The reaction of 1-acylpyridinium salts with nucleophiles has proven to be a valuable method for the synthesis of substituted dihydropyridines and pyridines. 132 However, the nucleophilic addition is frequently not regiospecific, and a mixture of isomeric dihydropyridines results. A small substituent at the 3-position ot a 1-acylpyridinium salt can exert an" ortho"-directing effect, causing nucleophilic attack to occur mainly at the 4-and 2- ...