Desilylation‐Promoted Phosphine Catalysis: Intramolecular Annulation/Nucleophilic Addition Sequence of Trimethylsilylethynyl Benzoxazinanones with N‐Tosyl Imines

Under phosphine catalysis facilitated through desilylation, intramolecular annulation/nucleophilic addition of trimethylsilylethynyl benzoxazinanones with electron-deficient imines or alkenes was achieved to afford a series of indole derivatives in moderate to high yields. The trimethylsilylethynyl benzoxazinanones without electron-withdrawing group on the alkyne moiety functioned as phosphine acceptors. Notably, the distinctive desilylation activation played a key role in catalytic process. Particularly, those indole derivatives could be readily transformed into various biologically significant gamma-carboline compounds. The use of chiral phosphine achieved asymmetric reaction, leading to a 95% ee of product.