[Development of Novel Preparations for Nitrogen Heterocycles Based on Cascade Reactions]

Nitrogen heterocycles are important skeletons in biologically active compounds such as medicines and natural alkaloids. However, in terms of the efficiency of the synthetic process, the many synthetic steps required to achieve the target compounds with complex architectures pose a significant problem. To overcome this challenge, novel approaches were developed to afford biologically active heterocycles, 1,2-diazepines, pyrroloisoquinolines, and pyrrolizidines utilizing cascade reactions that enable multiple bond formation in a one-pot process. This review discusses three one-pot reactions: 1) 1,2-diazepine synthesis from cyclobutenones and lithiodiazoesters via cascade 4π-8π electrocyclization; 2) synthesis of pyrroloisoquinolines from alkynylimino esters triggered by gold-catalyzed azomethine ylide formation; and 3) pyrrolizidine synthesis via three-component coupling reactions of iminoesters, acetylenes, and maleimides through the gold-catalyzed azomethine ylide generation/[3+2]-cycloaddition/enamine cyclization reaction.