Ever wanted to convert a terminal acetylene to a primary alcohol?
Well here’s a new way of doing it or rather an old way but with a new catalyst. The catalyst in question is a cyclopentadienylruthenium species here’s an x-ray. I always liked these sort of x-rays with compounds containing a cyclopentadienyl ring:
It was designed by Herzon etal from Yale and is air stable. It is easily prepared:
In acetonitrile at 60°C the yield is 95%. It is stable indefinitely when stored under argon. This is the result of a lot of optimisation work which is described in detail in the paper. Detailed rate studies were also carried out as was an investigation of the functional group tolerance. The reaction utilises 4.5 mol% of the catalyst 1 (depending upon the substrate), aqueous NMP and 4 equivalents of formic acid at room temperature and proceeds via the intermediate aldehyde which is then hydrogenated. A catalytic cycle is presented.
The reaction is reasonably kind towards other functional groups, in the presence of easily reduced groups, such as an alkene the yield of the hydrated acetylene is, not surprisingly lower. All the substrate scope studies were done on a very small scale, 500μmol and the products were isolated by chromatography. It would have been nice to see this done on a scale where one can actually see what one has, but never mind.
So a useful system for the anti-Markovnikov hydration of terminal acetylenes.
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