TEMPO-Catalyzed Oxidation of 3- O-Benzylated/Silylated Glycals to the Corresponding Enones Using a PIFA-Water Reagent System

Article abstract of DOI:10.1021/acs.joc.8b01191

A simple, highly efficient and regiospecific method for the direct conversion of 3-O-benzylated as well as silylated glycals into the corresponding enones has been developed using PIFA-TEMPO and water reagent system. The reaction is scalable on a gram sca

Full text of DOI:10.1021/acs.joc.8b01191

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Note
TEMPO-Catalyzed Oxidation of 3-O-Benzylated/Silylated Glycals
to the Corresponding Enones using PIFA-Water Reagent System
Ande Chennaiah, Ashish Kumar Verma, and Yashwant D. Vankar
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.8b01191 • Publication Date (Web): 20 Aug 2018
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The Journal of Organic Chemistry
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TEMPO-Catalyzed Oxidation of 3-O-Benzylated/Silylated Glycals to
the Corresponding Enones using PIFA-Water Reagent System
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Ande Chennaiah, Ashish Kumar Verma and Yashwant D. Vankar*
Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
Supporting Information Placeholder
the corresponding enones in moderate to good yields. Further-
more, a modified reagent system comprising of PIDA (2 equiv)
and Me3SiN3 (4 equiv) in CH2Cl2 at 5 C to room temperature
ABSTRACT: A simple, highly efficient and regiospecific
method for the direct conversion of 3-O-benzylated as well as
silylated glycals into the corresponding enones has been
developed using PIFA-TEMPO and water reagent system. The
reaction is scalable on gram scale under mild conditions with an
yield upto 86%.
o
was also reported by Kirschning et al.4d for the oxidation of 3-O-
silylated glycals to sugar derived 2,3-dihydro-4H-pyran-4-ones in
high yields. However, although these methods are popular, the
experimental protocol demands stringent anhydrous conditions
(the use of powdered molecular sieves 3 Å being essential). Fur-
ther, in the case of 3-O-Bn protected glycals, the expected C3-
oxidized product was obtained in low yields. Thus, development
of mild and efficient methods for the synthesis of sugar derived
2,3-dihydro-4H-pyran-4-ones from glycal derivatives is highly
desirable.
Hexenuloses or sugar derived 2,3-dihydro-4H-pyran-4-ones are
important carbohydrate derivatives which posses a highly reactive
,-unsaturated-ketone moiety occupying C-1, C-2 and C-3 posi-
tions of a sugar molecule.1a Since they are excellent Michael ac-
ceptors,1b these molecules have been widely utilized in the syn-
thesis of a variety of 2-deoxy-C- and O-glycosides1,c,d,e and 2-
phosphono-α-C-glycosides.1f Furthermore, they have been utilized
as chiral synthons in the synthesis of complex natural products
such as Thailanstatin A,2a (+)-Decarestrictine L,2b Mycalamides,2c
6-epi-phomonol2d (Figure 1), Diospongin A, ent-Diospongin A
and their epimers.2e In addition, the keto group can be easily re-
duced to obtain rare sugars such as D-allal and its derivatives.2f,g
Therefore, methods for the synthesis of compounds containing a
2,3-dihydro-4H-pyran-4-ones are of great significance.
Recently, we reported5 a highly regiospecific and stereoselective
synthesis of 2-azido-2-deoxysugars from differently protected
glycals in one-step by using water-mediated and TEMPO-
catalyzed PIFA−Me3SiN3 reagent system in the presence of
Bu4NHSO4 as a phase-transfer catalyst. In our studies, formation
of a small amount (~ 5%) of the corresponding 2,3-dihydro-4H-
pyran-4-one was observed from C3-OBn and C3-OTBDMS pro-
tected glycals during their reaction with PIFA-Me3SiN3-TEMPO-
H2O-Bu4NHSO4 reagent system in CH2Cl2. Intrigued by these
results and in continuation of our efforts for the functionalization
of glycals,6 we considered it worth developing reaction condi-
tions that could lead to higher yields of such enones. Herein, we
report our findings for an efficient and mild reaction condition for
the oxidation of 3-O-benzylated (as well as 3-O-silylated) glycals
to the corresponding 2,3-dihydro-4H-pyran-4-ones using PIFA-
water as an oxidizing reagent system along with TEMPO as a
catalyst.
