Fumaric dibromo

The bromination and hydrolysis of ketenes and bisketenes have been studied. The reaction of the bis(ketene) 289 with bromine has yielded the dibromo fumarate derivative 290, whose /r/mr-con figuration has been confirmed by X-ray crystallography (Scheme 41).366 The hydrolysis of the dibromo fumarate derivative 291 first provided the dibromo derivative (5//)-furanone 292. The prolonged reaction with water afforded the maleic anhydride 293. The methanolysis of the dibromo fumarate derivative 290 has resulted in the formation of an isomeric mixture of dimethyl... 

It was found that v/c-dihaloalkanes were highly stereospecifically reduced at a mercury cathode to the corresponding olefins in high yields, Eq. (32) [215]. The resulting electrochemistry suggests that the elimination of halogen atoms from the tro/z -periplanar conformation is strongly preferred. The detailed stereochemical course of the reaction was discussed by Brown and coworkers [216]. the stereospecific reduction of a, a -dibromo-succinates to fumarates and maleates was also reported earlier [217]. 

Reaction of a,a -Dibromo-o-xylene with Diethyl Fumarate in the Presence of Metallic Nickel... 

R RgCX—R3R4CX, the products of the initial two-electron electrode reaction are the halide ions and a more unsaturated species, RjR2C=CRgR4. The dualistic nature of the reaction can be illustrated in terms of the reduction of the meso, a, a -dibromo-succinic acid which forms only fumaric acid over the normal pH range and of the racemic a, a -dibromosuccinic acid which also forms maleic acid in varying amount in the intermediate pH range associated with the presence of the mono anion. ... 

Halogen-Substituted Compounds. Elving and co-workers [22, 83] investigated the reduction of meso- and racemic dibromo-succinic acids at a mercury cathode. At all pH values the meso acid gave only fumaric acid, i,e., trans-elimination of bromine occurred. Racemic dibromosuccinic acid gives various products depending on the pH fumaric acid alone is also formed in strongly acidic and alkaline solutions, i.e., cis-elimination of bromine occurs, but at pH values between 0.4 and 6.9 a mixture of fumaric acid and maleic acid is formed, and the latter is the main product at pH 4 (70% yield). 

---