Apparent 6‐endo‐trig Carbofluorination of Alkenes Enabled by Palladium‐Based Dyotropic Rearrangement

• Published in: Angewandte Chemie International Edition Vol. 61; no. 50; pp. e202211470 - n/a
• Main Authors: Gong, Jing, Wang, Qian, Zhu, Jieping
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 12.12.2022; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: Alkenes; Carbofluorination; Chemistry; Chemistry, Multidisciplinary; Chromane; Crystallography; Domino Process; Dyotropic Rearrangement; Fluorides; Oxidation; Palladium; Physical Sciences; Science & Technology; Dyotropic Rearrangement; SYMMETRY CONTROLLED REACTIONS; Carbofluorination; Chromane; SCOPE; Domino Process; Palladium; DIARYLATION; CLEAVAGE; CYCLIZATION-ANION CAPTURE; C-H FLUORINATION; BONDS; ESTERS; FLUOROARYLATION
• ISSN: 1433-7851; 1521-3773; 1521-3773
• DOI: 10.1002/anie.202211470

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‐PdII species resulting from the 5‐exo‐trig carbopalladation process is isolated and characterized by X‐ray crystallographic analysis. Its oxidation to PdIV complex triggers the chemoselective dyotropic rearrangement leading to the ring expansion product. Reversing the intrinsic cyclization mode. Pd‐catalyzed cyclization of 2‐(2‐alkylallyloxy)phenyl boronic acid derivatives in the presence of Selectfluor 2 provides chromanes 3 with concurrent generation of a tertiary alkyl fluoride function. A 5‐exo‐trig carbopalladation affords PdII intermediate A whose oxidation to PdIV followed by 1,2‐aryl/PdIV dyotropic rearrangement and C−F bond‐forming reductive elimination affords chromane 3.