Base‐Promoted Coupling of Carbon Dioxide, Amines, and Diaryliodonium Salts: A Phosgene‐ and Metal‐Free Route to O‐Aryl Carbamates

Abstract

A phosgene- and metal-free synthesis of O-aryl carbamates is realized through a three-component coupling of carbon dioxide, amines and diaryliodonium salts. The reaction only requires a base as the promoter, providing access to a diverse array of O-aryl carbamates in moderate to high yields with excellent chemoselectivity.

A Simple Zinc Catalyst for Carbamate Synthesis Directly from CO2

“…15 N-enriched aniline was purchased from Cambridge Isotope Laboratories. CO 2 was purchased from Showa Ta nsan.…”

“…The interaction betweena niline and the catalystc an be observed by NMR spectroscopy.F igures 6a nd 7s how 1 Ha nd 15 NNMR spectra of aniline with and without Zn(OAc) 2 /phen in CD 3 CN at room temperature. The NH 2 protons of aniline show no clear chemical shift on addition of phen, but ac hemical shift from 4.05 to 4.14 ppm was observed in the 1 HNMR spec-Scheme5.Gram-scale synthesis of 1.…”

“…trum on addition of both Zn(OAc) 2 and phen ( Figure 6). 15 N-enriched aniline showeda 15 NNMR peak at 55.59 ppm. The peak slightly shiftedt o5 5.68 ppm on addition of phen, but to 56.63 ppm after the addition of both Zn(OAc) 2 and phen ( Figure 7).…”

“…Twenty milliont onneso fP Ua re produced per year for use as surface coatings,synthetic fibers, and adhesives, and 96 %o fP Us contain aromatic amine units. [13] The use of N-tosylhydrazone [14] or diaryl iodonium salt [15] for carbamate synthesis is considered to be an alternative method, but only for aliphatic amine activation. Because phosgene is ah ighly toxic compound, the replacement of phosgenew ould be viewed as as ignificant synthetici mprovement.…”

“…Severalr outes for carbamate synthesis directly from CO 2 are shown in Scheme 1: A) Application of organic halides; [10] B) Addition of the corresponding alcohol; [11] C) Addition of acetal with adehydrating agent; [12] and D) The use of tin alkoxide. [13] The use of N-tosylhydrazone [14] or diaryl iodonium salt [15] for carbamate synthesis is considered to be an alternative method, but only for aliphatic amine activation. Routes Ba nd Cc annot activate aromatic amines,a nd routes Aa nd Dh ave negative environmental effects, because most of the organic halides are not natural products, and most of the organotin compounds are toxic.…”