Talk:Wittig reaction

Should we have a separate page for the Wittig reagent, or keep the information in this page? I am in two minds- it's nice to have all the information together, and clearly the Wittig reagent is pretty much always used for the Wittig reaction. At the same time this page will end up fairly long, and the section Wittig reaction#Wittig reagents could easily be made into a separate complete page once the structural information is added. There is already a short stub called ylide. What do others think? Walkerma 15:10, 23 May 2005 (UTC)

I don't think the list of Wittig reagents will be long enough to warrant seperate pages. I favor the single page approach. The ylide page is valid by itself in that not all ylides are involved in the Wittig reaction. On another note, I'll be drawing the mechanism of the Wittig reaction to include here. ~K 18:58, 23 May 2005 (UTC)

Thanks for that, nice job (though can you fix the PH?!) Walkerma 21:32, 1 Jun 2005 (UTC)

Oops. I'll get on it right now. ~K 02:57, 2 Jun 2005 (UTC)

I am in favor of chopping up articles as much as possible, my suggestion would be to move relevant content to phosphonium salt and replace it by mechanistic info. wittig reagent then stays on this page rikXL 22:09, 23 May 2005 (UTC)

I have done as suggested. Walkerma 21:32, 1 Jun 2005 (UTC)

Maybe the article can be written as a single article until it becomes apparent that it is too long. At that point, one can consider separating the article into two articles. I suspect after Walkerma finishes with this article, there will be no major expansions for a long time. At that point, if the article is not much over 30 kB, it can still be edited (by most people at least) and it can be kept that way perhaps indefinitely, especially since it is a specialized article which will not have a high volume in reading and editing. There have been other articles over 30 kB in length in Wikimedia. H Padleckas 01:57, 31 May 2005 (UTC)

I don't think it will get that long just yet- but we'll see! Walkerma 21:32, 1 Jun 2005 (UTC)

On another note, I noticed the first reaction image shows R₃P... for the ylide and R₃P=O for the product instead of Ph₃P... and Ph₃P=O. Are those 3 groups always phenyl groups in the Wittig reagent. If they always are, it might be worthwhile to change that R in the image to Ph. I think I'll do that while waiting for a response from you; then upload them if that's right. H Padleckas 01:57, 31 May 2005 (UTC)

I've modified the Image:Wittig_reaction_scheme.png image to show the triphenyl reactant and product and uploaded it to Image:Wittig_reaction.PNG, but I have yet to change the article. H Padleckas 08:59, 2 Jun 2005 (UTC)

One more note in the 2nd reaction image, the first 2 steps show the phenyls as PH and the rest shows Ph for the phenyls. I think I would have made it Ph all the way through. Also the labeling of the R groups is not consistent with the first image. I'll await for a response to see it that worth changing.

Otherwise, all in all, looks like the article is shaping up rather nicely. H Padleckas 01:57, 31 May 2005 (UTC)

I have added a bit more content. The Carruthers book states that R is nearly always phenyl, but then goes on to explain the reactivity of Wittig reagents that are derived from tetralkylphosphonium salts. We should probably amend the intro somehow to make it clear that we are using Ph because that is what is nearly always used. I will dig out some nice examples of the use, though ~K is welcome to do this instead if he/she wishes- I think his/her graphics are probably sharper than mine! Cheers, Walkerma 21:28, 1 Jun 2005 (UTC)

I really like your Schlosser modification image. Don't knock your own images. I think they are great. ~K 04:05, 2 Jun 2005 (UTC)

As you see below, the fact that phenyl groups are almost always used may have clouded our picture of the reaction. I think the fact is the reaction is poorly understood. Eugene Kwan 18:46, 17 December 2005 (UTC)

Mechanism

Hi there. I must dispute your mechanism for the Wittig reaction. There seems to be considerable evidence that there is, in fact, no betaine intermediates (JACS, 1990, 112, 3905-9). Oxaphosphetane formation from unstabilized ylides can be reversible for some aldehydes (Maryanoff et al, JACS 1986, 108, 7664.) while oxaphosphetane formation from stabilized ylides is irreversible (Vedejs, et al. JACS 1989, 111, 5861). Interestingly, when the syn oxaphosphetane is generated independently, the Z olefin is obtained. Also, if instead of using, say, triphenylphosphonium ylide, one uses a trimethoxyphosphonium ylide, poor E/Z selectivites are the result. A recent ASAP in JACS from Aggarwal addresses the origin of high E selectivity in stabilized ylides. I don't understand it very well myself, but it seems clear that the mechanism you've drawn cannot be operative. Comments? Eugene Kwan 09:11, 17 December 2005 (UTC)

I think that you've made some valid points. I'll work on it. I think we should also highlight the fact that there is still considerable research being conducted on the Wittig mechanism. ~K 17:43, 17 December 2005 (UTC)

HWE

I think we ought to have a separate page for the Horner Wadsworth Emmons reaction. I think it's not simply a more reactive alternative to the stabilized Wittig...I'm not even sure that's the case. There are a bunch of benefits, such as no triphenylphosphine oxide to remove, less epimerization, a wide variety of mild conditions, ability to get E or Z selectivity by varying the phosphonate ester type, etc. Also, the mechanism probably proceed via a betaine intermediate. I'm working on the aldol page right now, but when I'm done, perhaps I'll start a new page. Eugene Kwan 18:49, 17 December 2005 (UTC)

I quite agree, we need a separate page! The HWE is one of my ten favourite reactions! You will see that it is already red linked, and I have had it listed on my to do list for several months now. I suspect you know more about it anyway, I've only done it a handful of times. I am currently writing (offline) a page called phosphite ester, and I would like (prob. next summer) to make Michaelis-Arbuzov reaction into a full-length article (unless you get to that first?). Is this a fair division of our labours? I'd be happy to give up my plans for the HWE. Thanks, Walkerma 04:02, 18 December 2005 (UTC)