Figure.1 Examples of some natural products synthesized using
hexenuloses as a synthon
As mentioned above, in our recently reported studies5 (vide
supra) the reaction of tri-O-benzyl-D-galactal 1 with TMSN3 and
water in presence of PIFA, TEMPO and Bu4NHSO4 resulting in
the formation of 2-azido-2-deoxysugar was accompanied by a
small amount (~5%) of the corresponding enone. We therefore
reasoned that since there was no apparent role of TMSN3 (and
perhaps water) in such an oxidation route, excluding these may
suppress the formation of 2-azido-2-deoxysugar and permit get-
ting higher yields of the enones. Thus, in our initial studies, reac-
tion of tri-O-benzyl-D-galactal 1 with 1.0 equiv of PIFA in
Several methods have been reported for the synthesis of sugar
derived 2,3-dihydro-4H-pyran-4-ones, that include traditional
allylic oxidation of 3-hydroxy glycals using reagents such as
MnO2,3a PDC,3b Ag2CO3-Celite3c and (Bu3Sn)2O, NIS3d etc.3e-g In
this context, a seminal contribution by Kirschning4a and co-
workers for the direct oxidation of 3-O-protected glycals into the
corresponding enones by using hypervalent iodine reagents is
noteworthy. The report features the reaction of 3-OAc, 3-OBn,
3-silyl protected glycals with Koser’s reagent [PhI(OH)(OTs)]4b
(1.2 equiv) and MS 3 (Å), or alternatively by using (diacetoxyi-
odo)benzene4c (PIDA) (1.2 equiv) along with p-TsOH leading to
o
CH2Cl2 was carried out at 0 C which led to the corresponding
enone 2 in only 6% yield along with the recovered starting ma-
terial. Increasing the amount of PIFA to 2.0 equiv under same
conditions improved the yield of 2 to 28%. However, a significant
increase in the yield (78%) of 2 was observed (Table 1, entry 5)
when 0.2 equiv of TEMPO was used as a catalyst along with 2.2
equiv of PIFA in CH2Cl2 while performing the reaction at 0oC to
room temperature in 30 min. Next, we considered checking the
effect of water, if any, in this reaction which led to observe that
the use of 1.0 equiv of water as an additive under the same condi-
tions was effective and it led to a considerable increase in the
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yield of the desired product (86%). Dichloromethane was found to
85% and 90% respectively as single diastereomers. Next, protec-
tion of the 3-OH group as a TBDMS ether and benzyl ether gave
be the ideal solvent in the present work, and the next best solvent
was CH3CN which led to 63% of the enone whereas DMF, THF
and toluene failed to give the desired product. It is likely that
Lewis basic solvents such as CH3CN and DMF may deactivate7
PIFA and thus render them less effective than dichloromethane.
Among the hypervalent reagents, PIFA appeared best as other
hypervalent iodine reagents such as PIDA and PhIO were found
to be unreactive under these conditions. Therefore, the optimized
condition was found to be in using 2.2 equiv of PIFA, 0.2 equiv of
TEMPO and 1.0 equiv of water at 0 oC to room temperature in 30
min which gave 86% yield of 2 (Table 1, entry 6). Thus, the
present method offers a more effective catalyst system for the
direct oxidation of tri-O-benzyl-D-galactal 1 to corresponding
enone 2 as far as yield, time and mild reaction conditions are con-
cerned compared to the methods known in the literature.
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Table 2 Substrate Scope for the oxidation of Glycals into
enones
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Table 1 Optimization of reaction conditions for the forma-
tion of enone
compounds 17, 18, 20 and 21 in high yields which were subjected
to oxidation by following the procedure developed by us to give
the corresponding enones 2 and 8 in good yields (Table 3).
Scheme 1 Synthesis of derivatives of D-allal and D-idal
With the established reaction conditions in hand, we tested the
reactivity of different glycal derivatives. Thus, galactals and gluc-
als having –OBn group at C-3 (compounds 1, 3, 7, 9, Table 2)
were smoothly converted to the corresponding enones in good to
excellent yields. In addition, benzyl-protected D-arabinal 13 (en-
try 7) and D-xylal 15 (entry 8) also provided the corresponding
enone 14 in very good yields. Further, we checked the reactivity
of glycals with other protecting groups. Thus, per-O-silylated
glycals 5 and 11 (entries 3 and 6) under standard reaction condi-
tions gave exclusively the respective enones 6 and 12 in very
good yields.
To gain an additional insight as to whether this reagent system
can oxidize the –OBn and the –OTBDMS groups occupying dif-
ferent stereochemistry at C-3 position, we prepared a set of com-
pounds. Thus, the D-idal derivatives 17, 18, and D-allal deriva-
tives 20, 21 (Scheme 1) were prepared by performing the Luche
reduction8 of D-galactal and D-glucal derived enones respective-
ly. Thus, compounds 2 and 8 upon reaction with CeCl3·7H2O and
NaBH4 at 78 °C afforded D-idal 16 and D-allal 19 derivatives in
Further, when compound 229 bearing two allylic benzyl ethers,
was subjected to oxidation under present conditions, compound
23 was formed as a major product along with 2410 as a minor
product. We believe that compound 23 could serve as a good
synthon in organic chemistry, particularly in carbohydrate chemi-
stry, to synthesize C2-branched sugars.11 It is noteworthy that
under the present reaction conditions, glycals having 3-O-acetyl,
3-O-benzoyl or 3-O-methyl group did not undergo oxidation to
the corresponding enones. Further, simple allyl benzyl ether de-
rivatives such as (E)-(2-(benzyloxy)vinyl)benzene (derived from
benzyl protected cinammyl alcohol), and (E)-((prop-1-en-1-
yloxy)methyl)benzene (derived from benzyl protected crotyl al-
cohol) were also subjected to our present reaction conditions.12
Although the former gave the expected cinnamaldehyde, albeit in
only 30% yield (as confirmed by GC-MS analysis), it was conta-
minated with some other inseparable high molecular weight prod-
ucts. On the other hand, with the latter substrate, formation of a
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by Magnus,13 followed by its decomposition to a trivalent rad-
ical cation intermediate A'.12 The glycal then interacts with A'
forming intermediate C, via a -complex B, which under the
reaction conditions may lose a proton from C-3 leading to an
oxonium ion D along with the radical anion intermediate G.
