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.