Iridium Catalyzes Highly Selective Synthesis Of Aryl Cycloalkanes And 1,5-dihydroxy-2-ketone

Transfer hydrogenation catalyzed by transition metal is a hot topic in organic chemistry.In recent years,Several groups are committed to the study of green reduction reaction catalyzed by Iridium,and has achieved the reduction of ketones,aldehydes,C=C double bonds,C=N double bonds and deoxygenation of alcohols.Based on the high efficiency of iridium catalyst reduction,this thesis continued to study the stereoselectivity of iridium catalyzed alcohol deoxidation and the selective reduction of Achmatowicz rearrangement products:(1)Excellent and unique diastereoselectivity is observed in the iridium-catalyzed deoxygenation of tertiary cyclohexanols and cyclopentanols.Aryl cycloalkanes with favorable kinetics but relatively unstable thermodynamics are formed.The selectivity is decided by the steric environment of the carbocation intermediates and the steric hindrance of iridium hydride intermediates,and it is independent of the catalyst loading.The iridium hydride approaches the carbocation in directions perpendicular to the carbocation plane.The sterically large iridium hydride delivers its hydride in the sterically least hindered direction to the carbocation.Our deoxygenation is stereochemically very different from the coupling reactions and can be used to specifically synthesize stereoisomers that are not available via cross-couplings.(2)In the presence of iridium complex as catalyst,reducing agent formic acid can chemical selectively reduce the double bond and hemiacetal structure of Achmtowicz rearrangement(AR)products,while retaining the carbonyl part to obtain 1,5-dihydroxy-2-pentanone homolog,this selectivity is due to the large steric hindrance effect of iridium hydride intermediates,which prevents them from reacting with ketocarbonyl groups.The method can be completed in water,and allows a green and efficient entry to 1,2,5-trifunctionalized long carbon chains.