Studies on the Heck Reaction with Alkenyl Phosphates:  Can the 1,2-Migration Be Controlled? Scope and Limitations

Abstract

A catalyst system was identified which promotes the Heck coupling of nonactivated vinyl phosphates with electron deficient alkenes providing a new entry to diene products from simple and readily accessible starting materials. In contrast to our earlier work exploiting P(t-Bu)3 as the ligand in the presence of PdCl2(COD), the application of Buchwald's dialkylbiarylphosphines, X-Phos, effectively promoted the vinylic substitution with a wide range of alkenyl phosphates in the presence of 10 equiv of lithium chloride. Importantly, these reaction conditions suppressed 1,2-migration of the alkenyl palladium(II) intermediate. Further studies are also reported with the catalytic system which encourages isomerization in order to determine the range of vinyl phosphates that may participate in these coupling reactions. The extent of the 1,2-migration was dependent on the C1-substituent where best results were noted for substrates possessing a C1-alkyl quaternary carbon. Hence, with certain members of this class of alkenyl phosphates either the migrated or nonmigrated Heck products may be preferentially synthesized by selection of the phosphine ligand. Finally, competition experiments between an unactivated aryl chloride and a vinyl phosphate with a palladium catalyst possessing either X-Phos or P(t-Bu)3 as ligand demonstrated the ability to carry out Heck coupling reactions selectively with the aryl halide. Oxidative addition of the metal catalyst into the aryl chloride bond rather than the C-O bond of the alkenyl phosphate is therefore preferred.

Transition‐Metal‐Catalyzed Direct Arylation of (Hetero)Arenes by CH Bond Cleavage

“…Unfortunately, their improved stabilities translate into significantly reduced reactivity in catalytic coupling reactions. As a result, methods for palladiumcatalyzed direct arylation [183] through cleavage of C À H bonds with these aryl sulfonates were achieved only very recently. Thus, we reported the first palladium-catalyzed direct arylations of electron-rich heteroarenes with aryl tosylates as electrophilic coupling partners.…”

“…A ruthenium complex derived from HASPO [131] 374 allowed for the first direct arylation [183] with aryl tosylates. [238] Remarkably, electron-deficient as well as electron-rich tosylates could be employed, with pyridine, oxazoline, and pyrazole derivatives serving as pronucleophiles (Scheme 141).…”

Biarylphosphanliganden in der palladiumkatalysierten Aminierung

“…[2] Als Liganden für Gold, [3][4][5][6][7][8][9][10][11] Silber, [12] Rhodium, [13,14] Ruthenium [15][16][17] und Kupfer [18] verbesserten diese Phosphane die Reaktivität und Katalysatorstabilität. Die weitaus größte Bedeutung hatten sie aber für palladiumkatalysierte Reaktionen wie die Sonogashira-, [19] Negishi-, [20] Hiyama-, [21][22][23] Kumada- [24] und Suzuki-Kreuzkupplung [25][26][27][28][29][30] , die Heck-Reaktion, [31][32][33] die Enolatarylierung [34][35][36][37] und -allylierung, [38] die reduktive Cyclisierung [39] und Veretherung, [40][41][42][43] die Silylierung, [44] Borylierung, [45][46][47] Cyanierung, [48,49] Methylierung, …”

Biaryl Phosphane Ligands in Palladium‐Catalyzed Amination

“…[2] These phosphines have been used as ligands for gold, [3][4][5][6][7][8][9][10][11] silver, [12] rhodium, [13,14] ruthenium [15][16][17] and copper [18] where they have been shown to impart improvements in reactivity and catalyst stability. It is in reactions catalyzed by palladium, however, that they have had by far the greatest impact including the Sonogashira, [19] Negishi, [20] Hiyama, [21][22][23] Kumada [24] and Suzuki [25][26][27][28][29][30] cross-coupling reactions, Heck reaction, [31][32][33] enolate arylation [34][35][36][37] and allylation, [38] reductive cyclization [39] and etherification, [40][41][42][43] silylation, [44] borylation, [45][46][47] cyanation, [48,…”