Iron-Catalyzed Borylation of Propargylic Acetates for the Synthesis of Multisubstituted Allenylboronates

A novel iron-catalyzed borylation of propargylic acetates leading to allenylboronates has been developed. The method allows the preparation of a variety of di-, tri- and tetrasubstituted allenylboronates at room temperature with good functional group compatibility. Stereochemical studies show that an anti-S_N 2' displacement of acetate by boron occurs; this also allows transfer of chirality to yield enantiomerically enriched allenylboronates. The synthetic utility of this protocol was further substantiated by transformations of the obtained allenylboronates including oxidation and propargylation.

Ir-Catalyzed Enantioconvergent Synthesis of Diversely Protected Allenylic Amines Employing Ammonia Surrogates

The first iridium catalyzed, enantioconvergent amination of allenylic carbonates is reported. This process utilizes various commercially available carbamates and sulfonamides to generate allenylic amines including commonly employed protected groups (Boc, Fmoc, Cbz, Ts, Ns) in 62-82 % yield and 87-98 % ee. The products generated through this scalable procedure serve as effective linchpins for the rapid, enantiospecific synthesis of a wide range of complex structures.

Enantio- and Diastereoselective Synthesis of Homopropargyl Amines by Copper-Catalyzed Coupling of Imines, 1,3-Enynes, and Diborons

An efficient, enantio- and diastereoselective, copper-catalyzed coupling of imines, 1,3-enynes, and diborons is reported. The process shows broad substrate scope and delivers complex, chiral homopropargyl amines; useful building blocks on the way to biologically-relevant compounds. In particular, functionalized homopropargyl amines bearing up to three contiguous stereocenters can be prepared in a single step.

Controlling Regioselectivity in the Enantioselective N-Alkylation of Indole Analogues Catalyzed by Dinuclear Zinc-ProPhenol

The enantioselective N-alkylation of indole and its derivatives with aldimines is efficiently catalyzed by a zinc-ProPhenol dinuclear complex under mild conditions to afford N-alkylated indole derivatives in good yield (up to 86 %) and excellent enantiomeric ratio (up to 99.5:0.5 e.r.). This method tolerates a wide array of indoles, as well as pyrrole and carbazole, to afford the corresponding N-alkylation products. The reaction can be run on a gram scale with reduced catalyst loading without impacting the efficiency. The chiral aminals were further elaborated into various chiral polyheterocyclic derivatives. The surprising stability of the chiral N-alkylation products will open new windows for asymmetric catalysis and medicinal chemistry.

The isomerization of allylrhodium intermediates in the rhodium-catalyzed nucleophilic allylation of cyclic imines

Allylrhodium species generated from potassium allyltrifluoroborates can undergo isomerization by 1,4-rhodium(I) migration to give more complex isomers, which then react with cyclic imines to provide products with up to three new stereochemical elements. High enantioselectivities are obtained using chiral diene-rhodium complexes.