucleoside
are among the major products resulting from oxidative damage
of DNA.3 On a preparative scale, thymine glycols and the
analogous thio, alkoxy, and amine alcohols can be synthesized
regiospecifically at the C6 site of the thymine core, starting from
the thymine trans-bromohydrins in the presence of bases
(Scheme 1).4 Thymine epoxide is postulated to be the key
intermediate in these transformations,4a,b,5 and its existence was
confirmed by a 18O-labeled oxygen migration study, in which the
transfer of the hydroxyl group from C6 to C5 atom of 1,3-
dimethylthymine bromohydrin was observed.6 Thymine and
thymidine epoxides are also considered to react with
nucleophiles, such as, the amino acids and purines present in
human body, and thus their synthesis has been explored4a,7
In contrast to the dihydrothymine C6-thio-, C6-alkoxy-, and
C6-aminoalcohols, only a few examples of the respective C6
carbon-functionalized alcohols exist, presumably due to the
challenges in their preparation, i.e., selective carbon derivatiza-
tion of the nucleobase core. To date, C6 alkyl- or C6 aryl-
substituted dihydrothymine alcohols have been obtained merely
by photochemical reactions including γ-irradiation-initiated
Received: March 7, 2016
© XXXX American Chemical Society
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radical oxidation and UV-irradiation in aqueous media, with or
without additional oxidants.5a,7b,8 This class of compounds is
attractive in view of drug development and due to the importance
of the photochemical formation of nucleic acid−protein cross-
linkages in biological systems.7c,9 Additionally, dimeric dihy-
drothymidine alcohols have an important role in the develop-
ment of skin cancer, which is due to dimerization of adjacent
thymine residues in DNA upon its exposure to sunlight (Figure
1).10 This lesion interferes with DNA replication and tran-
To establish the scope of the reaction with organometallic
reagents, we developed a standard experimental procedure based
on the preliminary experiments of 2 with vinylmagnesium
bromide. From the initial experiments, it was important to add
the Grignard reagent to the reaction mixture in one portion since
the dropwise addition (over 10 min) decreased the product yield
by approximately 50%. Additionally, we did not observe the
formation of other regioisomers in any experiments (C5-
substitution), according to NMR spectroscopic measurements
of the crude and purified products.
The addition of n- and sec-alkyl Grignard reagents to 2 afforded
C6 alkyl-substituted dihydrothymine cis-alcohols 3−6 and 12 in
fair yields (Table 1, entries 1−4 and 15; for stereostructural
Table 1. Scope of the Reaction With 1 (Only One Enantiomer
Depicted)
Figure 1. Major type of thymidine photoproduct (6-4) and its highly
mutagenic Dewar-type isomer, triggered by UV irradiation of genomic
DNA.
scription and may lead to mutation and cell death.11 In humans,
damaged DNA lesions are repaired through complex enzymatic
processes, known as nucleotide excision repair mechanism
(NER).12
Owing to the biological significance of C6 carbon-substituted
dihydrothymine and thymidine cis-alcohols, which cover all
organisms,13 a generic synthesis of their derivatives is of
importance. Herein, we report an efficient method for the
generation and isolation of dimethylthymine and various N3-
protected thymidine 5,6-epoxides and detail their use as key
intermediates to introduce carbon−carbon link at C6 into
nucleobase core by epoxide ring opening with organometallic
reagents.
RESULTS AND DISCUSSION
■
We initiated the study by investigating the formation of 1,3-
dimethylthymine 5,6-epoxide 2 from bromohydrin 1 in the
presence of triethylamine (TEA, Scheme 1). We found that the
treatment of 1 with TEA in acetone generated 2 exclusively with
full conversion of 1, accompanied by a concurrent precipitation
of triethylamine hydrobromide. The quantitative conversion also
occurred in THF and MeCN, but the precipitation of
triethylamine hydrobromide was not as efficient as in acetone;
in which case the quantitative isolation of 2 from the reaction
mixture was accomplished simply by filtering and subsequent
evaporation of the solvent. In contrast, our attempts to isolate 2
after epoxidation of dimethylthymine with dimethyldioxirane
(DMDO) in acetone4e,14 proved unsuccesful.15
determination see later in the text). Even the bulky tert-
butylmagnesium bromide gave the corresponding alcohol 7
(entry 5). Surprisingly, we also detected the simultaneous
formation of the 5-hydroxy-5,6-dihydrothymine byproduct,16
which is presumably due to β-hydride transfer from tert-
butylmagnesium bromide to 2. The introduction of π-systems
into the thymine core, using vinyl-, phenyl-, and 2-thienylmag-
nesium bromides, afforded the respective alcohols 8−10 in good
yields (entries 6−8). Furthermore, the use of ethynylmagnesium
bromide as a nucleophile gave dihydrothymine alcohol 11 (entry
9). The less reactive phenyl- and vinylzinc bromides also added
to the epoxide affording 8 and 9 in good yields (entries 10 and
11). However, no reaction occurred with butylzinc bromide as a
nucleophile (entry 12). In terms of product yields, the reaction
performed well with trimethyl- and triphenylaluminum17 and
During investigation of its chemical behavior, we found that 2
was highly reactive toward nucleophiles, such as water, alcohols,
and amines, forming thymine glycol, 6-alkoxy, and 6-amino
alcohols (mixtures of cis and trans isomers), respectively, which
was in agreement with earlier reports.4 The epoxide was not
stable if stored for a prolonged time (7 days at room
temperature) in acetone under inert atmosphere. Also, attempts
to further purify 2 by column chromatography led to its
decomposition. However, as freshly prepared, 2 appeared to be a
versatile substrate for the regiospecific introduction of a carbon−
carbon bond into the thymine core by organometallic reagents,
thus, enabling the synthesis of an array of new thymine
derivatives.
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triphenylborane nucleophiles, resulting in phenyl- and methyl-
substituted 9 and 12 in very good yields (entries 13, 15, and 16).
Before obtaining the crystal structures of 3 and 9, confirming
their cis configuration, we attempted to establish the diaster-
Scheme 2. Proposed Mechanism (Only One Enantiomer
Depicted)
1
eochemical arrangement of the products by H−1H NOESY
NMR spectroscopy. Accordingly, gas-phase structures of cis and
trans isomers of the starting material 1 and the products 3−11
were calculated using density functional theory (DFT) at the
B3LYP/6-31(d) level. The computational results revealed a
minimal distance difference of 0.1−0.3 Å existing between CH3-9
and H6 in cis and trans isomers. The difference is too small to use
NOESY to unambiguously distinguish the cis and trans
configurations.18 However, DFT models showed significant
differences in H6−C6−C5-C9 torsion angles between the
diastereomers and thus in the heteronuclear coupling constants
Next we applied the developed synthetic methodology,
described above, to thymidine nucleoside, which provides access
to a range of synthetic derivatives of thymidine photoproducts
(Figure 1). These compounds can be highly useful in drug
development, such as anticancer and antiviral agents,1,24 and in
mechanistic studies of DNA repair by NER12a,c,d or photo-
lyases.25 Additionally, they find application in the construction of
fluorophores and chromophores to examine protein−protein
and protein−ligand interactions.26
3
between H6 and C9 (3JH6,C9). Therefore, we measured JH6,C9
values for each derivative using the phase-sensitive, heteronuclear
long-range coupling correlation NMR experiment, CBC-
HSQMBC,19 allowing for the extraction of nJHC-values (n = 2−
4) from the separation of antiphase lines in the correlation peak
multiplets. Consequently, molecular dynamics simulations
(MD) were performed for the products 1 and 3−11, and the
corresponding dihedral angles were transformed into hetero-
nuclear coupling constants, using the Karplus equation (eq 1).20
Comparison of these values, shown in Table 2, strongly suggests
Initially, we studied the epoxide formation from N-H-O,O-
TBS-dihydrothymidine bromohydrin (Scheme 3). The deoxy-
Scheme 3. Formation of Epoxides from N3-Unprotected
Thymidine Bromohydrins
Table 2. Experimental and Calculated Heteronuclear
Coupling Constants (Hz) of Dihydrothymine Alcohols 1 and
a
3−11
ribose (dR) alcohols were protected with tert-butyldimethylsilyl
groups (TBS), which selective removal from thymidine is well-
established,27 by treating thymidine with TBS-Cl in the presence
of pyridine and N,N-dimethylaminopyridine (DMAP). The
bromohydrin formation with N-bromosuccinimide (NBS) in
aqueous THF afforded a mixture of two trans-diastereomers (dr
= 3:2, i and ii, Scheme 3).4d However, generation of the
respective epoxides from both diastereomers independently
compd no.
exptl
3JH6,C9 (Hz) MDcis
MDtrans
3
4
2.9
3.1
3.8
4.9
3.6
3.8
4.3
3.9
4.6
2.1
3.2
3.1
4.1
4.2
4.0
3.6
4.8
4.4
3.6
2.9
1.8
2.0
1.6
1.6
1.8
1.6
1.1
1.4
2.0
2.0
5
6
1
7
using 1 equiv of TEA was low yielding (ca. 5−10% in 2 h, H
8
NMR, iii and iv, Scheme 3) and led to the formation of
unidentified products, which did not react further in a desired
manner. Even so, this could explain the excess of nucleophile (20
equiv) required for the efficient coupling of amines and amino
acid ethyl esters with the in situ generated N3-unprotected
thymidine epoxides7a and the contradictory results reported for
the synthesis of dihydrothymidine aryl sulfides from the
corresponding bromohydrins, in the presence of pyridine and
zinc oxide.4c,d
9
10
11
1
a
MD = Molecular dynamics calculations.
the cis diastereochemical arrangement for thymine alcohols 3−
11. Moreover, the experimental and calculated 3JH6,C9 couplings
in bromohydrin 1 are in agreement with its structure, which is
well established to possess a trans configuration (Table 2).6
As the protection of N3 was necessary, we chose to use the
robust methyl group in order to prevent potential side reactions.
Accordingly, N-methylation of O,O-TBS-thymidine with MeI in
28
DMF in the presence of K2CO3 and the subsequent reaction
3JCH = 4.5 − 0.78cos φ + 4.03cos 2φ
with NBS in THF-H2O gave dihydrothymidine trans-bromohy-
drins 13 and 14 (dr = 3:2), which were separated by flash column
chromatography (Scheme 4).
When 13 was treated with triethylamine, the stereospecific
elimination of HBr occurred as with bromohydrin 1. This key
step afforded thymidine epoxide 15 quantitatively, thus, opening
the route for its efficient modification by organometallic reagents.
The subsequent addition of phenylmagnesium bromide
furnished C6 phenyl-substituted dihydrothymidine alcohol 17
as a single product in good yield. Likewise, the addition of
(1)
The observed cis relative stereochemistry suggests that the
epoxide opens prior to nucleophilic attack, similarly to the
epoxide ring-openings of 2,3-piperidines with organozinc
compounds21 and glycals with Grignard22 or organoaluminum
reagents.23 Consequently, it is evident that the reaction proceeds
through an intramolecular nucleophilic attack of the coordinated
organometallic reagent to the zwitterionic iminium ion, as
illustrated in Scheme 2.
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Scheme 4. Quantitative Stereospecific Formation of
Thymidine Epoxides Followed by Regiospecific and
Diastereoselective Addition of Phenylmagnesium Bromide
Scheme 5. Reaction Sequence with N-Benzyl Protected
Thymidine and Efforts To Remove the Protecting Group
a
dihydrothymidine alcohol 24 in very good yield (80%).
Unfortunately, all our efforts to remove the benzyl protecting
group with NH4CO2-Pd/C,29 H2-Pd/C, t-BuOK-DMSO,30 or
KBr-oxone31 methods failed. Also, attempts to use benzylox-
ymethyl ether (BOM)32 protecting group were unsuccessful, as
the bromohydrin formation with NBS in H2O-THF was sluggish
and gave the product in low yield.
