2-SUBSTITUTED CYCLOIMINIUM SALTS IN AZAPHOSPHOLE SYNTHESIS

The [4 + 1] cyclocondensation reaction of 2-alkyl- and 2-aminocycloimi nium salts with suitable phosphorus(III) reagents provides an easy acc ess to a large variety of anellated azaphospholes with a bridgehead ni trogen atom. This [4 + 1] approach is complemented by two related synt hetic routes which, in place of the 2-substituted cycloiminium salts, use 2-unsubstituted 1-alkylcycloiminium salts or neutral 2-amino-subst ituted cyclic imines, and which thus follow the [3 + 2] pattern. In th ese cases, the ring is formed by cycloaddition with phosphaalkynes or by cyclocondensation with chloromethyl-dichlorophosphane, respectively .