Chemo, Regio, and Stereoselectivity in the Olefination of Hydrazone 1,4-Adducts Between Conjugated Azoalkenes and Sulphur Co-activated Methylene Compounds
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文摘
In the presence of sodium methoxide in catalytic amount, conjugated azoalkenes smoothly add at room temperature (phenylsulphonyl)acetamide, methyl (phenylsulphonyl)acetate, methyl (phenylsulphinyl)acetate, (arylsulphonyl)acetonitriles, bis(phenylsulphonyl)methane, and (arylsulphonyl)nitromethane to yield the corresponding α-functionalized hydrazone derivatives by 1,4-addition. In some cases these hydrazones were isolated, while in others their formation is accompanied by olefination products. Under the same reaction conditions and/or in methanol by means of gentle heating, several of these adducts give rise to the related α,β-olefinated hydrazone derivatives as pure isomeric forms or as EE/EZ mixtures by loss of the nitro, sulphonyl or sulphinyl group. It is noteworthy that for β-cyano-β-arylsulphonyl adducts it was mainly detected the elimination of the arylsulphonyl group affording β-cyano-α,β-olefinated hydrazones, while for analogous β-nitro-β-arylsulphonyl adducts it was principally observed the loss of the nitro moiety producing β-arylsulphonyl-α,β-olefinated hydrazones.