N-Glycosylation of 2,3-dideoxyfuranose derivatives having a (diethoxyphosphorothioyl)difluoromethyl group at the 3α-position

Article abstract of DOI:10.1016/j.tet.2003.09.069

Lewis acid-mediated N-glycosylation of 2,3-dideoxyribofunanosides having a (diethoxyphosphorothioyl)difluoromethyl group at the 3α-position with silylated nucleobases was examined. The phosphorothioyldifluoromethyl was found to be an effective functional group for the diastereoselective synthesis of β-N¹-pyrimidine-nucleotide analogues 26 and 28-30. However, the method was not useful for the diastereoselective synthesis of adenine nucleotide analogues. The nucleotide analogue 26 was transformed to the difluoromethylenephosphonate analogue 31 of thymidine-3′-phosphate by oxidation with m-CPBA, followed by aqueous work-up.

Full text of DOI:10.1016/j.tet.2003.09.069

Tetrahedron 59 (2003) 9059–9073
N-Glycosylation of 2,3-dideoxyfuranose derivatives
having a (diethoxyphosphorothioyl)difluoromethyl group
at the 3a-position
*
Tetsuo Murano, Yoko Yuasa, Soichiro Muroyama, Tsutomu Yokomatsu and Shiroshi Shibuya
School of Pharmacy, Tokyo University of Pharmacy and Life Science, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan
Received 4 September 2003; revised 22 September 2003; accepted 24 September 2003
Abstract—Lewis acid-mediated N-glycosylation of 2,3-dideoxyribofunanosides having a (diethoxyphosphorothioyl)difluoromethyl group
at the 3a-position with silylated nucleobases was examined. The phosphorothioyldifluoromethyl was found to be an effective functional
group for the diastereoselective synthesis of b-N 1-pyrimidine-nucleotide analogues 26 and 28–30. However, the method was not useful
for the diastereoselective synthesis of ade0nine nucleotide analogues. The nucleotide analogue 26 was transformed to the difluoromethylene-
phosphonate analogue 31 of thymidine-3 -phosphate by oxidation with m-CPBA, followed by aqueous work-up.
q 2003 Elsevier Ltd. All rights reserved.
1. Introduction
DFMPA) are considered to act as a non-hydrolyzable mimic
for phosphates (R–OPO3H2) due to the close similarity in
their structural and physical properties.5 Many DFMPA
derivatives have been prepared for potential enzyme
inhibitors and for a useful probe to elucidate biochemical
processes.6 The synthetic chemistry of 30-C-branched
20,30-dideoxyribonucleosides toward difluoromethylene
analogues 3 of 30-phosphorylated nucleosides 2 has also
received much attention because of their potential useful-
ness as building blocks of nuclease-resistant antisense
oligonucleotides (Fig. 1).7
Structural modification of naturally-occurring nucleosides
and nucleotides has been studied in the search for novel
nucleic acid analogues showing biological activity such as
antiviral and antitumor effects.1 Extensive studies have
b0een devoted to the structural modification of 30- or
5 -phosphorylated nucleosides to the metabolically stable
analogues, since the resulting nucleotide analogues serve as
potent and selective pseudoterminator of polymerase-
catalyzed RNA-synthesis2 or as important components of
antisense oligonucleotides having increased resistance to
nuclease.3
For the synthesis of a series of nucleotide analogues 3,
especially for a series of the 20-deoxy derivatives, establish-
ment of methodology for the stereoselective glycosylation
of 2,3-dideoxyfuranose derivatives is an important issu0e to
be solved. As 0a part of our work on a synthesis of 3 -C-
branched 20,3 -dideoxynucleotide analogues,8 we have
previously developed a new methodology for highly
b-selective N-glycosylation of 2,3-dideoxyfuranose deriva-
tives by means of a remote-controlled reaction using
glycosyl donor 4 having the diethoxyphosphorothioyl-
methyl group at the C3-position (Scheme 1).8c,d The high
diastereoselectivity would result, most possibly, by taking
the non-bonding bicyclic cationic intermediate B arising
from the neighbouring group participation of the phos-
phorothioylmethyl moiety toward the C1-position, rather
than the intermediate A.9 Thus, nucleophilic attack of the
activated pyrimidine bases to the less-hindered b-side of A
yields the b-nucleotide analogue 5 stereoselectively. The
sulphur of the phosphorothioyl group might significantly
contribute to the neighbouring group participation, since
the replacement of the sulphur by oxygen resulted in
Methods for the synthesis of 50-deoxy-50-difluoromethyl-
enephosphonate nucleotide analogues 1 have been studied,4
since a,a-difluoromethylenephosphonic acids (R–CF2PO3H2,
Figure 1.
Keywords: nucleotide analogues; N-glycosylations; neighbouring-group
effects; phosphorus; fluorine.
*
Corresponding author. Tel.: þ81-426763251; fax: þ81-426763239;
e-mail: yokomatu@ps.toyaku.ac.jp
0040–4020/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2003.09.069

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T. Murano et al. / Tetrahedron 59 (2003) 9059–9073
Scheme 1.
poor-diastereoselective glycosylation. Conversion of 5 to
the corresponding phosphonic acid analogue 6 was readily
achieved by oxidation with m-CPBA followed by aqueous
quenching (Scheme 1).
We have successively investigated whether the method-
ology could be widely applicable to synthesis of the
difluoromethylene analogues 3 (RvH). A part of the work
has been communicated recently.10 In this paper, we wish
to report experimental details for the synthesis of
20,30-dideoxy-30-difluoromethylenephosphonate nucleotide
analogues by the remote-controlled N-glycosylation with
pyrimidine bases, in addition to the results on N-glycosyl-
ation reaction with purine bases.
Scheme 2. Reagent and conditions: (a) (EtO)2P(O)CH2CO2But, NaH, THF,
93%; (b) LiCF2P(O)(OEt)2, THF, 2788C, 91%; (c) c. HCl, EtOH, 50%;
(d) TBDPSCl, imidazole, DMF, 93%; (e) CCl3C(vNH)OBn, TfOH,
CH2Cl2–petroleumether, 84%; (f) Lawesson’s reagent, toluene, 84% for 13,
76% for 14; (g) BH3·THF, THF, 08C, 92% for 15, 62% for 16; (h) CH(OEt)3,
cat. NH4NO3, EtOH, 808C, 90% for 17; 85% for 19. (i) Ac2O, pyridine, 96%.
corresponding phosphonothioate 13 and 14, respectively, by
the conventional method (Lawesson’s reagent, refluxing
toluene). Reduction of 13 and 14 with BH3·THF in THF at
08C gave the corresponding lactols 15 and 16, respectively,
as a mixture of anomeric isomers. Treatment of 15 and 16
with triethyl orthoformate in EtOH in the presence of a
catalytic amount of ammonium nitrate afforded the corre-
sponding 1-ethoxy derivative 17 and 19, respectively, as an
anomeric mixture (a/b¼1:1) in good yield. The lactol 15
was transformed to an anomeric mixture of 1-acetoxy
derivative 18 by the standard protocol.
2. Results and discussion
2.1. Preparation of glycosyl donors having a
phosphorothioyldifluoromethyl group
2.1.1. 5-O-TBDPS- and 5-O-Bn-protecting derivatives.
The glycosyl donors 17–19 having a (diethoxyphosphor-
oylthioyl)difluoromethyl group at the C3-position, in which
the 5-hydroxyl is protected by a tert-butyldiphenylsilyl
(TBDPS) or benzyl (Bn) group, were prepared as shown in
Scheme 2. Horner–Emmons–Wadsworth reaction of
1,2-O-isopropylidene-(R)-glyceraldehyde 7 with tert-butyl
diethylphosphonoacetate gave the unsaturated ester 8. The
Michael reaction of 8 with diethyl (lithiodifuruoromethyl)-
phosphonate11 at 2788C in THF afforded 9 in 91% yield as
a 1:1 mixture of diastereoisomers. Upon treatment of the
mixture with conc. HCl in EtOH at 258C, the trans-lactone
10 was obtained as the sole product in 50% yield through
lactonization of (3R,4S)-diastereoisomer of 9. In this
reaction, the alternative (3S,4S)-isomer decomposed with-
out any formation of the desired lactone.12 The relative
stereochemistry of 10 was deduced by a strong correlation
between H-3 and the methylene protons a to the hydroxyl
observed in an NOESY-experiment. Protection of the
hydroxyl group of 10 with TBDPS or Bn afforded 11 and
12. The compounds 11 and 12 were readily converted to the
2.1.2. 5-O-Bz-protecting derivatives. The 5-O-benzoyl-
protecting derivatives 21a and 21b were synthesized from
17. Treatment of 17 with tetrabutylanmonium fluoride
(TBAF) in THF gave a mixture of 20a and 20b in
quantitative yield. The individual diastereomers 20a and
20b were isolated in 49 and 48% yield, respectively, by
column chromatography on silica gel. Benzoylation of 20a
and 20b under the standard conditions gave 21a and 21b,
respectively (Scheme 3). The stereochemistry of 21a and
21b was confirmed on the basis of 2D NMR analysis
(NOESY and COSY).
2.2. N-Glycosylation of 5-O-Bz-protecting derivatives
with pyrimidine bases
With a variety of glycosyl donors in hand, we first
investigated N-glycosylation of 5-O-Bz-protecting glycosyl

T. Murano et al. / Tetrahedron 59 (2003) 9059–9073
9061
Figure 2. NOESY correlations of 23.
Scheme 3. Reagent and conditions: (a) TBAF, THF, followed by separation
on SiO2; (b) BzCl, pyridine.
respectively (entry 3). Thus, the reaction temperature was
found to affect strongly the distribution ratio of 22 and 23
(entry 2 vs 3).
donors 21a and 21b with silylated thymine T(TMS)2 under
the conditions (TiCl4/CH2Cl2/08C/3 h) that gave the best
results for the non-fluorinated analogue 4 (Scheme 4 and
Table 1).8c As shown in Table 1, the reaction with the
a-anomer 21a gave the desired N 1-adduct 22 in very low
yield along with large amounts of unexpected N 3-adduct 23
(entry 1). Although de of 22 was very poor, 23 was found to
possess a high degree of de. The relative stereochemisty of
23 and the site of glycosylation on the pyrimidine were
confirmed by characteristic downfield shift (d 6.75, dd,
J¼3.8, 9.1 Hz) of the anomeric proton in addition to the
observed NOESY correlations among protons in the sugar
and pyrimidine moieties depicted in Figure 2. Although
the distribution ratio of 22 and 23 was not improved, the
reaction of the b-anomer 21b with T(TMS)2 gave the
desired 22 of 70% de in 11% yield (entry 2). The b-anomer
seems to be the better glycosyl donor than the a-anomer in
respect of the diastereoselectivity. These results are
consistent with the fact that the neighbouring group
participation of the phosphonothioate works well in
N-glycosylation of the b-anomer of non-fluorinated ana-
logue 4 rather than the corresponding a-anomer.8c When the
N-glycosylation of 21b was carried out at 258C, the reaction
preferably occurred at the N 1-nitrogen of the pyrimidine to
give 22 (56% de) and 23 (98% de) in 50 and 23% yield,
The predominant formation of 23 in N-glycosylation of 21a
and 21b with T(TMS)2 at 08C might be accounted for by
considering the Lewis acid–base complex (s-complex) 24
as shown in Figure 3. It is known that T(TMS)2 forms a
s-complex at the electron-rich centre of the N 1-nitrogen
with Lewis acids such as SnCl4 and TMSOTf, and these
species (T(TMS)2, the s-complex, and the Lewis acid) exist
in an equilibrium.13a,c Therefore, the stronger Lewis acid
TiCl4 would bind to T(TMS)2 more tightly and set up
similar equilibrium between T(TMS) and the s-complex 24.
Since 24 is blocked at the N 1-nitrogen with the Lewis acid,
24 would react at the N 3-nitrogen rather than at the
N 1-nitrogen with the glycosyl donors to give N 3-adduct 23.
Figure 3.
Scheme 4.
Table 1. N-Glycosylation of 21a and 21b with silylated thymine
Entrya
Donor
Temperature (8C)
22
23
Yield (%)
de (%)
Yield (%)
de (%)
1
2
3
21a
21b
21b
0
0
25
6
11
50
20
70
56
79
69
23
90
92
98
a
All reactions were carried out in CH2Cl2 in the presence of TiCl4 (5 equiv.) and silylated thymine (2 equiv.).

