Synthesis of N-Substituted Pyrido[b]-Anellated Azaphospholes

Significance

Reported are the first examples of the syntheses and structures of 3-amino and 3-amido pyridine-2-phosphonates, and the conversion of the latter heterocycles into azaphospholo[4,5-b]pyridines. After considerable testing of various conditions, the phosphonates were synthesized in low yields via Pd-catalyzed cross-coupling of bromopyridines with triethyl phosphite. The low yields were suggested to be due to the deactivating effects of the pyridine nitrogen and the amino group. Reduction of the amido phosphonates with LiAlH₄, followed by reaction with DMF dimethyl acetal led to the previously unknown P=C-N heterocycles in good yields. However, the compounds were found to be highly air-sensitive and their purification proved impossible in some cases.