Cobalt-Catalyzed Asymmetric Addition of Silylacetylenes to 1,1-Disubstituted Allenes

Abstract

The asymmetric addition of silylacetylenes to 1,1-disubstituted allenes proceeded in the presence of a cobalt/chiral bisphosphine ligand to give the corresponding enynes with high enantioselectivity. The results of deuterium-labeling experiments indicated that a hydrogen atom at the chiral center is originated from the terminal alkyne, and they were in good agreement with the proposed catalytic cycle where enantioselectivity is determined by the reaction of the proposed π-allylcobalt intermediate with the terminal alkyne.

Redox Non‐Innocence of Coordinated 2‐(Arylazo) Pyridines in Iridium Complexes: Characterization of Redox Series and an Insight into Voltage‐Induced Current Characteristics

“…Nishimura et al50 reported the catalytic asymmetric addition of silylacetylenes 118 to 1,1‐disubstituted allenes 119 in the presence of cobalt/chiral diphosphine ligands to afford the corresponding exo ‐enynes 120 with high enantioselectivities along with certain amounts of the endo ‐enyne isomers 121 (Scheme ). A screening of diphosphine ligands revealed that diphosphino ferrocene 122 furnished the best stereoselectivities, ranging from 92 to 99.5 % ee , while limiting the formation of the undesired achiral endo ‐enynes 121 .…”

Iridium‐Catalyzed Enantioselective Hydroalkynylation of Enamides for the Synthesis of Homopropargyl Amides

“…Enamides with an acetal, ketone, and ester group underwent the hydroalkynylation smoothly (3 r-t), thus furnishing valuable homopropargyl amides in good enantioselectivity except for the ester-containing product 3 t. As in many catalytic hydroalkynylation reactions, the alkynes are currently limited to silylacetylenes. [8][9][10][11] Aryl-and alkyl-substituted terminal alkynes did not react under the current reaction conditions because of fast oligomerization of these alkynes.…”

“…compounds, [6] and electron-neutral alkenes such as allenes, 1,3-dienes, and norbornene. [8][9][10] We now have shown that an electron-rich enamide can undergo hydroalkynylation with high enantioselectivity. Although the b-position of an enamide is more electron rich than its a-position, the acetylide addition selectively occurs at the b-position.…”

Catalytic Enantioselective Protoboration of Disubstituted Allenes. Access to Alkenylboron Compounds in High Enantiomeric Purity

“…Nonetheless, methods for enantioselective protonation 2 of allylmetal species are scarce. 3 The difficulty in designing a catalytic enantioselective allyl anion protonation arises from the identification of a Brønsted acid that is compatible with the reaction conditions and contains a counterion component that allows proper acidity to be maintained while imparting sufficient bulk to cause stereochemical differentation. We envisioned that if a 1,1-disubstituted allene ( i , Scheme 1) were to undergo selective reaction with a chiral Cu–B(pin) complex (pin = pinacolato), 4 and the resulting allylcopper ( ii ) were to be γ-selectively and enantioselectively protonated via iii , 5 a Cu-catalyzed route to versatile unsaturated organoboron compounds ( iv ) would be in hand.…”