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T. Murano et al. / Tetrahedron 59 (2003) 9059–9073
Figure 5.
an additional 3 h, the glycosylation occurred at the
N 1-nitrogen to give 26 in 78% yield with the predominant
formation of the b-anomer (a/b¼12:88). When the reaction
was carried out at 08C for 3 h, N 1-adduct 26 was also
produced in 72% yield whereas the a/b ratio (30:70)
slightly decreased. The stereochemistry of 25 and 26 was
confirmed by careful analyses of their 2D NMR spectrum
including COSY and NOESY. The diagnostic NOESY
correlations for 26 are shown in Figure 4.
Scheme 5.
Predominant formation of 23 over 22 in the reaction at 08C
may suggest that 24 is the major species in the equilibrium
under the conditions. The equilibrium ratio for T(TMS)2 and
24 may be highly dependent on the reaction temperature,
since the major adduct was reversed from 23 to 22 upon
conducting the reaction at 258C as described above.
The above results reveal that the presumed N 3-adduct 27,
initially formed by the reaction of the glycosyl donor with
s-complex 24 at 2408C, further reacts with T(TMS)2 to
give 26 stereoselectively upon elevating the reaction
temperature to 08C. The reaction would involve processes
in which leaving of the nucleobase moiety of 27 occurs prior
to N-glycosylation and the resulting 1-sugar cation is
captured by T(TMS)2 from the b-face in a remote assistance
of the phosphonothioate group (Fig. 5). A mechanism for
rearrangement of 27 to 26 via the 1-sugar cation would be
ruled out by the following two experiments. Regeneration
of 27 from 25 with N,O-bis(trimethylsilyl)acetamide
in CH2Cl2, followed by treatment with one equivalent of
T(TMS)2 in the presence of TiCl4 (5 equiv.) at 08C for 3 h
gave an anomeric mixture (a/b¼15:85) of 26 in 97% yield.
However, decomposition of 25 was observed when the
similar reaction was carried out in the absence of T(TMS)2.
2.3. N-Glycosylation of 5-O-TBDPS-protecting
derivative with pyrimidine bases
As discussed in Section 2.2, concentration of T(TMS)2 and
s-complex 24 in the equilibrium would be critical to control
the regiochemical outcomes of the reaction site for the
pyrimidine in the N-glycosylation of 21a and 21b. The
equilibrium concentrations of T(TMS)2 and 24 were found
to be highly dependent on the temperature. The equilibrium
concentrations would be also highly dependent upon the
polarity of the solvent and subtle change of glycosyl donors
in the structure and basicity.13a,c Then we next examined
N-glycosylation of 5-O-TBDPS-protecting glycosyl donor
18 with T(TMS)2 in CH2Cl2 using TiCl4 as a Lewis acid at
varied temperatures. Since 18 possesses an acetoxy
function, the better leaving group than ethoxy, at the
C1-position, its high reactivity towards the Lewis acid
allowed us to survey the reactivity at varied temperatures
including below 08C. These results are summarized in
Scheme 5.
On the basis of the findings with the N-glycosylation of 18
and T(TMS)2, we examined similar N-glycosylation of the
glycosyl donor 17 in CH2Cl2 using TiCl4 as an acid
promotor. Since 17 possesses a less reactive ethoxy function
than acetoxy as a leaving group, the N-glycosylation did not
occur at below 08C and was best carried out under ice-
cooling conditions (Scheme 6 and Table 2). Treatment of 17
with T(TMS)2 under the conditions for 3 h afforded 93%
yield of 26 with the a/b ratio of 11:89 (entry 1). In this
reaction, the corresponding N 3-adduct was not detected.
The a/b ratio is better than that (30:70) for the product
derived from 18 under the same conditions (vide supra).
Therefore, N-glycosylation of 17 by the use of other TMS-
pyrimidines (U(TMS)2, 5FU(TMS)2, and NBz-C(TMS)2)
derived from uracil, 5-fluorouracil, and N-benzoylcytosine,
was further examined (entries 2–4). All reactions gave the
desired b-nucleotide analogues 28–30 in good yield in
comparable diastereoselectivity.
When 18 was treated with T(TMS)2 (2 equiv.) in CH2Cl2 in
the presence of TiCl4 (5 equiv.) at 2408C for 3 h, followed
by aqueous quenching, a diastereomeric mixture (a/b¼
66:34) of N 3-adduct 25 was obtained in 72% yield, without
detecting the N 1-adduct. In contrast to the results, when the
reaction was carried out at 2408C for 3 h and then at 08C for
The nucleotide analogue 26 (b/a¼89:11) thus obtained
could be easily converted to the difluoromethylene-
phosphonate analogue 31 of thymidine-30-phosphate in
64% yield by oxidation with m-CPBA, followed by aqueous
work-up. Diastereomerically pure 31 was isolated by
preparative HPLC (Scheme 7).
Figure 4. NOESY correlations of 26.

T. Murano et al. / Tetrahedron 59 (2003) 9059–9073
9063
Scheme 6.
2.4. Effect of a phosphonate functional group on the
N-glycosylation
Table 2. N-Glycosylation of glycosyl donor 17 with silylated pyrimidines
in the presence of TiCl4
Entrya
B(TMS)2
Product
R
Yield
Ratio (b/a)c
b
To clarify the usefulness of the phosphonothioate function-
ality in b-stereoselective N-glycosylation, N-glycosylation
of the phosphonate analogue 33, prepared from 11 in an
analogous manner for synthesis of the thioate 17, was
examined (Scheme 8). Treatment of 33 with T(TMS)2 in the
presence of TiCl4 in CH2Cl2 at 08C in analogy with the
synthesis of 26 gave a-N 3-nucleotide analogue 34 of 90%
de in 42% yield. These results strongly suggest that the
equilibrium concentration of s-complex 24 is significantly
high under the conditions. This may be due to subtle
changes of the glycosyl donor in the basicity by replacing
the sulphur atom with the less basic oxygen atom on the
C3-functional group.13a,c Although it is difficult to give
evidence for the reasons why the reaction proceeds with a
high a-selectivity, it may be the result from the fact that
T(TMS) traps the 1-sugar cation from the a-face to avoid a
bulky TBDPS group rather than a bicyclic cationic
intermediate hardly arising from neighbouring group
participation of the phosphonate to the C1-position.
1
2
3
4
T(TMS)2
U(TMS)2
26
28
29
30
Me
H
F
93
64
84
87
89:11
87:13
76:24
83:17
5-FU(TMS)2
NBz-C(TMS)2
–
a
All reactions were carried out at 08C for 3 h in the presence of 5.0 equiv.
of TiCl4 in CH2Cl2.
b
c
Prepared in situ from bis(trimethylsilyl)acetamide (4.0 equiv.) and the
base (2.0 equiv.) in the solvent.
Determined by 1H NMR (400 MHz, CDCl3).
2.5. N-Glycosylation with adenine bases
The results obtained for the synthesis of pyrimidine
nucleotide compounds were taken into consideration for
the synthetic application to the adenine nucleotide ana-
logues. For this study, we examined N-glycosylation of 17
with silylated N 6-benzoyladenine (NBz-A(TMS)2) under a
variety of conditions (Scheme 9). The representative results
are summarized in Table 3. Upon treatment of 17 with
2 equiv. of NBz-A(TMS)2 in CH2Cl2 in the presence of
TiCl4 (5 equiv.) at 08C for 15 h, a 48:52 mixture of 35a and
35b was produced in 23% yield (entry 1). In a similar
reaction carried out at 258C, decomposition of 17 was
observed and no desired N-glycosylation products were
detected (entry 2). When the reaction was carried out in
CH2Cl2 at 258C for 24 h by replacement of TiCl4 with the
weaker Lewis acid of SnCl4, decomposition of 17 was
partially suppressed and an 89:11 mixture of 35a and 35b
was obtained, though the yield (8%) was very poor (entry 3).
Upon conducting the reaction in CH3CN in the presence of
5 equiv. of SnCl4, a 58:42 mixture of 35a and 35b was
obtained in 51% yield (entry 4). CH3CN was found to be a
superior solvent to CH2Cl2 with respect to yield of the
N-glycosylation. The yield significantly increased to 77%
without changing the a/b ratio upon using 10 equiv. of
SnCl4 and 4 equiv. of NBz-A(TMS)2 (entry 5). TMSOTf
was found to be also a good Lewis acid as SnCl4 for
N-glycosylation in CH3CN (entry 6). Although all reactions
showed poor diastereoselectivity, it is worthy of note that
Scheme 7.
Scheme 8.

9064
T. Murano et al. / Tetrahedron 59 (2003) 9059–9073
Scheme 9.
Table 3. N-Glycosylation of 17 with NBz-A(TMS)2
b,c
Entrya
Lewis acid (equiv.)b
Solvent
Equiv. of NBz-A(TMS)2
Temperature (8C)
Yield (%)
35a/35bd
1
2
3
4
5
6
TiCl4 (5)
TiCl4 (5)
SnCl4 (5)
SnCl4 (5)
SnCl4 (10)
TMSOTf (5)
CH2Cl2
CH2Cl2
CH2Cl2
CH3CN
CH3CN
CH3CN
2
2
2
2
4
2
0
23
0
8
51
77
44
48:52
–
89:11
58:42
58:42
58:42
25
25
25
25
40
a
All reactions were conducted for 15–24 h.
Equivalent to the glycosyl donor 17.
b
c
d
Generated from N 6-benzoyladenine and N,O-bis(trimethylsilyl)acetamide in the solvent.
Determined by 1H NMR (300 MHz, CDCl3).
individual isomers 35a and 35b were readily separated by
column chromatography on silica gel. Thus, the stereo-
chemistry of 35a and 35b was easily confirmed by careful
analyses of their NOESY correlations.
diastereoselective synthesis of nucleotide analogues with
an adenine base, possibly owing to the low reactivity of the
silylated purine base to the glycosyl donors.13c
The poor diastereoselectivity for N-glycosylation of 17 with
NBz-A(TMS)2 indicates that the desired bicyclic cationic
intermediate arising from the neighbouring group partici-
pation of the phosphorothioyl group would not be formed
under the conditions and the reaction proceeded under the
steric influence of both substituents at C3- and C5-positions.
The observed low a-selectivity reveals that the reaction rate
from the a-face is slightly faster than that from the b-face,
most probably due to the steric congestion of the b-face by a
bulky TBDPS group. This postulate may be supported by
the fact that a mixture of 36a and 36b was produced in 42%
yield in modest b-selectivity (a/b¼39:61), when the
reaction of NBz-A(TMS)2 with 19 having the less bulky
Bn as a protecting group of 5-hydroxyl was carried out in
CH3CN in the presence of SnCl4 at 258C (Scheme 10).
3. Experimental
3.1. General
All melting points are uncorrected. All reactions were
carried out under nitrogen atmosphere. NMR data were
obtained on a Bruker DPX 400 for a solution in the indicated
solvent unless otherwise specified. 13C NMR (100 MHz)
and 31P NMR (162 MHz) were taken with broad-band H
1
decoupling. The chemical shifts of 31P are recorded relative
to external 85% H3PO4. 19F NMR spectra (376 MHz) were
measured using benzotrifluoride as an internal reference.
Mass spectra were recorded on a VG Auto Spec. or a
Micromass LCT using either electron impact ionization (EI)
or electrospray ionization (ESI) techniques.
In conclusion, the N-glycosylation of 2,3-dideoxyglycosyl
donors having a (diethoxyphosphorothioyl)difluoromethyl
functionality at the 3a-position by using pyrimidine base,
was found to give rise to formation of the b-anomers
predominantly. The method was not effective for the
3.1.1. tert-Butyl (2E)-3-[(4S)-2,2-dimethyl-1,3-dioxolan-
4-yl]prop-2-enoate (8). To a stirred suspension of NaH
(3.1 g, 66% dispersion in mineral oil) in THF (75 mL) was
added a solution of tert-butyl (diethoxyphosphoryl)acetate
(21.3 g, 84.5 mmol) in THF (15 mL) at 2158C. After being
Scheme 10.

