Palladium-Catalyzed Additions of Terminal Alkynes to Acceptor Alkynes

Abstract

The development of addition reactions wherein the product is the simple sum of the reactants plus anything else (only needed catalytically) constitutes an important goal for enhanced synthetic efficiency. The C−H bond of terminal alkynes (the donor alkynes) can be added to either terminal alkynes (self-coupling) or activated internal alkynes (cross-coupling) (the acceptor alkynes) in the presence of a catalytic amount of palladium acetate and an electron rich sterically encumbered ligand, tris(2,6-dimethoxyphenyl)phosphine. The activated internal alkynes for cross-coupling (the acceptor alkyne) include alkynes bearing an ester, sulfone, and ketone. Self-coupling is completely overwhelmed by cross-coupling, even at 1:1 ratios of donor and acceptor alkynes. The reaction exhibits extraordinary chemoselectivity with free carboxaldehydes, alcohols, ketones (saturated and conjugated), esters (saturated and conjugated), sulfones (saturated and conjugated), malonates, and silyl ethers all proving to be compatible. A 1:2 donor/acceptor alkyne adduct can also be optimized. Ethyl propiolate fails as an acceptor but its C-silylated analogue serves with the proper choice of silyl substituent. The products of the latter serve as useful precursors to β-keto esters. An iterative sequence is readily performed and led to a novel conformationally rigid retinoid analogue. The mechanism of this mild method for construction of conjugated enynes, versatile building blocks, is discussed.

Regio- and Stereoselective Homodimerization of Monosubstituted Acetylenes in the Presence of the Second Generation Grubbs Catalyst

“…Many examples of effective run of the process in the presence of transition metal complexes have been described. Catalytic activity in the process has been reported to be shown by complexes of such metals as palladium [4,[7][8][9][10][11][12][13], rhodium [14][15][16][17][18][19], ruthenium [20][21][22][23][24][25][26][27][28][29], nickel [30], iridium [31][32][33], osmium [34,35], iron [36] and the f-block metals [37][38][39]. However, a highly selective synthesis of conjugated enynes by dimerization is still a challenging process.…”

“…Protonation of enynyl species by the acidic proton of the terminal alkyne, produces enynes and regenerates the active catalyst. The insertion mechanism has been originally proposed by Trost for palladium complexes [8]. However, it has also been postulated for ruthenium complexes [48].…”

C-C and C-O Coupling Reactions of Terminal Alkynes by a Water Soluble Organoiridium Electron-transfer Mediator in Thin Layer of Water on Gold Electrode

“…This resulting anionic radical compound could produce highly reactive species which will be used to catalyze the activation of organic substrates such as alkynes. Metal-catalyzed hydration and oligomerization of alkynes provide important processes in organic chemistry to aldehydes, ketones, and conjugated olefin compounds since they are the carbon-oxygen [6][7][8][9][10] and -carbon [11][12][13][14][15][16][17][18][19] bond forming reactions which produce a variety of new inexpensive starting materials.…”

“…Among water-soluble ligands, PAr 3 (P(m-C 6 H 4 SO 3 Na) 3 ) is the most commonly used ligand to prepare water-soluble metal compounds [27][28][29][30][31][32]. Iridium-Cp * (C 5 Me 5 -) compounds have been investigated and have drawn much attention due to their diverse and interesting reactivity with alkynes [11][12][13][14][15][16][17][18][27][28][29][30][31][32][33][34][35][36][37].…”

“…Since it is well-known that terminal alkynes can be activated by organoiridium compounds [11][12][13][14][15][16][17][18], this voltammetric observation prompted us to look into details of reduced-metal catalyzed activation of alkynes in biphasic (H 2 O/CH 2 ClCH 2 Cl) solution. The biphasic…”