Phosgene-free and Chemoselective Synthesis of Novel Polyureas from Activated l-Lysine with Diphenyl Carbonate

Reactivity and Product Selectivity of Fluoroalkyl Carbonates in Substitution Reactions with Primary Alcohols and Amines

The present study reports a systematic investigation of the substitution reactions of a series of symmetric and unsymmetric fluoroalkyl carbonates with primary alcohols or amines. The reactivity of the haloalkyl carbonate depends mainly on the electrophilicity and steric crowdedness of the carbonyl group and the leaving ability of the haloalkyl alcohols. Diethyl carbonate as a reference substrate showed no reaction with the alcohol or amine. However, bis(2,2,2-trifluoroethyl) carbonate [(F₃-EtO)₂CO] having electron-withdrawing trifluoroethyl groups enabled substitution reactions, with relatively higher reactivities to those for diphenyl carbonate [(PhO)₂CO]. Furthermore, (F₆-iPrO)₂CO, bearing two sets of hexafluoroisopropyl groups, showed dramatic acceleration of the reactions, in which the observed reactivities were similar to those for bis(perfluorophenyl) carbonate [(F₅-PhO)₂CO]. The electrophilicity of the carbonyl group and the leaving ability of the alcohols in the series of haloalkyl carbonates were found to be correlated with the wavenumbers of their carbonyl groups in IR spectra and pK_a for the eliminated alcohols, respectively. Since the eliminated fluoroalkyl alcohols exhibit weak affinity with the organic products and have lower boiling points owing to a characteristic property of the fluoroalkyl group, they could be readily removed from the product by simple evaporation below 100 °C with or without reduced pressure.

An Inspection into Multifarious Ways to Synthesize Poly(Amino Acid)s

Poly(α-amino acid)s (PAAs) attract growing attention due to their essential role in the application as biomaterials. To synthesize PAAs with desired structures and properties, scientists have developed various synthetic techniques with respective advantages. Here, different approaches to preparing PAAs are inspected. Basic features and recent progresses of these methods are summarized, including polymerizations of amino acid N-carboxyanhydrides (NCAs), amino acid N-thiocarboxyanhydrides (NTAs), and N-phenoxycarbonyl amino acids (NPCs), as well as other synthetic routes. NCA is the most classical monomer to prepare PAAs with high molecular weights (MWs). NTA polymerizations are promising alternative pathways to produce PAAs, which can tolerate nucleophiles including alcohols, mercaptans, carboxyl acids, and water. By various techniques including choosing appropriate solvents or using organic acids as promoters, NTAs polymerize to produce polypeptoids and polypeptides with narrow dispersities and designed MWs up to 55.0 and 57.0 kg mol^-1 , respectively. NPC polymerizations are phosgene-free ways to synthesize polypeptides and polypeptoids. For the future prospects, detail investigations into polymerization mechanisms of NTA and NPC are expected. The synthesis of PAAs with designed topologies and assembly structures is another intriguing topic. The advantages and unsettled problems in various synthetic ways are discussed for readers to choose appropriate approaches for PAAs.

Photo-on-Demand Base-Catalyzed Phosgenation Reactions with Chloroform: Synthesis of Arylcarbonate and Halocarbonate Esters

Carbonate esters are utilized as solvents and reagents for C1 building blocks in organic synthesis. This study reports a novel photo-on-demand in situ synthesis of carbonate esters with CHCl₃ solutions containing a mixture of an aromatic or haloalkyl alcohol having relatively high acidity, and an organic base. We found that the acid-base interaction of the alcohol and base in the CHCl₃ solution plays a key role in enabling the photochemical reaction. This reaction allows practical syntheses of diphenyl carbonate derivatives, haloalkyl carbonates, and polycarbonates, which are important chemicals and materials in industry.