The dearomative [5 + 1] annulation of 2-methylindoles with new five-membered synthon was developed through cascade [1,5]-hydride transfer/dearomative cyclization in HFIP for the synthesis of spirochromanes bearing the 2-methylindolenine skeleton.
Isoxazolines are highly significant for the development of new synthetic methodology and pharmaceutics. Indolines and 2,3dihydrobenzofurans are also privileged structures in natural products and pharmaceuticals. In continuation of our ongoing research on transformations of 5-aminoisoxazoles and quinone derivaties, herein we report Sc(OTf) 3 -catalyzed dearomative [3 + 2] annulations of 5-aminoisoxazoles with quinone imine ketals (QIKs) and quinone monoacetals (QMAs). A variety of indolineand 2,3-dihydrobenzofuran-fused isoxazolines were afforded in moderate to good yields with excellent diastereoselectivities (all cases > 20 : 1 dr). This method featured mild reaction conditions, wide substrate scope, and gram-scale synthesis.
An aromatization-driven hydride transfer-involved α-C(sp3)–H bond functionalization of the oxygen atom was developed. Easily prepared p-quinone methides were applied to initiate [1,5]-hydride transfer/cyclization for generating spirochromanes.
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