Niigata University of Pharmacy and Applied Life Sciences, 265-1 Higashijima, Akiha-ku, Niigata 956-8603, Japan.
Molecules. 2011 Dec 13;16(12):10303-13. doi: 10.3390/molecules161210303.
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.
在我们研究用还原剂选择性地断裂六吡喃糖的亚苄基缩醛基团的碳-氧键的过程中，我们发现路易斯酸和还原剂的组合引发了甲基α-D-吡喃葡萄糖苷的吡喃糖环的开环反应。通过在 C-1 上附加氢原子形成无环硼酸酯表明，通过吡喃糖苷的 O5/O6 与路易斯酸的螯合产生的氧杂卡宾离子中间体，导致了与吡喃糖环氧原子的键的非环内断裂，随后是与 C1 上的氢原子的亲核取代反应。