T. Murano et al. / Tetrahedron 59 (2003) 9059–9073
9065
stirred at the same temperature for 30 min, a solution of 7
(10 g, 76.8 mmol) in THF (15 mL) was added dropwise.
The mixture was stirred at 2158C for 1 h and the reaction
was quenched by addition of saturated aqueous NH4Cl. The
biphasic mixture was extracted with ether and the extracts
were dried (MgSO4) and concentrated. The residue was
chromatographed on silica gel. Elution with hexane/AcOEt
(15:1) gave 8 (16.3 g, 93%) as an oil: [a]2D5¼þ32.4 (c¼1.1,
CHCl3); 1H NMR (400 MHz, CDCl3) d 6.76 (1H, dd, J¼5.9,
15.6 Hz), 6.01 (1H, dd, J¼1.4, 15.6 Hz), 4.68–4.59 (1H,
m), 4.17 (1H, dd, J¼6.5, 8.2 Hz), 3.67 (1H, dd, J¼7.4,
8.2 Hz), 1.48 (9H, s), 1.45 (3H, s), 1.40 (3H, s); 13C NMR
(100 MHz, CDCl3) d 165.1, 143.2, 124.2, 109.9, 80.5, 74.9,
68.7, 27.9, 26.3, 25.6; IR (film) 2983, 1715, 1370, 1309,
1258, 1154, 1064 cm21; EIMS m/z 213 (Mþ2Me). Anal.
calcd for C12H20O4: C, 63.14; H, 8.83. Found: C, 63.54; H,
8.64.
2 h. The solvent was evaporated in vacuo and the resulting
residue was chromatographed on silica gel. Elution with
hexane/AcOEt (1:1) afforded 10 (6.1 g, 50%) as an oil:
[a]2D5¼þ13.8 (c¼1.0, CHCl3); 1H NMR (400 MHz, CDCl3)
d 4.90–4.83 (1H, m), 4.38–4.23 (4H, m), 4.00 (1H, dd,
J¼2.6, 12.5 Hz), 3.72 (1H, dd, J¼2.9, 12.5 Hz), 3.40–3.22
(1H, m), 2.85 (2H, d, J¼8.4 Hz), 2.56 (1H, br), 1.40 (6H, t,
J¼7.1 Hz); 13C NMR (100 MHz, CDCl3) d 175.1, 119.1 (dt,
JCP¼215.4 Hz, JCF¼263.0 Hz), 78.6 (d, JCP¼4.0 Hz), 65.2
(d, JCP¼7.0 Hz), 65.0 (d, JCP¼7.1 Hz), 63.0, 40.1 (dt,
JCP¼15.8 Hz, JCF¼21.0 Hz), 20.3 16.0 (d, JCP¼5.2 Hz);
19F NMR (376 MHz, CDCl3) d 254.49 (1F, dd, JHF
¼
4.9 Hz, JPF¼105.2 Hz), 254.54 (1F, dd, JHF¼5.8 Hz, JPF¼
105.2 Hz); 31P NMR (162 MHz, CDCl3) d 5.76 (t, JPF¼
105.2 Hz); IR (film) 3427, 2988, 1789, 1645 cm21; EIMS
m/z 303 (Mþþ1). Anal. calcd for C10H17F2O6P: C, 39.74;
H, 5.67. Found: C, 39.43; H, 5.66.
3.1.2. tert-Butyl 2,3-dideoxy-3-[(diethoxyphosphoryl)(di-
fluoro)methyl]-4,5-O-(1-methylethylidene)-D-glycero-
pentonate (9). To a solution of LDA [prepared from
39.6 mL (282 mmol) of diisopropylamine and 176 mL
(282 mmol) of 1.6 M hexane solution of n-BuLi at 08C] in
THF (440 mL) was added a solution diethyl difluoromethyl-
phosphonate (48.6 g, 259 mmol) in THF (160 mL) at
2788C. After the stirring was continued for 20 min at the
same temperature, to this solution was added a solution of
8 (26.9 g, 118 mmol) in THF (110 mL) at 2788C. After the
stirring was continued for 12 h at the same temperature, the
reaction mixture was quenched with saturated aqueous
NH4Cl solution and extracted with ether. The extracts were
washed with brine, dried (MgSO4) and evaporated. The
resulting residue was chromatographed on silica gel
(hexane/AcOEt¼5:1) to give 9 (47.6 g, 91%) as an oil:
[a]2D5¼þ15.2 (c¼1.1, CHCl3); 1H NMR (400 MHz, CDCl3)
d 4.67 (0.5H, dt, J¼4.4, 6.8 Hz), 4.45 (0.5H, q, J¼6.6 Hz),
4.34–4.22 (4H, m), 4.16–4.10 (0.5H, m), 4.03–3.94 (0.5H,
m), 3.69 (1H, t, J¼7.9 Hz), 3.48–3.31 (0.5H, m),3.04–2.88
(0.5H, m), 2.76 (0.5H, dd, J¼4.6, 17.3 Hz) and 2.63 (0.5H,
dd, J¼6.0, 16.9 Hz), 2.57 (0.5H, dd, J¼6.8, 17.3 Hz) and
2.44 (0.5H, dd, J¼5.3, 16.9 Hz), 1.45 (9H, s), 1.43–1.31
(12H, m); 13C NMR (100 MHz, CDCl3) d 170.8 and 170.6,
120.7 (dt, JCP¼212.3 Hz, JCF¼263.8 Hz) and 120.4 (dt,
JCP¼212.8 Hz, JCF¼263.7 Hz), 108.8 and 108.3, 80.6 and
80.4, 73.1–72.8 (m) and 72.4–72.2 (m), 68.7 and 65.2,
3.1.4. (2S,3S)-{[2-(tert-Butyldiphenylsilanyloxymethyl)-
5-oxotetrahydrofuran-3-yl]difluoromethyl}phosphonic
acid diethyl ester (11). To a solution of 10 (27.2 g,
90 mmol) and imidazole (12.3 g, 180 mmol) in DMF
(270 mL) was added tert-butyldiphenylsilyl chloride
(27.7 mL, 108 mmol) at 08C. The mixture was kept at
room temperature for 1.5 h under stirring. The solvent was
evaporated in vacuo and water was added. The biphasic
mixture was extracted with CHCl3. The extracts were
washed with brine, dried (MgSO4), and evaporated. The
remaining residue was chromatographed on silica gel.
Elution with hexane/AcOEt (5:1) yielded 11 (45.0 g, 93%)
as an oil: [a]2D0¼þ16.7 (c¼1.0, CHCl3); 1H NMR
(400 MHz, CDCl3) d 7.68–7.60 (4H, m), 7.48–7.34 (6H,
m), 4.93–4.87 (1H, m), 4.37–4.20 (4H, m), 3.98 (1H, dd,
J¼2.1, 11.7 Hz), 3.71 (1H, dd, J¼2.2, 11.7 Hz), 3.46–3.28
(1H, m), 2.93–2.87 (2H, m), 1.38 (6H, t, J¼7.1 Hz), 1.05
(9H, s); 13C NMR (100 MHz, CDCl3) d 174.6, 133.5, 135.3,
132.5, 131.9, 129.9, 127.8, 119.2 (dt, JCP¼214.7 Hz, JCF
¼
263.1 Hz), 78.1 (dt, JCP¼4.2 Hz, JCF¼4.2 Hz), 65.0 (d,
JCP¼7.0 Hz), 64.9 (d, JCP¼6.0 Hz), 64.9, 40.6 (dt, JCP
15.5 Hz, JCF¼21.0 Hz), 29.0, 26.6, 19.1, 16.2 (d, JCP
¼
¼
5.2 Hz); 19F NMR (376 MHz, CDCl3) d 253.9 (1F, ddd,
JHF¼15.3 Hz, JPF¼105.2 Hz, JFF¼303.3 Hz), 255.2 (1F,
ddd, JHF¼18.5 Hz, JPF¼105.2 Hz, JFF¼303.3 Hz); 31P
NMR (162 MHz, CDCl3) d 5.96 (t, JPF¼105.2 Hz); IR
(neat) 2933, 2859, 1789, 1274, 1184, 1114, 1022 cm21
;
64.9–64.5 (m), 64.3 (d, JCP¼6.3 Hz), 43.5 (dt, JCP
¼
EIMS m/z 541 (Mþþ1). Anal. calcd for C26H35F2O6PSi: C,
15.0 Hz, JCF¼19.1 Hz) and 43.5 (dt, JCP¼15.2 Hz, JCF
¼
57.76; H, 6.53. Found: C, 57.59; H, 6.55.
18.7 Hz), 31.0 and 28.4, 27.9, 26.1 and 26.0, 25.2 and 24.7,
16.2; 19F NMR (376 MHz, CDCl3) d 247.1 (0.5F, ddd,
JFF¼307.5 Hz, JPF¼105.6 Hz, JHF¼15.0 Hz) and 248.1
(0.5F, ddd, JFF¼306.8 Hz, JPF¼105.2 Hz, JHF¼13.9 Hz),
3.1.5. (2S,3S)-[(2-Benzyloxymethyl-5-oxotetrahydro-
furan-3-yl)difluoromethyl]phosphonic acid diethyl ester
(12). To a stirred solution of 10 (6.21 g, 20.6 mmol) in
CH2Cl2 (80 mL) and petroleum ether (40 mL) was succes-
sively added Cl3CC(vNH)OBn (4.6 mL, 24.7 mmol) and
CF3SO3H (0.38 mL, 4.1 mmol) at 08C. The mixture was
stirred at the same temperature for 1 h and poured onto
saturated NaHCO3. The organic phase was separated. The
extracts were washed with brine, dried over MgSO4, and
concentrated. The residue was purified by column chroma-
tography on silica gel. Elution with hexane/AcOEt (3:1)
gave 12 (6.8 g, 84%) as an oil: [a]2D5¼þ15.4 (c¼1.1,
CHCl3); 1H NMR (400 MHz, CDCl3) d 7.43–7.24 (5H, m),
4.99–4.93 (1H, m), 4.60 (1H, d, J¼11.9 Hz), 4.53 (1H,
d, J¼11.9 Hz), 4.37–4.20 (4H, m), 3.80 (1H, dd, J¼2.2,
249.6 (0.5F, ddd, JFF¼306.8 Hz, JPF¼108.1 Hz, JHF
¼
20.2 Hz), 252.5 (0.5F, ddd, JFF¼307.5 Hz, JPF¼105.6 Hz,
JHF¼23.7 Hz); 31P NMR (162 MHz, CDCl3) d 6.39 (0.5P,
dd, JPF¼105.2, 108.1 Hz) and 6.23 (0.5P, t, JPF¼105.6 Hz);
IR (film) 2984, 2936, 1733, 1370, 1271, 1160, 1024 cm21
;
EIMS m/z 417 (Mþþ1). Anal. calcd for C17H31F2O7P: C,
49.03; H, 7.50. Found: C, 48.89; H, 7.31.
3.1.3. (2S,3S)-[Difluoro(2-hydroxymethyl-5-oxotetra-
hydrofuran-3-yl)methyl]phosphonic acid diethyl ester
(10). A mixture of 9 (16.5 g, 39.6 mmol), EtOH (30 mL)
and conc. HCl (11 mL) was stirred at room temperature for

9066
T. Murano et al. / Tetrahedron 59 (2003) 9059–9073
10.9 Hz), 3.63 (1H, dd, J¼2.6, 10.9 Hz), 3.35–3.20 (1H,
m), 2.86 (1H, dd, J¼9.4, 18.4 Hz), 2.81 (1H, dd, J¼6.1,
18.4 Hz), 1.39 (3H, t, J¼7.1 Hz), 1.38 (3H, t, J¼7.1 Hz);
13C NMR (100 MHz, CDCl3) d 174.6, 137.3, 128.4, 127.8,
127.5, 119.2 (dt, JCP¼214.0 Hz, JCF¼263.4 Hz), 77.0, 73.5,
70.7, 65.0 (d, JCP¼6.9 Hz), 64.9 (d, JCP¼7.0 Hz), 40.9 (dt,
JCP¼15.7 Hz, JCF¼21.1 Hz), 28.7 (d, JCP¼1.1 Hz), 16.2
(d, JCP¼5.2 Hz); 19F NMR (376 MHz, CDCl3) d 254.4 (1F,
ddd, JHF¼16.9 Hz, JFF¼303.4 Hz, JPF¼104.5 Hz), 255.3
(film) 2985, 1789, 1016 cm21; ESIMS m/z 431 (MþþNa),
409 (MþþH). Anal. calcd for C17H23O5F2PS; C, 50.00; H,
5.68. Found C, 50.20; H, 5.75.
3.1.8. A typical example of preparation of lactols. (2S,
3S)-{[2-(tert-Butyldiphenylsilanyloxymethyl)-5-hydroxy-
tetrahydrofuran-3-yl]-difluo-romethyl}phosphonothioic
acid O,O-diethyl ester (15). To a solution of 13 (2.9 g,
5.3 mmol) in THF (10 mL) was added 17.4 mL (18.4 mmol)
of BH3·THF (1 M solution in THF) in small portions under
ice-cooling. After stirring was continued for 12 h, the
reaction was quenched with 1 mL of 1 M HCl and saturated
NH4Cl solution. The mixture was extracted with CHCl3.
The extracts were washed with brine, dried (MgSO4) and
evaporated in vacuo. The remaining residue was chromato-
graphed on silica gel. Elution with hexane/AcOEt (20:1)
afforded 15 (2.7 g, 92%) as an oil: [a]2D0¼29.80 (c¼1.0,
CHCl3); 1H NMR (400 MHz, CDCl3) d 7.76–7.63 (4H, m),
7.49–7.34 (6H, m), 5.63–5.57 (0.1H, m), 5.49–5.41 (0.9H,
m), 4.59–4.55 (0.1H, m), 4.51–4.46 (0.9H, m), 4.31–4.13
(4H, m), 3.89 (0.9H, dd, J¼1.9, 11.2 Hz), 3.85–3.67 (0.3H,
m), 3.62 (0.9H, dd, J¼2.7, 11.2 Hz), 3.59–3.43 (0.9H, m),
2.53–2.27 (0.2H, m), 2.26–2.10 (1.8H, m), 1.34 (3H, t,
J¼7.1 Hz), 1.32 (3H, t, J¼7.1 Hz), 1.09 (8.1H, s), 1.02
(0.9H, s); 13C NMR (100 MHz, CDCl3) d 136.3, 136.0,
(1F, ddd, JHF¼17.8 Hz, JFF¼303.4 Hz, JPF¼104.5 Hz); 31
P
NMR (162 MHz, CDCl3) d 5.75 (t, JPF¼104.5 Hz); IR
(film) 2986, 2870, 1789, 1272, 1184, 1027 cm21; ESIMS
m/z 415 (MþþNa), 393 (MþþH). Anal. calcd for
C17H23O6F2P: C, 52.04; H, 5.91; Found C, 51.82; H, 5.83.
3.1.6. A typical example of thionylation with Lawesson’s
reagent. (2S,3S)-{[2-(tert-Butyldiphenylsilanyloxy-
methyl)-5-oxotetrahydrofuran-3-yl]difluoromethyl}phos-
phonothioic acid O,O-diethyl ester (13). A solution of
11 (13.5 g, 25 mmol) and Lawesson’s reagent (5.6 g,
13.8 mmol) in toluene (26 m) was heated at 1208C for 2 h.
The solvent was evaporated in vacuo and the remaining
residue was chromatographed on silica gel. Elution with
hexane/AcOEt (20:1) gave 13 (11.6 g, 84%) as an oil:
[a]2D0¼þ12.5 (c¼1.1, CHCl3); 1H NMR (400 MHz, CDCl3)
d 7.69–7.61 (4H, m), 7.48–7.34 (6H, m), 4.89–4.84 (1H,
m), 4.31–4.18 (4H, m), 3.98 (1H, dd, J¼2.1, 11.5 Hz), 3.72
(1H, dd, J¼2.3, 11.5 Hz), 3.70–3.53 (1H, m), 2.89 (2H, d,
J¼8.3 Hz), 1.35 (3H, t, J¼7.0 Hz), 1.34 (3H, t, J¼7.0 Hz),
1.05 (9H, s); 13C NMR (100 MHz, CDCl3) d 175.1, 136.0,
132.7, 132.5, 130.5, 130.4, 128.3 (2C), 121.6 (ddd, JCP
¼
178.9 Hz, JCF¼263.6, 270.2 Hz), 99.0, 79.9, 66.2, 65.1 (d,
JCP¼6.6 Hz), 64.6 (d, JCP¼6.8 Hz), 40.7 (dt, JCP¼16.3 Hz,
JCF¼20.5 Hz), 37.2, 27.2, 19.6, 16.5 (d, JCP¼5.9 Hz); 19F
NMR (376 MHz, CDCl3) d 248.4 (0.9F, ddd, JHF¼9.3 Hz,
JPF¼114.0 Hz, JFF¼287.7 Hz), 249.0–50.5 (0.1F, m),
253.7 (0.1F, ddd, JHF¼23.4 Hz, JPF¼110.8 Hz, JFF¼
288.3 Hz), 257.7 (0.9F, ddd, JHF¼22.9 Hz, JPF¼
109.4 Hz, JFF¼287.7 Hz); 31P NMR (162 MHz, CDCl3) d
75.5 (0.9P, dd, JPF¼109.4, 114.0 Hz), 75.6 (0.1P, dd, JPF¼
135.9, 133.0, 132.5, 130.4 (2C), 128.3, 120.6 (ddd, JCP
177.2 Hz, JCF¼267.0, 269.9 Hz), 78.9 (dt, JCP¼4.2 Hz,
¼
JCF¼3.6 Hz), 65.3 (d, JCP¼6.8 Hz), 65.2, 65.1 (d, JCP
¼
6.8 Hz), 40.3 (dt, JCP¼17.0 Hz, JCF¼21.3 Hz), 30.0 (t,
JCF¼3.6 Hz), 27.1, 19.6, 16.5 (d, JCP¼6.2 Hz); 19F NMR
(376 MHz,CDCl3) d 253.0 (1F, ddd, JHF¼13.6 Hz, JPF¼
110.2 Hz, JFF¼290.6 Hz), 255.6 (1F, ddd, JHF¼19.8 Hz,
JPF¼110.2 Hz, JFF¼290.6 Hz); 31P NMR (162 MHz,
CDCl3) d 74.4 (t, JPF¼110.2 Hz); IR (film) 2932, 2859,
1789, 1114, 1018 cm21; EIMS m/z 557 (Mþþ1). Anal.
calcd for C26H35F2O5PSSi: C, 56.10; H, 6.34. Found: C,
56.15; H, 6.37.
110.8, 112.6 Hz); IR (film) 2933, 2858, 1113, 1037 cm21
;
EIMS m/z 541 (Mþ2OH). Anal. calcd for C26H37F2O5PSSi:
C, 55.90; H, 6.68. Found: C, 55.61; H, 6.59.
3.1.9. (2S,3S)-[(2-Benzyloxymethyl-5-hydroxytetrahydro-
furan-3-yl)difluoromethyl]phosphonothioic acid O,O-di-
ethyl ester (16). This compound was prepared from 14
(2.65 g, 6.49 mmol) in an analogous manner to that for
preparation of 15. Purification by column chromatography
on silica gel (hexane/AcOEtc¼5:1) gave 16 (1.66 g, 62%)
as an oil: [a]2D5¼þ12.7 (c¼1.3, CHCl3); 1H NMR
(400 MHz, CDCl3) d 7.39–7.19 (5H, m), 5.61–5.54
(0.2H, m), 5.47–5.38 (0.8H, m), 4.67 (0.8H, d, J¼
11.8 Hz), 4.64–4.36 (2.2H, m), 4.31–4.13 (4H, m), 3.82–
3.71 (1H, m), 3.67–3.28 (2H, m), 2.44–2.27 (0.2H, m),
2.22–2.07 (1.6H, m), 2.04–1.89 (0.2H, m), 1.38–1.21 (6H,
m); 13C NMR (100 MHz, CDCl3) d 136.9, 128.6, 128.3,
128.0, 127.9, 127.6, 121.0 (ddd, JCP¼179.0 Hz, JCF¼264.4,
269.5 Hz), 98.8, 77.9 (dt, JCP¼3.1 Hz, JCF¼4.6 Hz), 73.7,
71.7, 64.6 (d, JCP¼6.8 Hz), 64.3 (d, JCP¼6.9 Hz), 41.1 (dt,
JCP¼16.5 Hz, JCF¼20.7 Hz), 36.4, 16.1 (d, JCP¼6.0 Hz);
3.1.7. (2S,3S)-[(2-Benzyloxymethyl-5-oxotetrahydro-
furan-3-yl)difluoromethyl]phosphonothioic acid O,O-di-
ethyl ester (14). This compound was prepared from 12
(16.9 g, 43.1 mmol) in 76% yield in an analogous manner to
that for preparation of 13. Purification by column chroma-
tography on silica gel (hexane/AcOEt¼15:1) gave 14
1
(13.5 g, 76%) as an oil: [a]2D5¼þ16.1 (c¼1.2, CHCl3); H
NMR (400 MHz, CDCl3) d 7.39–7.26 (5H, m), 4.98–4.91
(1H, m), 4.61 (1H, d, J¼12.0 Hz), 4.54 (1H, d, J¼12.0 Hz),
4.32–4.18 (4H, m), 3.81 (1H, dd, J¼2.1, 10.9 Hz), 3.62
(1H, dd, J¼2.9, 10.9 Hz), 3.52–3.35 (1H, m), 2.87–2.80
(2H, m), 1.35 (6H, t, J¼7.1 Hz); 13C NMR (100 MHz,
CDCl3) d 174.6, 137.3, 128.4, 127.8, 127.5, 119.9 (ddd,
JCP¼177.1 Hz, JCF¼266.7, 270.3 Hz), 77.4, 73.5, 70.7, 64.9
19F NMR (376 MHz, CDCl3) d 250.2 (1F, ddd, JHF
¼
(d, JCP¼6.9 Hz), 64.6 (d, JCP¼6.8 Hz), 40.3 (dt, JCP
¼
12.0 Hz, JFF¼288.0 Hz, JPF¼113.8 Hz), 255.9 (1F, ddd,
JHF¼20.4 Hz, JFF¼288.0 Hz, JPF¼109.6 Hz); 31P NMR
(162 MHz, CDCl3) d 75.2 (dd, JPF¼109.6, 113.8 Hz); IR
(film) 3435, 2982, 2935, 2867, 1454, 1027 cm21; ESIMS
m/z 433 (MþþNa), 393 (Mþ2OH); HRMS (ESI) calcd for
C17H25O5F2NaPS (MþþNa): 433.1026, Found: 433.1039.
16.9 Hz, JCF¼21.3 Hz), 29.3, 16.0 (d, JCP¼6.0 Hz); 19F
NMR (376 MHz, CDCl3) d 253.0 (1F, ddd, JHF¼13.6 Hz,
JFF¼290.9 Hz, JPF¼110.6 Hz), 255.4 (1F, ddd, JHF
¼
19.4 Hz, JFF¼290.9 Hz, JPF¼106.7 Hz); 31P NMR
(162 MHz, CDCl3) d 74.0 (dd, JPF¼106.7, 110.6 Hz); IR

