Rhodium-Catalyzed [6 + 2] Cycloaddition of Internal Alkynes with Cycloheptatriene: Catalytic Study and DFT Calculations of the Reaction Mechanism

Abstract

A rhodium-catalyzed [6 + 2] cycloaddition of internal alkynes with cycloheptatriene is described. A series of substituted alkynes were cycloadded to cycloheptatriene through a [6 + 2] addition to give a variety of substituted bicyclic compounds in excellent yields. The optimal catalytic system for these transformations was a [Rh(COD)Cl]2 (5.0 mol %) catalyst in combination with CuI (10 mol %) and PPh3 (10 mol %). The proposed mechanism for this system includes an initial oxidative coupling reaction between the coordinated cycloheptatriene and the internal alkyne, followed by a [1,3]-shift of the Rh metal center and a reductive elimination from the Rh(III)–allyl complex to give the final product. Calculations using a model Rh(I) catalyst were also carried out to further understand this mechanism.

Titanium‐Catalyzed [6π+2π]‐Cycloaddition of Alkynes and Allenes to 7‐Substituted 1,3,5‐Cycloheptatrienes

“…Analysis of published data demonstrates that 1,3,5‐cycloheptatriene and its derivatives are promising monomers for the synthesis of important bi‐ and tricyclic compounds 2. Codimerization reactions of 1,3,5‐cycloheptatriene with alkenes, 1,2‐, 1,3‐dienes, and alkynes in the presence of Ti,3 Cr,4 Co,5 Rh,6 Au, and Pt7 complexes have been studied in detail and are used in the stereoselective synthesis of some natural compounds 8…”

New in the Catalytic Synthesis of Practically Important Eight- and Nine-Membered Carbocycles by Cycloaddition Reactions with the Participation of 1,3,5-Cycloheptatrienes and 1,3,5,7-Cyclooctatetraenes

“…In the literature, there are preferably publications devoted to the study of reactions of thermally and photochemically induced cycloaddition of alkenes, 1,2-, 1,3-dienes and alkynes to Fe-, Ru-and Cr-containing carbonyl complexes CHT [10][11][12][13][14]. The catalytic variants of these transformations are represented by Ti-, Co-, Cr-, Mo-and Rh-catalyzed cyclodimerization of CHT [15][16][17][18][19][20][21].…”

Transition metal catalyzed [6 + 2] cycloadditions

“…The [6 + 2] cycloadditions do not occur using PPh 3 RhCl as catalyst at 60 °C. 36 The [6 + 2] cycloadditions at elevated temperature (120 °C) witness the formation of cycloadduct (64%). Further increase in reaction temperature causes decrease in yield of 20 (53%).…”