Chiral 2-alkenyloxazolines and 2-alkenylthiazolines react with isocyanates and ketenes to give formal hetero-Diels-Alder adducts with complete diastereocontrol. In each case an electron-rich double bond in the adduct is prone to a second addition of the heterocumulene. In the case of the oxazoline adducts the second addition is faster than the first, while with thiazolines the second addition is slower
手性 2-链烯基
恶唑啉和 2-链烯基
噻唑啉与
异氰酸酯和
乙烯酮反应,生成具有完全非对映控制的正式杂狄尔斯-阿尔德加合物。在每种情况下,加合物中的富电子双键易于再次加成杂枯草烯。在
恶唑啉加合物的情况下,第二次加成比第一次快,而对于
噻唑啉,第二次加成更慢,因此可以加入不同的杂枯草烯。