Modular Synthesis of Spiroisochromans with Spiro Quaternary Carbon Centers Via TBAT-Promoted Multicomponent Cascade Reactions

The construction of spiroisochroman frameworks featuring spiro quaternary carbon centers via multicomponent cascade reactions remains a formidable synthetic challenge. Herein, we report a tetrabutylammonium triphenyldifluorosilicate-initiated reaction system involving oxazolines, aryne precursors, and ketone derivatives. This protocol enables a facile one-pot synthetic approach to structurally challenging spiroisochroman scaffolds, including dispiro architectures and spiroisochromanone derivatives, which are otherwise difficult to synthesize. The transformation proceeds through aryne-triggered generation of reactive ortho- quinonoid intermediates, followed by selective [4 + 2] cycloaddition with carbonyl compounds. Notably, a substituent-controlled divergent pathway leading to phthalide derivatives was also discovered in this reaction system. The operational simplicity, broad applicability, and divergent reactivity highlight the synthetic utility of this cascade strategy.