The resonating oxonium ion E then reacts with water to give
the enone via a hemiacetal F. In the reaction of benzyl deriva-
tives, the GC-MS analysis of the crude reaction mixture
showed the presence of benzyl alcohol indicating that, as
shown in Scheme 2, the hemiacetal F indeed ejects the benzy-
loxy group at C-3 to let the oxidation complete. The interme-
diate G,12 on the other hand, loses trifluroacetate anion form-
ing a radical intermediate H which decomposes to iodoben-
zene and regenerates TEMPO to complete the catalytic cycle.
complex mixture was observed. Therefore, it appears most likely
that the present method is suitable for sugar derived allyl benzyl
ethers, where the double bond is part of an enol ether.
To check the practicality of the current protocol, a gram-scale
reaction (upto 5 gm) was performed with tri-O-benzyl-D-galactal
1 and tri-O-benzyl-D-glucal 7 which afforded the corresponding
enones 2 and 8 with no change in the isolated yields.
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Table 3. Substrate Scope for the oxidation of Glycals into
enones
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In conclusion, we have demonstrated a simple one-step protocol
for the direct oxidation of 3-O-benzyl or 3-O-silyl-protected glyc-
als to afford the corresponding enones with PIFA-TEMPO and
water reagent system. The reaction generally proceeds in high
yields under mild conditions in short time. In addition, this oxida-
tion was found to be independent of the stereochemistry of the
–OBn and -OTBDMS groups at C3 of glycals. Moreover, since
the reactions are performed in presence of water, exclusion of
moisture is not necessary and thus these simple reaction condi-
tions should make the current protocol synthetically useful.
EXPERIMENTAL SECTION
General Information
All experiments were performed in oven-dried apparatus and
under a nitrogen atmosphere in dry solvents. Commercial grade
solvents were dried by known methods and stored over 4 Å mole-
cular sieves. IR spectra were recorded as a thin film and expressed
in cm-1. High resolution mass spectra were recorded by Q-TOF
1
using the electrospray ionization (ESI) method. H (500 MHz or
400 MHz) and 13C (125 MHz or 100 MHz) NMR spectra were
recorded using CDCl3 as a solvent. TEMPO and PhI(OCOCF3)2
were purchased from the Alfa-Aesar Co. and Spectrochem Pvt.
Ltd. (Mumbai) respectively. Optical rotations were recorded on an
AUTOPOL II polarimeter at 25 °C in CH2Cl2. TLC plates were
prepared using thin layers of silica gel on microscopic slides, and
visualization of spots was done by exposure to iodine or spraying
with 10% H2SO4 and charring. Column chromatography was per-
formed over silica gel (100−200 Mesh) using hexane and ethyl
acetate as eluents.
A tentative mechanism based on these observations is shown in
Scheme 2. We propose that TEMPO may first react with PIFA to
form a tetrahedral intermediate A, as has also been proposed
Scheme 2 Tentative mechanism for the conversion of
glycals to enones
General procedure for oxidation of C-3 protected glycals to
enones ‘A’
To a stirred solution of a glycal (500 mg, 1.201 mmol) in CH2Cl2
(15 mL) at 0 °C under nitrogen was added PhI(OCOCF3)2 (1.03 g,
2.643 mmol), TEMPO (38 mg, 0.240 mmol) and water (22 L,
1.201 mmol). The resulting reaction mixture was slowly brought
to room temperature and stirred for appropriate time. Upon com-
pletion of the reaction (TLC monitoring), saturated aqueous
NaHCO3 solution (5 mL) was added and the mixture extracted
with CH2Cl2 (2 x 10 mL). The combined organic layers were
washed with brine (10 mL) and dried over anhydrous Na2SO4.
Evaporation of the solvent followed by silica gel column chroma-
tography of the resulting crude residue provided the pure product.