We then changed the N3-protecting group to benzoyl, which
can be removed from thymidine under basic conditions.33 The
treatment of O,O-TBS-thymidine with benzoyl chloride in
MeCN in the presence of TEA and pyridine and the subsequent
bromination with NBS gave the corresponding N-Bz-O,O-TBS
trans bromohydrins 26 and 27 (dr = 5:1, Scheme 6).
a
Reagents and conditions: (i) TBS-Cl, pyridine, DMAP, DMF, 70 °C,
14 h; (ii) MeI, K2CO3, DMF, 40 °C, 12 h; (iii) NBS, NaCl(aq)-THF,
rt, 40 min; and (iv) column chromatography.
phenylmagnesium bromide to the diastereomerically pure
epoxide 16 afforded 18 as the sole product. The reaction also
worked well when a mixture of 13 and 14 was used, albeit the
separation of the diastereomers was somewhat more complex.
The absolute configuration of 18 (5R, 6S) was established by a
single-crystal X-ray structure determination, revealing its stereo-
chemical resemblance to the UV-induced thymidine photo-
products shown in Figure 1. Due to the mechanistic aspects of
the reaction (Scheme 2), the confirmed structure of 18 allowed
us to determine the stereochemical arrangements of bromohy-
drins 13 (5R, 6R) and 14 (5S, 6S), as well as dihydrothymidine
alcohol 17 (5S, 6R). Additionally, with thymidine bromohydrin
13 as a substrate, the reaction proved effective with a series of
organomagnesium, -zinc and -aluminum reagents, providing C6-
substituted n-butyl, isopropyl, 2-thienyl, phenyl, and ethynyl
alcohols 19, 20, 21, 17, and 22 in fair to good yields, respectively
(Table 3).
Scheme 6. Phenyl Addition to N-Benzoyl-Protected
Thymidine Epoxides Generated from a Mixture of 26 and 27
The epoxidation of 26 or 27 was found to be significantly faster
than for those of N-methylated 13 and 14 or benzylated 23 (5
min versus 2 h, 1.5 equiv of TEA), ascribed to the electron-
withdrawing nature of the benzoyl group (EWG), reducing the
electron density in the pyrimidine ring. As a result, the epoxide
can be expected to be more electrophilic than the epoxides
generated from 13, 14, and 23 with electron-donating groups
(EDG) at N3, but organozinc reagents (PhZnBr, PhZnBr + BF3·
OEt2, or diphenylzinc) did not react, and thymidine glycol was
the major product obtained after quenching the reactions with
water. Apparently, with N-benzoylated thymidine epoxide,
stronger Lewis acidity (oxophilicity) of the organometallic
reagent is required to facilitate the formation of a reactive
iminium-alkoxide pair (Scheme 2). Grignard reagents proved
incompatible, and, for example, the addition of 1 equiv of
phenylmagnesium bromide to the epoxide generated from 26
resulted in several decomposition products, and only traces of 28
were observed among the crude products. Gratifyingly, organo-
aluminum compounds, which are easily accessible with various
methods,34 were amenable to the reaction and the addition of
triphenylaluminum17 to the mixture of epoxides from 26 and 27
gave 6-phenyl-substituted 28 and 29, in good overall yields of
70% (diastereomers were separable by column chromatography,
Scheme 6). Trimethylaluminum reacted also with the epoxide
but resulted in the loss of TBS groups to some extent, thus
necessitating other protecting groups, such as benzyl, in the
To evaluate the applicability of the method for thymidine with
removable protecting group at N3, we prepared N3-benzyl-
protected thymidine trans-bromohydrin 23 (major diastereomer,
dr = 5:1, Scheme 5). The treatment of 23 with TEA followed by
the addition of phenylzinc bromide afforded 6-phenyl
Table 3. Scope of the Reaction with Thymidine Bromohydrin
13
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deoxyribose moiety. Additionally, arylboranes were compatible
with the reaction as the addition of triphenylborane to 26 (90%
diastereomeric purity) gave 28 in good 82% yield.
aqueous KOH, resulting in DNA strand break formation.
Moreover, the N3−C4 bond cleavage by nucleophiles is
enhanced by the presence of EWG groups, such as benzoyl at
N3 (C4 more electrophilic), explaining the incompatibility of
Grignard reagents with N3-Bz-protected dihydrothymidine
epoxide (the reaction proceeded well with the respective
electron-donating N3-Me and N3-Bn epoxides).
Several methods for quantitative N-debenzoylation of
thymidine involve KOH-MeOH,33b NH3(aq)-MeOH,33a and
n- and sec alkylamines in various solvents.33c However, there are
no examples in the literature describing the N3-debenzoylation
of dihydrothymidines. In this respect, we were pleased to find
that the treatment of 28 with 1.5 equiv of n-BuNH2 for 1 h in
CHCl3 gave 25 regiospecifically and quantitatively, albeit we
were not able to separate the formed products by column
chromatography (N-butylbenzamide and 25). By utilizing n-
OctNH2 in the reaction, the target product 25 was obtained in an
excellent 97% yield after purification (Scheme 7). The absolute
CONCLUSIONS
■
We have developed an efficient method for the generation and
isolation of dimethylthymine and thymidine 5,6-epoxides from
the corresponding bromohydrins. These epoxides were utilized,
for the first time, in the regiospecific and stereoselective
construction of carbon−carbon bonds at C6 of the nucleobase
core using organometallic nucleophiles. The presented method-
ology possessed a broad substrate scope, performing well with
various alkyl, alkenyl, aryl, and alkynyl organomagnesium, -zinc,
-aluminum, or -boron reagents, especially with EDG protecting
groups (Me and Bn) at N3. With EWG benzoyl group at N3 in
thymidine the scope was more limited. This was due to the
decreased reactivity of the epoxide and stability of the
dihydropyrimidine ring, which makes the N3−C4 bond
susceptible to cleaving by nucleophiles through hemiaminal
formation. Regardless, the N3-Bz-dihydrothymidine epoxide was
compatible with organoaluminum and arylboron reagents, and
the quantitative Bz deprotection of the product was simply
achieved by using primary alkylamines.
Scheme 7. Regioselective N-Debenzoylation of 28 with n-
OctNH2 in CHCl3 and Dihydropyrimidine Rearrangement to
2-Oxazolidone with KOH or Aqueous NH3 in MeOH
Notably, the procedure featured excellent cis diastereoselec-
tivity enabling the stereoselective syntheses of C6-functionalized
cis-5-hydroxy-5,6-dihydrothymidines. As analogues of thymidine
(6-4) photoproducts, these compounds could be valuable, for
example, in the studies of DNA repair and strand break formation
and in drug development. Further expansion of the reaction
scope on various N3-protected dihydrothymidine alcohols as
well as the study of their dehydration to the respective C6-
substituted nucleosides is underway in our laboratory.
EXPERIMENTAL SECTION
■
configuration of 25 (5S, 6R) was confirmed by single-crystal X-
ray structural determination (Figure S4 in Supporting
Information), establishing also the stereochemical arrangements
of 26 (5R, 6R), 27 (5S, 6S) and 29 (5R, 6S).
General Experimental Details. All manipulations were performed
under argon atmosphere unless otherwise stated using Schlenk
technique. All solvents were dried by using automated solvent
purification system, except acetone which was dried over anhydrous
CaSO4 and distilled. All reagents were purchased from commercial
sources and used without further purification unless otherwise noted.
HRMS measurements were carried out using either ESI-TOF or EI mass
spectrometer. Melting points were determined with a capillary melting
point apparatus and were uncorrected. FT-IR spectra of neat
compounds were determined using FT-IR spectrometer equipped
with a one reflection attenuated total reflection (ATR) unit. Absolute
configuration of the products 3, 9, 18, and 25 was determined by X-ray
Unexpectedly, the treatment of 28 with KOH in MeOH (1
equiv, 20 min, rt) or aqueous NH3 in MeOH (4 equiv, 1.5 h, rt)
resulted in the dihydropyrimidine rearrangement, affording
novel 2-oxazolidone derivatives 30 and 31 as major products;
the former of which was purified and fully characterized (Scheme
7). Apparently, the presence of an ester bond at C4 in 30
indicates that the reaction proceeds through N3−C4 ring-
cleaved methyl ester and amide intermediates, followed by
cyclization and the loss of benzamide (for putative reaction
mechanism; see Scheme S1 in Supporting Information). It is
worth adding that the formation of 2-oxazolidone structure can
1
analysis (for detailed information; see Supporting Information). H
NMR and 13C NMR spectra were acquired at 27 °C using 300 MHz
(300 MHz 1H-frequency and 75 MHz 13C-frequency) or 500 MHz (500
MHz 1H-frequency and 125.7 MHz 13C-frequency) spectrometer.
Chemical shifts are reported in ppm, and the ppm scale was referenced
to residual solvent peaks (CHCl3 in CDCl3; 7.26 ppm for 1H and 77.16
ppm for 13C, acetone in acetone-d6; 2.05 ppm for 1H and 29.84 ppm for
13C). Coupling constants are reported in Hz. 13C NMR experiments
were performed using APT pulse sequence (13C{1H} proton
decoupling). The following abbreviations were used to describe the
multiplicities of resonances: br s = broad singlet, s = singlet, d = doublet,
t = triplet, q = quartet, m = multiplet. The 2D NMR experiments
(HSQC and HMBC) were used as additional techniques for NMR
signal assignments. All above-mentioned NMR spectra were processed
with MestReNova 7.1.2.
1
be easily detected by H NMR spectroscopy due to a notable
shift in the singlet proton signal of the original dihydropyr-
imidine CH3-7 from 1.9 to 1.0−1.1 in ppm (CDCl3).
Evidently, in contrast to thymidine, the absence of the
pyrimidine C5−C6 double bond and the resulting loss of ring
aromaticity render dihydrothymidines susceptible to N3−C4
bond-cleavage by nucleophiles, through hemiaminal formation.
This supplements recent observations that dimeric 5-thyminyl-
5,6-dihydrothymine (spore photoproduct, SP)35 and (6-4)
photoproduct36 undergo hydrolysis of N3−C4 bond in hot
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CBC-HSQMBC.37 All phase-sensitive CBC-HSQMBC-experiments
were performed at 27 °C using 500 MHz spectrometer (500 MHz 1H-
frequency and 125.7 MHz 13C-frequency) equipped with 5 mm PFG
inverse-detection 1H, X (X-coil tuned to 13C) probehead capable of z-
HRMS (EI) calcd for C7H11BrN2O3 (M+) 249.9953, found 249.9965
(79Br); calcd for C7H11BrN2O3 (M+) 251.9933, found 251.9942 (81Br);
Mp 133 °C (dec.).
2,4,6-Trimethyl-7-oxa-2,4-diazabicyclo[4.1.0]heptane-3,5-dione
(2). To a solution of 1 (0.50 g, 2.0 mmol) in dry acetone (7 mL) was
added triethylamine (0.56 mL, 4.0 mmol, 2.0 equiv) at room
temperature. The mixture was shaken and left standing, with gentle
sporadic shaking, for 2 h to allow triethylamine hydrobromide
precipitation. Then, the supernatant was transferred into another flask
under inert atmosphere through a membrane filter (0.45 μm GHP
ACRODISK 13). The remaining precipitate was washed once with dry
acetone (1.5 mL), and filtering was repeated. The solution was
evaporated under reduced pressure to afford the racemic title compound
2 as a colorless oil, which was used as such for the addition reactions. The
NMR spectroscopic data reported here are not consistent with earlier
reported data of 2, prepared by direct epoxidation of dimethylthymine
with MeReO3/H2O2 or dimethydioxirane.39 1H NMR (500 MHz,
acetone-d6, in 1 equiv of triethylamine): 1.52 (s, 3H), 3.10 (s, 3H), 3.19
(s, 3H), 4.84 (s, 1H) ppm; 13C{1H} NMR (75 MHz, acetone-d6, d1 = 15
s): 15.6, 28.2, 34.6, 56.0, 70.4, 152.1, 169.3 ppm; HRMS (EI) calcd
C7H10N2O3 (M+) 170.0691, found 170.0689.
General Procedure for the Addition of Grignard Reagents to
2. A Grignard reagent (2.4 mmol, 1.2 equiv) was added in one portion to
a freshly prepared solution of 2 (2.0 mmol) in THF (7 mL) under argon.
