Intramolecular Pd(II)-Catalyzed Cyclization of Propargylamides: Straightforward Synthesis of 5-Oxazolecarbaldehydes

Abstract

Direct synthesis of 2-substituted 5-oxazolecarbaldehydes was performed by intramolecular reaction of propargylamides through treatment with a catalytic amount of Pd(II) salts in the presence of a stoichiometric amount of reoxidant agent. The heterocyclization process was well-tolerated by a wide range of aryl, heteroaryl, and alkyl propargylamides. This protocol constitutes a valuable synthetic pathway to 5-oxazolecarbaldehydes, alternative to the formylation on oxazole rings, often unsatisfactory in term of regioselectivity and yields.

Novel Synthesis of Difluoromethyl‐Containing 1,4‐Disubstituted 1,2,3‐Triazoles via a Click–Multicomponent Reaction and Desulfanylation Strategy

“…Highresolution mass spectra (HR-MS) were recorded under electron impact conditions using a MicroMass GCT CA 055 instrument and recorded on a MicroMass LCTTM spectrometer. Compounds 1, [13] 3e-k, [17] 3l-n [18] were synthesized according to literature procedures. (2) A solution of the ethyl 2,2-difluoro-2-(phenylthio)acetate (1) …”

Ratio‐Au: A FRET‐based Fluorescent Probe for Ratiometric Determination of Gold Ions and Nanoparticles

“…Although the mechanism of this new reaction is not clear yet, we speculate that it may be similar to that of Pd 2 + -promoted cyclization of propargylamides to 5-oxazolecarbaldehydes. [12] However, the reaction mechanism remains to be investigated. Additionally, the absorption and emission spectra of compound 1 titrated with Au 3 + (Figure S5 in the Supporting Information) imply that compound 1 exhibits a fluorescence turn-on response to Au 3 + and may be further modified to afford a new ratiometric probe.…”

Transition Metal-Mediated Synthesis of Monocyclic Aromatic Heterocycles

“…The reaction produces a varity of oxazolocarbaldehydes containing aliphatic, aromatic, or heteroaromatic substituents in good yields (Scheme 335). 513 …”