Progress in Heterocyclic Chemistry (PHC), Volume 4 describes new and significant advances in the field of heterocyclic chemistry mainly based on the 1991 literature. It also presents the first review on the widely studied SO 2 -extrusion from heterocyclic compounds, which is of considerable mechanistic and preparative interest. The chapters are arranged according to ring-size as in the previous volumes and backed up by references, a subject index...