The resulting mixture was stirred at room temperature for 30 min,
whereupon the reaction was quenched with sat. aq NH4Cl (15 mL) and
stirring was continued for 5 min. Then, the mixture was extracted with
EtOAc (3 × 20 mL), and the combined organic layers were washed with
sat. aq NaHCO3 (20 mL) and brine (20 mL). The solution was dried
over Na2SO4, and the solvents were evaporated under reduced pressure
to give the crude product, which was purified by flash column
chromatography.
cis-6-Ethyl-5-hydroxy-1,3,5-trimethyldihydropyrimidine-2,4-
(1H,3H)-dione (3). According to the general procedure, 0.8 mL of 3 M
solution of ethylmagnesium bromide in diethyl ether was added in one
portion to the freshly prepared solution of 1.3-dimethylthymine epoxide
2 (2.0 mmol) in THF (7 mL). Purification by flash column
chromatography (EtOAc:hexane 1:1 (v/v), Rf = 0.3) afforded the title
product 3 as a white powder (227 mg, 57%). After recrystallization (i-
PrOH-H2O), the obtained transparent needles were dissolved in
acetone, and single crystals suitable for X-ray crystallography were
grown by slow evaporation of the solvent. 1H NMR (500 MHz, CDCl3):
0.92 (t, J = 7.5 Hz, 3H), 1.40−1.46 (m, 1H), 1.42 (s, 3H), 1.81−1.87 (m,
1H), 3.12 (s, 3H), 3.12−3.18 (m, 1H), 3.18 (s, 3H), 3.65 (br s, 1H, OH)
ppm; 13C{1H} NMR (125.7 MHz, CDCl3): 10.8, 22.5, 26.3, 28.4, 37.6,
66.3, 71.0, 152.3, 175.0 ppm; IR (neat): 3437 (broad.), 2984, 2938,
1709, 1664, 1471, 1440, 1280, 1180, and 1075 cm−1; HRMS (EI) calcd
C9H16N2O3 (M+) 200.1161, found 200.1160; Mp 77−78 °C.
1
gradient amplitudes up to 20 G/cm. The spectral widths for H- and
13C-dimensions were 5006.25 and 29996.30 Hz, respectively. The
CPMG-INEPT duration for polarization transfer via long-range
couplings between 1H and 13C was optimized for nJCH = 8 Hz, whereas
the CAGEBIRDr,X-element duration was tuned according to 1JCH = 145
Hz. The 90° pulse widths for 1H and 13C were 7.0 and 11.7 μs,
1
respectively. The simultaneous 180° H and 13C pulses in CPMG-
pulsetrains were flanked by 100 μs delays (i.e., 200 μs interpulse delay).
The relaxation delay was 1.0 s, and the number of transients was 16.
Before the actual accumulation of data set, 64 steady-state scans were
applied. The number of increments in the indirectly detected 13C-
dimension was 128. The number of acquired complex points was 5006
resulting in acquisition time of 1.0 s. All CBC-HSQMBC data were
processed using NMR spectrometer operating software Vnmr 6.1C. The
time-domain data in t2-dimesion was apodized by shifted Gaussian
function (gf = 0.259 s, gfs = 0.235 s) to improve the resolution, whereas
unshifted Gaussian function was applied in t1-dimension (gf1 = 0.00089
s). The data matrix was zero filled up to 8192(1H) × 256(13C) complex
3
points prior to Fourier transform. The JH6C9 values could be directly
measured from the separation of antiphase lines in the 1H-dimension of
the relatively simple H6,C9-correlation peak multiplets for the studied
class of compounds.
DFT Calculations. Prior to the geometry optimization with DFT
method, a conformational search for compounds 1 and 3−11 was
performed with the semiempirical RM1 method. DFT calculations were
performed using the B3LYP function in combination with the 6-31G*
basis set as implemented in Spartan’10.
MD Calculations. MD calculations for the structures 1 and 3−11
were performed by following the specific dihedral angles (H6−C6−
C5−C9) using the Hyperchem 8.0.4 software. All MD runs were done
using following parameters: heat time 0 ps, run time 1 ps, cool time 0 ps,
step size 0.001 ps, and constant temperature. Simulations were done at
27 °C in vacuo. The dihedral angles were transformed into
heteronuclear coupling constants using eq 1.20
Synthesis of N,N-Dimethylthymine. The modified procedure
described previously was used.38 To a solution of thymine (10 g, 80
mmol) in DMF (120 mL) was added K2CO3 (38 g, 278 mmol, 3.5
equiv) and iodomethane (138 mmol, 15 mL, 3.0 equiv), and the
resulting mixture was stirred at 50 °C for 48 h. Then water was added
(300 mL), and the solution was extracted with chloroform (5 × 60 mL).
The combined organic layers were washed with water (5 × 60 mL) and
brine (1 × 60 mL) and dried over Na2SO4. The solvent was evaporated
under reduced pressure to yield the crude title product as a white solid
(8.6 g, 70%), which was used for the next step without further
1
cis-6-Butyl-5-hydroxy-1,3,5-trimethyldihydropyrimidine-2,4-
(1H,3H)-dione (4). According to the general procedure, 1.2 mL of 2 M
solution of butylmagnesium chloride in THF was added in one portion
to the freshly prepared solution of 1.3-dimethylthymine epoxide 2 (2.0
mmol) in THF (7 mL). Purification by column chromatography
(EtOAc:hexane 1:1.5 (v/v), Rf = 0.45) afforded the title product 4 as a
purifications. H NMR (500 MHz, CDCl3): 1.91 (d, J = 1.2 Hz, 3H),
3.33 (s, 3H), 3.35 (s, 3H), 6.97 (q, J = 1.2 Hz, 1H); 13C{1H} NMR
(125.7 MHz, CDCl3): 13.1, 28.0, 36.8, 109.7, 139.1, 152.0, 164.2.
5-Bromo-6-hydroxy-1,3,5-trimethyldihydropyrimidine-2,4-
(1H,3H)-dione (1). To a solution of dimethylthymine (5.0 g, 32 mmol)
in THF (70 mL) was added water (14 mL) followed by the addition of
bromine (2.1 mL, 42 mmol, 1.3 equiv) in small portions. The resulting
solution was stirred at room temperature for 1 h (monitored by TLC;
EtOAc:hexane 1:1), whereupon water (120 mL) and EtOAc (120 mL)
were added, and the excess bromine was quenched by the addition of
solid Na2S2O5 in small portions under vigorous stirring until the solution
became colorless. The organic phase was separated, and the water layer
was extracted with EtOAc (3 × 50 mL). The combined organic layers
were washed with sat. aq NaHCO3 (2 × 60 mL), brine (60 mL), and
dried over Na2SO4. The solvent was evaporated under reduced pressure
to yield the crude product, which was concentrated in EtOAc and
precipitated by the addition of a mixture of diethyl ether/n-hexane (1:5
v/v to EtOAc) to afford racemic 1 (5.6 g, 70%) as a white powder. 1H
NMR (500 MHz, acetone-d6); 1.93 (s, 3H); 3.11 (s, 3H); 3.12 (s, 3H);
5.06 (d, J = 5.5 Hz, 1H); 6.10 (d, J = 5.5 Hz, 1H) ppm; 13C{1H} NMR
(125.7 MHz, acetone-d6): 24.4, 28.2, 34.9, 55.9, 86.1, 152.4, 168.3 ppm;
IR (neat): 3327, 2945, 1718, 1677, 1652, 1487, 1292, and 1030 cm−1;
1
white crystalline solid (292 mg, 64%) H NMR (500 MHz, CDCl3):
0.85−0.87 (m, 3H), 1.24−1.36 (m, 5H), 1.41 (s, 3H), 1,76−1.81 (m,
1H), 3.15−3.18 (m, 1H), 3.18 (s, 3H), 3.68 (br s, 1H, OH) ppm;
13C{1H} NMR (125.7 MHz, CDCl3): 14.0, 23.0, 25.9, 28.2, 28.5, 29.2,
37.3, 65.0, 71.0, 152.2, 175.1 ppm; IR (neat): 3438 (broad), 2957, 2930,
2862, 1712, 1661, 1466, 1283, and 1054 cm−1; HRMS (EI) calcd
C11H20N2O3 (M+) 228.1474, found 228.1463; Mp 72−73 °C.
cis-5-Hydroxy-6-isopropyl-1,3,5-trimethyldihydropyrimidine-2,4-
(1H,3H)-dione (5). According to the general procedure, 1.2 mL of 2.0 M
solution of isopropylmagnesium chloride in diethyl ether was added in
one portion to the freshly prepared solution of 1.3-dimethylthymine
epoxide 2 (2.0 mmol) in THF (7 mL). Purification by flash column
chromatography (EtOAc:hexane 1:1 (v/v), Rf = 0.3) afforded the title
1
product 5 as a white powder (248 mg, 58%). H NMR (500 MHz,
CDCl3): 0.76 (d, J = 6.9 Hz, 3H), 1.02 (d, J = 7.1 Hz, 3H), 1.42 (s, 3H),
2.24−2.30 (m, 1H), 3.14 (s, 3H), 3.15 (d, J = 3.3 Hz, 1H), 3.16 (s, 3H),
F
DOI: 10.1021/acs.joc.6b00495
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
3.70 (br s, 1H, OH) ppm; 13C{1H} NMR (125.7 MHz, CDCl3): 17.1,
22.0, 27.5, 28.1, 29.2, 39.1, 70.1, 70.3, 152.7, 175.2 ppm; IR (neat): 3397,
2965, 1704, 1656, 1473, 1281, 1175, and 1049 cm−1; HRMS (EI) calcd
for C10H18N2O3 (M+) 214.1317, found 214.1309; Mp 73−74 °C.
cis-6-Cyclohexyl-5-hydroxy-1,3,5-trimethyldihydropyrimidine-
2,4(1H,3H)-dione (6). According to the general procedure, 1.2 mL of 2.0
M solution of cyclohexylmagnesium bromide in diethyl ether was added
in one portion to the freshly prepared solution of 1.3-dimethylthymine
epoxide 2 (2.0 mmol) in THF (7 mL). Purification by flash column
chromatography (EtOAc:hexane 1:2 (v/v), Rf = 0.25) afforded the title
product 6 as a colorless oil. Crystallization from i-prOH/H2O gave 6 as
1H, -OH), 4.48 (s, 1H), 6.87−6.88 (d, J = 3.3 Hz, 1H), 6.95−6.97 (m,
1H), 7.26−7.27 (d, J = 4.1 Hz, 1H) ppm; 13C{1H} NMR (125.7,
CDCl3): 26.0, 28.5, 35.8, 65.2, 71.5, 126.6, 127.08, 127.14, 137.3, 152.6,
173.8 ppm; IR (neat): 3429 (broad), 2933, 1714, 1662, 1465, 1282, and
1044 cm−1; HRMS (EI) calcd for C11H14N2O3S (M+) 254.0725, found
254.0726.
cis-6-Ethynyl-5-hydroxy-1,3,5-trimethyldihydropyrimidine-2,4-
(1H,3H)-dione (11). According to the general procedure, 4.8 mL of 0.5
M solution of ethynylmagnesium bromide in THF was added in one
portion to a freshly prepared solution of 1.3-dimethylthymine epoxide 2
(2.0 mmol) in THF (7 mL). Purification by column chromatography
(EtOAc:hexanes 1:1 (v/v), Rf = 0.4) afforded the title product 11 as a
1
transparent needles (305 mg, 60%). H NMR (500 MHz, CDCl3):
1
0.95−1.23 (m, 5H), 1.35 (m, 1H), 1.42 (s, 3H), 1.62−1.73 (m, 4H),
1.88−1.96 (m, 1H), 3.09 (d, J = 3.5 Hz, 1H), 3.13 (s, 3H), 3.17 (s, 3H),
3.66 (s, 1H, OH) ppm; 13C{1H} NMR (125.7 MHz, CDCl3): 26.2, 26.5,
27.0, 27.4, 27.5, 28.1, 32.5, 39.1, 39.3, 70.08, 70.14, 152.7, 175.3 ppm; IR
(neat): 3369 (br.), 2931, 2855, 1702, 1660, 1447, 1281, and 1071 cm−1;
HRMS (EI) calcd for C13H22N2O3 (M+) 254.1630, found 254.1624; Mp
105−106 °C.
