Highly Site Selective Formal [5+2] and [4+2] Annulations of Isoxazoles with Heterosubstituted Alkynes by Platinum Catalysis: Rapid Access to Functionalized 1,3‐Oxazepines and 2,5‐Dihydropyridines

• Published in: Angewandte Chemie International Edition Vol. 56; no. 2; pp. 605 - 609
• Main Authors: Shen, Wen‐Bo, Xiao, Xin‐Yu, Sun, Qing, Zhou, Bo, Zhu, Xin‐Qi, Yan, Juan‐Zhu, Lu, Xin, Ye, Long‐Wu
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 09.01.2017; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: Alkynes; annulation; Catalysis; Chemistry; Chemistry, Multidisciplinary; heterocycles; homogeneous catalysis; Intermediates; Physical Sciences; Platinum; Science & Technology; ynamides; PI-ACID CATALYSIS; PHENOL SYNTHESIS; ENANTIOSELECTIVE GOLD CATALYSIS; MOLECULAR COMPLEXITY; IDENTIFICATION; 3+2 CYCLOADDITION; platinum; annulation; homogeneous catalysis; heterocycles; CARBENES; ynamides; CYCLOISOMERIZATION; CYCLIZATION
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201610042

Platinum‐catalyzed formal [5+2] and [4+2] annulations of isoxazoles with heterosubstituted alkynes enabled the atom‐economical synthesis of valuable 1,3‐oxazepines and 2,5‐dihydropyridines, respectively. Importantly, this Pt catalysis not only led to unique reactivity dramatically divergent from that observed under Au catalysis, but also proceeded via unprecedented α‐imino platinum carbene intermediates. Gold's deviant relative: Platinum‐catalyzed formal [5+2] and [4+2] annulations of isoxazoles and heterosubstituted alkynes provided valuable 1,3‐oxazepines and 2,5‐dihydropyridines (see scheme). This reactivity deviates dramatically from that observed under gold catalysis and involves the generation of an α‐imino platinum carbene. A computational study provided evidence for the proposed mechanism of this unusual tandem sequence.