Rhodium‐Catalyzed Formation of Stereocontrolled Trisubstituted Alkenes from Baylis–Hillman Adducts

Abstract

Efficient and general conditions for the formation of stereodefined trisubstituted alkenes by using the rhodium-catalyzed reaction of unactivated Baylis-Hillman adducts with either organoboronic acids or potassium trifluoro(organo)borates are reported (see scheme).We report here efficient and general conditions for the formation of stereodefined trisubstituted alkenes using the rhodium-catalyzed reaction of unactivated Baylis-Hillman adducts with either organoboronic acids and potassium trifluoro(organo)borates. The use of the [{Rh(cod)OH}(2)] precursor gave very fast coupling reactions under low catalyst loading, very mild reaction conditions (from room temperature up to 50 degrees C) and without the need of additional phosphane ligands. Based on the new reaction conditions, the reaction, originally limited to Baylis-Hillman adducts derived from esters, could be extended to a large variety of Baylis-Hillman adducts, bearing either keto, cyano or amido functionalities. Moreover, the reaction of Baylis-Hillman adducts bearing esters functionality was improved and could be conducted at lower temperature using lower catalyst loading.

Synthesis of Titanium Chabazite: A New Shape Selective Oxidation Catalyst with Small Pore Openings and Application in the Production of Methyl Formate from Methanol

“…The experimental evidence suggests a competitive catalytic pathway. The α‐benzyl acrylate 6 could arise from the η 1 ‐C rhodium species III through a syn β‐amido elimination pathway to afford IV in a process reminiscent of the elimination step proposed by Darses and co‐workers for the rhodium‐catalyzed reaction of unactivated Baylis–Hillman adducts with aryl boronic acids 17. Alternatively, a hydrolytic elimination pathway via V that involves the coordination of a proton source to a η 1 ‐C rhodium intermediate is postulated 18.…”

Catalytic Enantioselective Dieckmann‐Type Annulation: Synthesis of Pyrrolidines with Quaternary Stereogenic Centers

“…The a-benzyl acrylate 6 could arise from the h 1 -C rhodium species III through a syn b-amido elimination pathway to afford IV in a process reminiscent of the elimination step proposed by Darses and co-workers for the rhodium-catalyzed reaction of unactivated Baylis-Hillman adducts with aryl boronic acids. [17] Alternatively, a hydrolytic elimination pathway via V that involves the coordination of a proton source to a h 1 -C rhodium intermediate is postulated. [18] The dominant pathway appears to be dictated by a ligand-dependent equilibration between rhodium enolate species.…”

Kinetic Resolution of Hindered Morita–Baylis–Hillman Adducts by Rh(I)-Catalyzed Asymmetric 1,4-Addition/β-Hydroxyelimination

“…Although a wide range of electron-deficient alkenes have proven to be suitable substrates for the asymmetric Hayashi–Miyaura reactions, nonactivated α,α,β-trisubstituted alkenes are still challenging substrates for this type of reaction. Very recently, Darses and co-workers described a Rh(I)-catalyzed 1,4-addition of arylboronic acids 2 to hindered Morita–Baylis–Hillman (MBH) adducts 1 followed by a β-hydroxyelimination to furnish functionalized alkenes 3 in up to 91% yield (Scheme ) . Two examples for the asymmetric version with C 1 -symmetric chiral diene ligands developed by their own group gave the desired products 3 in 25% yield with 84% ee, which were still not satisfactory, while several well-established chiral phosphane ligands showed little activity for this transformation .…”