Steric carbonyl protection metalation and cleavage of highly hindered ureas. Preliminary communication
作者:Tillmann Hassel、Dieter Seebach
DOI:10.1002/hlca.19780610625
日期:1978.9.20
Ureas of type 3 with sterically protected carbonyl groups such as 4a-7a are prepared by successively adding 2 equivalents of a highly substituted sec. amine and an excess of dimethylamine to benzene or toluene solutions of phosgene. The piperidine derivatives 6a and 7a are metalated in high yields to 6b and 7b, respectively, with sec.-butyllithium/TMEDA in THF at 0° [see derivatives 6, 7, (c-i) in
通过连续添加2当量的高度取代的仲胺来制备具有空间保护的羰基的3型尿素(例如4a-7a)。胺和过量的二甲胺形成光气的苯或甲苯溶液。的哌啶衍生物6A和7A被金属化以高收率,以图6b和图7b分别与秒。丁基锂/ TMEDA在THF中的0°[见表1中的衍生物6、7((ci))]。描述了裂解氨基甲酸酯2(参见8 9)和尿素3的方法,其中在酸性水解条件下从7中除去哌啶环的Retro-Mannich反应对于有机合成中空间封闭的羰基化合物的其他应用似乎也很有希望。