Molecules 2011, 16(12), 10303-10313; https://doi.org/10.3390/molecules161210303
Ring Cleavage Reactions of Methyl α-D-Allopyranoside Derivatives with Phenylboron Dichloride and Triethylsilane
Niigata University of Pharmacy and Applied Life Sciences, 265-1 Higashijima, Akiha-ku, Niigata 956-8603, Japan
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Received: 31 October 2011 / Revised: 25 November 2011 / Accepted: 5 December 2011 / Published: 13 December 2011
(This article belongs to the Special Issue Stereoselective Synthesis)
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Abstract
In the course of our studies on the regioselective carbon-oxygen bond cleavage of the benzylidene acetal group of hexopyranosides with a reducing agent, we found that a combination of a Lewis acid and a reducing agent triggered a ring-opening reaction of the pyranose ring of methyl α-D-allopyranosides. The formation of an acyclic boronate ester by the attachment of a hydride ion at C-1 indicated that the unexpected endocyclic cleavage of the bond between the anomeric carbon atom and the pyranose ring oxygen atom proceeded via an oxacarbenium ion intermediate produced by the chelation between O5/O6 of the pyranoside and the Lewis acid, followed by nucleophile substitution with a hydride ion at C1.
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Kojima, M.; Nakamura, Y.; Ito, Y.; Takeuchi, S. Ring Cleavage Reactions of Methyl α-D-Allopyranoside Derivatives with Phenylboron Dichloride and Triethylsilane. Molecules 2011, 16, 10303-10313.
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