Visible light-induced iridium(III)-sensitized [2 + 2] and [3 + 2] photocycloadditions of 2-cyanochromone with alkenes.

2-Cyanochromone (1) readily undergoes visible light-induced photocycloadditions with diverse alkene partners mediated by (Ir[dF(CF)ppy](dtbpy))PF as the photosensitizer. While mono-, di- and trisubstituted styrenes and acrylonitriles as the reactants lead to [2 + 2] cycloadducts with good regiocontrol and high diastereoselectivity, the use of trialkyl-substituted alkenes allows for the isolation of cyclopentenone-fused chromones resulting from a [3 + 2] cycloaddition process in moderate yields.

Photocatalytic Azetidine Synthesis by Aerobic Dehydrogenative [2 + 2] Cycloadditions of Amines with Alkenes.

Photocatalytic dehydrogenative [2 + 2] cycloadditions between amines and alkenes were developed that allow for the stereoselective and high-yielding synthesis of functionalized azetidines. The oxidative formal Aza Paternò-Büchi reactions are induced by photoredox-catalyzed aerobic oxidation of dihydroquinoxalinones as the amines, and in the presence of structurally diverse alkenes intermolecular [2 + 2] cyclization to dihydro-1-azeto[1,2-]quinoxalin-3(4)-ones occurs. The utility of the method is illustrated by the selective conversion of amino acid derived dihydroquinoxalinones , including oxidation-prone lysine and tryptophan derivatives.

Value-added chemicals from biomass-derived furans: radical functionalisations of 5-chloromethylfurfural (CMF) by metal-free ATRA reactions.

Biomass-derived 5-chloromethylfurfural (CMF), a congener of the well-known carbohydrate-based platform chemical 5-hydroxymethylfurfural (HMF), can efficiently be functionalised by radical transformations of its benzylic chloromethyl group. We report here the first examples of these radical reactions by way of metal-free, triethylborane/oxygen-induced atom transfer radical addition (ATRA) reactions between CMF and styrenes, which proceed with high yield and selectivity. The key intermediate, the 2-formyl-5-furfuryl radical derived from CMF, and its radical addition reactions were studied with regard to its electronic structure, i.