An efficient method for the synthesis of pyranoid glycals

Article abstract of DOI:10.1016/j.carres.2016.05.013

A simple and efficient procedure was designed for the preparation of pyranoid glycals. In a novel fashion, a series of protected glycopyranosyl bromides underwent reductive elimination in the presence of zinc dust and ammonium chloride in CH₃CN at 30-60 °C. The corresponding glycals were obtained with excellent isolated yields (72-96%) in a short time (20-50 min). Furthermore, the transformation was compatible with different protection patterns and conveniently scalable (86% for 45 g acetobromoglucose) which made it very applicable in organic synthesis.

Full text of DOI:10.1016/j.carres.2016.05.013

Accepted Manuscript
An efficient method for the synthesis of pyranoid glycals
Heshan Chen, Ting Xian, Wan Zhang, Wenshuai Si, Xiaosheng Luo, Bo Zhang,
Meiyu Zhang, Zhongfu Wang, Jianbo Zhang
PII:
S0008-6215(16)30183-5
10.1016/j.carres.2016.05.013
CAR 7207
DOI:
Reference:
To appear in: Carbohydrate Research
Received Date: 20 April 2016
Revised Date: 27 May 2016
Accepted Date: 29 May 2016
Please cite this article as: H. Chen, T. Xian, W. Zhang, W. Si, X. Luo, B. Zhang, M. Zhang, Z. Wang, J.
Zhang, An efficient method for the synthesis of pyranoid glycals, Carbohydrate Research (2016), doi:
10.1016/j.carres.2016.05.013.
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Graphic Abstract
An efficient method for the synthesis of pyranoid glycals

ACCEPTED MANUSCRIPT
An efficient method for the synthesis of pyranoid glycals
Heshan Chena, Ting Xiana, Wan Zhanga, Wenshuai Sia, Xiaosheng Luoa,
Bo Zhanga, Meiyu Zhanga, Zhongfu Wangb, Jianbo Zhanga*
a Department of Chemistry, East China Normal University, Shanghai 200241, China;
b School of Life Sciences, Northwestern University, Xi’an 710069, China
E-mail: jbzhang@chem.ecnu.edu.cn
Abstract: A simple and efficient procedure was designed for the preparation of pyranoid glycals.
In a novel fashion, a series of protected glycopyranosyl bromides underwent reductive elimination
in the presence of zinc dust and ammonium chloride in CH3CN at 30-60oC. The corresponding
glycals were obtained with excellent isolated yields (72-96%) in a short time (20-50min).
Furthermore, the transformation was compatible with different protection patterns and
conveniently scalable (86% for 45g acetobromoglucose) which made it very applicable in organic
synthesis.
Key words: Glycals, Glycopyranosyl bromides, Zinc, Ammonium chloride, Acetonitrile
As versatile and useful intermediates, glycals are widely used in organic synthesis of
O-glycosides,1-3 C-glycosides,4-8 S-glycosides,9 N-glycosides,10-13 and even natural
products.14-17 They have also been used in the synthesis of iminosugars,18
sugar-heterocycle hybrid molecules,19 bioactive molecules,20, 21 and other sugar based
building blocks.22 Besides, the unsaturated part of the glycals allows many
straightforward modifications in the sugar rings such as rearrangement, epoxidation,
addition and substitution. For example, 2,3-unsaturated glycosides and
1,2-anhydroglycosides can be prepared from glycals conveniently.23-26 In addition,
glycals are often used as starting materials for the synthesis of 2-deoxy glycosides and
2-C-branched sugars.27-29 A traditional method for preparing glycals is the

