Chapter 4 - Four-Membered Ring Systems

Abstract

This chapter presents the synthesis and chemistry of four-membered ring systems—azetidines, azetines, and related systems. An approach for the preparation of oxazocines through a Ag(I)-catalyzed cascade reaction of azetidines with propargyl alcohols is presented in the chapter. Azetines are proposed as the intermediates of the gold-catalyzed reaction between 1,3-dienes and aldimines yielding cyclopent-2-enimines. The chapter provides an overview of the synthesis and reactivity of small strained spiroheterocycles, including spirooxetanes, and describes their applications in synthetic endeavors. The synthesis and reactivity of 3-haloazetidines, 3-sulfonyloxyazetidines, and 2-methylenezetidines are reviewed in the chapter. A novel series of azetidinyl ketolides for the treatment of susceptible and multidrug resistant community acquired respiratory tract infections are discovered. Theoretical and experimental results have provided evidence that 2-alkyl-2-carboxyazetidine scaffold is able to efficiently induce γ-turns when incorporated into short peptides, irrespective of their localization in the peptide chain.