Applications Of Hypervalent Iodine Reagents In Organic Synthesis

Over the past two decades,hypervalent iodine reagents have received much attention due to their low toxicity,ready availability,easy handling,and reactivities similar to those of heavy metal reagents. Recently,iodine（Ⅲ） and iodine（Ⅴ） derivatives are routinely used in organic synthesis as reagents for various selective oxidative transformations of complex organic molecules.Several areas of hypervalent organoiodine chemistry have recently attracted especially research activity.Based on the literature,the oxidation of alcohols,the a-acetoxylation of ketones and the aromatization of hantzsch-1,4-dihydropyridines have been developed by PhIO₂,NaIO₄ and Me₄NI as iodine reagents.1.Studies on the catalytic oxidation of alcohols using hypervalent iodine reagentThe catalytic oxidation of alcohols to the corresponding aldehydes and ketones have been received great attention,since this important functional group transformations were applied widely both in fundamental synthesis research and industrial manufacturing.Recently,hypervalent iodine reagents,such as o-iodoxybenzoic acid（IBX） and the Dess-Martin periodinane（DMP）,have been successfully used for oxidation of alcohols to the corresponding carbonyl compounds,while only limited reports dealt with use of iodoxybenzene as the oxidant.In this part,we successfully accomplished an efficient catalytic alcohol oxidation by Oxone/CTAB/PhIO₂.The yields of aldehydes and ketones were 27%to 98%.2.Studies on the a-acetoxylation of ketones using hypervalent iodinea-acetoxyketones are known as very useful intermediates for the synthesis of heterocyclic compounds. Previous methods for the preparation of a-acetoxy ketones include the acetolysis of both a-diazo ketones and a-bromo ketones.We used iodoxybenzene as oxidant and BF₃·OEt₂ as catalyst,and developed a facile method for the a-acetoxylation of ketones.The yields of a-acetoxyketones were 27%to 98%.In succession,hypervalent iodine reagents（Ⅶ） such as NaIO₄,KIO₄ and H₅IO₆ have been examined for the a-acetoxylation of ketones.Finally,we found that NaIO₄/PhI/BF₃·OEt₂ is a good system for the a-acetoxylation of ketones.The yields of a-acetoxyketones were 17%to 55%.3.Studies on the aromatization of hantzsch-1,4-dihydropyridines using inorganic iodine saltThe co-enzyme NADH have an important impacts of the redox reaction in biological system.And Hantzsch 1,4-dihydropyridines（DHPs） are a class of model compounds of NADH coenzyme.Recently,a lot of works has been reported for the aromatization of hantzsch 1,4-dihydropyridines.In this chapter,we design a system of H₂O₂/TsOH·H₂O/Me₄NI,which has been used for the aromatization of hantzsch 1,4-dihydropyridines.The yields of Pyridines were 25%to 99%.