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Fischer-Zach method, which uses zinc dust in acetic acid for reductive elimination of
acylated glycosyl bromides.30 Over the recent years, many synthetic methods for
glycals have been developed, including the reduction of protected glycosyl halides by
(Cp2TiCl)2,31 Cr(II),32 Al-Hg,33 Zn-PEG/600-H2O,34 Zn-NaH2PO4,35 Zn-β-CD-H2O,36
Zinc-nanoparticles37 or using thiophenyl glycosides, glycosyl sulfones and
electrochemical approach.38, 39 However, the above methods often suffer from some
disadvantages like low yields, long reaction times, stringent conditions and using of
expensive and toxic reagents. Thus, it is still interesting for the glycochemists to
develop a simple, efficient and economical reaction protocol for glycal preparation.
In our previous research, Zn–NH4Cl–CH3CN had been successfully applied in the
deprotection of the 2,2,2-trichloroethyl group at the anomeric oxygen of
carbohydrates, where most protective groups including ethers, esters, silyl ethers, and
ketals remained intact.40 Therefore, we tried to synthesize the glycals through the
reductive elimination of protected glucopyranosyl bromides. As we predicted, when
tetra-O-acetyl-D-glucopyranosyl bromide was treated with Zn dust and NH4Cl in
CH3CN (at reflux), tri-O-acetyl-
D
-glucal was obtained as the sole product. Inspired by
this preliminary result, we established optimal conditions with following steps. First,
several solvents were tested; and we found the conversion proceeded much better in
acetonitrile than other solvents (Table 1, entries 1-5). Subsequently, the reaction of 1
was carried out in the presence of different amounts of Zn/NH4Cl in CH3CN at
different temperature. After many trials, we were able to get the tri-O-acetyl- -glucal
D
with the highest yield (96%) in a short time (20min) using 7.5 equivalent of
Zn/NH4Cl (1:1) at 60oC (Table 1, entry 8). When smaller amount of Zn/NH4Cl was
used, the reaction required substantially longer time and the yield was decreased
(Table 1, entries 5-6). In addition, the reaction did not occur at all without the NH4Cl
(Table 1, entry 12), which indicated that NH4Cl is indispensable to this reaction.
To examine whether or not this method has generality, reactions involving 15
examples (Entries 1–15 in Table 2) were performed on a preparative scale. As show
in table 2, treatment of the acetobromosugars 1 and 3-7 with Zn/NH4Cl in CH3CN,

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affording the glycals 2 and 17-20 in good to excellent yields. As the glycopyranosyl
bromides 5-7 were unstable at 60oC, lower temperature was used to carry out the
transformations (Entries 4–6 in Table 2). Meanwhile, the benzoyl-protected glycals
21-23, were also obtained in excellent yields. Starting materials carrying unstable
protecting groups such as methanesulfonyl, p-tolylsulfonyl and azido groups were
also tolerated under the reaction conditions (Entries 10-12 in Table 2). Importantly,
using this method, disaccharide glycals 27–29 were accessible in very good yields;
while the 1,4-glycosidic bonds were not attacked. The structures of all the synthetic
glycals were elucidated from NMR and mass spectral data, and also by comparison
with the reported data.27-30 In all cases the glycals (2, 17–29) were obtained in
72–96% isolated yields at a short time (20-50min). Notably, the reaction could be
conducted on a large scale (45g acetobromoglucose) with excellent yield (2, 86%).
In the previous synthesis of glycals, various methods have been used for enhancing
the activity of zinc. However, in our procedure, the zinc dust did not need to be
pre-activated and the reaction avoided the acidic conditions, which further simplified
the reaction procedure.
In summary, we have developed an efficient and convenient method for the synthesis
of variously protected glycals using Zn/NH4Cl as an inexpensive system. This method
offers several advantages, such as low toxicity of reagents, simplicity in operation,
high yields and short reaction time. Furthermore, the efficient applicability of this
methodology to gram-scale amount of the starting acetobromoglucose substrates
makes this approach highly practical.
1. Experimental
All reagents were purchased with purity of AR and used as such. All the solvents for
chromatography were distilled before use. Silica gel (10–40 µm, Yantai, China) was
used for column chromatography. TLC plates (10–40 µm, Yantai, China) were
1
13
applied to monitor reactions. H and C NMR spectra were respectively recorded on
500 MHz and 125 MHz with a Bruker DRX 500 spectrometer in CDCl3. Chemical

