The multi-functionalized esters of n-butyric acid 1 are useful building blocks having three functional groups, each with different reactivity in the neighborhood of a chiral carbon atom. A variety of optically active substances can be synthesized by employing each functionality. For example, 1 can be converted to tetrahydrofuranone 2 by treatment with hydrochloric acid, pyrrolidinone 3 by treatment with ammonium hydroxide, and tetrahydrofuran 4 by treatment with hydrochloric acid after reducing to alcohol. Oxazolidinone 5 can also be obtained via hydrazide. Furthermore, the esters 1 are employed for the synthesis of the important bioactive substance 4-amino-3-hydroxybutyric acid (GABOB) 6 and carnitine 7.