white powder (247 mg, 63%). H NMR (500 MHz, CDCl3): 1.49 (s,
3H), 2.38 (d, J = 2.1 Hz, 1H), 3.12 (s, 3H), 3.23 (s, 3H), 3.70 (s, 1H,
OH), 3.94 (d, J = 2.1 Hz, 1H) ppm; 13C{1H} NMR (125.7 MHz,
CDCl3): 24.3, 28.6, 35.5, 57.4, 70.8, 75.1, 77.0, 152.7, 173.5 ppm; IR
(neat): 3399 (broad), 3257, 3222, 2113, 1707, 1662, 1473, 1448, 1287,
1180, and 1054 cm−1; HRMS (EI) calcd for C9H12N2O3 (M+) 196.0848,
found 196.0848; Mp 117 °C.
cis-6-(tert-Butyl)-5-hydroxy-1,3,5-trimethyldihydropyrimidine-
2,4(1H,3H)-dione (7). According to the general procedure, 1.2 mL of 2
M solution of tert-butylmagnesium chloride in diethyl ether was added
in one portion to the previously prepared solution of 1.3-
dimethylthymine epoxide 2 (2.0 mmol) in THF (7 mL). Purification
by flash column chromatography (EtOAc:hexane 1:1.5 (v/v), Rf = 0.5)
afforded the title product 7 as a white solid (132 mg, 30%). 1H NMR
(500 MHz, CDCl3): 1.00 (s, 9H), 1.42 (s, 3H), 3.02 (s, 1H), 3.14 (s,
3H), 3.17 (s, 3H), 3.72 (br s, 1H, OH) ppm; 13C{1H} NMR (125.7
MHz, CDCl3): 28.0, 28.4, 28.7, 37.7, 40.9, 71.7, 73.3, 152.7, 175.7 ppm;
IR (neat): 3442 (broad), 2957, 2914, 2875, 1710, 1657, 1468, 1394,
1287, and 1054 cm−1; HRMS (EI) calcd C11H20N2O3 (M+) 228.1474,
found 228.1474; Mp 75−76 °C.
cis-6-Ethyl-5-hydroxy-1,3,5-trimethyldihydropyrimidine-2,4-
(1H,3H)-dione (12). According to the general procedure, 0.8 mL of 3 M
solution of methylmagnesium bromide in diethyl ether was added in one
portion to the freshly prepared solution of 1.3-dimethylthymine epoxide
2 (2.0 mmol) in THF (7 mL). Purification by flash column
chromatography (EtOAc:hexane 1:1 (v/v), Rf = 0.25) afforded the
title product 12 as a colorless oil (248 mg, 67%). 1H NMR (500 MHz,
CDCl3): 1.14 (dd, J = 6.7, 1.0 Hz, 3H), 1.45 (d, J = 0.9 Hz, 3H), 3.08 (d, J
= 1.0 Hz, 3H), 3.21 (d, J = 1.0 Hz, 3H), 3.24−3.35 (m, 1H), 3.61 (s, 1H)
ppm; 13C{1H} NMR (125.7 MHz, CDCl3): 13.2, 25.6, 28.3, 35.6, 60.6,
71.3, 152.1, 174.7 ppm; HRMS (EI) calcd C8H14N2O3 (M+) 186.1004,
found 186.0999.
Synthesis of 8 and 9 Using Zinc Nucleophiles. Anhydrous zinc
bromide (586 mg, 2.6 mmol) was dissolved in 4 mL of THF, and the
solution was cooled to 0 °C using an ice bath. Next, 2.4 mL of 1.0 M
solution of vinylmagnesium bromide in THF or 0.8 mL of 3 M solution
of phenylmagnesium bromide in diethyl ether (2.4 mmol) was added,
and the resulting white suspension was warmed to room temperature
and stirred for 1 h. In a separate flask, freshly prepared epoxide 2 (1.99
mmol) was dissolved in 3 mL THF. The previously prepared zinc
nucleophile was then transferred via cannula in one portion, and the
mixture was stirred at room temperature for 30 min. The reaction was
quenched by addition of saturated ammonium chloride (3 mL), and the
zinc salts were dissolved upon addition of ammonium hydroxide 28%
(10 mL). The aqueous phase was extracted with EtOAc (3 × 20 mL),
and the combined organic layers were washed with sat. aq NaHCO3 (20
mL) and brine (20 mL). The solution was dried over Na2SO4, and the
solvents were evaporated under reduced pressure to give the crude
product, which was purified by column chromatography eluting with
EtOAc:hexane 1:1.5 to afford 8 as a white solid (329 mg, 83%, Rf = 0.3)
or 9 as transparent solid (407 mg, 82%, Rf = 0.4), depending on the
cis- 5-Hydroxy-1,3,5-trimethyl-6-vinyldihydropyrimidine-2,4-
(1H,3H)-dione (8). According to the general procedure, 2.4 mL of 1.0
M solution of vinylmagnesium bromide in THF was added in one
portion to the freshly prepared solution of 1.3-dimethylthymine epoxide
2 (2.0 mmol) in THF (7 mL). Purification by flash column
chromatography (EtOAc:hexane 1:1.5 (v/v), Rf = 0.3) afforded the
1
title product 8 as a white solid (245 mg, 62%). H NMR (500 MHz,
CDCl3): 1.50 (s, 3H), 3.08 (s, 3H), 3.19 (s, 3H), 3.56 (s, 1H, OH), 3.72
(dt, J = 5.7, 1.3 Hz, 1H), 5.06−5.14 (m, 1H), 5.28 (d, J = 10.5 Hz, 1H),
5.80 (ddd, J = 17.1, 10.5, 5.7 Hz, 1H) ppm; 13C{1H} NMR (125.7 MHz,
CDCl3): 25.9, 28.3, 35.6, 66.5, 71.5, 118.3, 130.9, 152.6, 174.1 ppm; IR
(neat): 3451 (broad), 2980, 1712, 1668, 1467, 1397, 1152, and 1072
cm−1; HRMS (EI) calcd for C9H14N2O3 (M+) 198.1004, found
198.1009; Mp 58−59 °C.
cis-5-Hydroxy-1,3,5-trimethyl-6- phenyldihydropyrimidine-2,4-
(1H,3H)-dione (9). According to the general procedure, 0.8 mL of 3
M solution of phenylmagnesium bromide in diethyl ether was added in
one portion to the freshly prepared solution of 1.3-dimethylthymine
epoxide 2 (2.0 mmol) in THF (7 mL). Purification by flash column
chromatography (EtOAc:hexane 1:1.5 (v/v), Rf = 0.4) afforded the title
product 9 as a colorless crystalline solid (357 mg, 74%). After
recrystallization from i-PrOH-H2O, the obtained transparent needles
were dissolved in acetone, and single crystals suitable for X-ray
crystallography were grown by slow evaporation of the solvent. 1H NMR
(500 MHz, CDCl3): 1.64 (s, 3H), 3.05 (s, 3H), 3.28 (s, 4H), 4.25 (s,
1H), 7.04−7.06 (m, 2H), 7.31−7.32 (m, 3H) ppm; 13C{1H} NMR
(125.7 MHz, CDCl3): 27.3, 28.5, 35.8, 69.0, 71.2, 127.5, 128.70, 128.74,
134.1, 152.8, 173.8 ppm; IR (neat): 3403, 2991, 2938, 1713, 1659, 1448,
1182, 1170, and 1050 cm−1; HRMS (EI) calcd for C13H16N2O3 (M)+
248.1161, found 248.1174; Mp 114−115 °C.
1
substrate. H and 13C NMR spectra of the products were identical to
those of obtained above using Grignard reagents.
Synthesis of 9 Using AlPh3. Triphenylaluminum was prepared by
adding 1.05 mL of 3 M phenylmagnesium bromide in Et2O (3.2 mmol)
into a solution of 0.5 M AlCl3 in THF (2.2 mL, 1.1 mmol) and stirred at
room temperature for 16 h under argon.17 In a separate flask, freshly
prepared epoxide 2 (0.86 mmol) was dissolved in 3 mL THF. The
previously prepared AlPh3 solution was then transferred via cannula in
one portion, and the mixture was stirred at room temperature for 0.5 h,
whereupon the reaction was quenched by addition of saturated
ammonium chloride (3 mL). EtOAc was added (40 mL), and the
aluminum salts were dissolved upon addition of 1 M NaOH (10 mL).
The organic layer was separated and washed with sat. aq NaHCO3 (20
mL) and brine (20 mL). The solution was dried over Na2SO4, and the
solvents were evaporated under reduced pressure to give the crude
product, which was purified by flash column chromatography
(EtOAc:hexane 1:1.5 (v/v), Rf = 0.4) affording 9 as transparent solid
(167 mg, 79%). 1H and 13C NMR spectra of the product were identical
to those of obtained above using PhMgBr.
cis-5-Hydroxy-1,3,5-trimethyl-6-(thiophen-2-yl)dihydro-
pyrimidine-2,4(1H,3H)-dione (10). According to the general procedure,
2.4 mL of 1.0 M solution of 2-thienylmagnesium bromide in THF was
added in one portion to the freshly prepared solution of 1.3-
dimethylthymine epoxide 2 (2.0 mmol) in THF (7 mL). Purification
by flash column chromatography (EtOAc:CHCl3 1:4 (v/v), Rf = 0.35)
afforded the title product 10 as a colorless oil (369 mg, 73%). 1H NMR
(500 MHz, CDCl3): 1.61 (s, 3H), 3.11 (s, 3H), 3.25 (s, 3H), 3.49 (br s,
G
DOI: 10.1021/acs.joc.6b00495
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The Journal of Organic Chemistry
Article
Synthesis of 12 Using AlMe3. A 2 M solution of AlMe3 (1.2 mL, 2.4
mmol) in toluene was added in one portion to a freshly prepared
solution of 2 (1.99 mmol) in THF (7 mL) under argon. The resulting
mixture was stirred at room temperature for 0.5 h, whereupon the
reaction was quenched by addition of saturated ammonium chloride (5
mL). EtOAc was added (40 mL), and the aluminum salts were dissolved
upon addition of 1 M NaOH (15 mL). The organic layer was separated
and washed with sat. aq NaHCO3 (20 mL) and brine (20 mL). The
solution was dried over Na2SO4, and the solvents were evaporated under
reduced pressure to give the crude product, which was purified by flash
column chromatography (EtOAc:hexane 1:1 (v/v), Rf = 0.25) affording
evaporated under reduced pressure to afford a crude mixture of
diastereomers, which were separated and purified by column
chromatography (EtOAc:hexane 1:7) to afford 13 (0.55 g, 45%, white
solid, Rf = 0.30) and 14 (0.38 g, 31%, white solid, Rf = 0.20).
trans-(5R,6R)-5-Bromo-1-((2R,4S,5R)-4-((tert-butyldimethylsilyl)-
oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-
6-hydroxy-3,5-dimethyldihydropyrimidine-2,4(1H,3H)-dione (13).
1H NMR (300 MHz, CDCl3) δ −0.04−0.24 (m, 12H), 0.89 (s, 9H),
0.92 (s, 9H), 1.99 (s, 3H), 2.07−2.34 (m, 2H), 3.24 (s, 3H), 3.73 (dd, J =
11.0, 2.0 Hz, 1H), 3.78 (dt, J = 4.3, 2.3 Hz, 1H), 3.84 (dd, J = 11.0, 2.4
Hz, 1H), 4.02 (d, J = 2.4 Hz, 1H, -OH), 4.34−4.49 (m, 1H), 5.06 (d, J =
2.4 Hz, 1H), 6.46−6.59 (t, J = 6.8 Hz 1H) ppm; 13C{1H} NMR (75
MHz, CDCl3) δ −5.4, −5.3, −4.7, −4.3, 18.1, 18.7, 23.8, 25.9, 26.1, 28.6,
38.5, 53.6, 62.0, 71.0, 80.0, 85.2, 86.0, 151.8, 167.2 ppm; IR (neat): 3319,
2952, 2927, 2855, 1719, 1648, 1469, 1107, 1082, 1029, and 831 cm−1.
HRMS (ESI+) m/z calcd for C23H45BrN2NaO6Si2 [M + Na]+ 603.1892,
found 603.1882. Mp 108−111 °C.
trans-(5S,6S)-5-Bromo-1-((2R,4S,5R)-4-((tert-butyldimethylsilyl)-
oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-
6-hydroxy-3,5-dimethyldihydropyrimidine-2,4(1H,3H)-dione (14).
