High pressure induced cycloaddition of Z and E nitronic esters (2) to 16-dehydro-20-oxo steroids (1) leads to regiospecific formation of steroido [16α,17α-d] tetrahydro-l',2'-oxazoles (3 and 4). It is shown that both modes (“exo-endo”) of dipolarophile approach to the dipole are realized for most steroids examined. All four possible isomers are isolated and their preferred conformations are established
Z和E
硝酸酯的高压诱导环加成(2)与16-脱氢20-氧代甾族化合物(1)导致甾体[16α,17α-d]四氢-1',2'-
恶唑的区域特异性形成(3和4)。结果表明,对大多数类
固醇而言,实现偶极亲近的偶极子亲和力的两种模式(“ exo-endo ”)都可以实现。分离了所有四种可能的异构体,并确定了它们的优选构象。结果表明,转化不稳定立体异构体的稳定的人(3“→4; 4”→3)前进作为同时氮反转和
异恶唑烷循环的构象变化(Ñ Ë→ë Ñ)。