Azetidines, as an important class of saturated four-membered azaheterocycles, are not only important raw materials, intermediates, chiral auxiliaries and catalysts in organic synthesis, but also crucial active structural units of amino acids, alkaloids, natural and synthetic biological and medicinal active compounds. Thus, it is critical to develop methods for constructing azetidine structural motifs. The review introduces the development of the synthesis of azetidines and mainly focuses on advances of the synthesis of azetidines during recent 10 years. Furthermore, it demonstrates the new achievements in the synthesis of azetidines mainly including cyclizations by the C-N bond formation and by the C-C bond formation, amine-catalyzed cycloaddition of allenoates and imines, photocycloadditions of imines and alkenes, ring contraction and expansion rearrangements, and reduction of azetidin-2-ones(β-lactams).
Contents
1 Introduction
2 Cyclizations by the C-N bond formation
2.1 Nucleophilic substitution reactions
2.2 Reductive cyclizations of β-haloalkylimines
2.3 Cyclizations of allylic and homoallylic amines
2.4 Opening of epoxides with amines
2.5 Opening of aziridines
2.6 Pd-Catalyzed cyclizations
3 Cyclizations by the C-C bond formation
3.1 Nucleophilic displacements
3.2 Cyclizations involving Michael additions
4 Cycloadditions
4.1 Amine-catalyzed cycloadditions of allenoates and imines
4.2[2+2]Photocycloadditions of imines and alkenes
5 Ring contraction and expansion rearrangements
5.1 Ring contractions of five-membered heterocycles
5.2 Ring expansions of three-membered heterocycles
6 Reduction of azetidin-2-ones
7 Conclusion