1H NMR (300 MHz, CDCl3) δ 0.07−0.12 (m, 12H), 0.88 (s, 9H),
0.92 (s, 9H), 1.97 (s, 3H), 2.26−2.45 (m, 2H), 3.20 (s, 3H), 3.71−3.83
(m, 1H), 3.90−4.01 (m, 2H), 4.34 (d, J = 5.1 Hz, 1H, -OH), 4.35−4.40
(m, 1H), 5.45 (d, J = 5.1 Hz, 1H), 5.87 (t, J = 6.0 Hz, 1H) ppm; 13C{1H}
NMR (75 MHz, CDCl3) δ −5.4, −5.1, −4.7, −4.4, 18.1, 18.8, 23.8, 25.9,
26.2, 28.3, 41.8, 58.3, 63.3, 71.2, 79.2, 87.4, 87.5, 150.6, 167.5 ppm; IR
(neat): 3393, 2955, 2929, 2857, 1717, 1672, 1463, 1109, 1074, 1027, and
832 cm−1. HRMS (ESI+) m/z calcd for C23H45BrN2NaO6Si2 [M + Na]+
603.1892, found 603.1900. Mp 123−126 °C.
Thymidine epoxides 15 and 16. To a solution of 13 or 14 (0.50 g,
0.86 mmol) in dry acetone (5 mL) under argon was added triethylamine
(0.240 mL, 1.72 mmol) at room temperature. The mixture was shaken
and left standing for 3 h to allow triethylamine hydrobromide
precipitation. After this time, the supernatant was transferred into
another flask under inert atmosphere through a membrane filter (0.45
μm GHP ACRODISK 13). The remaining precipitate was washed once
with dry acetone (1.5 mL), and filtering was repeated. Then, the solution
was evaporated under reduced pressure to afford the epoxides 15 (from
13) or 16 (from 14) as white solids, which were immediately subjected
to the Grignard addition reaction.
(1R,6S)-2-((2R,4S,5R)-4-((tert-Butyldimethylsilyl)oxy)-5-(((tert-
butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-4,6-dimethyl-
7-oxa-2,4-diazabicyclo[4.1.0]heptane-3,5-dione (15). 1H NMR (500
MHz, Acetone-d6, ∼0.5 equiv of TEA) δ 0.09−0.17 (m, 12H), 0.93 (m,
18H), 1.52 (s, 3H), 2.10 (ddd, J = 13.2, 6.0, 2.5 Hz, 1H), 2.33 (ddd, J =
13.2, 8.5, 6.0 Hz, 1H), 3.10 (s, 3H), 3.77−3.86 (m, 2H), 3.88 (dt, J = 3.7,
2.0 Hz 1H), 4.52 (app q, J = 3.6 Hz, 1H), 4.98 (s, 1H), 6.33 (dd, J = 8.5,
6.0 Hz, 1H) ppm; 13C{1H} NMR (126 MHz, acetone-d6) δ −5.3, −5.2,
−4.6, −4.5, 15.6 (C-8), 16.6, 18.9, 26.2, 26.4, 28.4, 39.8, 55.4, 64.1, 65.3,
73.5, 86.1, 87.9, 151.5, 169.2 ppm. HRMS (ESI+) m/z calcd for
C23H44N2O6Si2 [M + Na]+ 523.2630, found 523.2621.
(1S,6R)-2-((2R,4S,5R)-4-((tert-Butyldimethylsilyl)oxy)-5-(((tert-
butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-4,6-dimethyl-
7-oxa-2,4-diazabicyclo[4.1.0]heptane-3,5-dione (16). 1H NMR (300
MHz, Acetone-d6, ∼1 equiv of TEA) δ 0.09−0.24 (m, 18H), 0.93 (s,
12H), 1.56 (s, 3H), 2.13 (ddd, J = 13.2, 8.5, 6.0 Hz, 1H), 2.18−2.34 (m,
1H), 3.11 (s, 3H), 3.83−3.93 (m, 3H), 4.52 (dt, J = 5.4, 2.5 Hz, 1H),
5.02 (s, 1H), 6.30 (dd, J = 8.5, 5.8 Hz, 1H) ppm; 13C{1H} NMR (126
MHz, acetone-d6) δ −5.2, −4.6, −4.5, 15.7, 18.6, 19.0, 26.2, 26.4, 28.3,
40.1, 55.2, 64.2, 64.4, 73.5, 85.9, 87.8), 151.1, 168.7 ppm. HRMS (ESI+)
m/z calcd for C23H44N2O6Si2 [M + Na]+ 523.2630, found 523.2615.
Addition of Phenylmagnesium Bromide to 15 and 16. To a freshly
prepared solutions of 15 or 16 (0.5 g, 0.86 mmol) in THF (6 mL) under
argon were added 3 M solution of phenylmagnesium bromide in diethyl
ether (0.34 mL, 1.03 mmol, 1.2 equiv) in one portion. The resulting
mixture was stirred at room temperature for 1 h. After 1 h, the reaction
was quenched with 1 M HCl (10 mL) and stirring was continued for 5
min. Then the mixture was extracted with EtOAc (3 × 20 mL), and the
combined organic layers were washed with sat. aq NaHCO3 (20 mL)
and brine (20 mL) and dried over Na2SO4. The solvents were
1
12 as colorless oil (308 mg, 83%). H and 13C NMR spectra of the
product were identical to those of obtained using MeMgBr.
Synthesis of 9 Using BPh3. To a freshly prepared solution of 2 (0.5
mmol) in THF (3 mL) under argon, 145 mg BPh3 (0.6 mmol) was
added. The resulting mixture was stirred at room temperature for 30
min. The reaction was quenched with sat. aq NaHCO3 (7 mL) and
stirred for 10 min. Then, the mixture was extracted with EtOAc (3 × 10
mL), and the combined organic layers were washed with sat. aq
NaHCO3 (10 mL), water (10 mL), and brine (10 mL). The solution was
dried over Na2SO4, and the solvents were evaporated under reduced
pressure to give the crude product, which was purified by flash column
chromatography (EtOAc:hexane 1:1.5 (v/v), Rf = 0.4) to afford 9 as a
1
white solid (112 mg, 90%). H and 13C NMR spectra of the product
were identical to those of obtained using PhMgBr or AlPh3.
TBS Protection of Thymidine. To a solution of thymidine (4.0 g, 16.5
mmol) in DMF (50 mL) under argon were added tert-butyldimethylsilyl
chloride (6.0 g, 40 mmol, TBS), pyridine (5.3 mL, 66 mmol), and 4-
dimethylaminopyridine (DMAP, 0.2 g, 1.64 mmol). The resulting
solution was stirred at 70 °C for 14 h. Then, water (120 mL) and EtOAc
(250 mL) were added, and the organic layer was separated, washed with
water (5 × 50 mL), brine (50 mL), and dried over Na2SO4. The solvent
was evaporated under reduced pressure to afford O,O-TBS-thymidine as
a white solid (7.5 g, 96%), which was used for the next step without
1
further purification. H NMR (500 MHz, CDCl3) δ 0.00−0.18 (m,
12H), 0.81−0.98 (m, 18H), 1.90 (d, J = 1.3 Hz, 3H), 1.99 (ddd, J = 13.1,
7.9, 6.1 Hz, 1H), 2.24 (ddd, J = 13.1, 5.9, 2.6 Hz, 1H), 3.75 (dd, J = 11.4,
2.5 Hz, 1H), 3.86 (dd, J = 11.4, 2.6 Hz, 1H), 3.92 (m, 1H), 4.39 (dt, J =
5.6, 2.6 Hz, 1H), 6.32 (dd, J = 7.9, 5.9 Hz, 1H), 7.46 (d, J = 1.3 Hz 1H),
9.02 (s, 1H,) ppm; 13C{1H} NMR (126 MHz, CDCl3) δ −5.3, −5.2,
−4.7, −4.5, −3.5, 12.7, 18.1, 18.5, 25.8, 25.8, 25.9, 26.1, 41.5, 63.1, 72.4,
85.9, 87.9, 111.0, 135.6, 150.5, 164.0 ppm.
N-Methylation of O,O-TBS-Thymidine. To a solution of O,O-TBS-
thymidine (6 g, 12.7 mmol) in DMF (60 mL) under argon were added
K2CO3 (4.5 g, 25 mmol) and iodomethane (1.2 mL, 19.1 mmol), and
the resulting mixture was stirred at 40 °C for 12 h.28 Next, ice-cold water
(120 mL) and Et2O (200 mL) were added, and the organic phase was
separated, washed with water (3 × 50 mL) and brine (50 mL), and dried
over Na2SO4. The solvent was evaporated under reduced pressure to
give N-Me-O,O-TBS thymidine as a white solid (5.6 g, 95%), which was
used for the next step without further purification. 1H NMR (300 MHz,
CDCl3) δ 0.06−0.10 (m, 12H), 0.88 (s, 9H), 0.91 (s, 9H), 1.92 (d, J =
1.2 Hz, 3H), 1.95−2.04 (m, 1H), 2.26 (ddd, J = 13.1, 5.8, 2.7 Hz, 1H),
3.75 (dd, J = 11.3, 2.6 Hz, 1H), 3.86 (dd, J = 11.3, 2.6 Hz, 1H), 3.93 (m,
1H), 4.39 (dt, J = 5.6, 2.6 Hz, 1H), 6.35 (dd, J = 7.8, 5.8 Hz, 1H), 7.46 (d,
J = 1.2 Hz, 1H) ppm; 13C{1H} NMR (75 MHz, CDCl3) δ −5.3, −5.2,
−4.7, −4.5, 13.5, 18.1, 18.5, 26.0, 26.02, 28.0, 41.6, 63.1, 72.3, 85.7, 87.9,
110.0, 133.4, 151.4, 163.8 ppm.
trans-Bromohydrins 13 and 14. To a solution of N-Me-O,O-TBS
thymidine (1.0 g, 2.1 mmol) in THF (25 mL) under argon were added
brine (15 mL) and H2O (5 mL) followed by the addition N-
bromosuccinimide (1.84 g, 10.3 mmol). The resulting biphasic solution
was stirred vigorously at room temperature, and the reaction was
monitored by TLC (EtOAc:hexane 1:7). After 45 min, water (30 mL)
and EtOAc (60 mL) were added, and the excess bromine was quenched
by the addition of solid Na2S2O5 in small portions under vigorous
stirring until the solution became colorless. The organic phase was
separated, and the water layer was extracted with EtOAc (2 × 25 mL).
The combined organic layers were washed with sat. aq NaHCO3 (30
mL), brine (30 mL), and dried over Na2SO4. The solvents were
H
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The Journal of Organic Chemistry
Article
evaporated under reduced pressure to give the crude products, which
were purified by flash column chromatography to afford 17 (0.34 g, 69%,
colorless oil, flash column: EtOAc:hexane 1:6, Rf = 0.25) or 18 (0.35 g,
71%, white solid, flash column: EtOAc:hexane 1:5, Rf = 0.30), depending
on the starting material. With compound 18 the crystals suitable for X-
ray crystallography were grown from n-hexane at −20 °C.
cis-(5S,6R)-1-((2R,4S,5R)-4-((tert-Butyldimethylsilyl)oxy)-5-(((tert-
butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-5-hydroxy-3,5-
dimethyl-6-phenyldihydropyrimidine-2,4(1H,3H)-dione (17). 1H
NMR (300 MHz, CDCl3) δ 0.05−0.07 (m, 12H), 0.88 (s, 9H), 0.92
(s, 9H), 1.59 (s, 3H), 2.00−2.24 (m, 2H), 3.14 (s, 1H, -OH), 3.18−3.33
(m, 4H), 3.40 (dd, J = 11.0, 3.7 Hz, 1H), 3.73 (ddd, J = 5.3, 3.7, 2.0 Hz,
1H), 4.34 (dt, J = 5.2, 2.3 Hz, 1H), 4.67 (s, 1H), 6.25 (dd, J = 8.3, 5.7 Hz,
1H), 7.02−7.16 (m, 2H), 7.18−7.35 (m, 3H) ppm; 13C{1H} NMR (75
MHz, CDCl3) δ −5.3, −5.2, −4.6, −4.6, 18.1, 18.6, 25.9, 26.2, 26.4, 28.3,
38.6, 61.0, 63.5, 71.3, 72.7, 86.8, 87.2, 127.6, 128.2, 128.3, 136.5, 152.5,
173.7 ppm; IR (neat): 3455, 2953, 2928, 2857, 1719, 1673, 1463, 1253,
1028, and 831 cm−1; HRMS (ESI+) m/z calcd for C29H50N2NaO6Si2 [M
+ Na]+ 601.3100, found 601.3092.
