Atroposelective Arene-Forming Wittig Reaction by Phosphorus PIII/PV=O Redox Catalysis.

The Wittig reaction is renowned as exceptionally versatile method for converting a diversity of aldehydes and ketones into alkenes. Recently, strategies for chiral phosphine catalysis under PIII/PV=O redox cycling emerged to render this venerable transformation stereoselective. Herein, we describe that phosphine redox catalysis enables the enantioselective synthesis of pertinent biaryl atropisomers by means of a stereocontrolled arene-forming Wittig reaction. Key to the process is the release of an endogenous base from readily accessible tert-butyloxycarbonylated Morita-Baylis-Hillman adducts triggered by catalyst intramolecularization, permitting mild phosphine redox catalysis for atroposelective Wittig reactions. By this strategy, a broad diversity of biaryl atropisomers is obtained with up to 94 : 6 enantioselectivity.

Atroposelective PIII /PV =O Redox Catalysis for the Isoquinoline-Forming Staudinger-aza-Wittig Reaction.

Herein, we describe the feasibility of atroposelective PIII /PV =O redox organocatalysis by the Staudinger-aza-Wittig reaction. The formation of isoquinoline heterocycles thereby enables the synthesis of a broad range of valuable atropisomers under mild conditions with enantioselectivities of up to 98 : 2 e.r. Readily prepared azido cinnamate substrates convert in high yield with stereocontrol by a chiral phosphine catalyst, which is regenerated using a silane reductant under Brønsted acid co-catalysis. The reaction provides access to diversified aryl isoquinolines, as well as benzoisoquinoline and naphthyridine atropisomers. The products are expeditiously transformed into N-oxides, naphthol and triaryl phosphine variants of prevalent catalysts and ligands. With dinitrogen release and aromatization as ideal driving forces, it is anticipated that atroposelective redox organocatalysis provides access to a multitude of aromatic heterocycles with precise control over their configuration.

Allylboronic Esters as Acceptors in Radical Addition, Boron 1,2-Migration, and Trapping Cascades.

Radical 1,3-carboheteroarylation and 1,3-hydroalkylation of allylboronic esters comprising a 1,2-boron shift is reported. Allylboronic esters are generally used in synthesis as allylation reagents, where the boronic ester moiety gets lost. In the introduced cascades, alkylboronic esters are obtained with the boron entity remaining in the product. The carboheteroarylation of the allylboronic esters are conducted without a metal catalyst, and the 1,3-hydroalkylation is achieved using iron catalysis. Both reactions work efficiently under mild conditions.

Transition-Metal-Free Intramolecular Radical Aminoboration of Unactivated Alkenes.

An efficient transition-metal-free cyclizing radical aminoboration of unactivated alkenes is reported. The B2(OH)4 reagent was used as the boron source, and the interaction between B2(OH)4 and an aryloxyamide N-radical precursor enabled the chain reaction to be initiated upon irradiation in the absence of any catalyst. This transformation proceeds via cyclization of an N-radical with subsequent intermolecular C-radical borylation. The cascade shows a broad scope and provides a wide range of high-value cyclic 1,2-aminoboronic esters.

Remote Radical Desaturation of Unactivated C-H Bonds in Amides.

Desaturation of inert aliphatic C-H bonds in alkanes to form the corresponding alkenes is challenging. In this communication, a new and practical strategy for remote site-selective desaturation of amides via radical chemistry is reported. The readily installed N-allylsulfonylamide moiety serves as an N radical precursor. Intramolecular 1,5-hydrogen atom transfer from an inert C-H bond to the N-radical generates a translocated C-radical which is subsequently oxidized and deprotonated to give the corresponding alkene. The commercially available methanesulfonyl chloride is used as reagent and a Cu/Ag-couple as oxidant. The remote desaturation is realized on different types of unactivated sp3 -C-H bonds. The potential synthetic utility of this method is further demonstrated by the dehydrogenation of natural product derivatives and drugs.

Intramolecular Hydrogen Atom Transfer Induced 1,2-Migration of Boronate Complexes.

Radical α-C-H functionalization of alk-5-enyl boronic esters with concomitant functionalization of the alkene moiety is reported. These cascades comprise perfluoroalkyl radical addition to the alkene moiety of a boronate complex, intramolecular hydrogen atom transfer (HAT), single electron oxidation, and 1,2-alkyl/aryl migration. The boronate complexes are readily generated in situ by reaction of the alkenyl boronic esters with alkyl or aryl lithium reagents. Products are formed in a divergent approach by varying carbon radical precursors as well as alkyl/aryl lithium donors, and reactions proceed under mild conditions upon UV irradiation.

Preparation of α-Perfluoroalkyl Ketones from α,ß-Unsaturated Ketones via Formal Hydroperfluoroalkylation.

Formal hydroperfluoroalkylation of enones is achieved in a two-step process comprising conjugate hydroboration and subsequent radical perfluoroalkylation. The 1,4-hydroboration of the enone is conducted in the absence of any transition metal catalyst with catecholborane in 1,2-dichloroethane, and the generated boron enolate is in situ α-perfluoroalkylated with a perfluoroalkyl iodide upon blue LED irradiation in the presence of an amine additive. Both reactions proceed under very mild conditions at room temperature.

Cobalt complex catalyzed atom-economical synthesis of quinoxaline, quinoline and 2-alkylaminoquinoline derivatives.

A new phosphine-free Co(ii) complex-catalyzed synthesis of various quinoxalines via dehydrogenative coupling of vicinal diols with both o-phenylenediamines and 2-nitroanilines is reported. This complex was also effective for the synthesis of quinolines. The practical aspect of this catalytic system was revealed by the one-pot synthesis of 2-alkylaminoquinolines.