(720d) Regio- and Stereo- Selective Synthesis of Hexane-Tetrols and -Triols from Methyl Glycosides over Supported Metal Catalysts

Authors: 
Krishna, S. H., University of Wisconsin-Madison
Dumesic, J. A., University of Wisconsin-Madison
Huber, G. W., University of Wisconsin-Madison
Cao, J., Tohoku University
Tamura, M., Tohoku University
Nakagawa, Y., Tohoku University
Jacobson, G. S., University of Wisconsin, Madison
Tomishige, K., University of Tsukuba
De bruyn, M., Utrecht University
Weckhuysen, B. M., Utrecht University
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Siddarth Krishna Siddarth Krishna 2 30 2019-04-08T20:12:00Z 2019-04-08T20:12:00Z 2 323 1846 15 4 2165 15.00

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Partially
reduced C6 polyols are potentially valuable precursors to polymers,
surfactants, and solvents [1]. Sugars are a renewable feedstock for the
production of C6 polyols, but typical catalytic hydrogenolysis
processes are unselective towards C-OH bond cleavage at different positions and
do not preserve the sugar’s stereocenters. In mso-themecolor:text1">contrast, Tomishige and co-workers recently reported on
the selective cleavage of cis-vicinal OH groups of a variety of methyl
glycosides over a ReOx-Pd/CeO2 catalyst [2]. This
reaction step produces dideoxy sugars in which the chirality of the remaining
C-OH groups is preserved.

Here, we demonstrate the regio- and stereo-
selective synthesis of hexane-tetrols and hexane-triols from methyl glycosides over
supported metal catalysts 107%;font-family:" times new roman>(Scheme 1). First, the above method
is used to synthesize dideoxy sugars from sugar feedstocks. Next, these intermediates
are hydrolyzed and hydrogenated to produce hexane-tetrols and hexane-triols. The
reaction mechanism proceeds through initial methoxy bond hydrolysis to form a mixture
of intermediates. Different reaction intermediates are formed depending on the structure of the
feedstock. Hydrogenation of these intermediates over Pt/SiO2 produces
the final hexane-tetrols and -triols. 2,3-Dideoxy substrates are more reactive
than 3,4-dideoxy substrates due to the electron withdrawing nature of the C2-OH
group. 3,4-Dideoxy substrates also undergo aldose-ketose isomerization
at higher temperatures which decreases the stereoselectivity due to scrambling
of the C2-OH stereocenter. Stereoselectivity can be increased by introducing
an acid catalyst to facilitate hydrolysis at lower temperature.

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Scheme
1.
12.0pt;line-height:107%;font-family:" times new roman> Reaction network
for synthesis of hexane-tetrols
and –triols from methyl glycosides with cis-vicinal OH groups.

This
work demonstrates a novel catalytic route to produce valuable chemical
precursors from sugars, and provides insight into controlling stereoselectivity
in biomass conversion reactions.

107%;font-family:" times new roman>References.

normal;mso-layout-grid-align:none;text-autospace:none"> 12.0pt;font-family:" times new roman>1. Corma, A, et al. Chem. Rev. 2007,
107 (6), 2411-2502.

normal;mso-layout-grid-align:none;text-autospace:none"> 12.0pt;font-family:" times new roman>2. Tamura, M., et al.  Angew.
Chem. Int. Ed,
2018, 57 (27), 8058-8062.

normal;mso-layout-grid-align:none;text-autospace:none"> 12.0pt;font-family:" times new roman>