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shifts are expressed in parts per million (ppm) with TMS as the internal standard. MS
experiments were performed on LTQ-XL (Thermo Scientific, USA) with an
electrospray (ESI) ion source. Glycopyrannosyl bromide was prepared following the
literature.41
2. General procedure for the synthesis of glycals
Under nitrogen, the glycopyranosyl bromide (1.0 mmol) was dissolved in CH3CN,
and then zinc dust (7.5 mmol) and ammonium chloride (7.5 mmol) were added,
followed by stirring at corresponding temperature. Upon completion of the reaction
(monitored by TLC), inorganic salts and excessive zinc dust were removed by
filtration. The filtrate was concentrated in vacuo and the residue was purified by silica
gel flash column chromatography to afford the corresponding glycal in pure form.
3. Product characterization data
3,4,6-Tri-O-acetyl- ;
-glucal (2).34 White solid: mp 49-51 oC 1H NMR(CDCl3): δ(ppm) 6.47 ( d,
D
1H, J = 6.2 Hz), 5.35 (dd, 1H, J = 4.2, 3.7 Hz), 5.22 (dd, 1H, J = 7.5, 6.0 Hz), 4.85 (dd, 1H, J =
9.5, 3.3 Hz), 4.40 (dd, 1H, J = 12.2, 5.8 Hz), 4.26 (m, 1H), 4.20 (dd, 1H, J = 12.4, 3.1 Hz), 2.08 (s,
3H), 2.07 (s, 3H), 2.04 (s, 3H). 13C NMR (125MHz, CDCl3): δ 170.55, 170.36, 169.53, 145.59,
98.95, 73.90, 67.38, 67.12, 61.32, 20.95, 20.75, 20.68. MS (ESI): m/z Calculated for [M+Na]+
C12H16O7Na 295.09, found 295.17.
3,4,6-Tri-O-acetyl-
-galactal (17).34 Colorless syrup. 1H NMR(CDCl3): δ(ppm) 6.47 (dd, 1H, J =
D
4.7, 1.4 Hz), 5.56 (d, 1H, J = 0.8 Hz), 5.43- 5.42 (m, 1H), 4.74-4.73 (m, 1H), 4.34-4.20 (m,3H),
2.13 (s, 3H), 2.08 (s, 3H), 2.03 (s, 3H). 13C NMR (125MHz, CDCl3): δ 170.20, 169.93, 169.82,
145.13, 98.61, 72.52, 63.63, 63.45, 61.65, 20.49, 20.43, 20.34. MS(ESI): m/z Calculated for
[M+Na]+ C12H10O7Na 295.08, found 295.17.
3,4,6-Tri-O-acetyl-L-rhamnal (18).34 Colorless syrup. 1H NMR (CDCl3): δ(ppm) 6.46 ( d, 1H, J
= 6.0 Hz), 5.37 (m, 1H), 5.06 (dd, 1H, J = 8.0, 6.0 Hz), 4.81 (dd, 1H, J = 7.0, 3.0 Hz), 4.12 (m,
1H), 2.12 (s, 3H), 2.08 (s, 3H), 1.34 ( s, 3H). 13C NMR (125 MHz, CDCl3): δ 170.64, 169.90,

