(from preface)
Volume 26 contains three chapters. C.A.Ramsden reviews heterocy-clic betaines derived from six-membered heteroaromatic rings. These compounds have been intensively studied over the past 10 years and have not previously been comprehensively reviewed. O. Meth-Cohn and B. Tarnowski summarize the chemistry of the thiocoumarins, a somewhat neglected group of heterocycles. Finally, W. Friedrichsen has reviewed the chemistry of the benzo[r]furans which, unlike the aza and thia analogs, have not previously been considered in this series. Here again we have a group of compounds the chemistry of which has advanced considerably over the last decade.