Catalytic Transformations of Terminal Alkynes by Cationic Tris(1-pyrazolyl)borate Ruthenium Catalysts: Versatile Chemistry via Catalytic Allenylidene, Vinylidene, and π-Alkyne Intermediates

Abstract

In this report, we describe the catalytic activation of terminal alkynes using TpRuPPh 3 (MeCN) 2 X (X = PF 6 and SbF 6 ) complexes. These ruthenium species enable transformation of terminal alkynes into π-alkyne, vinylidene, and allenylidene intermediates, and provide new catalytic reactions via three different pathways. Due to the cationic nature and the coordinative unsaturation around the ruthenium center, we observed the formation and scission of new types of C-X (X = O, N, C) bonds occurring in the catalytic transformations of terminal alkynes, as well as structurally reorganized products. This review summarizes some important examples. 1 Introduction 2 Allenylidene Intermediate 2.1 Internal Redox Reaction 2.2 Cleavage of Carbon-Carbon Triple Bond 3 Vinylidene Intermediate 3.1 Cyclization of CIS-3-En-1-ynes 3.2 Cyclization of CIS-3-Eny-1-nyl Epoxides 3.3 Cyclization of 3,5-Dien-1-ynes 3.4 Cyclization of 3,5-Dien-1-ynes with Skeletal Rearrangement 3.5 Cyclization of 2′,2′-Disubstituted (o-ethynyl)styrenes 4 π-Alkyne Intermediates 4.1 Cyclization of Acyclic 6,6-Disubstituted 3,5-Dien-1-ynes 4.2 Aromatization of Enediynes with Catalytic Nucleophilic Additions 4.3 Aromatization of Endiynes with Catalytic C-H Bond Insertion 5 Concluding Remarks