Highly stereocontrolled synthesis of (2E,4Z)-dienoic esters with alumina catalyst. Its application to total syntheses of flavor components and insect pheromones
A new synthesis of 5-alkyl-2-furancarboxylates and 5-alkyl-2-selenophenecarboxylates via the direct oxidation of 2,4-alkadienoic esters with selenium dioxide is described.
A range of double unsaturated amides (15, 19, and 21), obtained by cross-coupling reactions was reacted with aldehydes to hemiaminals. Heating the hemiaminals in the presence of Ac2O and pyridine affected clean conversion to the corresponding enamides, such as 42, 45, and 47. Alternatively, N,S-acetals were prepared which were oxidized to the sulfones. Treatment with base also gave the enamides, favoring
alcohols can be oxidised with activated manganese dioxide in the presence of stabilised Wittig reagents to generate α,β-unsaturated esters directly. This simple procedure, which can also be utilised with diols to give double homologation, is generally useful and particularly valuable if the intermediate aldehydes are difficult to isolate, toxic or prone to isomerisation.