Hi, The problem was to propose a synthetic scheme for making maleic acid (cis-but-2-ene-1,4-dioic acid) from acetylene (as part of a larger synthesis where I would have to use the maleic anhydride in a Diels-Alders cycloaddition with 1,3-cyclopentadiene made from cyclopentanol to get a tricyclic molecule). After several hours of work, I worked out a synthesis that would synthesise a mixture of both maleic acid and fumaric acid (its trans isomer), but I can't achieve the required stereochemistry. I figured out that any synthesis will most probably proceed through the diol, which could then be oxidised to the acid. I used two disconnections in my retrosynthesis: first one of the terminal carbons containing OH (synthetic equivalent:Grignard addition) and then the double bonded carbon to which the previous carbon was attached (synthetic equivalent:Wittig reaction). Immediately after completing the analysis I felt that stereochemistry had not been ensured. I went back over my scheme trying to identify the steps controlling the stereochemistry. In one of the steps, I had proposed anti-Markownikoff (using peroxide) hydrobromination of a terminal alkyne, so that I could get an alkenyl Grignard reagent. I needed to make sure that the vinylic bromide formed in this step was cis to the hydroxymethyl group, after which the Grignard reaction with formaldehyde (methanal) would preserve this stereochemistry. However, as far as I know the free radical hydrobromination of an alkyne is not exclusively or dominantly syn. Can the synthesis be achieved with any minor modification to my scheme, or would I need some entirely different pathway? Thanks a lot for your help. Molu QUERY IN SUMMARY: Propose a synthesis of maleic anhydride from acetylene.