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146.01, 98.82, 72.54, 71.86, 68.33, 21.09, 20.91, 16.58. MS(ESI): m/z Calculated for [M+Na]+
C10H14O5Na 237.07, found 237.55.
3,4-Di-O-acetyl-
-arabinal (19).35 Colorless syrup. 1H NMR (500 MHz, CDCl3) δ 6.52 (d, 1H, J
D
= 6.0 Hz), 5.46 (t, 1H, J = 4.3 Hz), 5.23 – 5.17 (m, 1H), 4.89 – 4.84 (m, 1H), 4.07 – 3.97 (m, 2H),
2.09 (s, 3H), 2.08 (s, 3H). 13C NMR (125 MHz, CDCl3): δ 170.24, 169.64, 147.68, 97.41, 65.83,
62.73 (2C), 20.88, 20.61. HRMS (ESI): m/z Calculated for [M+Na]+ C9H12O5Na 223.0577, found
223.0497.
1
3,4-Di-O-acetyl-
D
-xylal (20).35 Colorless syrup. H NMR (CDCl3): δ(ppm) 6.60 (d, 1H, J = 6.0
Hz), 5.00 (m, 1H), 4.95-4.97 (m, 2H), 4.20 (m, 1H), 3.98 (dd, 1H, J = 12.5, 1.5 Hz), 2.10 (s, 3H),
2.07 (s, 3H). 13C NMR (125 MHz, CDCl3): δ 170.04, 169.93, 148.15, 97.52, 67.31, 63.74, 63.52,
21.24, 21.06. MS (ESI): m/z Calculated for [M+Na]+ C9H12O5Na 223.06, found 223.45.
1
3,4,6-Tri-O-benzoyl-
-glucal (21).34 Colorless syrup. H NMR (CDCl3): δ(ppm) 7.99-8.05 (m,
D
6H), 7.51-7.57 (m, 3H), 7.38-7.44 (m, 6H), 6.61 (d, 1H, J = 6.0 Hz), 5.80 (dd, 1H, J =6.0, 5.5 Hz),
5.71 (dd, 1H, J = 4.1, 4.0 Hz), 5.11 (dd, 1H, J = 6.0, 3.5 Hz), 4.68-4.69 (m, 3H). 13C NMR (125
MHz, CDCl3): δ 166.11, 165.79, 165.13, 145.97, 133.46, 133.22, 133.15, 129.89 (2C), 129.78
(2C), 129.74 (2C), 129.72, 129.70, 129.31, 128.49 (2C), 128.46 (2C), 128.41 (2C), 98.89, 74.02,
68.07, 67.58, 62.20. MS (ESI): m/z Calculated for [M+Na]+ C27H22O7Na 481.13, found 481.17.
3,4,6-Tri-O-benzoyl-
-galatcal (22).34 Colorless syrup. 1H NMR ( CDCl3) δ 8.10 – 7.99 (m, 4H),
D
7.90 (d, 2H, J = 7.3 Hz), 7.54 (m, 3H), 7.42 (t, 4H, J = 7.7 Hz,), 7.33 (t, 2H, J = 7.8 Hz), 6.63 (dd,
1H, J = 6.2, 1.1 Hz), 5.99 – 5.88 (m, 2H), 5.03 – 4.96 (m, 1H), 4.81 (dd, 1H, J = 11.5, 7.7 Hz),
4.75 – 4.67 (m, 1H), 4.58 (dd, 1H, J = 11.6, 4.7 Hz). 13C NMR (126 MHz, CDCl3): δ 166.35,
165.94, 165.68, 145.86, 133.55, 133.35, 133.26, 130.06 (2C), 129.88 (2C), 129.77 (2C), 129.68,
129.64, 129.42, 128.61 (2C), 128.53 (2C), 128.47(2C), 99.26, 73.21, 65.11, 64.78, 62.68. MS
(ESI): m/z Calculated for [M+Na]+ C27H22O7Na 481.13, found 481.17.
3,4-Di-O-benzoyl-
-xylal (23).36 White solid: mp 111-113oC; 1H NMR (500 MHz, CDCl3) δ 8.06
D
(d, 4H, J = 7.9 Hz), 7.58 (td, 2H J = 7.3, 1.2 Hz), 7.45 (t, 4H, J = 7.7 Hz), 6.72 (d, 1H , J = 6.2
Hz), 5.40 (dd, 2H, J = 14.7, 2.0 Hz), 5.21 – 5.11 (m, 1H), 4.42 (ddd, 1H, J = 12.2, 3.0, 1.7 Hz),
4.23 (dd, 1H, J = 12.2, 1.4 Hz). 13C NMR (125 MHz, CDCl3): δ 165.39, 165.37, 148.30, 133.34,

