Preparation and Suzuki-Miyaura Coupling Reactions of Tetrahydropyridine-2-boronic Acid Pinacol Esters

A study on the conversion of lactam-derived vinyl triflates and phosphates into the corresponding vinyl boronates was carried out. While delta-valerolactam-derived vinyl triflates were successfully converted into 1,4,5,6-tetrahydropyridine-2-boronic acid pinacol ester derivatives by Pd-catalyzed coupling reaction with both bis(pinacolato)diboron and pinacolborane, pyrrolidinone and epsilon-caprolactam derivatives either did not react or were readily reduced. The delta-valerolactam-derived vinyl boronates are thermally stable compounds that efficiently coupled, under Pd catalysis, with structurally diverse aryl and heteroaryl bromides and triflates, vinyl iodides and bromides, and aromatic acid chlorides, to give the corresponding 2-substituted piperidines in good to excellent yields. The number of electrophiles that can virtually be coupled with these new boronic esters makes them very useful reagents for the synthesis of N-heterocyclic compounds.