Palladium‐Catalyzed Highly Regioselective Mizoroki–Heck Arylation of Allylamines with Aryl Chlorides

Abstract

ChemCatChem 2014, 6, 311 -318 311 CHEMCATCHEM FULL PAPERS portant structural units in many natural products and pharmaceuticals and serve as versatile starting materials for the synthesis of various functionalized compounds. [14,15] There has been considerable interest in using palladium-catalyzed Mizoroki-Heck arylation of readily accessible allylamines to prepare arylated allylamines, but the regiocontrol remains problematic. [11b, 16, 17] Hallberg, [16a,b] Wu, [16c] Baxter, [11e] and Zhou [11b] reported that the catalyst prepared in situ from a diphosphine ligand and Pd(OAc) 2 could work well to catalyze the coupling reaction of aryl triflates with allylamines to provide the b-arylated products with high regioselectivities and yields; however, the drawbacks associated with the use of aryl triflates, such as base sensitivity and thermal lability, make this method less attractive. Ripin [17d] and Wilson [17e] reported that the palladium-catalyzed highly regioselective and stereoselective terminal arylation of allylamines could be accomplished in alcohol solvents under ligand-free conditions; however, only one aryl iodide substrate was tried. The groups of Sigman, [17h] Cacchi, [17i] and Correia [17j] described Pd 2 (dba) 3 -catalyzed preferential g-arylation of allylamines with arenediazonium salts in the absence of a ligand; however, the synthetic utility of this chemistry could be restricted by the intrinsic drawbacks of arenediazonium salts, such as instability and explosive potential. Despite these advances, it should be pointed out that none of these precedents enable the efficient and selective arylation of allylamines with aryl chlorides.During our investigation of the regioselective arylation of allylamines, [18] we reported that the highly regioselective internal Mizoroki-Heck arylation of N-Boc-allylamine (Boc = tert-butyloxycarbonyl) with aryl bromides could proceed smoothly with palladiumdppp (dppp = 1,3-bis(diphenylphosphino)propane) catalysts in ethylene glycol (EG) and Pd(OAc) 2 could catalyze the coupling reaction of aryl bromides with bulky N,N-diprotected allylamines under ligand-free conditions in water or DMF, preferentially giving the g-arylated products. [18a,b] More recently, we found that the highly regioselective direct arylation of allylamines with thiophenes and furans could be accomplished with Pd(OAc) 2 and suitable additives. [18c] Notably, the electronic and steric properties of allylamine substrates in these reactions have a significant effect on the catalytic activity and regiocontrol. Encouraged by these results and with our continued interest in the regioselective arylation of olefins, herein we report that a palladium catalyst system consisting of Pd(OAc) 2 and appropriate additives efficiently catalyzes the highly regioselective linear (g-)arylation of N,Ndiprotected allylamines with aryl chlorides under ligand-free conditions whereas N-protected allylamines could undergo a highly efficient internal (b-)arylation with aryl chlorides with the Pd-dppf catalyst (dp...

Controlling Reactivity and Selectivity in the Mizoroki–Heck Reaction: High Throughput Evaluation of 1,5-Diaza-3,7-diphosphacyclooctane Ligands

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Scalable Synthesis of Cinnamylamines Via the Heck Reaction: Application in the Synthesis of Abamine, Naftifine and Reboxetine

“…[15,16] The latter type of substrate however is generally undesired in large scale synthesis due to its thermal instability, the additional cost and reduced atom economy associated with the second Boc group. In addition to this, the protocols reported jointly by Zhang, Jiang et al (Scheme 2a) [17,18] use 10-20 mol % TEMPO which is cost prohibitive at these loadings for large scale applications. [19] The same group has also reported a trans-selective oxidative Heck variant using arylboronic acids and N-Boc-allylamine as the substrates.…”

Bromide-assisted chemoselective Heck reaction of 3-bromoindazoles under high-speed ball-milling conditions: synthesis of axitinib

“…Though aryl bromides are always interesting substrates for industrial applications [ 11 – 12 ], possessing the characteristics of lower cost, easier to obtain and stable to store, they face the problem of dehalogenations especially under metal-catalyzed reactions [ 8 , 13 – 18 ], affecting the reaction yield and selectivity. Currently, the Heck reaction is usually carried out by adding an excess of phase-transfer catalyst such as tetrabutylammonium bromide (TBAB) or tetrabutylammonium iodide (TBAI) to increase the reaction yield under both solvent-heating [ 19 – 23 ] and solvent-free conditions [ 24 – 27 ]. Despite two proposals for the role of quaternary ammonium salts NR 4 + X − , (1) Pd(0) stablizer and (2) phase transfer were suggested [ 28 – 30 ], their effects and functions remain unrevealed.…”