Chapter 4: Four-Membered Ring Systems

Abstract

Chemical research on four-membered heterocycles, where a non-carbon atom is part of the ring, has become a highly dynamic area of international priority and importance in many fields of Science, including organic chemistry, inorganic chemistry, medicinal chemistry, and material science. This chapter describes several oxygen- and nitrogen-containing heterocycles that dominate the field of four-membered heterocyclic chemistry. Oxazolidinone analogs bearing substituted azetidines with a methyl group at the 3-position of the four-membered ring exhibit reduced mitochondrial protein synthesis inhibition while retaining good antibacterial potency. It has been found that the introduction of 3-substituted azetidinyl substituents onto the 4,6-diaminopyrimidine scaffold allows the improvement of phosphodiesterase inhibiting activities. It is reported that aza-Michael adducts of chalcones and diethyl N -arylphosphoramidates undergo reductive cyclization with sodium borohydride followed by reaction with sodium hydride to afford 1,2,4-trisubstituted azetidines diastereoselectively in a one-pot procedure and produces excellent yields. The use of chemo-differentiating multicomponent reactions in diversity-oriented molecular construction, including spiro β-lactams, is reviewed in the chapter.