Pd(II)-Catalyzed Allylic C–H Amination for the Preparation of 1,2- and 1,3-Cyclic Ureas
摘要:
A general synthesis of 1,2- and 1,3-cyclic ureas is accomplished by intramolecular allylic C-H amination employing Pd(TFA)(2)/bis-sulfoxide as a catalyst. By careful modification of substrates and catalyst, a variety of 1,2-cyclic ureas are accessible from not previously employed terminal olefins substituted in allylic or vinylic positions. Furthermore, MS4A is found to be an effective additive for the synthesis of 1,3-cyclic ureas in good yields and excellent diastereoselectivities.
An efficient protocol for the stereoselective synthesis of 1,3-syn and -anti-tetrahydropyrimidinones (syn- and anti-11a) is reported The modular procedure is based on a stereodivergent cyclization of readily available urea-type substrates (10a) by intramolecular allylic substitution The cyclization proceeds with excellent yield (up to 99%) and selectivity (up to dr > 20:1), purely based on substrate control The product pyrimidines can be readily transformed into the corresponding free syn- and anti-amines