General procedure for reduction enone to enol ‘B’
To a solution of sugar enone (1 g, 3.082 mmol) in MeOH (20 mL)
at –78 °C was added CeCl3·7H2O (1.38 g, 3.698 mmol) followed
by NaBH4 (1.38 g, 3.698 mmol) in three portions over a period of
15 min. The solution was stirred for the appropriate time at –78
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[ ]2D8
°C, and upon completion of the reaction (TLC monitoring), it was
= 0.80 (hexane/EtOAc, 9:1);
= 138.0 (c 0.3, CH2Cl2); IR
quenched with satd. aqueous NH4Cl and extracted with ethyl ace-
tate (20 mL x 2). The combined organic layers were washed with
water (20 mL), brine (20 mL) and dried over anhydrous Na2SO4.
Removal of solvent and purification of the crude residue by silica
gel column chromatography gave the pure product.
1
2
3
4
5
6
1
(neat) max /cm-1: 2929, 1686, 1599, 836; H NMR (500 MHz,
CDCl3) δ 7.29 (d, J = 6.0 Hz, 1H), 5.34 (dd, J = 6.0, 1.3 Hz, 1H),
4.26 – 4.22 (m, 1H), 4.02 (dd, J = 2.6, 1.4 Hz, 1H), 3.93 (d, J =
6.4 Hz, 2H), 0.89 (s, 9H), 0.86 (s, 9H), 0.11 (s, 3H), 0.07 (s, 6H),
0.07 (s, 3H); 13C NMR (125 MHz, CDCl3) δ 191.2, 162.1, 104.9,
83.0, 69.6, 60.3, 25.9, 25.7, 18.3, -4.6, -5.2; HRMS Calcd for
C18H37O4Si2 [M + H]+ = 373.2230, found 373.2233.
General procedure for benzylation ‘C’
7
8
9
To a stirred solution of a 3-hydroxy glycal (500 mg, 1.531 mmol)
in dry DMF (10 mL) was added NaH (60% suspension in paraffin
oil, 44 mg, 1.839 mmol) followed by benzyl bromide (219 L,
1.839 mmol) at 0 °C. After the reaction mixture was stirred at
room temperature for an appropriate time, (TLC monitoring), it
was quenched with ice and the usual workup with ethyl acetate (3
× 10 mL) was followed. The organic phase was washed with brine
solution and then dried over anhydrous Na2SO4. In vacuo removal
of the solvent gave the crude compound which was purified by
column chromatography.
(2R,3R)-3-(benzyloxy)-2-((benzyloxy)methyl)-2H-pyran-4(3H)-
one (8).
Compound 8 was prepared from 7 (500 mg, 1.201 mmol) using
general procedure ‘A’ in 79% yield (308 mg) as a colorless oil; Rf
10
11
12
13
14
15
16
17
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[ ]2D8
= 0.30 (hexane/EtOAc, 8:2);
= 67.4 (c 0.6, CH2Cl2) ;IR
(neat) max /cm-1: 2922, 2108, 1682, 1100; H NMR (400 MHz,
CDCl3) δ 7.36 – 7.25 (m, 12H), 5.40 – 5.37 (m, 1H), 5.07 (d, J =
11.1 Hz, 1H), 4.58 (dd, J = 21.9, 10.6 Hz, 3H), 4.43 (dt, J = 11.6,
3.3 Hz, 1H), 4.23 (d, J = 11.6 Hz, 1H), 3.80 (d, J = 3.3 Hz, 2H);
13C NMR (100 MHz, CDCl3) δ 193.6, 162.4, 137.6, 137.5, 128.6,
128.5, 128.4, 128.1, 128.0, 127.9, 105.3, 81.1, 74.7, 74.2, 73.7,
67.9; HRMS Calcd for C20H21O4 [M + H]+ = 325.1440, found
325.1442.
1
General procedure for TBDMS protection ‘D’
To a solution of 3-hydroxy glycal (500 mg, 1.531 mmol) in dry
THF (10 mL) at 0 °C were added sodium hydride (60% suspen-
sion in paraffin oil, 44 mg, 1.839 mmol) and tert-
butylchlorodimethylsilane (TBDMS-Cl) (346 mg, 2.296 mmol).
The reaction mixture was allowed to warm to room temperature
and stirred for the required amount of time. Upon complete con-
sumption of starting material (TLC monitoring), the reaction mix-
ture was quenched with water (5 mL) and extracted using ethyl
acetate (2 ×10 mL). Combined organic extracts were dried over
anhydrous Na2SO4 and concentrated in vacuo. The residue was
purified by silica gel column chromatography to furnish pure
product.
(2R,3R)-3-(benzyloxy)-2-(((tert-butyldimethylsilyl)oxy)methyl)-
2H-pyran-4(3H)-one (10).