T. Murano et al. / Tetrahedron 59 (2003) 9059–9073
9067
3.1.10. (2S,3S)-{[2-(tert-Butyldiphenylsilanyloxymethyl)-
288.6 Hz, JPF¼114.5 Hz), 256.0 (0.5F, ddd, JHF
¼
25.1 Hz, JFF¼286.5 Hz, JPF¼108.7 Hz) and 256.2 (0.5F,
ddd, JHF¼20.8 Hz, JFF¼288.6 Hz, JPF¼111.0 Hz); 31P
NMR (162 MHz, CDCl3) d 75.6 (0.5P, dd, JPF¼108.7,
114.7 Hz) and 75.3 (0.5P, dd, JPF¼111.0, 114.5 Hz); IR
(neat) 2979, 2906, 1453, 1104, 1028 cm21; ESIMS m/z 461
(MþþNa). Anal. calcd for C19H29O5F2PS: C, 52.05; H,
6.67. Found: C, 52.18; H, 6.67.
5-ethoxytetrahydrofuran-3-yl]difluoromethyl}phospho-
nothioic acid O,O-diethyl ester (17). A mixture of
15 (2.37 g, 4.2 mmol), ethyl orthoformate (0.84 mL,
5.0 mmol), ammonium nitrate (10 mg) and EtOH (8.4 mL)
was heated at 908C for 12 h. NaHCO3 solution (5 mL) was
added to the reaction mixture and the mixture was extracted
with ether. The extract was evaporated and the remaining
residue was chromatographed on silica gel. Elutuion with
hexane/AcOEt (20:1) afforded 17 (2.24 g, 90%) as an oil:
[a]2D0¼þ1.51 (c¼1.2, CHCl3); 1H NMR (400 MHz, CDCl3)
d 7.75–7.65 (4H, m), 7.45–7.32 (6H, m), 5.27–5.20 (0.5H,
m) and 5.16–5.11 (0.5H, m), 4.49 (0.5H, dt, J¼4.0, 6.5 Hz)
and 4.44–4.37 (0.5H, m), 4.31–4.13 (4H, m), 3.96 (0.5H, d,
J¼2.3 Hz), 3.85–3.62 (2.5H, m), 3.50 (0.5H, dq, J¼9.6,
7.1 Hz) and 3.37 (0.5H, dq, J¼9.5, 7.1 Hz) 3.36–3.22
(0.5H, m) and 3.19–2.97 (0.5H, m), 2.38 (0.5H, ddd, J¼5.4,
10.5, 13.6 Hz), 2.21–2.06 (1.5H, m), 1.37–1.26 (6H, m),
1.22 (1.5H, t, J¼7.1 Hz), 1.12–0.98 (10.5H, m); 13C NMR
(100 MHz, CDCl3) d 135.6 (2C), 133.5, 133.4, 129.5, 127.6
(2C), 121.1 (ddd, JCP¼178.4 Hz, JCF¼263.3, 271.2 Hz),
120.9 (ddd, JCP¼178.9 Hz, JCF¼264.5, 273.8 Hz), 103.7
3.1.12. (4S,5S)-5-{[tert-Butyl(diphenyl)silyl]methyl}-4-
[(diethoxyphosphorothioyl)(difluoro)methyl]tetrahydro-
furan-2-yl acetate (18). To a solution of 15 (2.37 g,
4.2 mmol) in pyridine (5 mL containing 10 mg of dimethyl-
aminopyridine) was added acetic anhydride (0.48 mL,
5.1 mmol) at 08C, then the reaction mixture was allowed
to stand at room temperature for 24 h under stirring. To the
reaction mixture was added 5% KHSO4 and extracted with
CHCl3. The solvent was dried (MgSO4) and evaporated in
vacuo. The residue was chromatographed on silica gel.
Elution with hexane/AcOEt (15:1) gave 18 (2.43 g, 96%).
[a]2D5¼þ3.6 (c¼1.2, CHCl3); 1H NMR (400 MHz, CDCl3) d
7.75–7.64 (4H, m), 7.48–7.34 (6H, m), 6.38–6.32 (1H, m),
4.61–4.55 (0.2H, m), 4.54–4.48 (0.8H, m), 4.29–4.16 (4H,
m), 3.96 (0.2H, dd, J¼1.7, 11.4 Hz), 3.92 (0.8H, dd, J¼2.6,
11.2 Hz), 3.78–3.72 (1H, m), 3.57–3.44 (1H, m), 2.53
(0.2H, ddd, J¼5.5, 11.3, 14.5 Hz), 2.43–2.25 (1.6H, m),
2.24–2.13 (0.2H, m), 2.06 (0.6H, s), 1.82 (2.4H, s), 1.38–
1.30 (6H, m), 1.07 (7.2H, s), 1.05 (1.8H, s); 13C NMR
(100 MHz, CDCl3) d 170.1 (minor), 169.9 (major), 135.4,
135.3, 133.2 (major), 133.0 (minor), 132.9 (major), 132.8
(minor), 129.5 (2C), 127.5, 120.5 (ddd, JCP¼179.0 Hz,
JCF¼264.4, 270.0 Hz), 98.5 (minor), 98.0 (major), 81.3
(major), 80.0 (minor), 65.6 (minor), 65.5 (major), 64.5 (d,
JCP¼6.8 Hz, major), 64.4 (d, JCP¼6.8 Hz, minor), 64.2 (d,
JCP¼6.9 Hz, minor), 64.1 (d, JCP¼6.9 Hz, major), 64.0,
40.6 (dt, JCP¼16.6 Hz, JCF¼20.8 Hz, major), 40.5 (dt,
JCP¼15.2 Hz, JCF¼21.1 Hz, minor), 34.0 (major), 33.8
and 103.5, 79.8 and 77.6, 67.4 and 64.9, 64.6 (d, JCP
¼
6.9 Hz) and 64.5 (d, JCP¼6.8 Hz), 64.1 (d, JCP¼6.8 Hz),
63.3 and 62.4, 42.6 (dt, JCP¼15.9 Hz, JCF¼20.6 Hz) and
41.0 (dt, JCP¼16.1 Hz, JCF¼20.2 Hz) 34.3, 26.7, 19.3 and
19.2, 16.1 (d, JCP¼6.0 Hz), 15.2 and 14.9; 19F NMR
(376 MHz, CDCl3) d 247.3 (0.5F, ddd, JHF¼8.5 Hz, JPF¼
116.5 Hz, JFF¼288.1 Hz), 247.9 (0.5F, ddd, JHF¼8.4 Hz,
JPF¼115.6 Hz, JFF¼287.4 Hz), 256.3 (0.5F, ddd, JHF
¼
25.2 Hz, JPF¼110.2 Hz, JFF¼287.4 Hz), 257.2 (0.5F, ddd,
JHF¼23.9 Hz, JPF¼110.8 Hz, JFF¼288.1 Hz); 31P NMR
(162 MHz, CDCl3) d 76.1 (0.5P, dd, JPF¼110.2, 115.6 Hz),
75.6 (0.5P, dd, JPF¼110.8, 116.5 Hz); IR (film) 3072, 2932,
2858, 1428, 1390, 1113, 1027 cm21; EIMS m/z 586 (Mþ),
529 (Mþ2tert-Bu). Anal. calcd for C28H41F2O5PSSi: C,
57.32; H, 7.04. Found: C, 57.20; H, 7.11.
(minor), 26.6, 21.0 (major), 19.1 (minor), 15.9 (d, JCP
¼
3.1.11. (2S,3S)-[(2-Benzyloxymethyl-5-ethoxytetrahydro-
furan-3-yl)-difluoromethyl]phosphonothioic acid O,O-
diethyl ester (19). This compound was prepared from 16
(1.46 g, 3.5 mmol) in an analogous manner to that for
preparation of 17. Purification by column chromatography
on silica gel (hexane/AcOEt¼20:1) gave 19 (1.32 g, 85%)
as an oil: [a]2D5¼þ8.5 (c¼1.1, CHCl3); 1H NMR (400 MHz,
CDCl3) d 7.41–7.23 (5H, m), 5.25–5.19 (0.5H, m) and
5.18–5.12 (0.5H, m), 4.76–4.49 (2.5H, m), 4.48–4.41
(0.5H, m), 4.32–4.15 (4H, m), 3.82 (0.5H, d, J¼11.1 Hz),
3.79–3.66 (1H, m), 3.63 (0.5H, dd, J¼3.0, 10.1 Hz), 3.58
(0.5H, dd, J¼4.7, 11.1 Hz), 3.54–3.35 (1.5H, m), 3.19–
2.91 (1H, m), 2.37 (0.5H, ddd, J¼5.6, 10.9, 13.8 Hz),
2.20–2.06 (1.5H, m), 1.33 (6H, t, J¼7.1 Hz), 1.20 (1.5H,
t, J¼7.1 Hz) and 1.11 (1.5H, t, J¼7.1 Hz); 13C NMR
(100 MHz, CDCl3) d 138.6, 128.7, 128.2, 128.0, 127.9,
121.4 (ddd, JCP¼178.0 Hz, JCF¼262.9, 272.1 Hz) and 121.3
(ddd, JCP¼179.1 Hz, JCF¼264.6, 269.1 Hz), 104.2 and
5.9 Hz); 19F NMR (376 MHz, CDCl3) d 247.8 (0.8F, ddd,
JHF¼7.9 Hz, JFF¼288.7 Hz, JPF¼113.7 Hz), 249.7 (0.2F,
ddd, JHF¼12.1 Hz, JFF¼288.2 Hz, JPF¼116.3 Hz), 254.0
(0.2F, ddd, JHF¼23.3 Hz, JFF¼288.2 Hz, JPF¼112.2 Hz),
257.5 (0.8F, ddd, JHF¼23.2 Hz, JFF¼288.7 Hz, JPF¼
108.7 Hz); 31P NMR (162 MHz, CDCl3) d 75.7 (0.2P,
dd, JPF¼112.2, 116.3 Hz), 75.0 (0.8P, dd, JPF¼108.7,
113.7 Hz); IR (film) 2932, 2858, 1750, 1428, 1235, 1113,
1020 cm21; EIMS m/z 543 (MHþ2tert-Bu). Anal. calcd for
C28H38O6F2PSSi: C, 56.08; H, 6.39. Found: C, 55.91; H,
6.43.
3.1.13. (2S,3S,5S)-[(5-Ethoxy-2-hydroxymethyltetra-
hydrofuran-3-yl)difluoromethyl]phosphonothioic acid
O,O-diethyl ester (20a) and (2S,3S,5R)-[(5-ethoxy-2-
hydroxymethyltetrahydrofuran-3-yl)difluoromethyl]-
phosphonothioic acid O,O-diethyl ester (20b). To a
stirred solution of 17 (2.16 g, 3.68 mmol) in THF (15 mL)
was added TBAF (1.44 g, 5.52 mmol) under ice-cooling.
The mixture was stirred at room temperature for 2 h. The
solvent was removed in vacuo and the residue was portioned
between water and CHCl3. The organic extracts were
washed with brine, dried (MgSO4), and concentrated. The
residue was chromatographed on silica gel. Elution with
hexane/AcOEt (10:1) afforded 20b (614 mg, 48%) as an oil:
103.6, 78.5 and 76.6, 74.9, 73.8, 73.6, 71.3, 65.0 (d, JCP
¼
7.1 Hz) and 64.9 (d, JCP¼6.8 Hz), 64.7 (d, JCP¼6.9 Hz) and
64.6 (d, JCP¼6.9 Hz), 63.5 and 62.8, 43.6 (dt, JCP¼16.0 Hz,
JCF¼20.8 Hz) and 42.2 (dt, JCP¼16.0 Hz, JCF¼20.4 Hz),
34.6 (2C), 16.5 (d, JCP¼5.5 Hz), 15.6 and 15.4; 19F NMR
(376 MHz, CDCl3) d 248.3 (0.5F, dd, JFF¼286.5 Hz, JPF¼
114.7 Hz) and 249.3 (0.5F, ddd, JHF¼9.0 Hz, JFF¼

