Description

New methods for the construction of condensed five-membered ring systems continue to be developed at an accelerated pace. The challenges underlying this tremendous current upsurge of interest arise from several directions. One stems from the desire to elucidate and resolve those special problems associated with the incorporation of added strain not present when six-membered rings are mutually fused. The many structurally interesting polyquinane natural products isolated and characterized in recent years have provided a particularly delightful forum for application of various new synthetic protocols, many of which must equally well accommodate the particular stereochemical demands of each indi- vidual target. Synthetic elaboration of a marvellous array of new unnatural molecules also holds continued fascination. In the past, we have attempted to keep others abreast of developments in this rapidly burgeoning area by authoring a pair of comprehensive reviews in Topics in Current Chemistry that appeared in 1979 [1] and 1984 [2]. During this period, others have also surveyed the developments in cyclopentannulation [3] and the cyclopentanoid field in general [4]. In the last couple of years, the pace at which new synthetic facets have been reported has become more frenetic than ever before. Accordingly, a suitable updating of the exciting newer findings was deemed appropriate and the present overview, which extends approximately to mid - 1986, was written. Once again, our hope is that compilations of this type will serve to stimulate imaginative new scientific ventures that will propel the field forward to still greater maturity.