Synthesis of New Poly(ethyleneglycol)s with a High Loading Capacity¹

Synthesis of New Poly(ethyleneglycol)s with a High Loading Capacity1</sup

Structurally Simple Pyridine <i>N</i>-Oxides as Efficient Organocatalysts for the Enantioselective Allylation of Aromatic Aldehydes

A series of structurally simple pyridine N-oxides have readily been assembled from inexpensive amino acids and tested as organocatalysts in the allylation of aldehydes with allyl(trichloro)silane to afford homoallylic alcohols. (S)-Proline-based catalysts afforded the products derived from aromatic aldehydes in fair to good yields and in up to 84% enantiomeric excess (ee). The allylation of heteroaromatic, unsaturated, and aliphatic aldehydes was less satisfactory. By running the reaction in the presence of achiral and chiral additives and structurally different catalysts, we collected some insights into the relationship between the stereochemical outcome and the catalyst's structural features. Even if the ee's obtained are inferior to the best values observed with other catalysts, this work concurs to show that structurally simple pyridine N-oxides can also promote the allylation reaction with satisfactory stereocontrol

HSiCl₃‑Mediated Reduction of Nitro-Derivatives to Amines: Is Tertiary Amine-Stabilized SiCl₂ the Actual Reducing Species?

The mechanism of a recently reported, highly chemoselective metal-free protocol of wide general applicability for the reduction of aromatic and aliphatic nitro-derivatives to amines has been investigated. The reaction is supposed to occur through the generation of a Si­(II) reducing species; quantum mechanical calculations, and spectroscopic and experimental data strongly suggest the tertiary amine-stabilized dichlorosilylene to be the most probable reducing agent

A Poly(ethylene glycol)-Supported Quaternary Ammonium Salt: An Efficient, Recoverable, and Recyclable Phase-Transfer Catalyst

A quaternary ammonium salt readily immobilized on a soluble poly(ethylene glycol) polymer support efficiently catalyzes different reactions carried out under phase-transfer catalysis conditions; the catalyst, easily recovered by precipitation and filtration, shows no appreciable loss of activity when recycled three times

Continuous-Flow Stereoselective Organocatalyzed Diels–Alder Reactions in a Chiral Catalytic “Homemade” HPLC Column

Continuous-flow organocatalyzed Diels–Alder reactions have been performed with excellent enantioselectivity for the first time in a chiral “homemade” HPLC column, packed with silica on which a MacMillan catalyst has been supported by a straightforward immobilization procedure. The versatility of the system was also proven by running with the same column continuous-flow stereoselective reactions with three different substrates, showing that the catalytic reactor may efficiently work <i>in continuo</i> for more than 150 h; the regeneration of the HPLC column was also demonstrated, allowing to further extend the activity of the reactor to more than 300 operating hours