Abstract
Two complementary cascade cyclization reactions were described, namely KHSO4-promoted [1+2+3] cyclization and TMSCl-promoted four-molecular cascade cyclization for the concise synthesis of highly functionalized spirooxindoles in excellent yields. Between them, the improved TMSCl-promoted cyclization reaction of isatins, N,N-dimethylenaminones and amines was carried out to afford various desired products under milder conditions. The observed chemoselectivity of new TMSCl-promoted cyclization mechanism was reasonably explained by designing the intermediate bis-enaminones. Furthermore, the gram-scale synthesis and the synthetic applications were also evaluated.
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