9068
T. Murano et al. / Tetrahedron 59 (2003) 9059–9073
[a]2D0¼228.2 (c¼1.3, CHCl3); 1H NMR (400 MHz, CDCl3)
d 5.16–5.10 (1H, m), 4.60–4.53 (1H, m), 4.32–4.20 (4H,
m), 3.81 (1H, dd, J¼2.1, 12.0 Hz), 3.77 (1H, dq J¼7.1,
9.6 Hz), 3.58 (1H, dd, J¼3.9, 12.0 Hz), 3.51 (1H, dq, J¼7.1,
9.6 Hz), 3.41–3.23 (1H, m), 2.31–2.15 (2H, m), 1.36 (6H, t,
J¼7.1 Hz), 1.22 (3H, t, J¼7.1 Hz); 13C NMR (100 MHz,
CDCl3) d 120.9 (dt, JCP¼179.1 Hz, JCF¼266.9 Hz), 103.9,
for C19H27O6F2NaPS (MþþNa): 475.1132. Found:
475.1142.
3.1.15. Benzoic acid (2S,3S,5S)-3-[(diethoxythiophos-
phoryl)difluoromethyl]-5-ethoxytetrahydrofuran-2-yl-
methyl ester (21a). This compound was prepared from 20a
(760 mg, 2.18 mmol) in an analogous manner to that for
preparation of 20b. Purification by column chromatography
on silica gel (hexane/AcOEt¼15:1) gave 21a (970 mg,
80.5 (dt, JCP¼3.5 Hz, JCF¼4.2 Hz), 65.1, 64.5 (d, JCP
¼
6.8 Hz), 64.4 (d, JCP¼6.9 Hz), 63.6, 41.2 (dt, JCP¼16.0 Hz,
JCF¼20.8 Hz), 34.5, 16.1 (d, JCP¼6.2 Hz), 15.0; 19F NMR
(376 MHz, CDCl3) d 250.9 (1F, ddd, JHF¼13.2 Hz, JPF¼
112.8 Hz, JFF¼288.8 Hz), 254.8 (1F, ddd, JHF¼19.6 Hz,
JPF¼112.8 Hz, JFF¼288.8 Hz); 31P NMR (162 MHz,
CDCl3) d 75.3 (t, JPF¼112.8 Hz); IR (film) 3465, 2980,
2933, 1025 cm21; EIMS m/z 303 (Mþ2OEt). Anal. calcd
for C12H23F2O5PS: C, 41.38: H, 6.65. Found: C, 41.86; H,
6.72. Successive elution with hexane/AcOEt (8:1) gave 20a
(628 mg, 49%) as an oil: [a]2D0¼þ69.6 (c¼1.3, CHCl3); 1H
NMR (400 MHz, CDCl3) d 5.22–5.14 (1H, m), 4.41–4.33
(1H, m), 4.31–4.18 (4H, m), 3.94 (1H, dd, J¼2.3, 12.1 Hz),
3.74 (1H, dq, J¼7.1, 9.7 Hz), 3.68 (1H, dd, J¼3.9, 12.1 Hz),
3.47 (1H, dq, J¼7.1, 9.7 Hz), 3.12–2.94 (1H, m), 2.36 (1H,
ddd, J¼5.6, 10.9, 13.9 Hz), 2.21–2.12 (1H, m), 1.35 (6H, t,
J¼7.1 Hz), 1.20 (3H, t, J¼7.1 Hz); 13C NMR (100 MHz,
1
98%) as an oil: [a]D20¼þ28.6 (c¼0.9, CHCl3); H NMR
(400 MHz, CDCl3) d 8.07–8.01 (2H, m), 7.58–7.51 (1H,
m), 7.47–7.40 (3H, m), 5.26–5.20 (1H, m), 4.69 (1H, dd,
J¼2.2, 11.9 Hz), 4.65–4.59 (1H, m), 4.40 (1H, dd, J¼4.9,
11.9 Hz), 4.34–4.20 (4H, m), 3.76 (1H, dq, J¼7.1, 9.7 Hz),
3.49 (1H, dq, J¼7.1, 9.8 Hz), 3.18–2.98 (1H, m), 2.43 (1H,
ddd, J¼5.6, 10.8, 13.9 Hz), 2.22–2.14 (1H, m), 1.34 (6H, t,
J¼7.1 Hz), 1.21 (3H, t, J¼7.1 Hz); 13C NMR (100 MHz,
CDCl3) d 166.2, 133.0, 130.0, 129.6, 128.3, 120.6 (ddd,
JCP¼178.4 Hz, JCF¼263.4, 271.9 Hz), 103.1, 74.7, 65.5,
64.7 (d, JCP¼6.1 Hz), 64.4 (d, JCP¼6.7 Hz), 63.2, 42.7 (dt,
JCP¼16.3 Hz, JCF¼20.5 Hz), 34.2, 16.1 (d, JCP¼6.1 Hz),
15.1; 19F NMR (376 MHz, CDCl3) d 248.7 (1F, ddd,
JHF¼8.8 Hz, JPF¼114.6 Hz, JFF¼288.4 Hz); 255.6 (1F,
ddd, JHF¼23.6 Hz, JPF¼108.2 Hz, JFF¼288.4 Hz); 31P
CDCl3)
d
120.8 (ddd, JCP¼178.3 Hz, JCF¼263.6,
NMR (162 MHz, CDCl3)
d
75.3 (dd, JPF¼108.2,
271.4 Hz), 103.1, 77.1 (dt, JCP¼3.4 Hz, JCF¼6.6 Hz), 64.6
(d, JCP¼6.8 Hz), 64.3 (d, JCP¼6.9 Hz), 63.3, 63.0, 41.4 (dt,
JCP¼15.9 Hz, JCF¼20.5 Hz), 34.4 (d, JCP¼3.8 Hz), 16.1 (d,
JCP¼6.1 Hz), 15.1; 19F NMR (376 MHz, CDCl3) d 248.6
(1F, ddd, JHF¼9.1 Hz, JPF¼114.7 Hz, JFF¼287.8 Hz),
255.0 (1F, ddd, JHF¼24.0 Hz, JPF¼109.2 Hz, JFF¼
287.8 Hz); 31P NMR (162 MHz, CDCl3) d 75.6 (dd, JPF¼
114.6 Hz); IR (film) 2979, 1724, 1452, 1025 cm21
;
ESIMS m/z 475 (MþþNa); HRMS (ESI) calcd for
C19H27O6F2NaPS (MþþNa): 475.1132. Found: 475.1108.
3.1.16. A typical procedure for N-glycosylation of 21b.
Benzoic acid (2S,3S,5R)-3-[(diethoxythiophosphoryl)di-
fluoromethyl]-5-(5-methyl-2,4-dioxo-3,4-dihydro-2H-
pyrimidin-1-yl)tetrahydrofuran-2-ylmethyl ester (22)
and benzoic acid (2S,3S,5R)-3-[(diethoxythiophosphor-
yl)difluoromethyl]-5-(5-methyl-2,6-dioxo-3,6-dihydro-
2H-pyrimidin-1-yl)-tetrahydrofurn-2-ylmethyl ester
(23). A suspension of thymine (180 mg, 0.88 mmol) and
N,O-bis(trimethylsilyl)acetamide (200 mg, 0.44 mmol) in
CH2Cl2 (9 mL) was heated at 408C for 4 h. To this mixture
was added a solution of 21b (200 mg, 0.44 mmol) in
CH2Cl2 (3 mL). The mixture was treated with a solution of
TiCl4 (0.24 mL, 2.2 mmol) in CH2Cl2 (3 mL) at 08C. After
being stirred at 08C for 3 h, the reaction was quenched with
sat. NaHCO3. The mixture was extracted with CHCl3. The
extracts were washed with brine, dried (MgSO4) and
concentrated. The residue was purified by column chroma-
tography on silica gel (hexane/AcOEt¼1:1) to give a
mixture of 22 and 23 (187 mg, 80%). The mixture was
109.2, 114.7 Hz); IR (film) 3474, 2980, 2932, 1162 cm21
;
EIMS m/z 331 (Mþ2OH), 303 (Mþ2OEt). Anal. calcd for
C12H23F2O5PS: C, 41.38; H, 6.65. Found: C, 41.22; H, 6.69.
3.1.14. Benzoic acid (2S,3S,5R)-3-[(diethoxythiophos-
phoryl)difluoromethyl]-5-ethoxytetrahydrofuran-2-
ylmethyl ester (21b). To a stirred solution of 20b (840 mg,
2.4 mmol) in pyridine (0.5 mL) was added a solution of
benzoyl chloride (310 mg, 2.6 mmol) in CH2Cl2 (5 mL) at
08C. After being stirred at the same temperature for 12 h,
water was added. The mixture was extracted with CHCl3
and the extracts were washed with brine, dried (MgSO4),
and concentrated. The residue was chromatographed on
silica gel (hexane/AcOEt¼15:1) to give 21b (920 mg, 85%)
as an oil: [a]2D0¼223.4 (c¼1.1, CHCl3); 1H NMR
(400 MHz, CDCl3) d 8.14–8.07 (2H, m), 7.60–7.50 (1H,
m), 7.48–7.40 (2H, m), 5.21–5.16 (1H, m), 4.68 (1H, dt,
J¼3.5, 7.0 Hz), 4.51 (1H, dd, J¼3.5, 11.5 Hz), 4.40 (1H, dd,
J¼7.2, 11.5 Hz), 4.31–4.19 (4H, m), 3.73 (1H, dq, J¼7.1,
9.6 Hz), 3.41 (1H, dq, J¼7.1, 9.7 Hz), 3.34–3.16 (1H, m),
2.32–2.13 (2H, m), 1.34 (3H, t, J¼7.1 Hz), 1.33 (3H, t,
J¼7.1 Hz), 1.13 (3H, t, J¼7.1 Hz); 13C NMR (100 MHz,
CDCl3) d 166.3, 133.0, 130.0, 129.7, 128.3, 120.6 (ddd,
JCP¼179.5 Hz, JCF¼264.5, 269.7 Hz), 103.9, 67.8, 64.6
(d, JCP¼6.6 Hz), 64.4 (d, JCP¼6.6 Hz), 62.7, 43.3, 16.1 (d,
JCP¼6.2 Hz), 14.9; 19F NMR (376 MHz, CDCl3) d 249.1
(1F, ddd, JHF¼10.7 Hz, JPF¼114.4 Hz, JFF¼289.5 Hz),
256.2 (1F, ddd, JHF¼20.7 Hz, JPF¼111.2 Hz, JFF¼
289.5 Hz); 31P NMR (162 MHz, CDCl3) d 75.2 (dd,
JPF¼111.2, 114.4 Hz); IR (film) 2979, 1724, 1452,
1276 cm21; ESIMS m/z 475 (MþþNa); HRMS(ESI) calcd
1
analyzed by H NMR spectroscopy (400 MHz, CDCl3) to
determine the diastereoselectivity and the ratio of 22 and 23
(Table 1). The analytical samples for 22 and 23 were
obtained by preparative HPLC (Inertsil (GL-science),
hexane/AcOEt¼1:1). 22 (70% de): an oil [a]2D0¼28.19
1
(c¼1.1, CHCl3); H NMR (400 MHz, CDCl3) d 8.86 (1H,
broad s), 8.07–7.98 (2H, m), 7.63–7.56 (1H, m), 7.49–7.42
(2H, m), 7.27–7.23 (1H, m), 6.10 (1H, t, J¼6.4 Hz), 4.79
(1H, dd, J¼2.1, 12.2 Hz), 4.74–4.68 (1H, m), 4.53 (1H, dd,
J¼4.0, 12.2 Hz), 4.36–4.19 (4H, m), 3.47–3.29 (1H, m),
2.81 (1H, ddd, J¼6.5, 6.5, 13.9 Hz), 2.24 (1H, ddd, J¼6.5,
10.0, 14.3 Hz), 1.63 (3H, d, J¼1.0 Hz), 1.36 (6H, t,
J¼7.1 Hz); 13C NMR (100 MHz, CDCl3) d 165.9, 164.0,
150.2, 134.9, 133.5, 129.7, 129.4, 128.6, 120.3 (ddd,
JCP¼177.2 Hz, JCF¼265.9, 270.4 Hz), 111.1, 85.4, 76.9,

