Introducing Catalytic Lossen Rearrangements: Sustainable Access to Carbamates and Amines

Abstract

A new, highly efficient and environmentally benign catalytic variant of the Lossen rearrangement is described. Dimethyl carbonate (DMC) as green activation reagent of hydroxamic acids in presence of catalytic amounts of tertiary amine bases {1,5,7-triazabicycloA quantities of methanol initiate the rearrangement. Methyl carbamates were obtained in good to moderate yields when aliphatic hydroxamic acids were employed in this catalytic Lossen rearrangement; under the same conditions aromatic hydroxamic acids yielded anilines. Notably, the mixture of DMC/methanol was recycled several times without observing decreased yields, thus minimizing the produced waste. Moreover, several other organic carbonates were successfully employed in the introduced catalytic Lossen rearrangement procedure.

Renewable Non‐Isocyanate Based Thermoplastic Polyurethanes via Polycondensation of Dimethyl Carbamate Monomers with Diols

“…The subsequent Lossen rearrangement was accomplished using an excess of DMC and methanol by refluxing the mixture overnight . The yield of dimethyl carbamate 5 was at first quite low (32%), probably due to the low solubility.…”

“…Subsequently, hydrogenation was performed to obtain the C 18 ‐dimethyl dicarbamate monomer 6 in quantitative yields as colorless crystals (Scheme ). The synthesis of the C 8 ‐dimethyl dicarbamate monomer 9 from commercially available dimethyl sebacate 7b was performed using the same reaction pathway and conditions as mentioned before (see Supporting Information) …”

“…In contrast, a catalytic variant of the Lossen rearrangement offers a more sustainable alternative. Recently, our group reported on the first catalytic Lossen rearrangement, in which dimethyl carbonate (DMC) acts as an in situ activation reagent in the presence of methanol and catalytic amounts of tertiary amine bases . Thus, the use of nontoxic DMC and catalytic amounts of tertiary amine bases, as well as the possibility of recycling the applied solvents, make this Lossen rearrangement a sustainable alternative for the synthesis of carbamates.…”

Divergent Dendrimer Synthesis via the Passerini Three‐Component Reaction and Olefin Cross‐Metathesis

“…After aqueous workup and recrystallization, pure 5 was obtained in a high yield of 82% as colorless crystals. The application of a novel catalytic Lossen rearrangement procedure, developed in our group, afforded the methyl carbamate 6 . Here, the utilization of the sustainable, nontoxic, and environmentally friendly activation agent dimethyl carbonate (DMC) in the presence of methanol and catalytic amounts of the strong cyclic guanidine base 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD) proofed to be a useful approach to perform the Lossen rearrangement.…”

5-Membered cyclic ethers via phenonium ion mediated cyclization through carbonate chemistry

“…In this view, a variant of the Lossen rearrangement [34][35][36][37] via DACs chemistry was recently described (Scheme 2). Herein DMC acts as activation reagent of hydroxamic acids in the presence of tertiary amine bases such as 1,5,7- [38].…”