α,β-Didehydroamino acid derivatives with an isoxazolyl or a pyrazolyl moiety: The effect of substituents and reaction conditions on their stereoselective formation from 2H-pyran-2-ones

Abstract

2H-Pyran-2-ones 1 and 2 and hydroxylamine or hydrazines are used as synthons for the synthesis of E- or Z-α,β-didehydroamino acid derivatives 4 and 5 containing an isoxazolyl or a pyrazolyl ring attached at the β-position. The emphasis of our study is on the effect of substituents on both reagents as well as on the reaction conditions (solvent, catalyst, and temperature) influencing the ratio between (E)- and (Z)-isomers and, in some cases, decarboxylated analogues 6.