Addition of Alkynes to Aldehydes and Activated Ketones Catalyzed by Rhodium−Phosphine Complexes

Abstract

A mixture of 2-(di-tert-butylphosphino)biphenyl and dicarbonylacetonato rhodium(I) provides an effective catalyst system for the addition of alkynes to aldehydes and activated ketones. In contrast to the more common zinc-catalyzed processes, enolizable 1,2-dicarbonyls are excellent substrates for these rhodium-catalyzed additions. This reaction allows for the formation of propargylic alcohols under mild conditions, tolerating many functional groups (such as carboxylic acids) that are incompatible with other methods. Little selectivity was observed in cases of unsymmetrical 1,2-diketones. Addition of alkynes to aldehydes with an adjacent chirality center usually provides the Felkin addition product with excellent selectivity in some cases. Studies on the catalyst structure show that both the beta-diketonate and a carbon monoxide ligand appear to be bound to the active catalyst. The use of chiral phosphines to induce asymmetry in the propargyl alcohol products provided low enantioselectivity, which may be due to the phosphine having a distal relationship to the reacting centers. Modification of other ligands, such as the beta-diketonate, appears to be a more promising avenue for the development of an enantioselective variant.

Biarylphosphanliganden in der palladiumkatalysierten Aminierung

“…1998 haben wir eine neue Klasse luftbeständiger [1] Liganden mit DialkylbiarylphosphanGerüst eingeführt. [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] Cyanier...…”

Biaryl Phosphane Ligands in Palladium‐Catalyzed Amination

“…In 1998 we introduced a new class of air-stable [1] phosphine ligands based on the dialkylbiaryl phosphine backbone. [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]…”

Buchwald‐Type Ligands on Gold(I) Catalysis

“…[23] Between these two extremes, bulky dialkyl biarylphosphine ligands introduced by Buchwald in 1998 for Pdcatalyzed coupling reactions, [25] provide electronically and sterically an intermediate alternative. Due to their stability with respect to oxidation [26] and synthetic accessibility, [27] this class of ligands has been employed in numerous Pd-catalyzed CÀ C [28,29] and CÀ X (X=N, O, F) [30][31][32][33] bond-forming reactions as well as in combination with other transition metals such as Ag, [34] Rh, [35,36] Ru [37] and Cu. [38] Our group introduced the use of dialkyl biarylphosphine ligands in the context of gold(I) catalysis [39] resulting in a new family of highly electrophilic gold(I) complexes A-D which were found to catalyze diverse transformations upon chloride abstraction.…”