T. Murano et al. / Tetrahedron 59 (2003) 9059–9073
9069
65.1, 65.0 (d, JCP¼7.4 Hz), 64.7 (d, JCP¼6.5 Hz), 42.6 (dt,
JCP¼16.5 Hz, JCF¼20.6 Hz), 33.0, 16.1 (d, JCP¼5.9 Hz),
12.1; 19F NMR (376 MHz, CDCl3) d 250.5 (1F, ddd,
JHF¼12.0 Hz, JPF¼ 110.7 Hz, JFF¼290.6 Hz), 254.7 (1F,
ddd, JHF¼20.5 Hz, JPF¼105.7 Hz, JFF¼290.6 Hz); 31P
(d, JCP¼6.8 Hz), 43.5 (dt, JCP¼17.0 Hz, JCF¼19.4 Hz,
b-isomer), 41.7 (dt, JCP¼16.2 Hz, JCF¼20.1 Hz, a-isomer),
30.7 (b-isomer), 30.3 (a-isomer), 26.8 (a-isomer), 26.7
(b-isomer), 19.3 (a-isomer), 19.1 (b-isomer), 16.2 (d, JCP
¼
6.3 Hz, a-isomer), 16.1 (d, JCP¼6.7 Hz, b-isomer), 12.8;
19F NMR (376 MHz, CDCl3) d 246.3 (0.66F, dd, JFF¼
286.9 Hz, JPF¼112.2 Hz), 248.5 (0.34F, ddd, JHF¼6.9 Hz,
NMR (162 MHz, CDCl3)
d
74.2 (dd, JPF¼105.7,
110.7 Hz); IR (film) 3191, 2985, 1715, 1693, 1664, 1275,
1025 cm21; EIMS m/z 533 (Mþþ1), 407 (Mþ2thymine).
Anal. calcd for C22H27N2O7F2PS: C, 49.62; H, 5.11; N,
5.26. Found: C, 49.57; H, 5.27; N, 4.95. 23 (92% de): mp
52–538C; [a]2D0¼225.1 (c¼1.1, CHCl3); 1H NMR
(400 MHz, CDCl3) d 9.59 (1H, d, J¼5.6 Hz), 8.11–8.01
(2H, m), 7.54–7.47 (1H, m), 7.43–7.34 (3H, m), 7.01 (1H,
dd, J¼1.1, 5.6 Hz), 6.75 (1H, dd, J¼3.8, 9.1 Hz), 4.74–4.50
(3H, m), 4.33–4.17 (4H, m), 3.84–3.65 (1H, m), 2.75–2.54
(2H, m), 1.87 (3H, d, J¼1.1 Hz), 1.34 (3H, t, J¼7.1 Hz),
1.33 (3H, t, J¼7.1 Hz); 13C NMR (100 MHz, CDCl3) d
166.3, 163.6, 152.5, 135.2, 129.8, 129.6, 128.1, 120.7 (ddd,
JCP¼ 177.9 Hz, JCF¼263.8, 271.0 Hz), 110.2, 82.4, 78.0,
66.4, 64.7 (d, JCP¼6.6 Hz), 64.3 (d, JCP¼6.7 Hz), 44.1 (dt.
JCP¼ 16.9 Hz, JCF¼19.8 Hz), 30.7, 16.0 (d, JCP¼6.1 Hz),
JFF¼287.8 Hz, JPF¼113.9 Hz), 257.3 (0.34F, ddd, JHF
¼
24.6 Hz, JFF¼287.8 Hz, JPF¼107.5 Hz), 259.4 (0.66F, ddd,
JHF¼26.6 Hz, JFF¼286.9 Hz, JPF¼112.2 Hz); 31P NMR
(162 MHz, CDCl3) d 75.7 (0.66P, t, JPF¼112.2 Hz), 75.4
(0.34P dd, JPF¼107.5, 113.9 Hz); IR (KBr) 3237, 3072,
2933, 2858, 1720, 1660, 1429, 1043 cm21; ESIMS m/z 689
(MþþNa). Anal. calcd for C31H41N2O6F2PSSiz1/2H2O: C,
55.10; H, 6.26; N, 4.15. Found: C, 55.20; H, 6.12; N, 4.09.
3.1.18. O,O-Diethyl (2S,3S,5R)-[2-{[tert-butyl(diphenyl)-
siloxy]methyl}-5-(5-methyl-2,4-dioxo-3,4-dihydropyri-
midin-1(2H)-yl)tetrahydrofuran-3-yl](difluoro)methyl-
phosphonothioate (26). Method A. A solution of T(TMS)2
in CH2Cl2 (5.0 mL) was prepared from thymine (63 mg,
0.5 mmol) and N,O-bis(trimethylsilyl)acetamide (0.25 mL,
1.0 mmol). The solution was cooled to 2408C, and was
successively treated with a solution of 18 (150 mg,
0.25 mmol) in CH2Cl2 (1.5 mL) and TiCl4 (0.14 mL,
1.25 mmol) in CH2Cl2 (1.5 mL). After being stirred at
2408C for 3 h, the mixture was warmed to 08C during 3 h
and poured onto sat. NaHCO3. The biphasic mixture was
extracted with CHCl3. The extracts were washed with
brine, dried (MgSO4), and concentrated. The residue was
chromatographed on silica gel (hexane/AcOEt¼1:1) to give
26 (130 mg, 78%, a/b¼12:88) as colorless crystals: mp 59–
12.7; 19F NMR (376 MHz, CDCl3) d 248.9 (1F, ddd, JHF
¼
7.8 Hz, JFF¼288.8 Hz, JPF¼112.7 Hz), 256.9 (1F, ddd,
JHF¼23.8 Hz, JFF¼288.8 Hz, JPF¼107.6 Hz); 31P NMR
(376 MHz, CDCl3) d 74.9 (dd, JPF¼107.6, 112.7 Hz); IR
(KBr) 3247, 2983, 1720, 1656, 1276, 1025 cm21; EIMS
m/z 533 (Mþþ1), 407 (Mþ2thymine). Anal. calcd for
C22H27F2O7PSz1/2H2O: C, 48.80; H, 5.21; N, 5.17. Found:
C, 48.99; H, 5.22; N, 5.13.
3.1.17. N-Glycosylation of 18 with T(TMS)2 at 2408C. A
solution of T(TMS)2 in CH2Cl2 (8 mL) was prepared from
thymine (126 mg, 1.0 mmol) and N,O-bis(trimethylsilyl)-
acetamide (0.49 mL, 2.0 mmol) as described in Section
3.1.16. The solution was cooled to 2408C, and was
successively treated with a solution of 18 (300 mg,
0.5 mmol) in CH2Cl2 (4.0 mL) and TiCl4 (0.31 mL,
2.5 mmol) in CH2Cl2 (4.0 mL). After being stirred at
2408C for 3 h, the mixture was poured onto cold sat.
NaHCO3. The biphasic mixture was extracted with CHCl3.
The extracts were washed with brine, dried (MgSO4), and
concentrated. The residue was chromatographed on silica
gel (hexane/AcOEt¼1:1) to give 25 (240 mg, 72%) as an
anomeric mixture (a/b¼66:34). Mp 62–638C; [a]2D0¼
þ40.8 (c¼1.0, CHCl3); 1H NMR (400 MHz, CDCl3) d
9.23–9.15 (1H, m), 7.77–7.64 (4H, m), 7.45–7.30 (3H, m),
6.90–6.85 (1H, m), 6.82 (0.66H, t, J¼7.7 Hz), 6.70 (0.34H,
dd, J¼3.8, 9.1 Hz), 4.87–4.80 (0.66H, m), 4.47–4.39
(0.34H, m), 4.31–4.14 (4H, m), 4.01–3.95 (1H, m),
3.92 (0.34H, dd, J¼6.9, 11.0 Hz), 3.80–3.63 (1.32H, m),
3.60–3.45 (0.34H, m), 2.97 (0.66H, dt, J¼8.9, 12.1 Hz),
2.68–2.59 (0.34H, m), 2.57–2.45 (1H, m), 1.88 (1.98H, d,
J¼0.9 Hz), 1.84 (1.02H, s), 1.33 (6H, t, J¼7.1 Hz), 1.07
(5.94H, s), 1.02 (3.06H, s); 13C NMR (100 MHz, CDCl3) d
163.9 (a-isomer), 163.6 (b-isomer), 152.8 (a-isomer),
152.7 (b-isomer), 135.7 (a-isomer), 135.6 (2C), 135.5
(b-isomer), 134.9, 133.7 (b-isomer), 133.4 (2C), 133.1
(a-isomer), 129.5 (2C, a-isomer), 129.4 (two carbons,
b-isomer), 127.6 (a-isomer), 127.2 (b-isomer), 121.0 (dt,
JCP¼178.9 Hz, JCF¼271.9 Hz), 110.4, 83.2 (a-isomer),
82.4 (b-isomer), 81.3 (b-isomer), 80.2 (d, JCP¼7.5 Hz,
a-isomer), 66.2 (b-isomer), 64.7 (d, JCP¼6.7 Hz, b-iso-
mer), 64.6 (d, JCP¼6.7 Hz, a-isomer), 64.3 (a-isomer), 64.2
1
608C; [a]2D5¼þ45.8 (c¼1.0, CHCl3); H NMR (400 MHz,
CDCl3) d 8.07 (1H, b), 7.71–7.62 (4H, m), 7.49–7.34 (7H,
m), 6.19 (1H, t, J¼6.8 Hz), 4.46–4.40 (1H, m), 4.31–4.17
(4H, m), 4.16–4.08 (1H, m), 3.84 (1H, dd, J¼2.4, 11.6 Hz),
3.68–3.50 (1H, m), 2.78 (1H, dt, J¼14.0, 5.6 Hz), 2.16 (1H,
ddd, J¼7.2, 10.3, 14.0 Hz), 1.56–1.53 (3H, m), 1.36 (3H, t,
J¼7.0 Hz), 1.34 (3H, t, J¼7.0 Hz), 1.11 (9H, s); 13C NMR
(100 MHz, CDCl3) d 163.9, 150.3, 135.5, 135.2, 135.0,
133.1, 132.3, 130.0 (2C), 127.9 (2C), 120.9 (dt, JCP
176.5 Hz, JCF¼268.4 Hz), 111.3, 84.5, 78.9, 64.9 (d, JCP
¼
¼
6.7 Hz), 64.5 (2C), 41.5 (dt, JCP¼16.6 Hz, JCF¼20.4 Hz),
33.1, 26.9, 19.4, 16.1 (d, JCP¼5.7 Hz), 11.9; 19F NMR
(376 MHz, CDCl3) d 250.3 (1F, ddd, JHF¼13.1 Hz, JFF¼
289.5 Hz, JPF¼110.6 Hz), 254.7 (1F, ddd, JHF¼21.9 Hz,
JFF¼289.5 Hz, JPF¼107.7 Hz); 31P NMR (162 MHz,
CDCl3) d 74.9 (dd, JPF¼107.7, 110.6 Hz); IR (KBr) 3048,
2933, 2858, 1702, 1471, 1264, 1058, 1024 cm21; EIMS m/z
609 (Mþ2tert-Bu), 541 (Mþ2thymine). Anal. calcd for
C31H41N2O6F2PSSi: C, 55.84; H, 6.20; N, 4.20. Found: C,
55.65; H, 6.14; N, 4.01. Method B. To a solution of
T(TMS)2 in CH2Cl2 (10 mL), prepared from thymine
(126 mg, 1.0 mmol) and N,O-bis(trimethylsilyl)acetamide
(0.49 mL, 2.0 mmol) as above, were successively added a
solution of 17 (290 mg, 0.5 mmol) in CH2Cl2 (3.0 mL) and
a solution of TiCl4 (0.31 mL, 2.5 mmol) in CH2Cl2 (3 mL)
at 08C. The mixture was stirred at the same temperature for
3 h and worked up as above. Purification of the crude by
column chromatography (SiO2, hexane/AcOEt¼1:1) gave
26 (310 mg, 93%, a/b¼11:89) as crystals. The spectro-
scopic data and melting points of 26 were identical to those
of the authentic sample prepared by Method A. Method C. A