Compound 10 was prepared from 9 (500 mg, 1.135 mmol) using
general procedure ‘A’ in 81% yield (319 mg) as a colorless oil; Rf
[ ]2D8
= 0.60 (hexane/EtOAc, 8:2);
= 43.5 (c 0.3, CH2Cl2); IR
(neat) max /cm-1: 2928, 2111, 1679, 837; H NMR (500 MHz,
CDCl3) δ 7.38 – 7.27 (m, 7H), 5.44 (dd, J = 6.0, 1.6 Hz, 1H), 4.72
(d, J = 11.8 Hz, 1H), 4.50 (d, J = 11.8 Hz, 1H), 4.34 (ddd, J = 6.4,
2.4, 2.0 Hz, 1H), 3.97 (dd, J = 6.5, 3.2 Hz, 2H), 3.76 – 3.73 (m,
1H), 0.88 (s, 9H), 0.06 (d, J = 1.7 Hz, 6H); 13C NMR (100 MHz,
CDCl3) δ 193.8, 162.4, 137.7, 128.5, 128.3, 128.0, 105.0, 82.5,
74.7, 74.2, 61.5, 25.9, 18.4, -5.1, -5.2; HRMS Calcd for
C19H29O4Si [M + H]+ = 349.1835, found 349.1834.
1
(2R,3S)-3-(benzyloxy)-2-((benzyloxy)methyl)-2H-pyran-4(3H)-one
(2).
Compound 2 was prepared from 1 (500 mg, 1.201 mmol) using
general procedure ‘A’ in 86% yield (336 mg) as a colorless oil; Rf
[ ]2D8
= 0.30 (hexane/EtOAc, 8:2);
= 23.1 (c 0.7, CH2Cl2); IR
(2R,3R)-3-((tert-butyldimethylsilyl)oxy)-2-(((tert-butyldimethyl-
silyl)oxy)methyl)-2H-pyran-4(3H)-one (12).
Compound 12 was prepared from 11 (500 mg, 1.023 mmol) using
general procedure ‘A’ in 76% yield (286 mg) as a colorless oil; Rf
1
(neat) max /cm-1: 2920,1682; H NMR (400 MHz, CDCl3) δ 7.32
(m, 11H), 5.43 (d, J = 6.0 Hz, 1H), 4.71 (d, J = 11.9 Hz, 1H), 4.56
(d, J = 11.9 Hz, 1H), 4.53 – 4.45 (m, 3H), 3.91 (dd, J = 10.2, 7.1
Hz, 1H), 3.74 (dd, J = 10.2, 5.3 Hz, 1H), 3.69 (s, 1H); 13C NMR
(100 MHz, CDCl3) δ 189.4, 162.7, 137.4, 136.9, 128.49, 128.41,
128.2, 128.0, 127.9, 127.7, 105.1, 80.6, 74.1, 73.6, 71.9, 67.6.
HRMS Calcd for C20H21O4 [M + H]+ = 325.1440, found
325.1441.
[ ]2D8
= 0.80 (hexane/EtOAc, 9:1);
= 215.0 (c 0.8, CH2Cl2); IR
(neat) max /cm-1: 2925, 1699; 1H NMR (500 MHz, CDCl3) δ 7.28
(d, J = 5.8 Hz, 1H), 5.31 (d, J = 6.1 Hz, 1H), 4.43 (d, J = 12.1 Hz,
1H), 4.18 (dt, J = 12.2, 2.7 Hz, 1H), 3.99 (d, J = 2.7 Hz, 2H), 0.91
(s, 9H), 0.91 (s, 9H), 0.23 (s, 3H), 0.09 (s, 9H); 13C NMR (125
MHz, CDCl3) δ 191.3, 162.2, 104.9, 83.0, 69.6, 60.3, 25.8, 18.4, -
5.2; HRMS Calcd for C18H37O4Si2 [M + H]+ = 373.2230, found
373.2233.
(2R,3S)-3-(benzyloxy)-2-(((tert-butyldimethylsilyl)oxy) methyl)-
2H-pyran-4(3H)-one (4).
Compound 4 was prepared from 3 (500 mg, 1.135 mmol) using
general procedure ‘A’ in 83% yield (327 mg) as a colorless oil; Rf
(R)-3-(benzyloxy)-2H-pyran-4(3H)-one (14).
[ ]2D8
= 0.60 (hexane/EtOAc, 8:2);
= 96.0 (c 0.9, CH2Cl2); IR
Compounds 14 was prepared from 13 and 15 (500 mg, 1.687
mmol) using general procedure ‘A’ in 82% (281 mg) and 79%
(269 mg) respectively, as a colorless oil; Rf = 0.40 (hex-
(neat) max /cm-1: 2920, 2114, 1679, 831; H NMR (400 MHz,
CDCl3) δ 7.38 – 7.26 (m, 7H), 5.43 (dd, J = 6.1, 1.6 Hz, 1H), 4.72
(d, J = 11.8 Hz, 1H), 4.50 (d, J = 11.8 Hz, 1H), 4.36 – 4.31 (m,
1H), 3.97 (dd, J = 6.6, 1.5 Hz, 2H), 3.75 (dd, J = 2.4, 1.7 Hz, 1H),
0.88 (s, 9H), 0.06 (d, J = 1.4 Hz, 6H). 13C NMR (100 MHz,
CDCl3) δ 190.0, 162.8, 137.3, 128.5, 128.2, 128.0, 105.2, 82.2,
74.1, 72.2, 60.5, 25.9, 18.3, -5.30, -5.36; HRMS Calcd for
C19H29O4Si [M + H]+ = 349.1835, found 349.1834.
