Bromination Of 1,2-Cyclononadiene And 1,3-Dimethylallene

Much information has been obtained on the orientation of unsymmetrical reagents about substituted allenes. Although hydrogen halide addition to 1,2-propadiene yields 2-halopropenes,20,31 it has been ample demonstrated, at least in the case of halogenation and oxymercuration of the 1,2-alkyl substituted allenes, that the attacking electrophile ends up in the product attached to the central carbon of the original allenic system. 20,22,31,34,38,39,40 Using optically active 1,3-dimethylallene(15) it has been shown that the bromination and oxymercuration of 15 is stereospecific. 22,39Knowledge of the absolute configurations of the optically active addition products have made it possible to propose a plausible mechanism for the reactions (eq 1). 1,2-cyclononadiene(1) was brominated in methanol and a 40:60 mixture of two products corresponding to isomeric bromomrthoxycyclonenes was obtained. Preliminary, chemical, and spectral evidence indicated that the isomeric mixture definitely did not consist of cis-trans geometric isomers. The primary objective of the research then became the identification of the isomeric bromination products of 1,2-cyclononadiene(1) in various reactive solvents. The results are discussed with reference to the intermediates that may be involved in these reactions