Rhodium-Catalyzed Diastereoselective Cycloaddition Of N-Sulfonyl-1,2,3-Triazole And Glycals

The metal-catalyzed cycloaddition reaction is a hotspot for organometallic catalysis research in recent years.Compared with non-metal catalysis,it can carry out many difficult reactions,and achieve a better yield in some inefficient reactions.Among them,ruthenium catalysts have been widely concerned for their advantages such as high stereoselectivity and high conversion rate.It can catalyze a variety of cycloaddition reactions,and even the synthesis of medium-ring compounds.It provides a convenient way for the synthesis of many natural drugs.Carbohydrates are widely found in nature.Structurally,they are ether polyhydroxy aldehyde ketones or the polymers thereof.Carbohydrate is an indispensable class of molecules in all living organism,and it can be classified into monosaccharide(eg,glucose,galactose,etc.),disaccharide(eg,sucrose,maltose),and polysaccharide(eg,starch,glycogen,etc.).Among them,the glycal is a saccharide containing an unsaturated C-C bond,and it contains two types of intra-ring double bonds and extra-ring double bonds.The glycal containing a double bond in the ring is mainly composed of an unsaturated carbon-carbon double bond at the 1,2 position of the sugar.It is an important intermediate for the synthesis of sugar derivatives.Due to the presence of the C-C double bonds,it can undergo addition,substitution,oxidation and other reactions to synthesize various glycosides.However,the suger which have different protective groups are not suitable in same reaction conditions.N-Sulfonyl-1,2,3-triazole is an important class of heterocyclic compounds which are structurally stable and easy to store.In medicine,it has been wildly studied regarding its bioactivities such as anti-tumor,anti-viral.Meanwhile,in organic synthesis,it is an important class of 1,3-dipole precursors which can be denitrified by metal(such as,rhodium),and participate in the addition reaction.So,it provides a fast and efficient way to synthesis azo-heterocyclic compounds.Herein,we developed a rhodium-catalyzed olefinic sugar and N-Sulfonyl-1,2,3-triazole,which pyrano-dihydropyrrole were synthesized via denitrification and [2+3] cycloaddition.Instead of using chiral ligands,we used the chirality of the substrate itself to controlle the stereoselectivity of products which obtained specific configuration.Then different temperatures,solvents,and catalysts were used,we got the optimal condition.Farther more,we investigated the tolerance of different sugar protective groups to the reaction and the range of substrate adaptation under the optimal condition.And,a possible mechanism of the reaction was proposed.