Azetines are valuable 4-membered nitrogen-containing heterocycles with unique reactivity and useful synthetic applications. Recent methods to access these compounds and a comprehensive review of their application as intermediates is presented.
Four-membered nitrogen-containing heterocycles are highly desirable functional groups with synthetic and biological applications. Unsaturated 4-membered N-heterocycles, 1- and 2-azetines, are historically underexplored, but have recently been gaining increased interest due to the development of new synthetic methods to access these compounds, and to their potential as reactive intermediates. This review covers new strategies for the synthesis of 1- and 2-azetines with a particular focus on advances made since 2018. Additionally, the use of these compounds as intermediates to access other heterocycles (3- to 6-membered) and complex products is comprehensively discussed.
Cyclopentadienes are scaffolds in organometallic chemistry, synthetic organic chemistry, and catalysis. We herein describe a regioselective Lewis-acid-catalyzed method for the synthesis of highly functionalized cyclopentadienes incorporating electronically and sterically diverse subunits. Our experimental and theoretical investigations support a mechanism that is related to catalytic carbonyl-olefin metathesis reactions wherein Lewis-acid-catalyzed cycloadditions between carbonyl and alkene functionalities afford reactive oxetane intermediates. However, in lieu of a [2+2]-cycloreversion, stepwise oxetane fragmentation to intermediate carbocations results in the formation of functionalized cyclopentadienes via interrupted carbonyl-olefin metathesis. This work provides insights into the design of catalytic carbonyl-olefin metathesis reactions of aliphatic ketone substrates as stepwise oxetane fragmentation was previously only reported as a competing reaction pathway for aryl ketones.
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