Abstract
In this work, we report two cobalt-catalyzed olefins dimerization modes: (a) reductive dimerization of conjugated alkenes to yield directly the saturated linear diesters, dinitrile, and disulfone 2a-2g, offering a more convenient method to the synthesis of adipic acid and, (b) cobalt-catalyzed head-to-tail dimerization of vinylarenes 4a-4l in good yields. On the other hand, we have recently developed a reaction mode of cobalt-catalyzed tail-to-tail reductive dimerization of conjugated alkenes. This provides an efficient and mild route for the corresponding saturated linear products. Herein, we describe that application for the cobalt-catalyzed reaction mode to synthesis of macrocyclic di- and tetralactones 6a-6i in good yields under normal dilution conditions. The cobalt-catalyzed highly regio- and stereoselective reductive coupling reaction of alkynes and conjugated alkenes to form a new chain molecule 8a-8j, was conducted in the presence of CoI2(L) and zinc metal powder. Several 4-(4-alkyl phenyl)-3-butynyl acrylates also undergo reductive coupling macrocyclicization reaction to afford macrocyclic dilactone 12a-12c in 45-80% yields. This procedure allows for the synthesis of a variety of functionalized lactones, lactames and macrocyclic dilactones in moderate to good yields. Treatment of various propargyl alcohol with methyl acrylate proceeded successfully in the presence of CoI2(dppe), water and zinc metal powder in a mixture of acetonitrile and 1,4-dioxane (v/v = 1/1) at 80℃ affording the corresponding γ-methylideneδ-lactones 9a-9h in good yields. Several propargyl amines also react with methyl acrylate to afford γ-methylideneδ-lactames 9i-9k in 72-84% yields. Seven-membered lactones 10a-10i could also be prepared by slow addition of methyl 2-(3-hydroxy-1-alkynyl)benzoate to the reaction mixture of conjugated alkene in presence of CoI2(dppe), water and zinc metal powder and acetonitrile at 80℃. The above catalytic reactions are completely regioselective and highly stereoselective. Possible mechanisms for the reductive coupling cyclization reactions as well as unique features of these processes are discussed.