One-pot Mukaiyama type carbon-Ferrier rearrangement of glycals: Application in the synthesis of chromanone 3-C-glycosides.

One-pot carbon-Ferrier rearrangement of glycals with unactivated aryl methyl ketones has been developed under mild Silyl triflate catalysis. Keto methyl group of various aryl methyl ketones without being converted into silyl enol ether could directly attack anomeric position of glycals to form keto functionalized C-glycosides in moderate to good yields with high α-selectivity. The versatility of this method has been extended to the synthesis of a small library of chromanone 3-C-glycosides.

Tandem regio- and diastereo-selective synthesis of halogenated C-vinyl glycosides from unactivated arylacetylenes.

A highly regio- and diastereo-selective synthesis of halogenated C-vinyl glycosides has been achieved from glycals and unactivated aryl acetylenes in the presence of halogenated Lewis acids via a tandem glycosylation-halogenation reaction. The Lewis acid used served the dual purpose of activating the allylic acetoxy group of glycals and serving as halogen source for Markovnikov addition across the triple bond, which makes the process atom economic. The synthesized glycosyl vinyl halides have been used as precursors for various Pd catalyzed C-C cross coupling reactions.

Cyanuric chloride/sodium borohydride: a new reagent combination for reductive opening of 4,6-benzylidene acetals of carbohydrates to primary alcohols.

In the first such example, NaBH4 in combination with cyanuric chloride (TCT) has been used to obtain 6-hydroxy-4-benzyl ether derivatives from 4,6-benzylidene acetals of carbohydrates. The nature of hydride donor determines the regioselectivity of acetal opening. High regioselectivity, scope for using a broad range of substrates, functional group tolerance, mild reaction conditions, easy handling process, inexpensive reagents and wide application mark the benefits of the newly developed reagent system.

Copper mediated stereoselective synthesis of C-glycosides from unactivated alkynes.

A highly stereoselective rapid C-glycosylation reaction has been developed between glycal and unactivated alkynes in the presence of coppertriflate and ascorbic acid at low catalyst loading and at room temperature. A wide variety of glycals and aryl acetylenes participate in the reaction smoothly. TfOH generated during the reduction of Cu(OTf)2 by ascorbic acid may be the active catalyst for the glycosylation.

2,4,6-Trichloro-1,3,5-triazine (TCT) mediated one-pot sequential functionalisation of glycosides for the generation of orthogonally protected monosaccharide building blocks.

Orthogonally protected monosaccharide building blocks have been prepared using TCT in a one-pot multicomponent transformation. The process involves successive steps of arylidene acetalation, esterification and regioselective reductive acetal cleavage. High regioselectivity, scope for using a broad range of substrates, functional group tolerance, mild reaction conditions, easy handling process and wide application range are a few advantages of the current process.