Synthesis of 4-alkyl-3,5-dibromo-, 3-bromo-4,5-dialkyl- and 3,4,5-trialkylpyridines via sequential metalation and metal-halogen exchange of 3,5-dibromopyridine

Lithiation of 3,5-dibromopyridine with LDA and subsequent reaction with electrophiles provided 4-alkyl-3,5-dibromopyridines 2 in high yield. 3-Bromo-4,5-dialkylpyridines 3 were synthesized by metal-halogen exchange of 2 with one equivalent n-BuLi and reaction with a second electrophile. Further metal-halogen exchange of 3 and reaction with a third electrophile provided 3,4,5-trisubstituted pyridines 4. Copyright (C) 1996 Elsevier Science Ltd