9070
T. Murano et al. / Tetrahedron 59 (2003) 9059–9073
solution of 25 (a/b¼66:34, 67 mg, 0.1 mmol), thymine
(13 mg, 0.1 mmol) and N,O-bis(trimethylsilyl)acetamide
(74 mL, 0.3 mmol) in CH2Cl2 (2 mL) was heated at reflux
for 4 h. To the solution was added a solution of TiCl4
(0.05 mL, 0.5 mmol) at 08C. The mixture was stirred at
the same temperature for 3 h. Work-up and purification as
above gave 26 (65 mg, 97%, a/b¼15:89) as crystals. The
spectroscopic data and melting points of 26 were identical to
those of the authentic sample prepared by Method A.
31P NMR (162 MHz, CDCl3) d 74.5 (t, JPF¼108.8 Hz); IR
(KBr) 3177, 3074, 2933, 2859, 1719, 1471, 1263, 1115,
1016 cm21; EIMS m/z 613 (Mþ2tert-Bu). Anal. calcd for
C30H38N2O6F3PSSi: C, 53.72; H, 5.71; N, 4.18. Found C,
53.39; H, 5.80; N, 3.95.
3.1.21. (2S,3S,5R)-{[5-(4-Benzoylamino-2-oxo-2H-pyri-
midin-1-yl)-2-(tert-butyldiphenylsilanyloxymethyl)tetra-
hydrofuran-3-yl]-difluoromethyl}phosphonothioic acid
O,O-diethyl ester (30). This compound was prepared in
87% yield as an anomeric mixture (a/b¼17:83) from
N-benzoylcytosine (220 mg, 1.0 mmol) and 18 (290 mg,
0.5 mmol) in a similar manner to that described in Method B
of Section 3.1.18. Mp 58–608C; [a]2D5¼þ56.4 (c¼1.0,
CHCl3); 1H NMR (400 MHz, CDCl3) d 8.57 (1H, broad s),
8.42 (1H, d, J¼7.0 Hz), 7.92–7.83 (2H, m), 7.72–7.64 (4H,
m), 7.63–7.57 (1H, m), 7.54–7.36 (9H, m), 6.19 (1H, dd,
J¼4.2, 7.0 Hz), 4.53–4.47 (1H, m), 4.32–4.14 (5H, m),
3.88 (1H, dd, J¼2.2, 11.9 Hz), 3.57–3.39 (1H, m), 2.90
(1H, dt, J¼14.4, 7.0 Hz), 2.31 (1H, ddd, J¼4.2, 8.9,
14.4 Hz), 1.35 (3H, t, J¼7.1 Hz), 1.34 (3H, t, J¼7.1 Hz),
1.13 (9H, s); 13C NMR (100 MHz, CDCl3) d 166.7, 162.2,
154.5, 144.2, 135.6, 135.2, 132.9, 132.6, 132.0, 129.9,
3.1.19. (2S,3S,5R)-{[2-(tert-Butyldiphenylsilanyloxy-
methyl)-5-(2,4-dioxo-3,4-dihydro-2H-pyrimidin-1-yl)-
tetrahydro-furan-3-yl]-difluoromethyl}phosphonothioic
acid O,O-diethyl ester (28). This compound was prepared
in 64% yield as an anomeric mixture (a/b¼13:87) from
urasil (112 mg, 1.0 mmol) and 18 (290 mg, 5.0 mmol) in a
similar manner to that described in Method B of Section
3.1.18. Mp 52–538C; [a]2D5¼þ37.6 (c¼1.0, CHCl3); 1H
NMR (400 MHz, CDCl3) d 8.53 (1H, b), 7.86 (1H, d,
J¼8.1 Hz), 7.71–7.60 (4H, m), 7.48–7.33 (6H, m), 6.18
(1H, t, J¼6.0 Hz), 5.31 (1H, dd, J¼1.8, 8.1 Hz), 4.46–4.38
(1H, m), 4.33–4.17 (4H, m), 4.13 (1H, d, J¼11.9 Hz), 3.86
(1H, dd, J¼1.9, 11.9 Hz), 3.65–3.44 (1H, m), 2.77 (1H, dt,
J¼14.1, 6.9 Hz), 2.20 (1H, ddd, J¼5.1, 9.3, 14.1 Hz), 1.36
(3H, t, J¼6.9 Hz), 1.34 (3H, t, J¼7.2 Hz), 1.10 (9H, s); 13C
NMR (100 MHz, CDCl3) d 163.7, 150.3, 139.8, 135.6,
128.8, 127.9, 127.8, 127.5, 120.5 (ddd, JCP¼178.2 Hz, JCF
¼
264.3, 271.3 Hz), 96.4, 86.6, 80.8, 64.9 (d, JCP¼6.7 Hz),
64.2 (d, JCP¼6.9 Hz), 64.0, 40.1 (dt, JCP¼16.4 Hz, JCF
20.5 Hz), 34.8 (d, JCP¼2.7 Hz), 26.9, 19.2, 16.0 (d, JCP
¼
¼
135.2, 132.9, 132.0, 130.0 (2C), 127.9, 120.6 (dt, JCP
¼
177.5 Hz, JCF¼268.1 Hz) 102.3, 84.8, 79.9, 64.9 (d, JCP
¼
5.9 Hz); 19F NMR (376 MHz, CDCl3) d 248.5 (1F, ddd,
JHF¼7.7 Hz, JFF¼288.9 Hz, JPF¼114.0 Hz), 257.2 (1F,
ddd, JHF¼23.2 Hz, JFF¼288.9 Hz, JPF¼105.1 Hz); 31P
6.7 Hz), 64.3 (d, JCP¼6.8 Hz), 64.3, 40.8 (dt, JCP¼16.5 Hz,
JCF¼20.4 Hz), 34.0, 26.9, 19.3, 16.1 (d, JCP¼5.9 Hz); 19F
NMR (376 MHz, CDCl3) d 249.5 (1F, ddd, JHF¼10.1 Hz,
NMR (162 MHz, CDCl3)
d
74.6 (dd, JPF¼105.1,
JFF¼289.1 Hz, JPF¼111.9 Hz), 256.4 (1F, ddd, JHF
¼
114.0 Hz); IR (KBr) 2932, 1670, 1485, 1316, 1258, 1113,
1021 cm21; ESIMS m/z 756 (MþþH). Anal. calcd for
C37H44N3O6F2PSSi·H2O: C, 57.42; H, 5.99; N, 5.43. Found
C, 57.67; H, 5.91; N, 5.44.
22.6 Hz, JFF¼289.1 Hz, JPF¼106.6 Hz); 31P NMR
(162 MHz, CDCl3) d 74.6 (dd, JPF¼106.6, 111.9 Hz); IR
(KBr) 2933, 1689, 1463, 1391, 1275, 1113, 1022 cm21
;
EIMS m/z 595 (Mþ2tert-Bu), 541 (Mþ2uracil). Anal.
calcd for C30H39N2O6F2PSSi ·1/2H2O; C, 54.45; H, 6.09; N,
4.23. Found C, 54.41; H, 6.01; N, 3.96.
3.1.22. (2S,3S,5R){[2-(tert-Butyldiphenylsilanyloxy-
methyl)-5-(5-methyl-2,4-dioxo-3,4-dihydro-2H-pyrimi-
din-1-yl)-tetrahydrofuran-3-yl]-difluoromethyl}phos-
phonic acid diethyl ester (31). To a solution of 26 (180 mg,
0.27 mmol) in CH2Cl2 (8 mL) was added m-chloroperben-
zoic acid (230 mg, 1.35 mmol) at 08C. After being stirred at
room temperature for 4 h, the mixture was poured onto 5%
NaHCO3 solution and extracted with CHCl3. The extracts
were washed with brine and evaporated in vacuo. The
remaining residue was choromatographed on silica gel.
Elution with hexane/AcOEt (1:1) afforded 34 (110 mg,
64%, a/b¼11:89). Diastereomerically pure 34 was obtained
by preparative HPLC (Inertsil (GL-science), hexane/
AcOEt¼1:1). Mp 53–558C; [a]2D0¼þ40.8 (c¼1.0,
CHCl3); 1H NMR (400 MHz, CDCl3) d 8.24 (1H, bs),
7.71–7.61 (4H, m), 7.48–7.33 (6H, m), 6.19 (1H, t, J¼
6.9 Hz), 4.48–4.42 (1H, m), 4.35–4.21 (4H, m), 4.16–4.08
(1H, m), 3.84 (1H, dd, J¼2.5, 11.6 Hz), 3.46–3.25 (1H, m),
2.85–2.73 (1H, m), 2.24–2.12 (1H, m), 1.54 (3H, s), 1.38
(6H, t, J¼7.1 Hz), 1.10 (9H, s); 13C NMR (100 MHz,
CDCl3) d 163.9, 150.3, 135.5, 135.4, 135.2, 133.1, 132.3,
3.1.20. O,O-Diethyl (2S,3S,5R)-[2-{[tert-butyl(diphenyl)-
silyl]methyl}-5-(5-fluoro-2,4-dioxo-3,4-dihydropyrimi-
din-1(2H)-yl)tetrahydrofuran-3-yl](difluoro)methyl-
phosphonothioate (29). This compound was prepared in
84% yield as an anomeric mixture (a/b¼24:76) from
5-fluorourasil (130 mg, 1.0 mmol) and 18 (290 mg,
0.5 mmol) in a similar manner to that described in Method
B of Section 3.1.18. Mp 75–768C; [a]2D5¼þ40.8 (c¼1.4,
CHCl3); 1H NMR (400 MHz, CDCl3) d 8.34–8.19 (1H, m),
7.91 (1H, d, J¼5.9 Hz), 7.71–7.63 (4H, m), 7.49–7.36 (6H,
m), 6.12 (1H, t, J¼6.2 Hz), 4.46–4.42 (1H, m), 4.30–4.18
(4H, m), 4.08 (1H, d, J¼11.2 Hz), 3.80 (1H, dd, J¼2.4,
11.2 Hz), 3.59–3.42 (1H, m), 2.81 (1H, dt, J¼14.0, 6.5 Hz),
2.18 (1H, ddd, J¼6.1, 9.8, 14.0 Hz), 1.35 (3H, t, J¼7.0 Hz),
1.33 (3H, t, J¼7.0 Hz), 1.10 (9H, s); 13C NMR (100 MHz,
CDCl3) d 157.0 (d, JCF¼26.7 Hz), 148.9, 140.5 (d, JCF
¼
238.8 Hz), 135.7, 135.3, 132.5, 132.1, 130.0, 127.9 (2C),
123.7 (d, JCF¼33.7 Hz), 120.6 (dt, JCP¼178.2 Hz, JCF
¼
¼
268.0 Hz), 85.3, 79.8, 64.9 (d, JCP¼6.7 Hz), 64.5 (d, JCP
130.0 (2C), 127.9 (2C), 119.9 (dt, JCP¼214.3 Hz, JCF
¼
6.2 Hz), 64.5, 41.3 (dt, JCP¼16.9 Hz, JCF¼20.4 Hz), 33.7,
26.9, 19.2, 16.1 (d, JCP¼5.8 Hz); 19F NMR (376 MHz,
CDCl3) d 249.9 (1F, ddd, JHF¼11.8 Hz, JFF¼289.4 Hz,
JPF¼108.8 Hz), 255.5 (1F, ddd, JHF¼21.8 Hz, JFF¼
289.4 Hz, JPF¼108.8 Hz), 2100.7 (1F, d, JHF¼5.9 Hz);
263.3 Hz), 111.3, 84.5, 78.5, 64.9 (d, JCP¼6.8 Hz), 64.8 (d,
JCP¼7.0 Hz), 64.6, 42.3 (dt, JCP¼15.0 Hz, JCF¼20.2 Hz),
32.7, 26.9, 19.4, 16.3 (d, JCP¼5.2 Hz), 11.9; 19F NMR
(376 MHz, CDCl3) d 251.1 (1F, ddd, JHF¼14.5 Hz, JFF¼
302.9 Hz, JPF¼106.8 Hz), 254.0 (1F, ddd, JHF¼21.5 Hz,

