RESUMO
α-C-arylglycosides can be obtained through the addition of aryl zinc reagents to sugar epoxides. The required aryl zinc nucleophiles can be easily obtained from the corresponding boronic acids by B-Zn exchange and attack sugar 1,2 epoxides in a highly diastereoselective fashion to generate 1,2-cis-α-hexapyranosyl aryl glycosides under ligand- and base-free conditions.
Assuntos
Ácidos Borônicos/química , Glicosídeos/síntese química , Zinco/química , Catálise , Glicosídeos/química , Estrutura Molecular , Estereoisomerismo , Relação Estrutura-AtividadeRESUMO
A palladium-catalyzed regio- and diastereoselective diarylation of glycals and pseudoglycals, which is a kind of Heck-Suzuki arylation, is described. A wide range of arylboronic acids reacted under these conditions smoothly. Selectivity was C1-C2(α,α) in the case of glycals but C2-C3(ß,ß) for pseudoglycals. Quantum chemical analysis has been carried out to establish the reaction mechanism, which may involve Pd(II)/Pd(O). TEMPO plays a key role in the formation of diaryl glycoside due to its radical nature.
Assuntos
Óxidos N-Cíclicos/química , Glicosídeos/química , Paládio/química , Catálise , Estrutura Molecular , EstereoisomerismoRESUMO
Zinc mediated alkynylation reaction was studied for the preparation of C-glycosides from unactivated alkynes. Different glycosyl donors such as glycals and anomeric acetates were tested towards an alkynyl zinc reagent obtained from alkynes using zinc dust and ethyl bromoacetate as an additive. The method provides simple, mild and stereoselective access to alkynyl glycosides both from aromatic and aliphatic acetylenes.
Assuntos
Alcinos/química , Glicosídeos/síntese química , Zinco/química , Glicosídeos/química , Conformação Molecular , EstereoisomerismoRESUMO
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.
Assuntos
Acetileno/análogos & derivados , Glicosídeos/química , Compostos de Vinila/química , Acetileno/química , Alcinos/química , Carbono/química , Catálise , Glicosídeos/síntese química , Glicosilação , Halogenação , Ácidos de Lewis/química , Paládio/química , EstereoisomerismoRESUMO
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.