cis-(5R,6S)-1-((2R,4S,5R)-4-((tert-Butyldimethylsilyl)oxy)-5-(((tert-
butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-5-hydroxy-3,5-
dimethyl-6-phenyldihydropyrimidine-2,4(1H,3H)-dione (18). 1H
NMR (500 MHz, CDCl3) δ −0.12 (s, 3H), −0.07 (s, 3H), 0.12 (s,
3H), 0.13 (s, 3H), 0.81 (s, 9H), 0.94 (s, 9H), 1.57 (ddd, J = 13.4, 7.7, 6.1
Hz, 1H), 1.61 (s, 3H), 1.66 (ddd, J = 13.4, 6.1, 3.6 Hz, 1H), 3.14 (s, 1H,
-OH), 3.27 (s, 3H), 3.65 (dd, J = 10.6, 4.5 Hz, 1H), 3.69−3.78 (m, 2H),
4.10 (dt, J = 6.3, 3.6 Hz, 1H), 4.74 (s, 1H), 6.47 (dd, J = 7.7, 6.1 Hz, 1H),
7.05−7.14 (m, 2H), 7.27−7.35 (m, 3H) ppm; 13C{1H} NMR (126
MHz, CDCl3) δ −5.1, −5.1, −4.8, −4.7, 18.0, 18.7, 25.8, 26.3, 26.4, 28.5,
37.4, 58.9, 63.1, 71.35, 71.41, 84.3, 86.0, 127.7, 128.5, 128.6, 136.0,
152.8, 173.9 ppm; IR (neat): 3453, 2953, 2929, 2857, 1720, 1674, 1463,
1253, 1029, and 833 cm−1; HRMS (ESI+) m/z calcd for
C29H50N2NaO6Si2 [M + Na]+ 601.3100, found 601.3086.
Synthesis of Compound 17 Using PhZnBr. Phenylzinc bromide was
prepared by adding 0.30 mL of 3 M phenylmagnesium bromide (1.0
mmol) in THF into a solution of 248 mg of zinc bromide (1.1 mmol)
dissolved in 2 mL of THF. In a separate flask, freshly prepared epoxide
15 (0.86 mmol) was dissolved in 3 mL THF. The previously prepared
zinc nucleophile was then transferred via cannula in one portion, and the
mixture was stirred at room temperature for 1.5 h. The reaction was
quenched by addition of saturated ammonium chloride (10 mL), and
the zinc salts were dissolved upon addition of ammonium hydroxide
28% (10 mL). The aqueous phase was extracted with EtOAc (3 × 20
mL), and the combined organic layers were washed with sat. aq
NaHCO3 (20 mL) and brine (20 mL). The solution was dried over
Na2SO4, and the solvents were evaporated under reduced pressure to
give the crude product, which was purified by flash column
chromatography (EtOAc:hexane 1:6, Rf = 0.25) to afford 17 as colorless
oil in 81% yield (1H NMR was identical to that of (5S,6R)-cis 17
prepared above with PhMgBr).
RMgX, PhZnBr or AlPh3) in one portion. The resulting mixture was
stirred at room temperature for 90 min. After this time, the reaction was
quenched with sat. NH4Cl (10 mL) and stirring was continued for 5
min. Then the mixture was extracted with EtOAc (3 × 20 mL), and the
combined organic layers were washed with sat. aq NaHCO3 (20 mL)
and brine (20 mL) and dried over Na2SO4. The solvents were
evaporated under reduced pressure to give the crude products 19−22,
which were purified by flash column chromatography.
cis-(5S,6R)-6-Butyl-1-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-
5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-5-hy-
droxy-3,5-dimethyldihydropyrimidine-2,4(1H,3H)-dione (19). Butyl-
magnesium chloride (0.65 mL, 2 M solution in THF) as a nucleophile
afforded 19 (173 mg, 36%) as colorless oil after flash column
chromatography (EtOAc:hexane 1:5, Rf = 0.45). 1H NMR (300 MHz,
CDCl3) δ 0.07−0.08 (m, 12H), 0.81−0.92 (m, 3H), 0.89 (s, 9H), 0.91
(s, 9H), 1,19−1.36 (m, 4H)1.38 (s, 3H), 1.43−1.53 (m, 1H), 1.65−1.75
(m, 1H), 1.98 (ddd, J = 12.7, 5.6, 2.7 Hz, 1H), 2.05−2.18 (m, 1H), 3.18
(s, 3H), 3.50 (s, 1H, -OH), 3.53 (t, J = 5.3 Hz, 1H), 3.62−3.74 (m, 2H),
3.82−3.86 (m, 1H), 4.26−4.47 (m, 1H), 6.10 (dd, J = 8.3, 5.5 Hz, 1H)
ppm; 13C{1H} NMR (75 MHz, CDCl3) δ −5.3, 5.2, −4.6, −4.5, 14.1,
18.1, 18.6, 23.2, 25.9, 25.9, 26.2, 28.0, 28.6, 31.3, 38.9, 57.6, 63.6, 71.4,
72.3, 86.9, 86.9, 151.9, 175.2 ppm; IR (neat): 3438, 2954, 2928, 2857,
1717, 1463, 1253, 1079, and 831 cm−1. HRMS (ESI+) m/z calcd for
C27H54N2NaO6Si2 [M + Na]+ 581.3413, found 581.3422.
cis-(5S,6R)-1-((2R,4S,5R)-4-((tert-Butyldimethylsilyl)oxy)-5-(((tert-
butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-5-hydroxy-6-
isopropyl-3,5-dimethyldihydropyrimidine-2,4(1H,3H)-dione (20).
Isopropylmagnesium chloride (0.65 mL, 2 M solution in diethyl
ether) as a nucleophile afforded 20 (258 mg, 55%) as colorless oil after
flash column chromatography (EtOAc:hexane 1:5, Rf = 0.45). 1H NMR
(300 MHz, CDCl3) δ 0.07 (m, 12H), 0.81 (d, J = 7.0 Hz, 3H), 0.89 (s,
9H), 0.90 (s, 9H), 0.97 (d, J = 7.0 Hz, 3H), 1.41 (s, 3H), 1.96−2.20 (m,
2H), 2.21−2.38 (m, 1H), 3.15 (s, 3H), 3.43 (d, J = 3.8 Hz, 1H), 3.54 (s,
1H, -OH), 3.70 (dd, J = 4.6 and 2.3 Hz, 2H), 3.83 (td, J = 4.3 and 3.1 Hz,
1H), 4.37 (dt, J = 6.2 and 3.1 Hz, 1H), 5.81 (dd, J = 7.6, 5.9 Hz, 1H)
ppm; 13C{1H} NMR (75 MHz, CDCl3) δ −5.3, −5.2, −4.6, −4.5, 18.1,
18.6, 18.8, 21.3, 25.9, 26.2, 26,9, 27.8, 29.8, 39.4, 63.5, 63.6, 71.1, 72.2,
87.0, 88.9, 151.9, 175.3 ppm; IR (neat): 3448, 2955, 2929, 2857, 1717,
1471, 1253, 1079, and 832 cm−1. HRMS (ESI+) m/z calcd for
C26H52N2NaO6Si2 [M + Na]+ 567.3256, found 567.3281.
cis-(5S,6S)-1-((2R,4S,5R)-4-((tert-Butyldimethylsilyl)oxy)-5-(((tert-
butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-5-hydroxy-3,5-
dimethyl-6-(thiophen-2-yl)dihydropyrimidine-2,4(1H,3H)-dione
(21). 2-Thienylmagnesium bromide (1.3 mL, 1 M solution in THF) as a
nucleophile afforded 21 (354 mg, 71%) as colorless oil after flash
column chromatography (EtOAc:hexane 1:6, Rf = 0.25). 1H NMR (300
MHz, CDCl3) δ 0.05−0.09 (m, 12H), 0.88 (s, 9H), 0.92 (s, 9H), 1.54 (s,
3H), 2.09−2.18 (m, 2H), 3.22 (s, 3H), 3.37 (s, 1H, -OH), 3.45−3.64
(m, 2H), 3.81 (dt, J = 5.9, 3.0 Hz, 1H), 4.36 (dt, J = 5.3, 2.6 Hz, 1H), 4.98
(s, 1H), 6.19 (dd, J = 7.8, 5.7 Hz, 1H) 6.81−6.89 (m, 2H), 7.19 (dd, J =
4.9, 1.4 Hz, 1H) ppm; 13C{1H} NMR (75 MHz, CDCl3) δ −5.3, −5.1,
−4.7, −4.5, 18.1, 18.6, 25.2), 25.9, 26.2, 28.2, 38.5, 57.1, 63.4, 71.5, 72.3,
86.6, 87.3, 125.7, 126.5, 126.6, 139.5, 151.9, 173.7 ppm. HRMS (ESI+)
m/z calcd for C27H48N2O6SSi2 [M + Na]+ 607.2664, found 607.2673.
cis-(5S,6R)-1-((2R,4S,5R)-4-((tert-Butyldimethylsilyl)oxy)-5-(((tert-
butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-6-ethynyl-5-
hydroxy-3,5-dimethyldihydropyrimidine-2,4(1H,3H)-dione (22).
Ethynylmagnesium bromide (2.6 mL, 0.5 M solution in THF) as a
nucleophile afforded 22 (272 mg, 60%) as white solid after flash column
chromatography (EtOAc:hexane 1:5, Rf = 0.30). 1H NMR (300 MHz,
CDCl3) δ 0.06−0.011 (m, 12H), 0.88 (s, 9H), 0.92 (s, 9H), 1.39 (s, 3H),
1.98−2.04 (m, 2H), 2.28 (d, J = 2.1 Hz, 1H), 3.23 (s, 3H), 3.54 (broad s,
1H, -OH), 3.75 (app t, J = 3.3 Hz, 2H), 3.92 (td, J = 3.3, 2.1 Hz, 1H),
4.32−4.38 (m, 1H), 4.44 (d, J = 2.1 Hz, 1H), 6.18−6.36 (m, 1H) ppm;
13C{1H} NMR (75 MHz, CDCl3) δ −5.4, −5.2, −4.7, −4.6, 18.1, 18.7,
Synthesis of Compound 17 Using AlPh3. Triphenylaluminum was
prepared by adding 1.05 mL of 3 M phenylmagnesium bromide in Et2O
(3.2 mmol) into a solution of 0.5 M AlCl3 in THF (2.2 mL, 1.1 mmol)
and stirred at room temperature for 16 h under argon.17 In a separate
flask, freshly prepared epoxide 15 (0.86 mmol) was dissolved in 3 mL
THF. The previously prepared AlPh3 solution was then transferred via
cannula in one portion, and the mixture was stirred at room temperature
for 1.5 h, whereupon the reaction was quenched by addition of saturated
ammonium chloride (3 mL). EtOAc was added (40 mL), and the
aluminum salts were dissolved upon addition of 1 M NaOH (10 mL).
The organic layer was separated and washed with sat. aq NaHCO3 (20
mL) and brine (20 mL). The solution was dried over Na2SO4, and the
solvents were evaporated under reduced pressure to give the crude
product, which was purified by flash column chromatography
(EtOAc:hexane 1:6, Rf = 0.25) afforded 17 as colorless oil in 74%
yield (1H NMR was identical to that of (5S,6R)-cis 17 prepared
previously with PhMgBr).
23.3, 25.9, 26.2, 28.4, 39.5, 49.0, 63.4, 71.2, 72.4, 73.2, 73.2, 79.3, 85.6,
87.4, 151.9, 173.5 ppm; IR (neat): 3438, 3313, 2954, 2928, 2858, 1672,
1463, 1253, 1112, and 832 cm−1. HRMS (ESI+) m/z calcd for
C25H46N2NaO6Si2 [M + Na]+ 549.2787, found 549.2806.
