Chemoselective, Dearomative Reduction of Epoxide‐Tethered Indoles en Route to HFIP‐Promoted Diastereoselective Synthesis of 1,7‐Fused Indolines

Abstract The reductive dearomatization reaction of N ‐alkylindoles represents an expedient approach to the generation of N ‐alkylindolines that are primed for elaboration into more complex target molecules but difficult to access in synthetically acceptable yields directly from (NH)‐indolines via their N ‐alkylation. However, its application to obtain N ‐alkylindolines bearing reducible functional groups remains a more challenging and long‐standing problem due to functional group compatibility issues. In this context, we have achieved a dearomative, chemoselective reduction of epoxide‐tethered indoles promoted by NaBH 3 CN/AcOH to obtain hitherto unreported trans ‐benzylic epoxide‐tethered indolines. Notably, these products can be diastereoselectively cyclized into 1,7‐fused indolines bearing two contiguous sp 3 stereocenters in a subsequent HFIP‐promoted epoxide–indoline cyclization step.