β-Aminocarbonates in Regioselective and Ring Expansion Reactions

Microwave-Assisted Aminoalkylation of Phenols via Mustard Carbonate Analogues

A microwave-assisted chlorine-free direct phenol substitution is presented, which is indicated as a key green chemistry research area for pharmaceuticals manufacturers. The reaction of β-aminocarbonates (mustard carbonates) with several substituted phenols in the presence of a polar solvent (acetonitrile or butanol) led to the related aminoalkylated products via the anchimeric assistance of the nitrogen incorporated in the organic carbonate backbone. The aminoalkylation required short reaction time (7 min) and the related products were isolated in high yields (>90%) via quick liquid-liquid extraction or column chromatography depending on the solvent employed. Furthermore, microwave irradiation also promoted the one-pot aminoalkylation of phenol in excellent yield. In this approach a β-aminoalcohol was reacted with phenol in the presence of diethyl carbonate, used for the in situ formation β-aminocarbonate, key intermediate in the consequent anchimerically driven alkylation. The resulting product, namely N,N-dimethyl-2-phenoxyethanamine, was isolated as pure in almost quantitative yield.

Synthetic Applications of Aziridinium Ions

Nonactivated aziridine with an electron-donating group at the ring nitrogen should be activated to an aziridinium ion prior to being converted to cyclic and acyclic nitrogen-containing molecules. This review describes ways to generate aziridinium ions and their utilization for synthetic purposes. Specifically, the intra- and intermolecular formation of aziridinium ions with proper electrophiles are classified, and their regio- and stereoselective transformations with nucleophiles are described on the basis of recent developments.

Alkylative Aziridine Ring-Opening Reactions

In this study, the highly strained three-membered aziridine ring was successfully activated as the aziridinium ion by alkylation of the ring nitrogen with a methyl, ethyl or allyl group, which was followed by ring opening with external nucleophiles such as acetate and azide. Such alkylative aziridine ring opening provides an easy route for the synthesis of various N-alkylated amine-containing molecules with concomitant introduction of an external nucleophile at either its α- or β-position.

Dialkyl Carbonates in the Green Synthesis of Heterocycles

This review focuses on the use of dialkyl carbonates (DACs) as green reagents and solvents for the synthesis of several 5- and 6-membered heterocycles including: tetrahydrofuran and furan systems, pyrrolidines, indolines, isoindolines, 1,4-dioxanes, piperidines, and cyclic carbamates. Depending on the heterocycle investigated, the synthetic approach used was different. Tetrahydrofuran systems, pyrrolidines, indolines, isoindoline, and 1,4-dioxanes were synthesized using dimethyl carbonate (DMC) as sacrificial molecule (BAc2/BAl2 mechanism). Cyclic carbamates, namely 1,3-oxazin-2-ones, were prepared employing DACs as carbonylating agents, either by BAc2/BAl2 mechanism or through a double BAc2 mechanism. Piperidines were synthetized taking advantage of the anchimeric effect of a new family of dialkyl carbonates, i.e., mustard carbonates. Finally, in the case 5-hydroxymethylfurfural (HMF), DMC has been employed as efficient extracting solvent of this extensively investigated bio-based platform chemical from the reaction mixture. These synthetic approaches demonstrate, once again, the great versatility of DACs and their-yet to be fully explored-potential as green reagents and solvents in the synthesis of heterocycles.