Indeno[1,2?d]pyridazine derivatives have wide applications in pesticides,pharmaceuticals,and other fields due to their excellent biological activities.Therefore,the development of rapid and efficient synthetic methods for these compounds has attracted increasing attention from researchers.A novel acid?catalyzed cyclization reaction between allylbenzene and tetrazine was designed.Reaction intermediates were trapped,and their structures,along with those of the products,were characterized using nuclear magnetic resonance spectroscopy.The results indicate that the reaction proceeds through intermolecular [4+2] cycloaddition and intramolecular Friedel?Crafts alkylation processes,enabling one?step synthesis of indeno[1,2?d]pyridazine derivatives.The reaction also exhibits a broad substrate scope and good functional group compatibility,yielding a series of indeno[1,2?d]pyridazine derivatives with 67%~95% yields.In gram scale experiments,the target product was obtained with an 81% yield, demonstrating the potential practical value of this reaction.

A new method for the synthesis of esters by C=C bond breaking in olefins has been realised using cobalt nanoparticles (Co?NC?900) as catalysts and oxygen as oxidant.The catalytic system has a wide range of substrate applications and functional group compatibility.A diverse set of mono? and multi?substituted aromatic and aliphatic alkenes could be effectively cleaved and converted into the corresponding esters by C=C bond cleavage. In addition, the catalyst can be recycled up to six times without significant loss of activity.Characterization analysis revealed nanostructured nitrogen?doped graphene?layer coated cobalt nanoparticleis possibly responsible for excellent catalytic activity.Mechanistic studies revealed that alcohols or ketones derived from olefins under oxidative conditions are formed as intermediates,which subsequently are converted to esters through a tandem sequential process.

Organic sulfides widely exist in natural resources such as petroleum and coal,which have abundant resource reserves.In the petroleum refining industry,the cleavage of C-S bonds is usually required for the desulfurization of petroleum fractions. Among them,the transition metal?catalyzed cleavage reactions of C-S bonds have attracted the attention of researchers owing to the advantages of high efficiency,mild conditions,and low pollution.This review summarizes the progress in transition metal?catalyzed C-S bond cleavage reactions of different types of organic sulfides,and provides insights into Pd,Cu,Ni and Fe catalytic systems and mechanisms.Moreover,the development of such reactions is proposed.