T. Murano et al. / Tetrahedron 59 (2003) 9059–9073
9071
JFF¼302.9 Hz, JPF¼106.8 Hz); 31P NMR (162 MHz,
CDCl3) d 6.31 (t, JPF¼106.8 Hz); IR (KBr) 2932, 1695,
1472, 1272, 1025 cm21; EIMS m/z 593 (Mþ2tert-Bu).
Anal. calcd for C31H41N2O7F2PSi·H2O; C, 55.68; H, 6.48;
N, 4.19. Found C, 55.68; H, 6.27; N, 4.01.
an anomeric mixture (a/b¼95:5) from thymine (250 mg,
2.0 mmol) and 33 (570 mg, 1.0 mmol) in a similar manner
to that described in Method B of Section 3.1.18. Mp 56–
1
578C; [a]2D5¼þ60.4 (c¼1.3, CHCl3); H NMR (400 MHz,
CDCl3) d 9.56 (1H, d, J¼5.6 Hz), 7.74–7.62 (4H, m), 7.48–
7.31 (6H, m), 6.91 (1H, dd, J¼1.1, 5.6 Hz), 6.83 (1H, t, J¼
7.7 Hz), 4.90–4.83 (1H, m), 4.34–4.19 (4H, m), 4.02–3.94
(1H, m), 3.82–3.74 (1H, m), 3.64–3.45 (1H, m), 3.02 (1H,
ddd, J¼8.4, 12.4, 12.4 Hz), 2.59–2.48 (1H, m), 1.89 (3H, d,
J¼1.1 Hz), 1.37 (3H, t, J¼7.1 Hz), 1.36 (3H, t, J¼7.1 Hz),
1.07 (9H, s); 13C NMR (100 MHz, CDCl3) d 163.9, 152.6,
135.6, 135.5, 135.0, 133.4, 133.1, 129.6, 127.6, 120.1
(dt, JCP¼216.2 Hz, JCF¼263.7 Hz), 110.3, 83.1, 79.8, 64.7
3.1.23. (2S,3S)-Diethyl(2-{[tert-butyl(diphenyl)silyl]-
methyl}-5-ethoxytetrahydrofuran-3-yl)(difluoro)methyl-
phosphonate (33). To a stirred solution of 11 (1.23 g,
2.28 mmol) in THF (5 mL) was added dropwise a THF-
solution of BH3·THF (7.9 mmol, 7.7 mL of 1.04 M solution)
at 08C. After stirring had been continued for 18 h at the same
temperature, the reaction mixture was quenched with 1 M
HCl (2.5 mL) and saturated NH4Cl aqueous solution. The
mixture was extracted with Et2O and dried (Mg2SO4) and
evaporated. The residue was chromatographed on silica gel.
Elution with hexane/AcOEt (5:1) afforded the lactol 32
(d, JCP¼6.7 Hz), 64.5 (d, JCP¼6.9 Hz), 64.1, 42.3 (dt, JCP
14.4 Hz, JCF¼20.7 Hz), 29.9, 26.8, 19.3, 16.4 (d, JCP
¼
¼
5.2 Hz), 12.9; 19F NMR (376 MHz, CDCl3) d 247.1 (1F,
dd, JFF¼300.9 Hz, JPF¼105.7 Hz), 258.5 (1F, ddd, JHF
¼
1
(850 mg, 69%) as an oil. H NMR (400 MHz, CDCl3) d
26.1 Hz, JFF¼300.9 Hz, JPF¼111.5 Hz); 31P NMR
(162 MHz, CDCl3) d 6.77 (dd, JPF¼105.7, 111.5 Hz); IR
(KBr) 3182, 3073, 2932, 2858, 1719, 1658, 1429, 1265,
1114, 1040 cm21; EIMS m/z 593 (Mþ2tert-Bu). Anal.
calcd for C31H41N2O7F2PSi·1/2H2O: C, 56.44; H, 6.42; N,
4.25. Found: C, 56.61; H, 6.42; N, 4.22.
7.73–7.60 (4H, m), 7.47–7.32 (6H, m), 5.62–5.57 (0.2H,
m), 5.48–5.43 (0.8H, m), 4.56–4.53 (0.2H, m), 4.52–4.46
(0.8H, m), 4.34–4.17 (4H, m), 3.90 (0.8H, dd, J¼2.2,
11.2 Hz), 3.85 (0.2H, dd, J¼2.8, 11.1 Hz), 3.79–3.68 (0.4H,
m), 3.65 (0.8H, dd, J¼3.1, 11.2 Hz), 3.39–3.21 (0.8H, m),
2.57–2.47 (0.2H, m), 2.27–2.15 (1.8H, m), 1.41–1.28
(6H, m), 1.09 (7.2H, s), 1.05 (1.8H, s); ESIMS m/z 525
(Mþ2OH). Since 32 is unstable at room temperature, 32
was immediately used for the next reaction. A solution of
32 (850 mg, 1.57 mmol), triethylorthoformate (0.31 mL,
1.88 mmol) and ammonium nitrate (3 mg) in EtOH (3 mL)
was heated at 908C for 18 h. The mixture was quenched with
NaHCO3 and extracted with Et2O. The solvent was
evaporated and the residue was chromatographed on silica
gel. Elution with hexane/AcOEt (15:1) afforded 33 (950 mg,
67%) as an oil: [a]D25¼þ3.8 (c¼1.1, CHCl3); 1H NMR
(400 MHz, CDCl3) d 7.77–7.65 (4H, m), 7.45–7.31 (6H,
m), 5.28–5.21 (0.5H, m), 5.19–5.13 (0.5H, m), 4.55–4.48
(0.5H, m), 4.47–4.41 (0.5H, m), 4.33–4.18 (4H, m), 3.98
(0.5H, d, J¼11.3 Hz), 3.86–3.64 (2.5H, m), 3.50 (0.5H, dq,
J¼9.7, 7.1 Hz), 3.37 (0.5H, dq, J¼9.5, 7.1 Hz), 3.24–2.91
(1H, m), 2.40 (0.5H, ddd, J¼5.4, 10.7, 13.7 Hz), 2.28–2.12
(1.5H, m), 1.41–1.30 (6H, m), 1.21 (1.5H, t, J¼7.1 Hz),
1.08 (4.5H, s), 1.07 (4.5H, s), 1.06 (1.5H, t, J¼7.1 Hz); 13C
NMR (100 MHz, CDCl3) d 135.6, 135.5, 133.5, 133.4,
129.5, 127.6, 120.1 (dt, JCP¼217.4 Hz, JCF¼261.9 Hz),
103.7 and 103.4, 79.3 and 77.3, 67.3 and 64.9, 64.4, 63.2
and 62.5, 43.2 (dt, JCP¼14.9 Hz, JCF¼20.4 Hz) and 41.7 (dt,
JCP¼14.9 Hz, JCF¼20.2 Hz), 33.9, 26.7, 19.2 (2C), 16.3 (d,
JCP¼5.4 Hz), 15.2 and 14.9; 19F NMR (376 MHz, CDCl3) d
247.7 (0.5F, ddd, JHF¼8.8 Hz, JFF¼300.5 Hz, JPF¼
109.0 Hz), 249.1 (0.5F, ddd, JHF¼10.2 Hz, JFF¼
300.4 Hz, JPF¼109.0 Hz), 255.4 (0.5F, ddd, JHF¼24.7 Hz
3.1.25. A typical procedure for N-glycosylation of 17
with NBz-A(TMS)2. (2S,3S,5S)-{[5-(6-Benzylamino-
purin-9-yl)-2-(tert-butyl-diphenylsilanyloxymethyl)-
tetrahydrofuran-3-yl]-difluoromethyl}-phosphonothioic
acid O,O-diethyl ester (35a) and (2S,3S,5R)-{[5-(6-
benzylamino-purin-9-yl)-2-(tert-butyldiphenylsilanyloxy-
methyl)tetrahydrofuran-3-yl]-difluoromethyl}phospho-
nothioic acid O,O-diethyl ester(35b). A suspension of
N-benzoyladenine (120 mg, 0.5 mmol) and N,O-bis(tri-
methylsilyl)acetamide (0.25 mL, 1.0 mmol) in CH3CN
(5 mL) was heated at 408C for 3 h. To the resulting
homogeneous solution was added successively a solution
of 17 (150 mg, 0.25 mmol) in CH3CN (3 mL) and SnCl4
(0.29 mL, 2.5 mmol) at 08C. The mixture was stirred at
258C for 24 h, and then poured onto sat. NaHCO3. The
biphasic mixture was extracted with CHCl3. The extracts
were washed with brine, dried (MgSO4) and concentrated.
The residue was purified by column chromatography on
silica gel. Elution with hexane/AcOEt (1:2) gave 35a
(76.8 mg, 38%) as colourless crystals: mp 53–548C; [a]2D5¼
þ21.9 (c¼1.1, CHCl3); 1H NMR (400 MHz, CDCl3) d 9.03
(1H, b), 8.80 (1H, s), 8.21 (1H, s), 8.03 (2H, d, J¼7.4 Hz),
7.76–7.66 (4H, m), 7.61 (1H, t, J¼7.4 Hz), 7.53 (2H, t,
J¼7.4 Hz), 7.48–7.34 (6H, m), 6.55 (1H, t, J¼6.3 Hz),
4.84–4.78 (1H, m), 4.30–4.15 (4H, m), 4.01 (1H, dd, J¼
1.9, 11.4 Hz), 3.79 (1H, dd, J¼2.7, 11.4 Hz), 3.76–3.58
(1H, m), 2.99 (1H, ddd, J¼6.3, 9.5, 13.9 Hz), 2.82 (1H, dt,
J¼7.0, 13.9 Hz), 1.31 (3H, t, J¼7.1 Hz), 1.30 (3H, t, J¼
7.1 Hz), 1.12 (9H, s); 13C NMR (100 MHz, CDCl3) d 164.8,
152.5, 151.4, 149.4, 140.7, 135.5 (2C), 133.7, 132.7, 132.5,
JFF¼300.4 Hz, JPF¼109.0 Hz), 257.2 (0.5F, ddd, JHF
¼
24.6 Hz, JFF¼300.5 Hz, JPF¼109.0 Hz); 31P NMR (162 MHz,
CDCl3) d 7.06 (0.5P, t, JPF¼109.0 Hz), 6.91 (0.5P, t,
JPF¼109.0 Hz); IR (film) 3012, 2932, 2858, 1429, 1270,
1217, 1113, 1031 cm21; EIMS m/z 513 (Mþ2tert-Bu).
Anal. calcd for C28H41O6F2PSi: C, 58.93; H, 7.24. Found:
C, 58.70; H, 7.29.
129.8 (2C), 128.6, 127.8, 127.7, 123.4, 120.6 (ddd, JCP
¼
177.6 Hz, JCF¼265.5, 270.3 Hz), 85.4, 79.9, 65.4, 64.8 (d,
JCP¼6.6 Hz), 64.3 (d, JCP¼6.8 Hz), 42.2 (dt, JCP¼16.7 Hz,
JCF¼20.8 Hz), 34.2, 26.8, 19.2, 16.0 (d, JCP¼6.2 Hz); 19F
NMR (376 MHz, CDCl3) d 249.3 (1F, ddd, JHF¼11.8 Hz,
3.1.24. Diethyl (2S,3S,5S)-[2-{[tert-butyl(diphenyl)silyl]-
methyl}-5-(5-methyl-2,6-dioxo-3,6-dihydropyrimidin-
1(2H)-yl)tetrahydrofuran-3-yl](difluoro)methylphos-
phonate (34). This compound was prepared in 42% yield as
JFF¼288.7 Hz, JPF¼111.3 Hz), 255.5 (1F, ddd, JHF¼
22.1 Hz, JFF¼288.7 Hz, JPF¼107.5 Hz); 31P NMR
(162 MHz, CDCl3) d 74.6 (dd, JPF¼107.5, 111.3 Hz); IR
(KBr) 2933, 2858, 1700, 1610, 1582, 1456, 1251, 1113,

9072
T. Murano et al. / Tetrahedron 59 (2003) 9059–9073
1017 cm21; ESIMS m/z 780 (MþþH). HRMS (ESI) calcd
for C38H45N5O5F2PSSi (MHþ): 780.2616. Found:
780.2623. Anal. calcd for C38H44N5O5F2PSSi; C, 58.52;
H, 5.69; N, 8.98. Found C, 58.10; H, 5.78; N, 8.83.
Successive elution with hexane/AcOEt (1:2) gave 35b
(43.2 mg, 22%) as colorless crystals: mp 56–578C; [a]2D5¼
þ17.8 (c¼1.1, CHCl3); 1H NMR (400 MHz, CDCl3) d 8.99
(1H, broad s), 8.77 (1H, s), 8.31 (1H, s), 8.02 (2H, d,
J¼7.5 Hz), 7.65–7.57 (5H, m), 7.53 (2H, t, J¼7.5 Hz),
7.44–7.37 (2H, m), 7.36–7.28 (4H, m), 6.39 (1H, t, J¼
5.9 Hz), 4.61–4.54 (1H, m), 4.32–4.21 (4H, m), 4.06 (1H,
dd, J¼2.2, 11.6 Hz), 3.82 (1H, dd, J¼3.7, 11.6 Hz), 3.79–
3.64 (1H, m), 2.93 (1H, dt, J¼14.0, 6.9 Hz), 2.84 (1H, ddd,
J¼5.1, 9.1, 14.0 Hz), 1.35 (3H, t, J¼7.1 Hz), 1.34 (3H, t,
J¼7.1 Hz), 1.05 (9H, s); 13C NMR (100 MHz, CDCl3) d
164.6, 152.5, 151.2, 149.5, 141.2, 135.5, 135.3, 133.7,
132.7, 132.6, 132.5, 129.7 (2C), 128.7, 127.8, 127.7, 127.6,
123.3, 120.6 (ddd, JCP¼177.8 Hz, JCF¼265.9, 269.9 Hz),
a-isomer), 43.0 (dt, JCP¼18.4 Hz, JCF¼19.3 Hz, a-isomer)
and 42.2 (dt, JCP¼16.3 Hz, JCF¼20.8 Hz, b-isomer), 34.0,
16.1 (d, JCP¼5.9 Hz); 19F NMR (376 MHz, CDCl3) d 249.4
(0.6F, ddd, JHF¼10.8 Hz, JFF¼289.6 Hz, JPF¼109.3 Hz)
and 249.5 (0.4F, ddd, JHF¼12.1 Hz, JFF¼288.7 Hz, JPF¼
112.2 Hz), 255.1 (0.4F, ddd, JHF¼21.1 Hz, JFF¼288.7 Hz,
JPF¼105.7 Hz) and 255.6 (0.6F, ddd, JHF¼21.5 Hz, JFF¼
289.6 Hz, JPF¼109.3 Hz); 31P NMR (162 MHz, CDCl3) d
74.4 (0.6P, t, JPF¼109.3 Hz) and 74.3 (0.4P, dd, JPF¼105.7,
112.2 Hz); IR (neat) 2983, 1700, 1611, 1582, 1517, 1454,
1253, 1027 cm21; ESIMS m/z 632 (MþþH); HRMS (ESI)
calcd for C29H33N5O5F2PS: 632.1908 (MþþH). Found:
632.1884.
Acknowledgements
This work was supported in part by Grant-in-Aids for
Scientific Research (C) (to S. S. and T. Y.) and for
Encouragement of Young Scientists (to T. M.) from the
Ministry of Education, Culture, Sports, Science and
Technology of Japan.
84.7, 80.4, 64.8 (d, JCP¼6.7 Hz), 64.5, 64.4 (d, JCP
¼
6.7 Hz), 41.6 (dt, JCP¼16.4 Hz, JCF¼20.6 Hz), 33.6, 26.8,
19.1, 16.1 (d, JCP¼6.1 Hz); 19F NMR (376 MHz, CDCl3)
d 249.0 (1F, ddd, JHF¼9.7 Hz, JFF¼289.4 Hz, JPF¼
109.7 Hz), 256.0 (1F, ddd, JHF¼23.2 Hz, JFF¼289.4 Hz,
JPF¼109.7 Hz); 31P NMR (162 MHz, CDCl3) d 74.6 (t,
JPF¼109.7 Hz); IR (KBr) 2932, 1703, 1610, 1580, 1456,
1252, 1114, 1025 cm21; ESIMS m/z 780 (MþþH). Anal.
calcd for C38H44N5O5F2PSSi: C, 58.52; H, 5.69; N, 8.98.
Found: C, 58.12; H, 5.69; N, 8.86.
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