HETEROCYCLIC [3,2-B]-FUSED PENTALENES AND THEIR BENZO ANALOGS - REACTIVITY AND UTILIZATION

Reactivities of heterocyclic [3,2-b]-fused pentalenes and their benzo- anneallated derivatives in typical reactions of basic five-membered he terocycles and their applications are surveyed. The alpha-positions ar e activated for substitution reactions. Electrophilic aromatic substit utions are widely used for the preparations of pentalene derivatives b ut their applications are limited due to their sensitivity to acids. M etallations and tranmetallations are convenient methods for the prepar ation of derivatives which are not accessible by the electrophilic aro matic substitution. Diels-Alder reactions are discussed as the most of ten used electrocyclic reactions. The reactivity of the compounds cont aining thiophene moiety in oxidations and desulfurations is also discu ssed.