Palladium-Catalyzed Direct Alkenylation of 2-Oxazolones: An Entry to 3,4,5-Trisubstituted 2-Oxazolones

Abstract

Described herein is a novel method for the synthesis of 3,4,5-trisubstituted 2-oxazolones featuring the first Pd-catalyzed dehydrogenative alkenylation of 2-oxazolones, which is realized by employing 10 mol % of Pd(OAc)2 as the catalyst and the use of readily available Cu(OAc)2 as the oxidant. A wide range of functional groups, such as F, Cl, Br, OMe, ester, ketone, amide, alkyl, and aryl substituents, are found to be compatible under the reaction conditions. The utilization of the C-H functionalization strategy provides a straightforward, convenient, and highly atom-economical approach for the construction of 3,4,5-trisubstituted 2-oxazolones. It is worth noting that the 4-alkenyl 2-oxazolones can be smoothly converted into naphtho[1,2-d]oxazol-2-ones via a photochemical transformation.

Facile synthesis of 4,4'-bis-sydnones

“…The initial electronic attack of Pd (II) on 3-arylsydnone (1) and the subsequent deprotonation form species A. [24][25] The resulting species A reacted with another 3-arylsydnone molecule to generate the corresponding intermediate B. …”

Site‐Selective Pd‐Catalysed Fujiwara‐Moritani type Reaction of N,S‐Heterocyclic Systems with Olefins

“…The selected examples given in Figure 2 illustrate the structural diversity of the targeted products which are intrinsically related to important pharmaceutical properties. They also show that the Pd(II)‐catalysed oxidative Heck C−H alkenylation occurs with high selectivity at the nucleophilic enamide position ( A , D , G ), [5a,d,g,j] vinyl ether ( B , I ) [5b,i] or N ‐oxide equivalent ( C ) [5c] . Interestingly, the exception was obtained in the case of sulphur heterocycles ( E , F ) [5e,f] in which the olefination at the sulphur α position is highly privileged even if the β‐position is free in F [5f] …”

A Convenient Access to Functionalized Oxazol-2-One-5-Carboxylates from β-Aminoalcohols Through NBS-Light Mediated Oxidation of Cis- or Trans-N-Alkyloxazolidinones

“…These heterocycles have broad utilities for the synthesis of several organic molecules [14][15][16] and are used as important building blocks for the construction of complex molecules, through cycloaddition [17][18][19], radical [20] and organometallic reactions [21][22][23][24][25][26][27][28] and other transformations [29][30][31][32][33][34]. For example, the oxazolone moiety can be readily functionalized or rearranged to be transformed to natural alkaloids [35,36].…”