Modular Synthesis of Heterocyclic Carbene Precursors

A series of N-heterocyclic carbene precursors, containing an imidazoline or tetrahydropyrimidine
framework, were prepared from ω-chloroalkanoyl chlorides. The sequential attachment of nitrogen
nucleophiles and subsequent ring closure gave, depending on the reagents used, either the desired
dihydroimidazolium and tetrahydropyrimidinium salts or their parent heterocycles. In this latter case, the
second substituent was introduced in an alkylation step. The preparation of carbene precursors bearing
chiral or bulky substituents was acieved with comparable efficiency.