Protecting of a thermolabile protecting group: "click-clack" approach.

A new method for attaining higher stability of thermolabile protecting groups (TPG) using an intramolecular cyclization through a "click-clack" approach was demonstrated. It was found that during intramolecular cyclization of 2-pyridyl type of TPG the thermally stable 3-pyridyl-[1,3,2]oxazaphospholidine ring was formed and thermolabile properties were declined. Thermolability could be recovered upon hydrolytic ring-opening of a 3-pyridyl-[1,3,2]oxazaphospholidine. "Click-clack" chemistry was applied to the synthesis of biologically important phosphate esters and their analogues and some H-phosphonate derivatives.