Reaction of benzolactams with triethyl phosphite prompted by phosphoryl chloride affords benzoannulated monophosphonates instead of expected bisphoshonates

Highlighst•Reaction of benzoannulated cyclic lactams with PO(Et)3 and POCl3 was studied.•A series of beznoannulated mono- and bisphosphonates were synthesised in one step.•Esters appeared to be unstable upon acidic hydrolysis results, in C–P bond cleavage.•Mechanism of acid catalyzed degradation of these compounds has been proposed.•Structures were elucidated by NMR, MS, IR.

In contrast to aliphatic lactams, which gave cyclic aminomethylene-gem-bisphosphonates in reaction with triethyl phosphite and phosphoryl chloride, the corresponding benzoannulated lactams usually provide monophosphonates of variable structures, which depend on size of the substrate aliphatic ring. Most likely they are obtained by dephosphonylation of bisphosphonates, which form as initial products of this reaction. These phosphonate esters appeared to be unstable upon acid hydrolysis and upon storage. Mechanism of acid catalyzed degradation of these compounds has been proposed.

Graphical abstractReaction between benzoannulated lactams, diethyl phosphite and phosphoryl chloride, designed to produce bisphosphonates, gave unexpectedly a variety of monophosphonates, structures of which strongly depend on the size of aliphatic ring. Approach to convert these phosphonates into phosphonic acids failed and resulted in breakage of carbon-to-phosphorus bond.Figure optionsDownload full-size imageDownload as PowerPoint slide