Photoredox-Enabled Synthesis of β-Substituted Pyrroles from Pyrrolidines

The merger of photoredox-initiated enamine-imine tautomerization and nucleophilic addition processes to access β-substituted pyrroles from pyrrolidines has been achieved. The significant advantage of this method is suppressing the Friedel-Crafts reaction, which usually occurs between N-aryl pyrrolidines and the highly electrophilic ketoesters. The good functional group tolerance, high atom economy, and high regioselectivity as well as easy handling conditions make it an appealing alternative to synthesize β-substituted pyrroles.

Tandem dihetero-Diels–Alder and Huisgen cycloaddition reactions. Synthesis, crystal structure and hydrolysis of the novel cage phosphoranes

The reaction of 2-(1-phenylvinyloxy)benzo-1,3,2-dioxaphosphole with activated carbonyl compounds leads to the stereoselective formation of cage phosphoranes.

Versatile iridicycle catalysts for highly efficient and chemoselective transfer hydrogenation of carbonyl compounds in water

Cyclometalated iridium complexes are shown to be highly efficient and chemoselective catalysts for the transfer hydrogenation of a wide range of carbonyl groups with formic acid in water. Examples include α-substituted ketones (α-ether, α-halo, α-hydroxy, α-amino, α-nitrile or α-ester), α-keto esters, β-keto esters and α,β-unsaturated aldehydes. The reduction was carried out at substrate/catalyst ratios of up to 50 000 at pH 4.5 and required no organic solvent. The protocol provides a practical, easy and efficient way for the synthesis of β-functionalised secondary alcohols, such as β-hydroxyethers, β-hydroxyamines and β-hydroxyhalo compounds, which are valuable intermediates in pharmaceutical, fine chemical, perfume and agrochemical synthesis.

Stereospecific substitution at alpha-carbon to trifluoromethyl group: application to optically active fluorinated amino acid syntheses

This account summarizes how we performed the intramolecular nucleophilic substitutions of the hydroxy groups at alpha-position to trifluoromethyl group. The origin of the steric hindrance of the trifluoromethyl group was found to be the electrostatic repulsive force between the nucleophile and the negatively charged fluorine atoms.

A New Strategy for the Synthesis of alpha-Difluoromethyl-Substituted alpha-Hydroxy and alpha-Amino Acids

A new method for the preparation of alpha-chlorodifluoromethyl-, alpha-bromodifluoromethyl-, and alpha-difluoromethyl-substituted alpha-hydroxy and alpha-amino acid esters 11, 19-21 is described. The key step of the synthesis is the regioselective alkylation of ketones 5, 7-9 and imines 16-18 with C-nucleophiles. The ketones 7-9 are readily available from 3,3,3-trifluorolactate 1 by a five-step procedure. Subsequent removal of the protecting groups from 19-21 provides the corresponding free amino acids 25, 26, 28.