Methyl 2-acetylaminoacrylate in the reaction with aliphatic dienes

Abstract

Cycloaddition reactions (Huisgen reaction, DielsAlder reaction) of diazo compounds and dienes with dehydroamino acids derivatives (dehydroalanine, dehydrophenylalanine) are a convenient method for the synthesis of functionalized ring systems like pyrazolines [1], pyrazoles [2], cyclopropanes [3,4], norbornenes [5,6], and 9,10-ethanoanthracenes [7]. The interest in these carbo-and heterocycles representa-tives is due to the possibility of their use as precursors for the synthesis of cyclic α-amino acids, which are promising in terms of their structural and biological properties [8-10].We first carried out the reaction of methyl 2-acetylaminoacrylate I with aliphatic dienes, the 2,3-dimethylbutadiene and isoprene. Dehydroalanine I was shown to react with 2,3-dimethylbutadiene in toluene under reflux over 5 h to give methyl 3,4-dimethyl-1-acetylaminocyclohexen-1-ylcarboxylate II in 62% yield.To obtain isoprene in situ under the reaction conditions, we used 3-methylsulfolene as a synthetic precursor. In this case, more rigid reaction conditions are required due to the desulfonation of the latter. The reaction of dienophile I with 3-methylsulfolene was carried out in p-xylene under reflux over 24 h. The reaction was completed with the formation of regioisomeric 3(4)-methylcyclohexenes III and IV in 1:3 ratio.