Low temperature dehydrations of non-activated alcohols via halide catalysis†
Activating kinetically inert C–O bonds such as in primary alcohols is an important challenge for the transformation of biomass-derived feedstocks. The herein described methodology addresses this issue through a combination of halide and acid catalysis. The novel mechanistic pathway proposed based on detailed experimental studies enables selective olefin formation from alcohols – as opposed to ether formation – at relatively low temperatures. Suitable substrates are tertiary, secondary, and even primary alcohols. Furthermore, the observed selectivity for the Hoffman elimination product and the realization of a non-rearranging Friedel–Crafts alkylation suggest that the reaction medium with high concentrations of halide (NBu4Br) enables reaction outcomes that cannot be obtained through carbocation intermediates.