Ferrier–Nicholas pyranosidic cations: application to diversity-oriented synthesis

Abstract

Pyranosidic allylic (Ferrier) cations that share dicobalt hexacarbonyl propargyl (Nicholas) stabilization at C-1, can be easily generated by treatment of hexacarbonyldicobalt alkynyl glycals with BF 3 ·OEt 2 , and display a remarkable reactivity leading to a variety of products. The substituent at O-6 in these glycals plays a pivotal role in directing the outcome of the transformations. Accordingly, 6-O-benzyl or 6-O-allyl groups cause a series of transformations resulting in the stereoselective formation of oxepanes through a process that involves an initial hydride transfer step from the allyl or benzyl substituent to the Ferrier-Nicholas cation. On the contrary, 6-OH derivatives undergo an overall ring contraction to branched tetrahydrofuran derivatives. 6-O-Silyl derivatives, in the presence of heteroaryl nucleophiles, were transformed into C-3 branched bis-C-Cglycosides, containing two of such molecules.

C-Glycopyranosyl Arenes and Hetarenes: Synthetic Methods and Bioactivity Focused on Antidiabetic Potential

“…In the following step, the bis-C,C-glycosyl derivatives 754 were obtained by the regio-and stereoselective addition of pyrrole in the presence of BF 3 • OEt 2 . 413,414 A 1-C-methyl glycal 755, upon oxidation by DMDO to 756 followed by nucleophilic substitution with a Grignard reagent, afforded derivatives 757 predominantly displaying an α-oriented phenyl group on the C-1 center (Scheme 88). Similar reactions were highly dependent on the nucleophile and the 3-Oprotecting group, and variable stereoselectivities were observed.…”

“…First the C -3 benzyloxy group was substituted with different C -nucleophiles to give glycals 753 in good yields and high stereocontrol. In the following step, the bis- C , C -glycosyl derivatives 754 were obtained by the regio- and stereoselective addition of pyrrole in the presence of BF 3 ·OEt 2 . , …”