N-benzylation of O,O-TBS-thymidine. To a solution of O,O-TBS-
thymidine (1 g, 2.12 mmol) in DMF (10 mL) under argon were added
Synthesis of Compounds 19−22 Using Grignard Reagents. To a
freshly prepared solutions of 15 (0.5 g, 0.86 mmol) in THF (6 mL)
under argon was added organometallic reagent (1.03 mmol, 1.2 equiv,
I
DOI: 10.1021/acs.joc.6b00495
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K2CO3 (0.41 g, 3 mmol) and benzyl bromide (0.27 mL, 2.3 mmol), and
the resulting mixture was stirred at rt for 14 h, whereupon water (3 mL)
was added and stirred for 1 h. Then water (30 mL) and Et2O (60 mL)
were added, and the organic phase was separated, washed with water (1
× 20 mL) and brine (20 mL), and dried over Na2SO4. The solvent was
evaporated under reduced pressure to give the crude product, which was
purified by column chromatography (EtOAc:Hex 1:6, Rf = 0.50) to
2H) ppm; 13C{1H} NMR (75 MHz, CDCl3) δ −5.3, −5.2, −4.6, −4.6,
18.1, 18.6, 25.9, 26.2, 26.2, 38.5, 45.0, 60.7, 63.5, 71.2, 72.8, 86.7, 87.3,
127.7, 128.0, 128.6, 129.8, 136.1, 136.5, 152.0, 173.5 ppm; IR (neat):
3438, 3225, 2954, 2929, 2856, 1672, 1463, 1253, 1108, 1028, and 831
cm−1 HRMS (ESI+) m/z calcd for C35H54N2NaO6Si2 [M + Na]+
677.3413, found 677.3432. Mp 101−104 °C.
N-Benzoylation of O,O-TBS-thymidine. To a solution of O,O-TBS-
thymidine (1 g, 2.12 mmol) in MeCN (10 mL) under argon were added
TEA (0.59 mL, 4.22 mmol), pyridine (0.17 mL, 2.12 mmol), and
benzoyl chloride (0.27 mL, 2.3 mmol). The resulting slurry was heated
at 80 °C for 1 h with vigorous stirring. Then water (1 mL) was added and
stirring continued while the mixture was cooled down to room
temperature. Two M NaOH (15 mL) and Et2O (70 mL) were added
and stirred until all the solids were dissolved. The organic phase was
separated, washed with 2 M HCl (2 × 10 mL), 1 M NaOH (15 mL), and
brine (15 mL), and dried over Na2SO4. The solvent was evaporated
under reduced pressure to give the crude N-Bz-O,O-TBS-thymidine as
light brown solid (1.2 g, 98%), which was used in the next step without
further purification.1H NMR (300 MHz, CDCl3) δ −0.07−0.14 (m,
12H), 0.88 (s, 9H), 0.95 (s, 9H), 1.96 (d, J = 1.2 Hz, 3H), 1.98−2.11 (m,
1H), 2.28 (ddd, J = 13.0, 5.7, 2.5 Hz, 1H), 3.57−4.12 (m, 3H), 4.23−
4.53 (m, 1H), 6.33 (dd, J = 8.0, 5.7 Hz, 1H), 7.32−7.78 (m, 3H,), 7.91−
7.94 (m, 2H) ppm; 13C{1H} NMR (75 MHz, CDCl3) δ −5.3, −5.2,
−4.7, −4.5, 12.7, 18.1, 18.6, 25.8, 26.1, 41.6, 63.3, 72.5, 85.3, 88.2, 111.0,
129.2, 130.6, 131.9, 135.0, 149.5, 163.0, 169.1 ppm.
1
afford N-Bn-O,O-TBS-thymidine as a colorless oil (1.03 g, 87%). H
NMR (300 MHz, CDCl3) δ 0.07−0.11 (m, 12H), 0.89 (s, 9H), 0.92 (s,
9H), 1.94 (d, J = 1.1 Hz, 3H), 1.95−2.04 (m, 1H), 2.25 (ddd, J = 13.1,
5.8, and 2.6 Hz, 1H), 4.04−3.60 (m, 3H), 4.39 (dt, J = 5.5, 2.5 Hz, 1H),
5.14 (app q, 2H), 6.38 (dd, J = 7.9 and 5.8 Hz, 1H), 7.21−7.32 (m, 3H,),
7.45−7.49 (m, 3H) ppm; 13C{1H} NMR (75 MHz, CDCl3) δ −5.3,
−5.2, −4.7, −4.5, 13.4, 18.1, 18.5, 25.9, 26.1, 41.4, 44.6, 63.1, 72.4, 85.6,
87.9, 110.2, 127.6, 128.5, 129.3, 133.7, 137.1, 151.1, 163.6 ppm.
(5R,6R)-3-Benzyl-5-bromo-1-((2R,4S,5R)-4-((tert-butyldimethyl-
silyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-
yl)-6-hydroxy-5-methyldihydropyrimidine-2,4(1H,3H)-dione (23). To
a solution of N-Bn-O,O-TBS-thymidine (1.0 g, 1.8 mmol) in THF (12
mL) was added water (1.2 mL) followed by the addition N-
bromosuccinimide (1.3 g, 7.2 mmol). The resulting solution was stirred
at room temperature for 45 min, whereupon water (10 mL) and Et2O
(40 mL) were added, and the excess bromine was quenched by the
addition of solid Na2S2O5 in small portions under vigorous stirring until
the solution became colorless. The organic phase was separated and
washed with water (3 × 10 mL), sat. aq NaHCO3 (10 mL), and brine
(10 mL) and dried over Na2SO4. The solvents were evaporated under
reduced pressure to afford a crude product, which was purified by
column chromatography (EtOAc:hexane 1:7, Rf = 0.40) to afford a
mixture of diastereomers (dr = 5:1, 1H NMR, 0.97 g, 82%, colorless oil),
wherein 23 was the major diasteromer. By collecting first few fractions
after further column chromatography (EtOAc:hexane 1:7) gave 23 in
90% diastereomeric pyrity (0.15 g), which was used for the next step.
The spectroscopic data are reported only for the major diastereomer 23:
1H NMR (300 MHz, CDCl3) δ 0.08−0.12 (m, 12H), 0.89 (s, 9H), 0.93
Synthesis of Thymidine trans-Bromohydrins 26 and 27. To a
solution of N-Bz-O,O-TBS-thymidine (1.0 g, 1.74 mmol) in THF (12
mL) was added water (1.2 mL) followed by the addition N-
bromosuccinimide (1.26 g, 7.0 mmol). The resulting solution was
stirred vigorously at room temperature for 40 min, whereupon water (10
mL) and Et2O (50 mL) were added, and the excess bromine was
quenched by the addition of solid Na2S2O5 in small portions under
vigorous stirring until the solution became colorless. The organic phase
was separated and washed with water (3 × 10 mL), sat. aq NaHCO3 (10
mL), and brine (10 mL), and dried over Na2SO4. The solvents were
evaporated under reduced pressure to give a crude mixture of
(s, 9H), 2.02 (s, 3H), 2.08−2.34 (m, 2H), 3.65−3.92 (m, 3H), 4.01 (s,
1H, OH), 4.40−4.43 (m, 1H), 4.90−5.15 (m, 3H), 6.54 (t, J = 6.9 Hz,
1H), 7.10−7.50 (m, 5H) ppm; 13C{1H} NMR (75 MHz, CDCl3) δ
−5.4, −5.3, −4.7, −4.3, 18.1, 18.7, 23.8, 25.9, 26.2, 38.6, 45.0, 53.8, 62.2,
71.0, 80.0, 85.3, 86.1, 127.3, 127.9, 128.5, 137.0, 151.6, 167.1 ppm.
HRMS (ESI+) m/z calcd for C29H49BrN2NaO6Si2 [M + Na]+ 679.2205,
found 679.2226.
1
diastereomers (dr = 4:1, H NMR), which was purified by column
chromatography (EtOAc:hexane 1:4, Rf = 0.40) to afford a mixture of
diastereomers (dr 5:1, 1H NMR, 0.51 g, 45%), wherein 26 was the major
diasteromer.
trans-(5R,6R)-3-Benzoyl-5-bromo-1-((2R,4S,5R)-4-((tert-
butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)-
tetrahydrofuran-2-yl)-6-hydroxy-5-methyldihydropyrimidine-2,4-
cis-(5S,6R)-3-Benzyl-1-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-
5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-5-hy-
droxy-5-methyl-6-phenyldihydropyrimidine-2,4(1H,3H)-dione (24).
To a solution of 23 (0.15 g, 0.23 mmol, 90% diastereomeric purity) in
dry acetone (3 mL) under argon was added triethylamine (0.063 mL,
0.45 mmol) at room temperature. The mixture was shaken and left
standing for 3 h to allow triethylamine hydrobromide precipitation.
After this time, the supernatant was transferred into another flask under
inert atmosphere through a membrane filter (0.45 μm GHP
ACRODISK 13). The remaining precipitate was washed twice with
dry acetone (1.0 mL), and filtering was repeated. The solution was
evaporated under reduced pressure, and the resulting white solid residue
was dissolved in THF (3 mL). Then a solution of PhZnBr (0.23 mmol)
in Et2O-THF (prepared from 3.0 M PhMgBr in Et2O and 0.5 M ZnBr2
in THF, rt, 1h) was added, and the solution stirred for 1 h. The reaction
was quenched with NH4Cl (2 mL), and the zinc salts were dissolved
upon addition of ammonium hydroxide 28% (10 mL). The aqueous
phase was extracted with EtOAc (3 × 10 mL), and the combined organic
layers were washed with sat. aq NaHCO3 (10 mL) and brine (10 mL).
The solution was dried over Na2SO4, and the solvents were evaporated
under reduced pressure to give the crude product, which was purified by
flash column chromatography (EtOAc-Hex 1:5, Rf = 0.30) to afford 24
as colorless oil (0.108 mg, 80%): 1H NMR (300 MHz, CDCl3) δ 0.03−
0.05 (m, 12H), 0.86 (s, 9H), 0.91 (s, 9H), 1.58 (s, 3H), 2.03−2.16 (m,
2H), 3.11 (s, 1H, -OH), 3.22 (dd, J = 10.9 and 5.1 Hz, 1H), 3.35 (dd, J =
10.9 and 3.6 Hz, 1H), 3.60−3.77 (m, 1H), 4.31 (m, 1H), 4.62 (s, 1H),
3.99 (m, 2H), 6.27 (dd, J = 8.1, 5.9 Hz, 1H), 6.80−6.89 (m, 2H), 6.98−
7.09 (m, 2H), 7.09−7.18 (m, 2H), 7.28−7.33 (m, 3H), 7.30−7.45(m,
1
(1H,3H)-dione (26). H NMR (300 MHz, CDCl3) δ 0.10−0.15 (m,
12H), 0.89 (s, 9H), 0.96 (s, 9H), 2.06 (s, 3H), 2.16−2.34 (m, 2H),
3.75−3.91 (m, 3H), 4.28 (d, J = 2.3 Hz, 1H, OH), 4.40−4.48 (m, 1H),
5.21 (d, J = 2.3 Hz, 1H), 6.48 (t, J = 6.8 Hz, 1H), 7.45−7.64 (m, 3H),
8.01−8.03 (m, 2H) ppm; 13C{1H} NMR (75 MHz, CDCl3) δ −5.3,
−5.2, −4.7, −4.3, 18.1, 18.7, 23.1, 25.9, 26.2, 38.7, 53.8, 62.2, 71.1, 80.8,
87.3, 87.8, 129.2, 130.6, 132.2, 150.1, 166.0, 168.0 ppm; HRMS (ESI+)
m/z calcd for C29H47BrN2NaO7Si2 [M + Na]+ 693.1997, found
693.2021.
trans-(5S,6S)-3-Benzoyl-5-bromo-1-((2R,4S,5R)-4-((tert-
butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)-
tetrahydrofuran-2-yl)-6-hydroxy-5-methyldihydropyrimidine-2,4-
1
(1H,3H)-dione (27). H NMR (500 MHz, CDCl3) δ 0.06−0.15 (m,
12H), 0.87 (s, 9H), 0.95 (s, 9H), 2.01 (s, 3H), 2.30−2.40 (m, 2H),
3.75−3.96 (m, 3H), 4.35−4.40 (m, 1H), 4.77 (d, J = 5.0 Hz, 1H, OH),
5.57 (d, J = 5.0 Hz, 1H), 5.88 (t, J = 6.8 Hz, 1H), 7.45−7.64 (m, 3H),
8.01−8.03 (m, 2H) ppm; 13C{1H} NMR (75 MHz, CDCl3) δ −5.3,
−5.2, −4.7, −4.3, 18.1, 18.7, 23.1, 25.9, 26.2, 41.9, 53.8, 63.6, 71.6, 80.1,
85.3, 86.1, 129.2, 130.4, 132.6, 149.0, 163.3, 168.6 ppm; HRMS (ESI+)
m/z calcd for C29H47BrN2NaO7Si2 [M + Na]+ 693.1997, found
693.2021.
