Cyclopropenones methylene compounds with

Radialenes which are structurally related to 44, i.e. cyclopropanes bearing two quinoid and another acceptor-substituted methylene substituent, were obtained by condensation of bis(4-hydroxyphenyl)cyclopropenones with active methylene compounds, followed by oxidation (Scheme 6)19. Radialenes 45a-f are brilliantly colored solids that are blue or blue-violet in solution but appear metallic gold or red in reflected light. Instead... 

The condensation of appropriate reactive methylene compounds such as malononitrile with cyclopropenones yields the methylenecyclopropene either directly... 

A superior route to these compounds using the condensation procedures involves the use of alkoxycyclopropenyl cations (equation 73) . These can be prepared readily by alkylation of cyclopropenones with trialkyloxonium tetrafluoroborates . This process can be extended to a large number of active methylene compounds if the conditions of the reaction are controlled carefully and the tertiary non-nucleophilic base diisopropylethy-lamine is used Otherwise, a large number of side reactions are observed. 

Triafulvenes stabilized by electron-withdrawing groups at the e.vo-methylene carbon and alkyl or aryl groups in the three-membered ring can be prepared by Knoevenagel-type condensation of cyclopropenone derivatives with active methylene compounds under acidic conditions (heating in acetic anhydride). The procedure is simple, but the yields are generally poor. °... 

The reaction of cyclopropenones (16) with compounds containing active methylene groups leads to methylenecyclopropenes (17), which on oxidation give a new family of alkylidenequinocyclopropanes (18). These are highly coloured. 

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