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133.16, 129.96, 129.87 (2C), 129.68 (2C), 129.58, 128.42 (2C), 128.40 (2C), 97.53, 67.71, 64.17,
63.93. MS (ESI): m/z Calculated for [M+Na]+ C19H16O5Na 481.09, found 347.17.
3,4-Tri-O-acetyl-6-O-tosyl-
-glucal (24).36 Colorless syrup. 1H NMR (500 MHz, CDCl3) δ 7.78
D
(d, 2H , J = 8.3 Hz), 7.35 (d, 2H , J = 8.0 Hz), 6.34 (dd, 1H, J = 6.1, 0.7 Hz), 5.26 (t, 1H , J = 4.0
Hz), 5.15 – 5.09 (m, 1H), 4.81 (dd, 1H , J = 6.1, 3.5 Hz), 4.28 – 4.16 (m, 3H), 2.44 (s, 3H), 2.03
(s, 3H), 2.02 (s, 3H). 13C NMR (125 MHz, CDCl3): δ 170.06, 169.27, 145.27, 145.06, 132.76,
129.84 (2C), 127.98 (2C), 98.96, 73.28, 67.08, 66.66, 66.50, 21.52, 20.79, 20.57. HRMS (ESI):
m/z Calculated for [M+Na]+ C17H20O8NaS 407.0771, found 407.0803.
3,4-Tri-O-acetyl-6-O-mesyl-
-glucal (25).34 Colorless syrup. 1H NMR (500 MHz, CDCl3) δ 6.47
D
(dd, 1H, J = 6.1, 1.1 Hz), 5.36 – 5.30 (m, 1H), 5.20 (dd, 1H, J = 7.3, 5.6 Hz), 4.88 (dd, 1H , J =
6.2, 3.4 Hz), 4.47 (dd, 1H , J = 11.6, 6.2 Hz), 4.38 – 4.29 (m, 2H), 3.07 (s, 3H), 2.10 (s, 3H), 2.05
(s, 3H). 13C NMR (125 MHz, CDCl3): δ 170.41, 169.70, 145.42, 99.49, 73.69, 67.07, 66.94, 65.74,
37.94, 21.08, 20.90. HRMS (ESI): m/z Calculated for [M+Na]+ C11H16O8NaS 331.0458, found
331.0481.
3,4-Tri-O-acetyl-6-deoxy-6-azido-
-glucal (26).36 Colorless syrup. 1H NMR (500 MHz, CDCl3)
D
δ 6.50 (dd, 1H, J = 6.2, 1.1 Hz), 5.35 – 5.31 (m, 1H), 5.18 (dd, 1H, J = 7.2, 5.4 Hz), 4.88 (dd, 1H,
J = 6.2, 3.4 Hz), 4.22 (td, 1H, J = 7.1, 3.8 Hz), 3.57 (dd, 1H, J = 13.3, 7.0 Hz), 3.44 (dd, 1H, J =
13.3, 3.8 Hz), 2.10 (s, 3H), 2.07 (s, 3H). 13C NMR (125 MHz, CDCl3): δ 170.43, 169.69, 145.49,
99.19, 74.93, 68.13, 67.05, 50.23, 21.14, 20.93. (ESI): m/z Calculated for [M+Na]+ C10H13N3O5Na
278.07, found 278.16.
3,6,2′,3′,4′,6′–Hexa-O-acetyl-
-lactal (27).34 Colorless syrup. 1H NMR (500 MHz, CDCl3) δ 6.39
D
(d, 1H, J = 6.1 Hz), 5.41 – 5.36 (m, 1H), 5.34 (d, 1H, J = 3.2 Hz), 5.17 (dd, 1H, J = 10.4, 8.0 Hz),
4.98 (dd, 1H, J = 10.5, 3.4 Hz), 4.82 (dd, 1H, J = 6.0, 3.4 Hz), 4.64 (d, 1H, J = 8.0 Hz), 4.41 (dd,
1H, J = 11.7, 2.4 Hz), 4.20 – 4.03 (m, 4H), 3.98 (dd, 1H, J = 7.3, 5.5 Hz), 3.89 (t, 1H, J = 6.8 Hz),
2.13 (s, 3H), 2.09 (s, 3H), 2.06 (s, 3H), 2.04 (s, 3H), 2.03 (s, 3H). 13C NMR (125 MHz, CDCl3): δ
170.28, 170.26, 170.06, 169.95, 169.81, 169.14, 145.40, 100.99, 98.94, 74.64, 74.20, 70.85, 70.79,
68.99, 68.70, 66.80, 61.84, 60.99, 20.94, 20.68, 20.49 (2C), 20.47, 20.39. MS (ESI):m/z
Calculated for [M+Na]+ C24H32O15Na 583.16, found 583.36.

