Segregation of Separate Steps in Chromium-Catalyzed Reactions for Convenience and Mechanistic Analysis

Abstract

[structure: see text] We have developed an apparatus for carrying out redox-coupled chromium-manganese or chromium-zinc reactions on solid-supported substrates which allows recycling of the stoichiometric reductant. In addition to providing a greatly simplified procedure for these reactions, we observe striking differences in the recyclability of Mn and Zn. A preliminary extension of the methodology to the catalytic coupling of allylchromium reagents with solid-supported aldehydes is also reported.

A Mild and Efficient One-Step Synthesis of Quinolines

“…4 As part of a continuing effort in our laboratory toward the development of new methods for the expeditious synthesis of biologically relevant heterocyclic compounds, 5 we became interested in the possibility of developing a onepot analogue of the Friedla ¨nder synthesis, in which the intermediate o-aminobenzaldehyde was not isolated, but rather immediately converted in situ to a quinoline. We anticipated that, by analogy to our earlier work, 6 lead to concomitant condensation with the reduced arene, providing the quinoline in a single synthetic operation.…”

“…As part of a continuing effort in our laboratory toward the development of new methods for the expeditious synthesis of biologically relevant heterocyclic compounds, we became interested in the possibility of developing a one-pot analogue of the Friedländer synthesis, in which the intermediate o -aminobenzaldehyde was not isolated, but rather immediately converted in situ to a quinoline. We anticipated that, by analogy to our earlier work, reaction of 2-nitrobenzaldehyde with catalytic amounts of CrCl 2 in the presence of Mn or Zn dust and TMSCl would provide for catalytic reduction of the nitroarene. If this were done in the presence of an enolizable carbonyl compound, we reasoned that formation of a Cr, Mn, or Zn enolate would lead to concomitant condensation with the reduced arene, providing the quinoline in a single synthetic operation.…”

Biomimetic and bioinspired molecular electrets. How to make them and why does the established peptide chemistry not always work?

“…That is, the Cr 3+ | Cr 2+ redox couple aids electron shuttling from the solid metal to the nitro compound. Implementation of this procedure in solid-phase synthesis requires a closed flow system with two reaction vessels, one containing the solid metal and the other -the resin solid support [175]. The reducing metal enriches the solvent of chromium salts in Cr 2+ , which diffuses or flows to the resin in the other compartment [175].…”