Synthesis of 28 and 29. To a solution of a mixture of 26 and 27 (dr =
5:1, 0.25 g, 0.37 mmol) in dry acetone (5 mL) under argon was added
triethylamine (0.068 mL, 0.49 mmol) at room temperature. The mixture
was gently shaken and left standing (with no further shaking!) for 1 h to
allow triethylamine hydrobromide precipitation as transparent needles.
Then the supernatant was transferred into another flask under inert
J
DOI: 10.1021/acs.joc.6b00495
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
atmosphere through a membrane filter (0.45 μm GHP ACRODISK 13).
The remaining precipitate was washed twice with dry acetone (1.0 mL),
and filtering was repeated. The solution was evaporated under reduced
pressure to afford the respective epoxides as white foamy solids. Next,
the solids were dissolved in dichloromethane (5 mL) and cooled to −60
°C. Freshly prepared solution of triphenylaluminum in THF (0.45
mmol, prepared from 3 M PhMgBr and AlCl3, rt Fourteen h)17 was
added to the solution containing the epoxides in one portion, and the
mixture was stirred until warmed up to 0 °C (∼40 min). The reaction
was quenched by addition of saturated ammonium chloride (4 mL),
Et2O (50 mL) added, and the aluminum salts were dissolved upon
addition of 2 M NaOH (15 mL). The organic layer was separated and
washed with sat. aq NaHCO3 (15 mL) and brine (15 mL). The solution
was dried over Na2SO4, and the solvents were evaporated under reduced
pressure to give the crude product, which was flash column
chromatographed (EtOAc:hexane 1:4) to afford 28 (146 mg, 59%, Rf
= 0.25) as white solid and 29 (27 mg, 11%, Rf = 0.32) as colorless oil.
Compound 29 could not be fully purified from the byproduct
(approximately 85% purity, 1H NMR), presumably thymidine 5,6-
glycol (see NMR spectra on Supporting Information), which formation
was due to incomplete reaction or presence of water during the reaction.
cis-(5S,6R)-3-Benzoyl-1-((2R,4S,5R)-4-((tert-butyldimethylsilyl)-
oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-
5-hydroxy-5-methyl-6-phenyldihydropyrimidine-2,4(1H,3H)-dione
(28). 1H NMR (300 MHz, CDCl3) δ 0.03−0.11 (m, 12H), 0.85 (s, 9H),
0.95 (s, 9H), 1.85 (s, 3H), 2.12−2.26 (m, 2H), 2.98 (s, 1H, -OH), 3.38
(dd, J = 11.0 and 4.6 Hz, 1H), 3.43−3.53 (m, 1H), 3.74−3.78 (m, 1H),
4.33−4.38 (m, 1H), 4.80 (s, 1H), 6.17−6.20 (m, 1H), 7.28−7.44 (m,
5H), 7.48−7.51 (m, 2H), 7.63−7.66 (m, 1H), 7.90−7.92 (m, 2H) ppm;
13C{1H} NMR (75 MHz, CDCl3) δ −5.3, −5.1, −4.7, −4.6, 18.1, 18.6,
25.8, 25.9, 26.2, 38.9, 61.8, 63.6, 71.9, 72.7, 86.9, 87.5, 127.8, 128.5,
129.2, 130.4, 132.6, 135.0, 135.7, 150.7, 169.0, 172.9 (C-4) ppm; IR
(neat): 3448, 2955, 2929, 2857, 1672, 1463, 1250, 1109, and 831 cm−1.
HRMS (ESI+) m/z calcd for C35H52N2NaO7Si2 [M + Na]+ 691.3205,
found 691.3221. Mp 91−95 °C.
cis-(5R,6S)-3-Benzoyl-1-((2R,4S,5R)-4-((tert-butyldimethylsilyl)-
oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-
5-hydroxy-5-methyl-6-phenyldihydropyrimidine-2,4(1H,3H)-dione
(29). 1H NMR (300 MHz, CDCl3) δ −0.12 (s, 6H), −0.07 (s, 6H), 0.80
(s, 9H), 0.97 (s, 9H), 1.61−1.78 (m, 2H),1.88 (s, 3H), 2.93 (s, 1H,
-OH), 3.62−3.77 (m, 3H), 4.12−4.16 (m, 1H), 4.87 (s, 1H), 6.43−6.48
(m, 1H), 7.36−7.45 (m, 5H), 7.47−7.52 (m, 2H), 7.62−7.68 (m, 1H),
7.89−7.92 (m, 2H) ppm; 13C{1H} NMR (75 MHz, CDCl3) δ −5.0,
−4.8, −4.7, 18.0, 18.8, 25.8, 25.8, 26.3, 36.7, 59.7, 63.0, 71.1, 72.0, 83.9,
86.2, 127.9, 128.9, 129.2, 130.4, 132.7, 135.0, 135.2, 151.1, 169.2, 173.0
ppm; HRMS (ESI+) m/z calcd for C35H52N2NaO7Si2 [M + Na]+
691.3205, found 691.3193.
solution of 28 (50 mg, 0.075 mmol) in CHCl3 (1 mL), 18.5 μL n-
octylamine (0.11 mmol, 1.5 equiv) was added and stirred at room
temperature for 1 h. Then the solvent was evaporated in vacuo, and the
resulting crude mixture flash column chromatographed through silica
gel (EtOAc:hexane 1:4, Rf = 0.12) to afford 25 as a white powder (41 mg,
97%). Crystals suitable for X-ray crystallography were grown from a
mixture of i-PrOH-H2O. 1H NMR (300 MHz, CDCl3) δ 0.04−0.07 (m,
12H), 0.87 (s, 9H), 0.92 (s, 9H), 1.65 (s, 3H), 1.89−2.32 (m, 2H), 2.95
(broad s, 1H, -OH), 3.24 (dd, J = 11.0, 5.2 Hz, 1H), 3.38 (dd, J = 11.0,
3.7 Hz, 1H), 3.72 (ddd, J = 5.4, 3.6, 1.9 Hz, 1H), 4.33 (dt, J = 5.5, 2.1 Hz,
1H), 4.67 (s, 1H), 6.20 (dd, J = 8.4, 5.6 Hz, 1H), 7.20−7.20 (m, 5H),
7.81 (broad s, 1H, -NH) ppm; 13C{1H} NMR (75 MHz, CDCl3) δ −5.3,
−5.2, −4.6, −4.6, 18.2, 18.6, 25.9, 26.20, 26.27, 38.6, 62.2, 63.5, 71.6,
72.7, 86.3, 87.3, 127.7, 128.36, 136.09, 151.4, 173.3 ppm; IR (neat):
3217, 2955, 2929, 2858, 1672, 1253, 1094, 1028, 835, and 774 cm−1.
HRMS (ESI+) m/z calcd for C28H48N2NaO6Si2 [M + Na]+ 587.2943,
found 587.2936.
(4R,5S)-Methyl 3-((2R,4S,5R)-4-((tert-Butyldimethylsilyl)oxy)-5-
(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-5-meth-
yl-2-oxo-4-phenyloxazolidine-5-carboxylate (30). To a solution of 28
(30 mg, 0.044 mmol) in MeOH (1 mL), 89.6 μL of 0.5 M KOH in
MeOH (0.044 mmol, 1.0 equiv) was added and stirred at room
temperature for 20 min, whereupon water (4 mL) and EtOAc (15 mL)
were added. The organic layer was separated, washed once with water (5
mL) and brine (5 mL), and dried over Na2SO4, and the solvents were
evaporated under reduced pressure to give the crude product, which was
purified by column chromatography (EtOAc:hexane 1:4, Rf = 0.50)
1
affording 30 as a colorless oil (14 mg, 55%). H NMR (300 MHz,
CDCl3) δ −0.05 (m, 6H), 0.01 (s, 3H), 0.02 (s, 3H) 0.83 (s, 9H), 0.84
(s, 9H), 1.09 (s, 3H), 1.89 (ddd, J = 12.8, 5.6, 2.1 Hz, 1H), 2.29 (ddd, J =
13.1, 8.9, 5.3 Hz, 1H), 2.63 (dd, J = 10.6, 8.6 Hz, 1H), 3.05 (dd, J = 10.7,
5.0 Hz, 1H), 3.48−3.74 (m, 1H), 3.86 (s, 3H), 4.19−4.22 (m, 1H), 5.07
(s, 1H), 5.61 (dd, J = 8.8, 5.6 Hz, 1H), 7.24−7.27 (m, 1H), 7.37−7.40
(m, 4H) ppm; 13C{1H} NMR (75 MHz, CDCl3) δ −5.3, −5.3, −4.7,
−4.6, 18.1, 18.5, 20.2, 25.9, 26.1, 36.3, 53.5, 63.4, 65.0, 73.0, 82.2, 85.0,
86.8, 128.4, 128.7, 129.2, 135.2, 155.8, 172.8 ppm. IR (neat): 2955,
2929, 2857, 1772, 1258, 1028, 833, and 744 cm−1. HRMS (ESI+) m/z
calcd for C29H49NO7Si2 [M + Na]+ 602.2940, found 602.2936.
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.joc.6b00495.
Crystallographic data for (CCDC-934918 (3), CCDC-
934919 (9), CCDC-1004127 (18), and CCDC-1448807
(25) (CIF)
Synthesis of 28 Using BPh3. To a solution of 26 (0.10 g, 0.15 mmol,
1
90% diastereomeric purity, H NMR) in dry acetone (3 mL) under
argon was added triethylamine (0.025 mL, 0.18 mmol) at room
temperature. The mixture was gently shaken and left standing (with no
further shaking!) for 1 h to allow triethylamine hydrobromide
precipitation as transparent needles. Then, the supernatant was
transferred into another flask under inert atmosphere through a
membrane filter (0.45 μm GHP ACRODISK 13). The remaining
precipitate was washed twice with dry acetone (0.5 mL), and filtering
was repeated. The solution was evaporated under reduced pressure to
afford the respective epoxide as white foamy solid. Next, the epoxide was
dissolved in THF (3 mL), BPh3 (44 mg, 0.28 mmol) was added, and the
solution was stirred at rt for 1h. The reaction was quenched with sat. aq
NaHCO3 (7 mL) and stirred for 10 min. Et2O (30 mL) was added, and
the organic layer was separated and washed with sat. aq NaHCO3 (10
mL), water (10 mL), and brine (10 mL). The solution was dried over
Na2SO4, and the solvents were evaporated under reduced pressure to
give the crude product, which was purified by flash column
chromatography (EtOAc:hexane 1:4 (v/v), Rf = 0.25) to afford 28 as
a white solid (74 mg, 82%). 1H NMR spectrum was identical to that of
28 prepared using AlPh3.
DFT results and copies of NMR spectra for all new
compounds. X-ray crystallographic data of compounds 3,
9, 18, and 25. Crystallographic data contains the
supplementary crystallographic data and can be obtained
free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif) (PDF)
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: timo.repo@helsinki.fi.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank Rocket Wrigstedt, Dr. Kostiantyn Chernichenko, Dr.
Alistair King and Dr. E. Jesus Perea for their precious help in the
manuscript preparation.
cis-(5S,6R)-1-((2R,4S,5R)-4-((tert-Butyldimethylsilyl)oxy)-5-(((tert-
butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-5-hydroxy-5-
methyl-6-phenyldihydropyrimidine-2,4(1H,3H)-dione (25). To a
K
DOI: 10.1021/acs.joc.6b00495
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The Journal of Organic Chemistry
Article
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DOI: 10.1021/acs.joc.6b00495
J. Org. Chem. XXXX, XXX, XXX−XXX