Intermolecular Methoxycarbonylation of Terminal Alkynes Catalyzed by Palladium(II) Bis(oxazoline) Complexes

Abstract

Boxing clever: Direct conversion of a terminal alkyne group into a beta-methoxyacrylate is realized with the aid of the bis(oxazoline) ligand (box). Acetyl and ketal protecting groups, free hydroxy groups, and acid-sensitive glycosidic bonds are not affected under the reaction conditions. The one-pot synthesis of (+/-)-dihydrokawain from the homopropargyl alcohol is also achieved. tfa = trifluoroacetate.

Chemicals from Alkynes with Palladium Catalysts

“…Among these palladium-catalyzed Reppe reactions with alkynes, the reaction using carbon monoxide and water leading to carboxylic acids (hydrocarboxylation) has been much less frequent than the reaction with alcohols (hydroesterification or hydroalkoxycarbonylation) and amines (aminocarbonylation Under these reaction conditions, (E)-cinnamic acid (72) was obtained as the major product, whereas the branched 2-phenylacrylic acid (73) was obtained in only a 4%…”

“…and the bis-oxazoline ligand (S)-PhBox (76) (7.5 mol%) in the presence of pbenzoquinone (Scheme 26). 73 Internal alkynes have been less common substrates than terminal ones for these types of carbonylation reactions, as regioselectivity is a frequent problem. The use of CO has also been avoided in the case of the aminocarbonylation reaction, for instance, by using formamides.…”

Alkoxide-catalyzed addition of alkyl carbonates across alkynes – stereoselective synthesis of (E)-β-alkoxyacrylates

“…23 The palladium-catalysed methoxycarbonylation of terminal alkynes reported by Kato and Akita (C) is efficient but suffers from the use of toxic carbon monoxide and stoichiometric amounts of benzoquinone (BQ) as the oxidant. 24,25 From a sustainable chemistry standpoint, the addition of alkyl carbonates across terminal alkynes would represent one of the best conceivable synthetic concepts to access (E)-β-MOA.…”

Vielfältige Reaktivitäten: aktuelle Entwicklungen bei metallkatalysierten Alkinreaktionen

“…[12] Kürzlich entdeckten nun Kato et al, dass sich Palladiumkatalysatoren für den intermolekularen Prozess eignen. [13] 3 Ln-Katalysatoren (Binol = 1,1'-Bi-2-naphthyl) entwickelten. [14] 2007 führten Shibasaki et al eine neue Klasse von zweikernigen Schiff-Basen als Katalysatoren ein (Schema 7), die eine Vielzahl von hoch enantioselektiven Umwandlungen vermitteln können, [15,16] unter anderem die Addition an aktivierte Alkine.…”

“…Dort koordiniert das Acetylen so an das Ru-Zentrum, dass beide CH-Protonen des Acetylens eine Wasserstoffbrücke zu den Pyridin-Stickstoffatomen der Liganden bilden. [23] 13 C-markierte Acylgruppe um d = 1.6 ppm. [23] Die restlichen Reaktionsschritte bestehen wahrscheinlich aus einer Protonierung des Ru-Zentrums durch das Pyridyl-NH-Proton mit anschließender reduktiver Eliminierung eines Aldehyds oder einer direkten Protonierung der Acylgruppe durch das NH-Proton.…”