Squaramides are presented as highly modular, easy to optimize and highly efficient catalysts for the conversion of epoxides and carbon dioxide into cyclic organic carbonates (COCs). The catalytic potential of these squaramides, in combination with a suitable halide nucleophile, is particularly noted when internal epoxides are examined as substrates and their transformation into disubstituted COCs marks a rare case of an effective organocatalyst for these challenging conversions. Control experiments support the mechanistic view that the squaramides are predominantly involved in the stabilization of intermediate oxo- and carbonato-anions which, after their formation, are able to displace a bromide nucleophile from an initially formed 1:1 assembly comprising the squaramide host.
Pushing the Limits with Squaramide-based Organocatalysts in Cyclic Carbonate Synthesis
ACS Catal. 2017, 7, 3532-3539, DOI: 10.1021/acscatal.7b00475.