PIDA‐Mediated Formal Olefinic C=C Bond Cleavage of α‐Oxo‐Ketene N,N‐Acetals toward Substituted Oxazolines

Abstract

The hypervalent iodine reagent PhI(OAc) (PIDA) mediated the formal oxidative C=C bond cleavage and subsequent cyclization of internal olefins, that is, α-oxo-ketene N,N-acetals, which afforded substituted oxazolines. Isothiazoline derivatives were obtained from the reactions of α-thioxo-ketene N,N-acetals with PIDA under the same conditions. Hydrolysis of the resultant oxazoline derivatives led to highly functionalized oxazolones. A plausible mechanism was proposed based upon the formation of isothiazoline-type intermediates.

PIFA-Mediated Tandem Hofmann-Type Rearrangement and Cyclization Reaction of α-Acyl-β-aminoacrylamides: Access to Polysubstituted Oxazol-2(3H)-ones

“…On the basis of the obtained results, a proposed mechanism for the oxidative cyclization of α-acyl-β-aminoacrylamide 3 is depicted in Scheme . Initially, acrylamide 3 reacts with PIFA in the presence of TFA to form iodonium intermediate A by deprotonation of the amide group. , A redox process is followed to generate an aziridin-2-one B along with the elimination of iodobenzene (PhI) and TFA . The PIFA-induced Hofmann-type rearrangement is complete by a subsequent ring-opening reaction of B to give isocyanate intermediate C , , in which the iminium ion may be stabilized by the neighboring aryl group R, especially those bearing one or more electron-donating substituents .…”

Synthetic Access to α-Oxoketene Aminals by the Nucleophilic Addition of Enol Silane-Derived Palladium(II) Enolates to Carbodiimides

“…1 3,3-Bis((4-methoxyphenyl)amino)-1-phenylprop-2-en-1-one (6h). 87 The reaction was carried out according to the general method using N,N′-methanediylidenebis(4-methoxyaniline) (5h, 100 mg, 0.39 mmol, 1 equiv), trimethyl((1-phenylvinyl)oxy)silane (2a, 96.0 mg, 0.50 mmol, 1.3 equiv), and Pd(OAc) 2 (8.7 mg, 0.039 mmol, 0.1 equiv). The crude product was purified by flash column chromatography using silica gel and a gradient of EtOAc and petroleum ether (ratio = 30:70) to afford the title product as a paleyellow solid (80.2 mg, yield: 55%).…”

Synthesis of Oxazoline and Oxazole Derivatives by Hypervalent-Iodine-Mediated Oxidative Cycloaddition Reactions

“…14,51,53,54 Numerous synthetic strategies for the construction of the oxazoline ring have been explored. Particularly important are synthetic approaches using hypervalent iodine reagents, such as (diacetoxyiodo)arenes, [55][56][57][58][59][60][61][62][63][64][65] iodosylarenes, 66 (difluoroiodo)arenes, 67 in situ generated iodine(III) species, [68][69][70][71][72][73] or iodonium ylides. 74,75 This section covers synthetic methodologies for the preparation of various oxazoline derivatives from appropriate substrates using hypervalent iodine species.…”