Transition Metal-Catalyzed One-Pot Reactions For The Synthesis Of Polysubstituted Furans And Oxazoles And Synthesis Of L-lyxose From L-arabinose

Oxazoles are a variety of natural products which have lots of biological activities. Naturally occurring oxazoles were considered rare until the late 1980s when a number of unprecedented natural products were isolated,which are mainly from marine organisms.These oxazoles arederived from enzymatic post-translational modifications of peptide based precursors.Due to their fascinating structures and interest in their biological activities,oxazole-containing natural products have attracted the attention of many research groups who pursue their total syntheses.Furans are a structural component of a vast number of biologically active natural and unnatural compounds.Synthesis of them has been the objective of research for over a century,and a variety of well-established classical methods are now available in the literature.Transition-metal-catalyzed reactions are so popular that transition-metal-catalyzed tandem reactions have emerged as a useful tool for the synthesis of heterocyclic compounds because of the intriguing selectivity,atom economy,and exceptional ability to activateÏ€systems,especially alkynes,towards intermolecular and intramolecular nucleo-philic attack.Among a variety of new synthetic transformations,transition metal catalyzed reactions are the most attractive methodologies,But in the past methods,the preparation of furans needs advanced starting material,and needs noble metal as catalyst,for example,several transition metal compounds such as Ruthenium,Gold, Rhenium,have been developed to catalyze these reactions.However,they are not environmentally friendly,and such specific and high cost of the catalysts make a barrier,so it couldn't apply in large scale.Therefore,development of ageneral, efficient,cheap,and commercially available catalyst for synthesis of heterocyclic compounds which is also developed from imple readily available starting materials remains an important objective. Herein,we describe an efficient transition-metal-catalyzed tandem reaction for the synthesis of heterocycles such as furans and oxazales.The success of the method depended on the use of Cu(OTf)₂ and AgOTf as catalyst only.Our reaction compares favorably with the reported method in terms of both the product yields and operational simplicity.Our method uses only a catalytic amount of catalyst, requiring no stop during the middle of the reaction.Here one pot synthesis of furans and oxazales has come true really.L-Lyxose,believed to be a rare sugar in nature,is very expensive due to its scarcity and it can be obtained only by chemical synthetic methods.For example from L-galactonic acid by the Ruff degradation periodate oxidation of D-galactol and deprotection.However,these methods are too elaborate and laborious,so they are not suitable for mass production of this rare sugar.Here,we describe a simple method for the production of L-lyxose from the cheaper L-arabinose in six steps.