Formations and reactions of allenes

Aryl and alkyl l-bromoallenes, 1-iodoallenes, 1,1-dibromoallenes and 1-halo-l-deuteroallenes have been prepared; the mechanism of their formation and their spectroscopic properties are discussed. Conversion of propargylic alcohols to 1-cyanoallenes either directly or via the corresponding allenic bromides is described. The mechanism of formation of cyanoallenes and their spectral properties are discussed. l-oyanoallenes have been converted to enamines, to allenic amides and to allenic acids. Evidence for the structures of dimerisation products of 1-cyanoallenes is presented.1,4-Elimination reactions of l-bromoallenes are shown to give alkenynes in good yield. 1-Bromoallenes form Grignard compounds and these are reacted with carbon dioxide, water, oxygen and acetone to give mixtures of acetylene and allenic products.