Cycloamidination of Aminoalkenes with Nitriles: Synthesis of Substituted 2‐Imidazolines and Tetrahydropyrimidines

Abstract

AbstractThe first catalytic cycloamidination of aminoalkenes with nitriles has been achieved by using rare‐earth complexes. This reaction is equivalent to the desired intramolecular hydroamination of alkenylamidines, and allows a new direct access to substituted 2‐imidazolines and tetrahydropyrimidines in high yields under operationally simple reaction conditions. Moreover, the methodology is also efficient for synthesis of symmetric and unsymmetric bridged diimidazolines. Compared with the traditional stepwise‐mediated synthetic approaches, the present method avoids the use of additives and harsh reaction conditions, and thus leads to a completely different product distribution. Mechanistic data suggest that the reaction involves the initial NH activation by lanthanide complex followed by nitrile insertion into a LnN bond to form an amidinate lanthanide intermediate which undergoes the cyclization.