I. Introduction 29 II. The Chemistry of Azetidin-3-ones 29 A. Structural Data 29 B. Synthetic Methods for Azetidin-3-ones 31 B.1. Carbonyl Group Generation in the Azetidine Ring 31 B.2. Intramolecular Cyclization Reactions 34 B.3. 1,3-Dipolar Cycloaddition Reactions 36 C. Chemical Properties of Azetidin-3-ones 37 C.1. Transformations of the Carbonyl Group 37 C.2. Condensation Reactions − Synthesis of 2-Benzylideneazetidin-3-ones 40 C.3. Ring Transformations of Azetidin-3-ones 40 C.4. Miscellaneous 41 III. The Chemistry of Oxetan-3-ones 42 A. Structural Data 42 B. Synthetic Methods for Oxetan-3-ones 43 B.1. Decomposition of Diazoketones 43 B.2. Oxidation Reactions 44 B.3. Intramolecular Displacement Reactions 46 B.4. Miscellaneous 47 C. Chemical Properties of Oxetan-3-ones 48 C.1. Ring Opening and Ring Expansion of Oxetan-3-ones 48 C.2. Transformations of the Carbonyl Group 49 IV. The Chemistry of Thietan-3-ones 50 A. Synthetic Methods for Thietan-3-ones 51 A.1. Synthesis from Acyclic Precursors 51 A.2. Synthesis by Ring Transformations 53 B. Chemical Properties of Thietan-3-ones 54 B.1. Transformations of the Carbonyl Group 55 B.2. Aldol Reactions 56 B.3. Ring Transformations 56 V. Acknowledgments 58 VI. References 58

The synthesis of 4-(1-haloalkyl)-2-azetidinones and 4-(2-haloalkyl)-2-azetidinones was investigated with use of the Staudinger reaction between in situ generated ketenes and alpha-haloimines or beta-haloimines. This new class of functionalized 2-azetidinones was further evaluated for its potential use as intermediates in the synthesis of highly functionalized compounds. The reaction of 4-(1-haloalkyl)-2-azetidinones and 4-(2-haloalkyl)-2-azetidinones with sodium methoxide in methanol yielded ring-opened products, i.e., methyl 2-alkoxy-4-(alkylamino)pentenoate and methyl 5-(alkylamino)pentenoate, respectively. Further attention was paid in detail to the reaction mechanism involved in this peculiar transformation. It was proven that these reactions proceeded via intermediate aziridines or azetidines.

An easy synthesis of 2-aryl-3,3-dichloroazetidines, a rather unexplored class of azaheterocycles, is described. The title compounds were easily obtained by reduction of the corresponding 4-aryl-3,3-dichloro-2-azetidinones with monochloroalane, which in turn were synthesized by a ketene-imine [2 + 2] cycloaddition. The reactivity of 3,3-dichloroazetidines with bases was investigated, yielding 2-[dimethoxy(aryl)methyl]aziridines by ring contraction when treated with sodium methoxide. Furthermore, reacting the 3,3-dichloroazetidines with sodium hydride in DMSO, followed by aqueous workup, afforded 1-alkyl-2-aroylaziridines, by hydrolysis of the intermediate 2-azetines and ring closure of the transient 3-amino-2-chloro-1-phenyl-1-propanone derivatives. Monitoring this reaction in an NMR tube, using sodium hydride in DMSO-d(6), allowed the characterization of the intermediate strained heterocyclic enamines, i.e., 2-azetines, by (1)H and (13)C NMR.

The synthesis of para di-and monosubstituted benzhydrylamines by addition of Grignard reagents to benzonitriles and subsequent reduction, is evaluated and discussed. The reduction step with sodium borohydride allows simple handling and mild conditions. An optimized synthesis of 4,4'-dimethoxybenzhydrylamine by this method is disclosed.

No abstract