Highly Diastereoselective Self-1,3-Dipolar [3+3] Cycloaddition of Azomethine Ylides Promoted by Cesium Catalyst

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A highly diastereoselective self-1,3-dipolar [3+3] cycloaddition reaction catalyzed by cesium carbonate has been established for the synthesis of 2,5-dispirooxindole-piperazines.This reaction involves the reaction of azomethine ylides derived from unprotected isatins with tetrahydroisoquinolines.The method is characterized by its simplicity, avoidance of excess external acids and high diastereoselectivity.As privileged structures, spirocyclic oxindoles are frequently found in natural products, drugs and pharmaceutical active molecules, 1 rendering them significant synthetic objectives in the realms of organic and medicinal research.2 In recent years, 1, 3-dipolar cycloaddition (1,3-DC) of azomethine ylides derived from isatins has attracted an increasing amount of interest owing to their distinctive ability to construct a wide array of spirooxindole ring systems.3 For example, the azomethine ylides, which are formed in situ from isatin derivatives and specific amino substrates, undergo reactions with various electrophilic reagents as dipolarophiles.These reagents include electron-deficient alkenes, 4 alkynes, 5 chromane derivatives, 6 azirines, 7 or α, β-unsaturated ketones.8 These reactions result in the formation of structurally intricate spirooxindole derivatives through multicomponent 1,3-dipolar cycloaddition reactions.Although effective and innovative approaches for the diversity-oriented synthesis of spirooxindoles have been developed, these methods typically necessitate the utilization of specific secondary α-amino acids or amino compounds in conjunction with an excess of strong acid additives to generate the crucial azomethine ylides.Furthermore, although many metal salts, such as copper, 9 silver etc., 10 have been used as catalyst for the cycloaddition of imino esters-derived azomethine ylides, the research of employing metal salts as catalyst in the transformation of isatin-derived azomethine ylides remains less-explored.11