Several bidentate dihydroimidazolines were prepared and investigated as catalysts for hydrogen transfer reduction of C═N bond with Hantzsch ester. Highly efficient reactions were observed for quinolines and imines with low catalyst loading of 2 mol %. The presence of halogen bonding was elucidated using NMR studies and isothermal calorimeric titrations. Binding constants of the XB donors were also measured using isothermal calorimeric titrations (ITC).

Highly enantioselective allylic alkynylation of racemic bromides under biphasic condition is furnished in this report. This approach employs functionalized terminal alkynes as pro-nucleophiles and provides 6- and 7-membered cyclic 1,4-enynes with high yields and excellent enantioselectivities (up to 96% ee) under mild conditions. Enantioretentive derivatizations highlight the synthetic utility of this transformation. Cold-spray ionization mass spectrometry (CSI-MS) and X-ray crystallography were used to identify some catalytic intermediates, which include guanidinium cuprate ion pairs and a copper-alkynide complex. A linear correlation between the enantiopurity of the catalyst and reaction product indicates the presence of a copper complex bearing a single guanidine ligand at the enantio-determining step. Further experimental and computational studies supported that the alkynylation of allylic bromide underwent an anti-S2' pathway catalyzed by nucleophilic cuprate species. Moreover, metal-assisted racemization of allylic bromide allowed the reaction to proceed in a dynamic kinetic fashion to afford the major enantiomer in high yield.

Herein, we report the conjugate addition of a,bunsaturated carbonyl compounds to thiophene derivatives. We used a2 -iodoimidazolinium triflate salt as ah alogenbonding donor,w hich afforded moderate-to-excellent yields of the corresponding alkylated thiophenes. Insight into the catalytic process was obtained from 1 HNMR spectroscopy studies and DFT calculations, which indicated ah alogenbonding-supportedm echanism with limited Brønsted acid catalysis.

An enantioconvergent synthesis of chiral cyclic allylboronates from racemic allylic bromides was achieved by using ag uanidine-copper catalyst. The allylboronates were obtained with high g/a regioselectivities (up to 99:1) and enantioselectivities (up to 99 %e e), and could be further transformed into diverse functionalized allylic compounds without erosion of optical purity.E xperimental and DFT mechanistic studies support an S N 2' borylation process catalyzed by am onodentate guanidine-copper(I) complex that proceeds through as pecial direct enantioconvergent transformation mechanism.Scheme 1. Synthesis of enantioenriched tertiary allylboronates.

Visible-light photoredox catalysis plays an important role in various reactions which are inaccessible under typical thermal conditions. Distinctly different from common visible-light photoredox catalysis which often involves transition-metal complexes, conjugated organic dyes, or electron donor−acceptor complexes, herein, the use of ion-pair charge-transfer (IPCT) complex-induced visible-light photoredox catalytic reactions are described, wherein the cyclization−methoxylation of N-vinyl amides in methanol was achieved under irradiation with blue LEDs. The reaction employs a heteroarenium iodide as the photocatalyst and can be extended to cyclization−alkoxylation, −acyloxylation, and −hydroxylation. This protocol provides an eco-friendly synthetic route to a wide range of oxazoline derivatives. Mechanistic investigations with UV−visible spectroscopy and control experiments confirm the existence of the IPCT absorption band in the visible region for the heteroarenium iodide, which is responsible for the observed reactivity.