1
[ ]2D8
ane/EtOAc, 8:2);
= +84.1 (c 0.5, CH2Cl2); IR (neat) max
/cm-1: 1678, 1597, 1098; H NMR (400 MHz, CDCl3) δ 7.39 –
7.28 (m, 7H), 5.42 (dd, J = 6.0, 1.0 Hz, 1H), 4.85 (d, J = 11.9 Hz,
1H), 4.62 (d, J = 11.9 Hz, 1H), 4.48 (dd, J = 12.4, 6.4 Hz, 1H),
4.37 (dd, J = 12.4, 4.0 Hz, 1H), 3.83 (ddd, J = 6.3, 4.0, 1.0 Hz,
1H); 13C NMR (100 MHz, CDCl3) δ 190.5, 163.1, 137.3, 128.6,
128.3, 128.2, 105.4, 73.6, 72.6, 71.4; HRMS Calcd for C12H13O3
[M + H]+ = 205.0865, found 205.0862.
1
(2R,3S)-3-((tert-butyldimethylsilyl)oxy)-2-(((tert-
butyldimethylsilyl)oxy)methyl)-2H-pyran-4(3H)-one (6).
Compound 6 was prepared from 5 (500 mg, 1.023 mmol) using
general procedure ‘A’ in 75% yield (298 mg) as a colorless oil; Rf
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The Journal of Organic Chemistry
(neat) max /cm-1: 2951, 1642, 731; 1H NMR (400 MHz, CDCl3) δ
7.34 – 7.19 (m, 15H), 6.42 (dd, J = 6.1, 0.9 Hz, 1H), 4.89 – 4.81
(m, 2H), 4.65 (d, J = 2.9 Hz, 1H), 4.61 (t, J = 3.6 Hz, 1H), 4.55 (t,
J = 8.8 Hz, 3H), 4.21 (dd, J = 6.1, 2.1 Hz, 1H), 4.06 (ddd, J = 8.2,
4.9, 2.9 Hz, 1H), 3.89 – 3.73 (m, 3H); 13C NMR (100 MHz,
CDCl3) δ 144.8, 138.4, 138.2, 138.0, 128.4, 128.0, 127.89,
127.83, 127.7, 100.0, 75.8, 74.4, 73.8, 73.5, 70.5, 68.6; HRMS
Calcd for C27H29O4 [M + H]+ = 417.2066, found 417.2061.
(2R,3R,4S)-3-(benzyloxy)-2-(benzyloxymethyl)-3,4-dihydro-2H-
pyran-4-ol (16).
Compound 16 was prepared from 2 (400 mg, 1.233 mmol) using
general procedure ‘B’ in 85% yield (342 mg) as a colorless oil; Rf
1
2
3
4
5
6
7
8
[ ]2D8
= 0.30 (hexane/EtOAc, 8:2);
= 18.2 (c 0.2, CH2Cl2); IR
(neat) max /cm-1: 3100, 1648, 921; 1H NMR (400 MHz, CDCl3) δ
7.41 – 7.24 (m, 10H), 6.36 (d, J = 6.1 Hz, 1H), 4.77 – 4.72 (m,
1H), 4.68 (t, J = 10.1 Hz, 2H), 4.57 (d, J = 11.9 Hz, 1H), 4.48 (d,
J = 11.9 Hz, 1H), 4.33 (dd, J = 6.5, 2.7 Hz, 1H), 4.18 (td, J = 6.5,
2.3 Hz, 1H), 3.92 – 3.87 (m, 1H), 3.79 (dd, J = 10.0, 6.6 Hz, 1H),
3.63 (dd, J = 10.1, 5.6 Hz, 1H), 2.36 (t, J = 9.5 Hz, 1H); 13C NMR
(100 MHz, CDCl3) δ 144.3, 137.8, 128.7, 128.5, 128.2, 127.9,
103.0, 75.2, 74.3, 73.6, 73.2, 68.2, 62.9; HRMS Calcd for
C20H23O4 [M + H]+ = 327.1596, found 327.1593.
((2R,3R,4S)-3-(benzyloxy)-2-(benzyloxymethyl)-3,4-dihydro-2H-
pyran-4-yloxy)(tert-butyl)dimethylsilane (21).
