methyl group of the starting materialNitration of p-chlorobenzoic acid gives the desired product, because the directing effects ofthe chlorine (ortho, para) and the carboxyl (meta) groups reinforce each other.(j)The desired synthetic route becomes apparent when it is recognized that the Zalkenestereoisomer may be obtained from an alkyne, which, in turn, is available by carboxylation ofthe anion derived from the starting material.The desired reaction sequence isHydrogenation of the carbon–carbon triple bond of 2-butynoic acid over the Lindlar catalystconverts this compound to the Zisomer of 2-butenoic acid.19.24(a)Only the cis stereoisomer of 4-hydroxycyclohexanecarboxylic acid is capable of forming alactone, as can be seen in the following drawings or with a molecular model. The most stable
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