Decarboxylative Cross‐Coupling of Mesylates Catalyzed by Copper/Palladium Systems with Customized Imidazolyl Phosphine Ligands

Abstract

Decarboxylative cross-coupling reactions have recently emerged as a powerful methodology for the regioselective construction of CÀC and CÀheteroatom bonds. [1] Their key advantage over traditional cross-coupling reactions is that they draw on stable and readily available carboxylate salts as sources of carbon nucleophiles rather than expensive and sensitive organometallic reagents. In the last decade, a rapidly growing number of decarboxylative reactions have been discovered including decarboxylative Heck reactions, [2] allylations, [3] redox-neutral cross-coupling reactions, [4] oxidative coupling reactions, [5] CÀH arylations, [6] homocouplings, [7] and Chan-Lam-type reactions. [8] Redox-neutral decarboxylative cross-couplings mediated by Cu/Pd or Ag/Pd bimetallic catalyst systems proved to have a particularly broad scope with regards to both carboxylates and carbon electrophiles. In this variant, the decarboxylation step is mediated by a Cu I [9] or Ag I [10] catalyst, while a Pd complex catalyzes the coupling with the carbon electrophile. Whereas aryl bromides and iodides can be converted with very simple ligand systems, [11] the activation of aryl chlorides, [12] triflates, [13] and tosylates [14] requires the use of sophisticated catalyst systems containing electron-rich, bulky phosphine ligands. However, all attempts to develop decarboxylative couplings of the notoriously hard-to-activate methanesulfonates (mesylates) have failed so far (Scheme 1).Aryl and alkenyl mesylates are particularly attractive carbon electrophiles for preparative-and industrial-scale syntheses, since they have the lowest molecular weight of all sulfonate leaving groups. They are easily accessible by Angewandte Chemie 2955

Copper-catalyzed decarboxylative C−P cross coupling of arylpropiolic acids with dialkyl hydrazinylphosphonates leading to alkynylphosphonates

“…Notably, the 3-(p-tolyl)propiolic acid 1b and meta-substituted counterpart 1c afforded similar yields of 70% and 61%, respectively, but sterically demanding 3-(o-tolyl)propiolic acid only gave a very low yield of 9%, illustrating that this coupling reaction is sensitive to steric hindrance (entries 2 and 3). Interestingly, fluoro group substituted substrates such as 1f, 1g and 1h could well be coupled with diethyl hydrazinylphosphonate 2a, affording the desired products in moderate yields ( Table 2, [10][11][12]. To gain more insight into the substrate scope of the reaction, in addition to 1a, the alkynylation of diisopropyl hydrazinylphosphonate (1b) and P,P-diphenylphosphinic hydrazide were also detected.…”

“…The transformation could not proceed without the participation of CuSO 4 , revealing that CuSO 4 catalyst was essential to achieve a high yield of product 2a. To advance the process further, the effect of solvents was also investigated, such as CH 3 CN, 1, 4-dioxane and toluene, however, no desired product was observed (entries [10][11][12]. Subsequent survey on the role of oxidants disclosed H 2 O 2 or tert-butyl hydroperoxide (TBHP) could not promote this reaction (entries [13][14].…”

“…In the past few years, the decarboxylative coupling reaction as a new synthetic strategy has wide applications in the construction of C-C and C-heteroatom bonds. [10][11][12][13][14][15][16][17][18][19] Among these couplings, as a practical alternative, using arylpropiolic acids instead of terminal alkynes as the coupling partner is safer and more promising since arylpropiolic acids are usually solid-state without unpleasant smell and easy to prepare, store, and transport. [20] Following this viewpoint, in 2011, Yang's group first reported the Pd/Cu cocatalyzed decarboxylative coupling of arylpropiolic acid with H-phosphonate for the synthesis alkynylphosphonates.…”

Pd‐Catalyzed Decarboxylative Cross‐Coupling of 2‐Carboxyazine N‐Oxides with Various (Hetero)aryl Halides

“…[9] More recently, the Wu and Stoltz research groups achieved the bimetallic Pd 0 /Cu I -catalyzed decarboxylative coupling of unsubstituted 2-azynylcarboxylic acids by using only aryl bromides as coupling partners (Scheme 1, [Eq. Two mechanisms have been considered; 1) the conventional bimetallic-catalyzed decarboxylative cross-coupling reaction (Figure 1, cycles A and C) [2,15,16] and 2) the direct CÀH arylation of the protodemetalated N-oxide substrate (Figure 1, cycles B and C). [10] Recent calculations and studies of this dual catalysis (Pd/Cu or Pd/Ag) revealed that the decarboxylative metalation likely proceeds by means of an ipso-interaction of the metal (Cu I or Ag I ) on the carboxylate function, and could be facilitated by the electron-withdrawing effect of a heteroatom at the orthoposition.…”

“…[10] Recent calculations and studies of this dual catalysis (Pd/Cu or Pd/Ag) revealed that the decarboxylative metalation likely proceeds by means of an ipso-interaction of the metal (Cu I or Ag I ) on the carboxylate function, and could be facilitated by the electron-withdrawing effect of a heteroatom at the orthoposition. Two mechanisms have been considered; 1) the conventional bimetallic-catalyzed decarboxylative cross-coupling reaction (Figure 1, cycles A and C) [2,15,16] and 2) the direct CÀH arylation of the protodemetalated N-oxide substrate (Figure 1, cycles B and C). Moreover, N-oxidation of azines is one of the most employed activation methods to introduce various substituents at the C2 position.…”