Compound 21 was prepared from 19 (300 mg, 0.919 mmol) using
general procedure ‘C’ in 86% yield (378 mg) as a colorless oil; Rf
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
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53
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55
56
57
58
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60
[ ]2D8
= 0.70 (hexane/EtOAc, 8:1);
= 14.1 (c 0.2, CH2Cl2); IR
(neat) max /cm-1: 2967, 1651, 752; 1H NMR (400 MHz, CDCl3) δ
7.35 – 7.25 (m, 11H), 6.34 (dd, J = 6.1, 1.1 Hz, 1H), 4.82 (d, J =
11.3 Hz, 1H), 4.67 – 4.61 (m, 2H), 4.56 (s, 2H), 4.36 – 4.33 (m,
1H), 4.08 – 4.04 (m, 1H), 3.78 (dd, J = 10.8, 5.5 Hz, 1H), 3.68
(ddd, J = 14.4, 9.6, 4.3 Hz, 2H), 0.90 (s, 9H), 0.08 (d, J = 4.8 Hz,
6H); 13C NMR (100 MHz, CDCl3) δ 143.5, 138.1, 128.54, 128.51,
128.0, 127.9, 127.7, 103.6, 74.1, 73.6, 69.1, 68.8, 25.9, 18.1, 0.1, -
4.2, -4.5; HRMS Calcd for C26H37O4Si [M + H]+ = 441.2461,
found 441.2459.
(2R,3R,4S)-3,4-bis(benzyloxy)-2-(benzyloxymethyl)-3,4-dihydro-
2H-pyran (17).
Compound 17 was prepared from 16 (300 mg, 0.919 mmol) using
general procedure ‘C’ in 83% yield (318 mg) as a colorless oil; Rf
[ ]2D8
= 0.70 (hexane/EtOAc, 8:2);
= 62.4 (c 0.7, CH2Cl2); IR
(neat) max /cm-1: 2963, 1656, 735; 1H NMR (400 MHz, CDCl3) δ
7.37 – 7.22 (m, 15H), 6.36 (dd, J = 6.2, 1.4 Hz, 1H), 4.89 – 4.83
(m, 2H), 4.67 – 4.59 (m, 3H), 4.45 (dd, J = 32.4, 11.9 Hz, 2H),
4.17 (dd, J = 3.6, 2.5 Hz, 2H), 3.95 – 3.92 (m, 1H), 3.78 (dd, J =
10.1, 7.2 Hz, 1H), 3.64 (dd, J = 10.1, 5.2 Hz, 1H); 13C NMR (100
MHz, CDCl3) δ 144.2, 138.5, 138.4, 138.0, 128.48, 128.42, 128.2,
128.0, 127.7, 127.6, 127.5, 100.0, 75.7, 73.5, 73.4, 71.3, 70.9,
70.8, 68.5; HRMS Calcd for C27H28NaO4 [M + Na]+ = 439.1885,
found 439.1881.
(2R,3S)-3-(benzyloxy)-2,5-bis(benzyloxymethyl)-2H-pyran-
4(3H)-one (23).
To a well stirred solution of 22 (200 mg, 0.372 mmol) in CH2Cl2
(7 mL) was added PhI(OCOCF3)2 (353 mg, 0.819 mmol),
TEMPO (12 mg, 0.074 mmol) and water (7 L, 0.372 mmol). The
resulting reaction mixture was slowly brought to room tempera-
ture and stirred until completion of the reaction (TLC monitor-
ing). The reaction mixture was treated with satd. aq. NaHCO3
solution (5 mL) and extracted with CH2Cl2 (2 x 10 mL). The
combined organic layers were washed with brine (10 mL) and
dried over anhydrous Na2SO4. Evaporation of the solvent fol-
lowed by silica gel column chromatography of the resulting crude
residue provided 23 in 62% (103 mg) and 24 in 20% (33 mg) as a
((2R,3S,4S)-3-(benzyloxy)-2-(benzyloxymethyl)-3,4-dihydro-2H-
pyran-4-yloxy)(tert-butyl)dimethylsilane (18).
Compound 18 was prepared from 16 (300 mg, 0.919 mmol) using
general procedure ‘C’ in 83% yield (365 mg) as a colorless oil; Rf
[ ]2D8
= 0.70 (hexane/EtOAc, 8:1);
= 41.8 (c 0.9, CH2Cl2); IR
(neat) max /cm-1: 2941, 1660, 738; 1H NMR (400 MHz, CDCl3) δ
7.37 – 7.24 (m, 10H), 6.30 (dd, J = 6.2, 1.4 Hz, 1H), 4.90 (d, J =
11.9 Hz, 1H), 4.67 (ddd, J = 6.2, 3.1, 1.1 Hz, 1H), 4.58 (d, J =
11.9 Hz, 1H), 4.44 (q, J = 12.0 Hz, 3H), 4.19 (s, 1H), 3.78 – 3.71
(m, 2H), 3.57 (dd, J = 10.3, 4.7 Hz, 1H), 0.90 (s, 9H), 0.09 (d, J =
2.1 Hz, 6H); 13C NMR (100 MHz, CDCl3) δ 143.3, 138.6, 138.1,
128.5, 128.4, 128.1, 128.0, 127.8, 127.7, 103.3, 75.8, 73.5, 73.2,
68.6, 25.9, 18.2, -4.3, -4.6; HRMS Calcd for C26H37O4Si [M + H]+
= 441.2461, found 441.2459.
