Apparent 6‐<i>endo‐</i>trig Carbofluorination of Alkenes Enabled by Palladium‐Based Dyotropic Rearrangement
Jing Gong, Qian Wang, Jieping Zhu
Abstract
Abstract Alkene difunctionalization featuring an intramolecular carbometallation step has been developed into a powerful transformation in organic synthesis. The 5‐ exo ‐trig carbometallation is in general highly favored over the alternative 6‐ endo ‐trig cyclization. We report herein a formal 6‐ endo ‐trig carbofluorination protocol by combining the conventional 5‐ exo ‐trig carbopalladation with a chemoselective 1,2‐aryl/Pd dyotropic rearrangement. Treatment of 2‐(2‐alkylallyloxy)phenyl boronic acid derivatives in the presence of a catalytic amount of Pd(dba) 2 , 4,4′‐di‐ tert ‐butyl‐2,2′‐bipyridine and Selectfluor affords chromanes with concurrent generation of a tertiary alkyl fluoride function. A σ‐alkyl‐Pd II species resulting from the 5‐ exo ‐trig carbopalladation process is isolated and characterized by X‐ray crystallographic analysis. Its oxidation to Pd IV complex triggers the chemoselective dyotropic rearrangement leading to the ring expansion product.