Telomerization of 1,3-butadiene with highly substituted alcohols using Pd/NHC-catalysts — Structure-reactivity-relationship of the O-nucleophile

Abstract

Catalytic telomerization of 1,3-butadiene with alcohols is a catalytic reaction and an effective tool to synthesize 2,7-octadienyl ethers with different characteristics depending on the alcoholic substrate. While Pd/phosphine type catalysts were studied in depth, highly active Pd/NHC (=N-heterocyclic carbene) catalysts have been studied in the telomerization almost exclusively along with methanol. In the course of employing alcohols from renewables, e.g., lignin, cellulose or terpenes etc., a deeper understanding of the reactivity of these catalysts is needed.In this work, we present comprehensive investigations with linear and branched alcohols of different chain-lengths. Distinct tendencies in reaction behavior between primary and secondary alcohols were found and the lower reactivity of secondary alcohols could clearly be attributed to electronic properties, along with steric hindrance.Furthermore, the influence of double bonds in the alcohol chain has been studied. Interestingly, alcohols with double bonds that are not conjugated to the hydroxyl groups were shown to be more active than saturated alcohols. Allylic alcohols, however, are significantly less reactive than their saturated analogs.With the gathered information, we were able to deduce a structure reactivity-relationship of certain functional groups and substitution patterns. These findings were proved by employing terpenols to gain new allylic terpenol ethers.