My apologies- wordpress just went a bit mad and published an early version-this (I hope) is the final one.
So this week has caused me a whole world of trouble. I just presumed that if you have discovered what becomes a so called “named reaction”, then you should be easy to find out about so I can knock up a quick biography. With week 9’s Mega Chemist this was not the case, and having received no correct answers or help with additional biographical information this is as good as it gets:
My name is Donald John Peterson, and in 1968 I discovered the Peterson olefination.
He does have a facebook page, but any leads went directly into brick walls! A scifinder search does suggest, as I mentioned in the clues, a move into industry. There seem to be a lot of patents for tin based pesticides. Nice.
This weeks paper(s), is Perterson’s 1968 JOC article “Carbonyl olefination reaction using silyl-substituted organometallic compounds”. I will also throw in for free a nice formal Peterson elimination-lactone opening (of the C-O bond) variant that I tried and failed to use during my PhD. This methodology was published by Professor Garry Procter of “Advanced Practical Organic Chemistry” fame – a really great textbook, though I challenge you to get your boss to but the “minimum required equipment”.
The first real report of a Peterson type elimination was proposed by Gilman and Tomasi in JOC in 1962. In their attempt to synthsise vinyl silicon compounds from organosilylmethylides and benzophenone via a Wittig reaction, they instead observed the synthesis of allenes. To account for this they proposed a mechanism (scheme 1) that proceeded through the addition of ylide 1 to benzophenone to give 2, but instead of the expected Wittig type elimination with the oxanion attacking phosphorous, it instead attacks the siliane moiety resulting in the formation of ylide 3, which can go on to form allene 4 through traditional Wittig chemistry. Silane elimination generating an alkene is now an established mechanistic pathway, and is what we now refer to as the Peterson olefination.
Considering Gilman and Tomasis’s observations, and that “silicon, like phosphorus, (a) is readily attacked by alkoxides, (b) forms strong bonds with oxygen, and (c) has d orbitals which can conceivably enter into pentacovalent bond formation”, Peterson suggested that silicon substituted carbanions, on reaction with carbonyls, would undergo conversion to olefins in a manner analogous to the Wittig reaction.
Initial investigation of the reaction of trimethylsilylmethylmagnesium chloride and a range of ketones resulted only in the addition of the Grignard to the ketone – no elimination was observed (scheme 2, 1). Pleasingly though, Peterson showed that the potassium and sodium alkoxides generated by deprotonation of the generated carbinols resulted in the target elimination products (scheme 2, 2). It was apparent that the Mg alkoxides generated from the addition of silyl grignards to carbonyl compounds were too stable to eliminate.
After demonstrating the elimination could be mediated by acid as well as base, Peterson wanted to look at increasing the generality of the reaction – which was currently limited by the availability of the chloroalkylsilanes used to form the Grignard reagents. Using what were recently established findings – the metalation of silanes with nBuLi – Peterson demonstrated than lithiated silanes on reaction with carbonyls underwent direct elimination – unlike analogous silyl Grignards – to give olefins (scheme 3). And thus was born the Peterson elimination. Find mechanisms and details here and here, and a summary of references and applications here.
This little bit of methodology that follows is something that I failed to get to work in my natural product synthesis (for full details see my thesis; available soon from Amazon at the generous price of £99.99), but I thought it was worth putting in here as a nice example of the evolution of the Peterson elimination. In Procter’s syntheses of trans-alkene peptide isosteres he uses fluoride nucleophiles (CsF, TBAF) to initiate what is formally a Peterson olefination of beta-silyllactones but does not proceed through either of the standard mechanisms (scheme 4).