Carbodiimides react effectively with β-aryl/alkyl-β-hydroxy-α,α-difluorocarboxylic acids to afford a vast array of fully substituted gem-difluorodihydrouracils through a two step reaction sequence. In the first step, condensation between the two reactants leads in most cases to the formation of a mixture of the desired dihydrouracils and N-acylurea co-products. However, the latter could be easily recovered and efficiently converted into the target compounds. The sequence works well in very mild conditions (CH2Cl2, 20 ËC) and the reaction resulted to be completely regioselective when asymmetric carbodiimides were used. When the N-acylurea derivatives are not sufficiently stable for isolation, the process could be done in a one-pot fashion leading to the direct formation of the desired dihydrouracils, although in lower yields.
碳二
亚胺与β-芳基/烷基-β-羟基-α,α-二
氟羧酸有效反应,通过两步反应序列提供大量完全取代的宝石-二
氟二氢尿
嘧啶。在第一步中,两种反应物之间的缩合在大多数情况下导致形成所需二氢尿
嘧啶和N-酰基
脲联产物的混合物。然而,后者可以很容易地回收并有效地转化为目标化合物。该序列在非常温和的条件(
CH2Cl2,20°C)下运行良好,并且当使用不对称碳二
亚胺时,反应具有完全的区域选择性。当 N-酰基
脲衍
生物对于分离来说不够稳定时,该过程可以以一锅法完成,从而直接形成所需的二氢尿
嘧啶,尽管产率较低。