[kalos]

Hi there,
is it possible to use the baylis hillman reaction with an silyl enol ether instead of an aldehyde? If so, how exactly does the mechanism look like? A professor asked me in an exam about the product of a michael system with a tertiary amine and a silyl enol ether. I couldn't answer it and he told me that the product would be the same as with a normal aldehyde. I just don't understand how that's supposed to work. Is he wrong or am I confused?

I've already looked for it on the net and scifinder, but couldn't find anything.

[Doc Oc]

I think that depends on the silyl protecting group, it's not necessarily true for all of them.  TMS-mediated aldol reactions are commonly referred to as Mukaiyama aldols.  It sounds like your prof maybe tried to blend a couple different conditions to make a challenge question, but this one doesn't seem particularly well crafted in my opinion.

[Dan]

I don't really see any reason to use a silyl enol ether. The Michael acceptor is the pre-nucleophile and the aldehyde is the electrophile. If the aldehyde is replaced by a silyl enol ether, a nucleophile, the only way I see the Baylis-Hillman reaction happening is if it hydrolyses to the corresponding carbonyl in situ. In that case the mechanism would just be silyl enol ether hydrolysis followed by a normal Baylis-Hillman.  Given it on paper, I would have predicted the silyl enol ether adding 1,4 across the Michael acceptor.

Masking the electrophile (aldehyde/ketone) as a nucleophile (silyl enol ether) does not seem to be sensible, because your nucleophile (Michael acceptor-amine adduct) is already masked as an electrophile (Michael acceptor). In other words, the pre-nucleophile (an elecrophilic Michael acceptor) and the pre-electrophile (a nucleophilic silyl enol ether) could react with each other.

[kalos]

Thanks a lot for your answers.
The prof asked me about Mukaiyama before this question. The difference is that a lewis acid is used instead of the tertiary amine. My problem was and still is that I've never seen a silyl enol ether reacting as an electrophile. Do you know any examples where that has happened?