Dehydrogenative Heck Annelations of Internal Alkynes

Abstract

This review covers the palladium-catalyzed annelations of internal alkynes through reactions leading to the loss of only two hydrogens from the substrates. They occur via (i) dual C-H bond activation, (ii) both C-H and N-H bond activation, (iii) successive amino(or oxy)palladation and C-H bond activation, or (iv) C-H bond activation followed by a Heck-type process. The proposed mechanisms are described with, in some cases, personal commentary.

Palladium Catalysis: Dependence of the Efficiency of C−C Bond Formation on Carboxylate Ligand and Alkali Metal Carboxylate or Carboxylic Acid Additive. Part C: The Domino Diarylation and Annelation Reactions

“…In fact, a number of dehydrogenative Heck annelations has been carried out with diphenylacetylene [36] under Pd(OAc) 2 catalysis, such as the reaction with -N,N-dimethylindolizine-1-carboxamide using O 2 in DMSO as reoxidant [37] in yield depending on the nature of the RCO 2 H additive (Scheme 11a), [38] -8-(p-tolyl)-BODIPY under conditions improved in absence of RCO 2 H, especially with PdCl 2 (PhCN) 2 as the catalyst and AgOCOt-Bu as the oxidant in ClCH 2 CH 2 Cl (Scheme 11b), [39] -cyclohexyl furan-2-carboxylate under oxygen in DMF containing stoichiometric amounts of both carboxylic acid and carboxylate, the best result being obtained with EtCMe 2 CO 2 H and EtCMe 2 CO 2 Na (Scheme 11c) and the absence of one of these two additives being prejudiciable to the yield, [40] -1-benzylpyrazole under air in DMF with AgOAc rather than AgOCOt-Bu, in yield increased by addition of t-BuCO 2 H (Scheme 11d), [41] -(E)-but-1-ene-1,3-diyldibenzene using CF 3 CO 2 H and O 2 /Cu(OAc) 2 in xylene, no annulation arising under acid-free conditions (Scheme 11e). [42] A simplified catalytic cycle leading to annelation 1-benzylpyrazole is presented in Scheme 11f.…”

“…In fact, a number of dehydrogenative Heck annelations has been carried out with diphenylacetylene [36] under Pd(OAc) 2 catalysis, such as the reaction with…”