Stereoselective Synthesis of Enamides by Palladium Catalyzed Coupling of Amides with Electron Deficient Olefins

Palladium-Catalyzed Oxidant Dependent Switchable Aza-Wacker Cyclization and Oxidative Dimerization of Benzimidates

An oxidant dependent switchable palladium-catalyzed synthesis of 1,3-oxazines and benzohydrazonates (azines) from O-homoallyl benzimidates has been developed. The reaction involved aza-Wacker-type intramolecular cyclization of O-homoallyl benzimidates with Cu(OAc)2 as oxidant under Pd-catalysis to deliver 4-methylene-1,3-oxazines, whereas dimerization of O-homoallyl benzimidates with K2S2O8 as oxidant resulted remarkably in benzohydrazonates (azines). The reaction is atom economic with an easily operational procedure for divergent synthesis of important scaffolds.

Metal-Free Stereoselective Synthesis of (E)- and (Z)-N-Monosubstituted β-Aminoacrylates via Condensation Reactions of Carbamates

N-monosubstituted β-aminoacrylates are building blocks, which have been used in the preparation of amino acids and pharmaceuticals. Two efficient, stereoselective methods of preparation, via acid- or base-promoted condensation reactions of carbamates, are described. The base-promoted reaction is E-selective, while acid catalysis can, through the choice of solvent, selectively form E or Z. The acid-catalyzed E-selective process proceeds through a crystallization obviating the need for chromatographic purification.

Ru(II)-Catalyzed Controlled Cross-Dehydrogenative Coupling of Benzamides with Activated Olefins via Weakly Coordinating Primary Amides

Ru(II)-catalyzed regioselective ortho-alkenylation of primary benzamides with activated olefins has been realized over the competitive cyclized products. This reaction overall proceeds via a cross-dehydrogenative coupling (CDC) reaction using a simple and weakly coordinating primary amide group in the presence of an inexpensive Ru(II) salt and allows the controlled introduction of olefin motifs at the ortho-position of benzamides. The key to the success of this strategy depends on fine-tuning the reaction conditions. The developed protocol has demonstrated excellent regio/diastereoselectivity and a good functional group tolerance with wide substrate scope and obviates the requirement of external auxiliaries as well as the costly metal catalyst. Detailed mechanistic studies indicate the involvement of the base-assisted internal electrophilic-type substitution (BIES) step in the reaction mechanism.

Base-Mediated Anti-Markovnikov Hydroamidation of Vinyl Arenes with Arylamides

We investigated a base-promoted protocol for the intermolecular anti-Markovnikov hydroamidation of vinyl arenes with arylamides to furnish the arylethylbenzamides with excellent chemo- and regioselectivity. The reaction tolerates an extensive variety of functional groups and has been successfully extended with electronically varied handles, aminobenzamides, electron-rich/electron-deficient heterocyclic amides, and vinyl arenes to afford the hydroamidated products. Excellent chemoselectivity was observed for the amide group over amine. The proposed mechanism and vital role of the solvent was well supported by deuterium labeling studies and control experiments.

Convergent and Stereoselective Method for the Synthesis of Acyclic α-Chloroenamides

A direct, stereocontrolled synthesis of acyclic α-chloroenamides is presented. Our methodology showed good yields and substrate scope. Mechanistic insights are provided that account for the high levels of stereoselectivity reported. Subsequent synthetic manipulation of the α-chloroenamides provides direct entry to polyfunctionalized acyclic enamides, compounds of wide use in organic chemistry and the pharmaceutical industry.

Tertiary Enamides: Versatile and Available Substrates in Synthetic Chemistry

BACKGROUND

Enamines and their variant enamides as powerful and versatile synthons have attracted great attention in synthetic chemistry. Enamides display unique stability and reduce enaminic reactivity in view of the electron-withdrawing effect of N-acyl group. A great deal of satisfactory achievements in the synthesis and application of enamides has been made in recent years. Especially, tertiary enamides without N-H bond regarded as low reactivity of compounds in the past can act as excellent nucleophiles to react with electrophiles for the construction of various nitrous molecules.

OBJECTIVE

This review focuses on recent advances on tertiary enamides in the synthetic strategies and applications including addition, coupling reaction, functionalization and electro- or photo-chemical reaction.

CONCLUSION

Tertiary enamides as electron-deficient nucleophiles display a satisfactory balance between stability and reactivity to offer multiple opportunities for the construction of various functionalized nitrogencontaining compounds. Further exploration of the reactive mechanisms involved tertiary enamides and the development of novel and efficient transformations to generate ever more complex building blocks starting from tertiary enamides are particularly worth pursuing.

Aza-Wacker-type reaction between electron-deficient olefins and N-alkylsulfonamides

A palladium-catalyzed oxidative amination protocol of electron-deficient olefins by aza-Wacker-type reaction with N-alkylsulfonamides was developed. The presence of the stoichiometric amount of methanesulfonic acid was crucial for the success of this transformation. The reactions were conducted in green solvent under mild conditions and scalable with excellent E-type stereoselectivity. In addition, a Pd(II)/Pd(0) catalytic cycle with the existence of a very strong oxidant (Selectfluor) was proposed.

Synthesis of substituted oxazoles from enamides

2,5- and 2,4,5-substituted oxazoles were prepared in one-pot by the NBS/Me₂S-mediated cyclization of enamides in the presence of base.

Stereoselective synthesis of enamides by Pd-catalyzed hydroamidation of electron deficient terminal alkynes

Hydroamidation of electron-deficient terminal alkynes by amides in presence of Pd-catalyst has been exploited for the stereoselective synthesis of Z-enamides. The possible intramolecular hydrogen bonding between the amido proton and carbonyl oxygen of ester group provides the extra stability to the Z-isomer of vinyl-palladium complex, which subsequently undergoes protodepalladation and leads to the Z-enamide selectively. This process is found to be mild and operationally simple with broad substrate scope.