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Compared to other nitrogen heterocycles such as aziridines, pyrrolidines, or piperidines, the chemistry of azetidines is much less developed, probably because of their limited availability. In this account, recent synthetic routes to these strained heterocycles starting from readily available enantiomerically pure starting compounds will be detailed. The ring strain in these heterocycles makes them excellent candidates for nucleophilic ring-opening or ring-expansion reactions yielding higher ring systems or highly substituted acyclic amines. These useful transformations will be described in the second section of this account. 1 Introduction 1.1 Synthesis of Azetidines from ?-Amino Alcohols 2 Synthetic Transformation of 2-Cyanoazetidines 3 Ring Expansion of Functionalized Azetidines 3.1 Ring Expansion to Pyrrolidines 3.2 Ring Expansion to Azepanes 4 Ring Opening of Azetidines and Azetidinium Ions 5 Reactivity of Azetidinium Ylides 6 Synthetic Applications 7 Concluding Remarks [ABSTRACT FROM AUTHOR]

Evidence for the formation of an ovoid chiral cage, resulting from the auto-assembly of two hexafunctional and three tetrafunctional modules reacting through dynamic covalent bond formation, is provided. [ABSTRACT FROM AUTHOR]

Enantiomerically pure N-allyl azetidinium ions undergo a stereoselective [2,3]-sigmatropic shift to give azetidines with an α-quaternary center. These compounds are direct precursors of �2-alkyl-2-carboxy-azetidines, a new class of constrained α-amino acids. [ABSTRACT FROM AUTHOR]

Upon treatment with DAST (diethylaminosulfur trifluoride) enantiopure 2-hydroxyalkylazetidines rearrange into 3-fluoropyrrolidines. The reaction is stereospecific and involves a bicyclic 1-azoniabicyclo[2.1.0]pentane intermediate which is regioselectively opened by a fluoride anion. [ABSTRACT FROM AUTHOR]

An eight-step total synthesis of the 15-membered ring cyclopeptide alkaloid mucronine E is reported. Key steps include the formation of the highly substituted aromatic core using an asymmetric hydrogenation-Vilsmeier formylation sequence. Central to our approach was a macroamidation protocol using a copper-catalyzed coupling reaction to install the enamide with a concomitant straightforward macrocyclization. This synthesis also allowed for the assignment of both relative and absolute configurations of mucronine E. [ABSTRACT FROM AUTHOR]