Organic dyes are an attractive alternative to the use of transition-metal complexes in photoredox catalysis. Herein, we report an inexpensive organic dye (eosin Y)-catalyzed radical coupling of α-bromocarbonyl compounds with allyltrifluoroborates under visible light irradiation. This reaction was accelerated by either Bu₄NF or CsF. Based on mechanistic studies, the cation exchange between potassium allyltrifluoroborate and Bu₄NF proceeded to generate KF. The generated KF or CsF acts as a Lewis acid to promote a single electron transfer (SET) from eosin Y to α-halocarbonyls. The protocol was applied to bromoesters, bromoketones, and bromoamides to give the coupling products in high yields.

The Group 14 enolates play an important part in many organic reactions. Herein, the reduction of an α-bromo ketone with germanium(II) salts cleanly afforded the corresponding germyl enolate as an isolatable species. This experimental reductive generation of a germyl enolate enabled us to characterize both C- and O-bound tautomers derived from an identical precursor and to unveil the tautomeric mechanisms, including the kinetic parameters and the relative stability of these tautomers, along with confirmation from DFT calculations. Moreover, the highly coordinated germyl enolates were isolated by a stabilization process induced by adding ligands. All products were characterized by NMR spectroscopy and X-ray crystallography.

A sequential addition of silyl cyanide and ketene silyl acetals to esters was achieved by a gallium trihalide catalyst to produce β-cyano-β-siloxy esters. This is the first example of the sequential addition of two different carbon nucleophiles to esters. The employment of lactones provided α,α-disubstituted cyclic ethers with a cyano group and an ester moiety. A variety of esters and lactones are applicable to this reaction system.

Boron complexes that contain new tridentate ligands, tris(o-oxyaryl)methanes and -silanes, were prepared. These complexes had a cage-shaped structure around a boron center and showed higher Lewis acidity and catalytic activity than open-shaped boron compounds. The cage-shaped ligands determined the properties of the borates by altering the geometry and were consistently bound to the metal center by chelation. The synthesized compounds were L⋅B(OC₆H₄)₃CH, L⋅B(OC₆H₄)₃SiMe, and its derivatives (L=THF or pyridine as an external ligand). Theoretical calculations suggested that the cage-shaped borates had a large dihedral angle (C_ipso-O-B-O) compared with open-shaped borates. The geometric effect due to the dihedral angle means that compared with open-shaped, the cage-shaped borates have a greater Lewis acidity. The introduction of electron-withdrawing groups on the aryl moieties in the cage-shaped framework increased the Lewis acidity. Substitution of a bridgehead Si for a bridgehead C decreased the Lewis acidity of the boron complexes because the large silicon atom reduces the dihedral angle of C_ipso-O-B-O. The ligand-exchange rates of the para-fluoro-substituted compound B(OC₆H₃F)₃CH and the ortho-phenyl-substituted compound B(OC₆H₃Ph)₃CH were less than that of the unsubstituted borate B(OC₆H₄)₃CH. The ligand-exchange rate of B(OC₆H₄)₃SiMe was much faster than that of B(OC₆H₄)₃CH. A hetero Diels–Alder reaction and Mukaiyama-type aldol reactions were more effectively catalyzed by cage-shaped borates than by the open-shaped borate B(OPh)₃ or by the strong Lewis acid BF₃⋅OEt₂. The cage-shaped borates with the bulky substituents at the ortho-positions selectively catalyzed the reaction with less sterically hindered substrates, while the unsubstituted borate showed no selectivity.

The reductive system of allyl bromide and indium(0) in water generated monoallylindium(III) dibromide and diallylindium(III) bromide. These compounds were characterized by X-ray analysis after complexation with 3,5-dibromopyridine or 4-(dimethylamino)pyridine, respectively. Both isolated complexes showed high nucleophilicity and reacted with benzaldehyde to give the allylation product. The diallylindium(III) bromide was less stable in water than the monoallylindium(III) dibromide. The reaction of the diallylindium(III) with benzhydrol gave a (μ-alkoxido)indium species that showed nucleophilicity. This result suggests that allyl(μ-hydroxido)indium also acted as a nucleophile in an aqueous Barbie-type reaction system.

The cover picture shows the species generated in the reductive system of allyl bromide with indium(0) in water. They include monoallylindium(III) dibromide, diallylindium(III) bromide, and allyl(μ-oxido)indium(III). These compounds were characterized on the basis of X-ray analysis. The allylindium compounds showed nucleophilicity towards carbonyl compounds with different reactivities. Details are discussed in the Short Communication by M. Yasuda, A. Baba et al. on p. 5359 ff.