Bicyclopropylidenylalkyl-substituted nitrones 6 and 7 undergo regio- and diastereoselective intramolecular cycloadditions to afford exclusively the ring-fused adducts 8 and 9, respectively. The thermal rearrangement of the cycloadducts 8 and 9 under acidic conditions (TFA) leads to the tricyclic β-lactams 12 and 14, respectively. Under the reaction conditions, 12 undergoes lactam-amide bond cleavage to yield the bicyclic N-trifluoroacetylated β-amino acid derivative 13.
                                    双环丙叉取代基亚
硝基化合物6和7分别发生区域选择性和非对映选择性分子内环加成反应,唯一得到环融合加合物8和9。在酸性条件下(
三氟乙酸),环加合物8和9的热重排反应分别生成
三环β-内酰胺12和14。在反应条件下,12发生内酰胺-酰胺键断裂,产生双环N-三
氟乙酰化β-
氨基酸衍
生物13。