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1
3,6,2′,3′,4′,6′–Hexa-O-acetyl-
D
-maltal (28). 37 Colorless syrup. H NMR (500 MHz, CDCl3) δ
6.43 (d, 1H, J = 6.1 Hz,), 5.50 (d, 1H, J = 3.9 Hz), 5.40 (t, 1H, J = 9.9 Hz), 5.17 (t, 1H, J = 3.9
Hz), 5.05 (t, 1H, J = 9.9 Hz), 4.86 – 4.78 (m, 2H), 4.36 (qd, 2H, J = 12.0, 4.7 Hz), 4.29 (dd, 1H, J
= 10.0, 5.9 Hz), 4.23 (dd, 1H, J = 12.4, 4.1 Hz), 4.09 (dd, 1H, J = 12.4, 1.9 Hz), 4.06 – 3.99 (m,
2H), 2.12 (s, 3H), 2.10 (s, 3H), 2.05 (s, 3H), 2.04 (s, 3H), 2.03 (s, 3H), 2.01 (s, 3H). 13C NMR
(125 MHz, CDCl3): δ 170.27, 170.18, 170.11, 170.09, 169.73, 169.31, 145.48, 98.50, 95.75, 74.07,
72.54, 70.38, 69.59, 69.21, 68.29, 68.26, 61.81, 61.67, 20.84, 20.53, 20.42, 20.40, 20.35, 20.30.
(ESI):m/z Calculated for [M+Na]+ C24H32O15Na 583.16, found 583.25.
37
1
3,6,2′,3′,4′,6′–Hexa-O-acetyl-D-cellobial (29).
White solid: mp 139-141oC; H NMR (500
MHz, CDCl3) δ 6.40 (d, 1H, J = 6.1 Hz), 5.45 – 5.38 (m, 1H), 5.18 (t, 1H, J = 9.5 Hz), 5.07 (t, 1H
, J = 9.7 Hz), 5.01 – 4.91 (m, 1H), 4.81 (dd, 1H, J = 6.0, 3.3 Hz), 4.68 (d, 1H, J = 8.0 Hz), 4.44
(dd, 1H, J = 11.7, 2.3 Hz), 4.30 (dd, 1H, J = 12.4, 4.5 Hz), 4.25 – 4.10 (m, 2H), 4.06 (dd, 1H, J =
12.3, 2.0 Hz), 3.97 (dd, 1H, J = 7.4, 5.8 Hz), 3.73 – 3.62 (m, 1H), 2.11 (s, 3H), 2.08 (s, 3H), 2.04
(s, 3H ), 2.03 (s, 3H ), 2.01 (s, 3H), 1.99 (s, 3H). 13C NMR (125 MHz, CDCl3): δ 170.50, 170.28,
170.13, 169.82, 169.20, 169.07, 145.40, 100.52, 99.03, 74.66, 74.38, 72.81, 72.08, 71.50, 68.48,
68.25, 61.87, 61.80, 20.89, 20.70, 20.55, 20.45 (3C). (ESI): m/z Calculated for [M+Na]+
C24H32O15Na 583.16, found 583.25.
Acknowledgments
This project was financially supported by Natural Science Foundation of Shanghai
(11ZR1410400), “DAXIA” Foundation of East China Normal University (No. 2011DX-288) and
large instruments Open Foundation of East China Normal University (2014-03&20151043)
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ACCEPTED MANUSCRIPT
Table 1 Optimization of the synthesis of 3,4,6-tri-O-acetyl-D-glucal from the tetra-O-acetyl-α- -
D
glucopyranosyl bromide
Entry
Promoter(Zn/NH4Cl)
Solvent
Temperature
Time
(min)
240
60
Yield a(%)
(equiv)
6/6
(oC)
1
2
3
4
5
DCM
Toluene
THF
40
NRb
80
6/6
80
6/6
80
50
78
6/6
CH3OH
CH3CN
60
30
75
6/6
80
20
90
6
7
4/4
80
80
60
40
60
60
60
90
20
70
94
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
7.5/7.5
7.5/7.5
7.5/7.5
7.5/5
8
20
96
9
90
85
10
11
12
30
82
7.5/3
90
51
7.5/0
240
NRb
a Isolated yields
b NR, no reaction

ACCEPTED MANUSCRIPT
Table 2 Synthesis of substituted glycals from pyranosyl bromides
Entry
Reactant
Product
Time(min)
20
Yield(%)
96 (86)a
1
2
2
1
3
2
25
85
3
4
35
45
84
17
18
4
5
81b
5
25
85c
19
20
6
6
7
30
45
87d
82
7
21
22
8
9
8
9
45
20
87
84
23
10

ACCEPTED MANUSCRIPT
10
11
30
35
82
90
11
12
13
24
25
12
13
35
40
72
83
26
27
14
14
15
50
80
82
28
29
15
16
50
aYield for a gram-scale reaction;
Reaction temperature: b 50 ; c 40 ; d 30 , the others were 60
.

ACCEPTED MANUSCRIPT
Highlights
ꢀ Synthesis of pyranoid glycals using Zn/NH4Cl system.
ꢀ High yields and short reaction time.
ꢀ Simple operation and broad functional group compatibility.
ꢀ Efficient synthesis of glucal in gram-scale amount.