Macrocyclization under Kinetic Control. A Theoretical Study and its Application to the Synthesis of Macrocyclic Poly(thiolactones)

A kinetic model for macrocyclization reactions of bifunctional chains undergoing simple and double ring closure reactions has been proposed. Numerical integration of the proper set of differential rate equations allows yields and distributions of cyclic oligomers to be calculated as a function of initial concentrations of reactants and effective molarities (EM(i)) of the rings being formed. In terms of computer time the present model is less demanding than analogous models previously published, in that a high degree of accuracy is obtained without taking into account explicitly linear oligomers with high polymerization degree. The model has been successfully applied to the synthesis of macrocyclic poly(thiolactones) via irreversible reaction of 2,2-dibutyl-1,2,3-dithiastannolane with glutaryl and pimeloyl chlorides. The best fits of the experimental oligomer distributions to the general equations gave the effective molarities from monomer to tetramer in both series.