Multicomponent Reactions between Heteroatom Compounds and Unsaturated Compounds in Radical Reactions

In this mini-review, we present our concepts for designing multicomponent reactions with reference to a series of sequential radical reactions that we have developed. Radical reactions are well suited for the design of multicomponent reactions due to their high functional group tolerance and low solvent sensitivity. We have focused on the photolysis of interelement compounds with a heteroatom-heteroatom single bond, which readily generates heteroatom-centered radicals, and have studied the photoinduced radical addition of interelement compounds to unsaturated compounds. First, the background of multicomponent radical reactions is described, and basic concepts and methodology for the construction of multicomponent reactions are explained. Next, examples of multicomponent reactions involving two interelement compounds and one unsaturated compound are presented, as well as examples of multicomponent reactions involving one interelement compound and two unsaturated compounds. Furthermore, multicomponent reactions involving intramolecular cyclization processes are described.

Phosphorus-Recycling Wittig Reaction: Design and Facile Synthesis of a Fluorous Phosphine and Its Reusable Process in the Wittig Reaction

This study shows that phosphorus sources can be recycled using the appropriate fluorous phosphine in the Wittig reaction. The designed fluorous phosphine, which has an ethylene spacer between its phosphorus atom and the perfluoroalkyl group, was synthesized from air-stable phosphine reagents. The synthesized phosphine can be used for the Wittig reaction process to obtain various alkenes in adequate yields and stereoselectivity. The concomitantly formed fluorous phosphine oxide was extracted from the reaction mixture using a fluorous biphasic system. The fluorous phosphine was regenerated by reducing the fluorous phosphine oxide with diisobutylaluminum hydride. Finally, a series of gram scale phosphorus recycling processes were performed, which included the Wittig reaction, separation, reduction, and reuse.

A SF5 Derivative of Triphenylphosphine as an Electron-Poor Ligand Precursor for Rh and Ir Complexes

The synthesis of the triarylphosphine, P(p-C₆H₄SF₅)₃ containing a SF₅ group, has been achieved. The experimental and theoretical studies showed that P(p-C₆H₄SF₅)₃ is a weaker σ-donor when compared with other substituted triarylphosphines, which is consistent with the electron-withdrawing effect of the SF₅ moiety. The studies also revealed a moderate air stability of the phosphine. The σ-donor capabilities of P(p-C₆H₄SF₅)₃ were estimated from the phosphorus-selenium coupling constant in SeP(p-C₆H₄SF₅)₃ and by DFT calculations. The behavior of P(p-C₆H₄SF₅)₃ as ligand has been investigated by the synthesis of the iridium and rhodium complexes [MCl(COD){P(p-C₆H₄SF₅)₃}], [MCl(CO)₂{P(p-C₆H₄SF₅)₃}₂] (M = Ir, Rh), or [Rh(µ-Cl)(COE){P(p-C₆H₄SF₅)₃}]₂, and the molecular structures of [IrCl(COD){P(p-C₆H₄SF₅)₃}] and [Rh(µ-Cl)(COE){P(p-C₆H₄SF₅)₃}]₂ were determined by single X-ray diffraction. The structures revealed a slightly larger cone angle for P(p-C₆H₄SF₅)₃ when compared to other para-substituted triarylphosphines.

Perfluorinated phosphine and hybrid P–O ligands for Pd catalysed C–C bond forming reactions in solution and on Teflon supports

The synthesis of two types of phosphine ligands that feature perfluorinated ponytails is reported. A bidentate (RfCH₂CH₂)₂PCH₂CH₂P(CH₂CH₂Rf)₂ (Rf = CF₃(CF₂)_n; n = 5, 7) and an alkoxyphosphine made by ring opening a fluorous epoxide, RfCH₂CH(OH)CH₂PR₂ (Rf = CF₃(CF₂)₇), have been prepared and spectroscopically characterised. The electronic effects of the fluorous chains have been elucidated from either the ¹J_Pt–P or ¹J_P–Se coupling constants in Pt(ii) or phosphine selenide compounds. Whilst the bidentate phosphines do not give stable or active Pd catalysts, the hybrid ligand does allow Susuki, Heck and Sonogashira catalysis to be demonstrated with low catalyst loadings and good turnovers. Whilst a fluorous extraction methodology does not give good performance, the ligand can be adsorbed onto Teflon tape and for the Suzuki cross coupling reaction the catalytic system can be run 6 times before activity drops and this has been traced to oxidation of the ligand. Additionally the crystal structure of the hybrid phosphine oxide is reported and the non-covalent interactions discussed.

Phosphine ligands containing a perfluorous ponytail can be sorbed onto Teflon tape and used as ligands for C–C cross coupling reactions with little leaching.

Aroyl chlorides as novel acyl radical precursors via visible-light photoredox catalysis

Abundant and inexpensive aroyl chlorides have been employed for the first time as novel acyl radical precursors in visible-light photocatalysis.