[ ]2D8
colorless oil. Data for 23: Rf = 0.50 (hexane/EtOAc, 7:3);
=
69.7 (c 0.18, CH2Cl2); IR (neat) max /cm-1: 2976, 1653, 763; 1H
NMR (500 MHz, CDCl3) δ 7.48 (s, 1H), 7.35 – 7.22 (m, 15H),
4.70 (d, J = 11.9 Hz, 1H), 4.58 – 4.51 (m, 3H), 4.52 – 4.46 (m,
3H), 4.17 (dd, J = 31.2, 11.8 Hz, 2H), 3.90 (dd, J = 10.2, 6.9 Hz,
1H), 3.76 (dd, J = 10.2, 5.5 Hz, 1H), 3.73 (d, J = 2.5 Hz, 1H); 13C
NMR (125 MHz, CDCl3) δ 188.7, 162.1, 138.2, 137.6, 137.1,
128.59, 128.50, 128.3, 128.1, 128.0, 127.88, 127.84, 127.7, 113.7,
80.7, 73.9, 73.7, 72.5, 72.1, 67.6, 63.8; HRMS Calcd for
C28H28NaO5 [M + H]+ = 467.1834, found 467.1831.
(2R,3R,4S)-3-(benzyloxy)-2-(benzyloxymethyl)-3,4-dihydro-2H-
pyran-4-ol (19).
Compound 19 was prepared from 8 (200 mg, 0.616 mmol) using
general procedure ‘B’ in 90% yield (181 mg) as a colorless oil; Rf
ASSOCIATED CONTENT
Supporting Information
[ ]2D8
= 0.30 (hexane/EtOAc, 8:2);
= 56.4 (c 0.6, CH2Cl2); IR
(neat) max /cm-1: 3100, 1661, 917; 1H NMR (400 MHz, CDCl3) δ
7.40 – 7.23 (m, 11H), 6.38 (dd, J = 6.0, 1.4 Hz, 1H), 4.78 (d, J =
11.6 Hz, 1H), 4.74 – 4.68 (m, 1H), 4.68 – 4.64 (m, 1H), 4.62 (d, J
= 1.7 Hz, 1H), 4.57 (dd, J = 12.0, 1.7 Hz, 1H), 4.32 (s, 1H), 3.97
(dd, J = 6.4, 2.7 Hz, 1H), 3.82 – 3.78 (m, 2H), 3.67 (ddd, J = 9.6,
3.1, 1.5 Hz, 1H), 2.02 (d, J = 5.1 Hz, 1H); 13C NMR (100 MHz,
CDCl3) δ 144.5, 138.2, 137.7, 128.5, 128.4, 127.9, 127.8, 127.7,
102.7, 76.7, 73.7, 73.6, 69.0, 68.7; HRMS Calcd for C20H23O4 [M
+ H]+ = 327.1596, found 327.1593.
The Supporting Information is available free of charge on the
ACS Publications website.
AUTHOR INFORMATION
Corresponding Author
*E-mail: vankar@iitk.ac.in.
Notes
The authors declare no competing financial interest.
(2R,3S,4S)-3,4-bis(benzyloxy)-2-(benzyloxymethyl)-3,4-dihydro-
2H-pyran (20).
Compound 20 was prepared from 19 (300 mg, 0.919 mmol) using
general procedure ‘C’ in 83% yield (318 mg) as a colorless oil; Rf
ACKNOWLEDGMENT
We thank the CSIR, New Delhi for senior research fellowship to
AC and to IIT Kanpur for a senior research fellowship to AV.
[ ]2D8
= 0.70 (hexane/EtOAc, 8:2);
= 38.6 (c 0.4, CH2Cl2); IR
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289–290. (c) Kirschning, A. Oxidation of Fully Protected
YDV thanks the DST, New Delhi for the J. C. Bose National Fel-
lowship (JCB/SR/S2/JCB-26/2010).
Glycals by Hypervalent Iodine Reagents. J. Org. Chem.1995,
60, 1228–1232. (d) Kirschning, A.; Hary, U.; Plumeier, C.;
Ries, M.; Rose, L. Simple oxidation of 3-O-silylated glycals:
application in deblocking 3-O-protected glycals. J. Chem. Soc.
Perkin Trans 1. 1999, 519–528. (e) Kirschning, A.; Bechthold,
A.; Rohr, J. Chemical and biochemical aspects of deoxysugars
and deoxysugar oligosaccharides. Top. Curr. Chem. 1997, 188,
1–84.
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7
ACS Paragon Plus Environment