Schrock molybdenum alkylidene catalyst enables selective formation of macrocyclic unsaturated lactones by ring-closing metathesis at high-concentration

Abstract

A set of macrocyclic unsaturated musk compounds was obtained from unbiased dienes via ring-closing metathesis at 20-40 times higher concentration than recommended in state-of-the-art, proceeding via formation of oligomers and then by a backbiting metathesis reaction. As the commercial Schrock catalyst Mo1 does not lead to the parasitic C-C double bond migration process, the above reactive distillation proceeded with very high chemical selectivity, leading to pure macrocyclic musk products in 24-92% yield and selectivity around 90% or higher. It was also shown that this process can be performed under user-friendly conditions, using Schrock catalyst Mo1 suspended in paraffin tablet, cheap PAO-6 engine oil as a diluent, on air, in simple distillation glassware, and with a standard laboratory vacuum pump. In addition, most of the substrates were obtained from bio-sourced oleic acid, making the high-concentration RCM (HC-RCM) process even more environmentally friendly.