This review presents allylic substitution of the monoacetate of 4-cyclopentene-1,3-diol with organoborates/Ni cat reagents, copper-based reagents, and the modified malonate/Pd cat reagent to produce 4-substituted-2-cyclopenten-1-ols (1,4-isomers) or 2-substituted-3-cyclopenten-1-ols (1,2-isomers) highly stereo-and regioselectively. The groups installed to the monoacetate include alkyl, alkenyl, and aryl groups, which were previously unsuccessful. The high selectivity allows an access to a new class of cyclopentanoids such as jasmonoids and isoprostanes, which are described in the latter part of the review. One of the two side chains with the thermodynamically unstable cis orientation in the jasmonoids is constructed by using copper-based reagents giving the 1,4-isomers. In the synthesis of isoprostanes with the dienone structure, the side chain characterized by the cis allylic moiety is constructed by using the malonate/Pd cat reagent or propargylic-MgBr/CuCN reagent efficiently.