Talk:Carroll rearrangement
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does anyone know what the claisen adaptor actually makes?!! does it make tablets?!!
- I have no idea what you mean, the article is about the Carroll rearrangement: no adaptors there. V8rik 16:54, 15 November 2007 (UTC)
Carroll Rearrangement v.s. Palladium Catalyzed Decarboxylative Allylic Alkylation
[edit]I'll have to go hunt down the references, but I know it was determined around the late 80s that palladium catalyzed decarboxylative allylic alkylations (of which there are many types) cannot actually be considered Carroll rearrangements due to large differences in the mechanism. While both reactions take beta-carbonyl allyl esters and produce the corresponding alpha allyl carbonyl compounds following a decarboxylation event, the Carroll rearrangement is a pericyclic concerted rearrangement similar to a Claisen that goes through the enol toughtomer form of the beta carbonyl allyl ester while palladium catalyzed decarboxylative allylic alkylations go through the step-wise metal catalyzed fragmenting, decarboxylation, and allylic alkylation that is depicted on the page.
One of the key distinguishing points in their difference is patterns of substitution in terms of reactivity and product isomer formation. For instance, a Carroll rearrangement cannot take place under any conditions if the carbon between the beta-carbonyl and the allyl ester is tetrasubstituted because the necessary enol taughtomer for the Carroll rearrangement cannot form. For the palladium catalyzed decarboxylative allylic alkylations however, having the alpha carbon tetrasubstituted has little to no effect on the mechanism and so the reaction proceeds with out a hitch, as shown in some of the examples at the bottom of this page such as the Stoltz et-all one with the 2-methyl cyclohexanone derived substrate.
The allyl products also show different substitution effects. As a Claisen-like reaction the Carroll rearrangement has perfect preservation for substitution on the allyl. The tip of the allyl in the substrate becomes the portion of the allyl bound alpha to the carbonyl in the Carroll rearrangement. Thus under a Carroll rearrangement, a prenyl ester would form a gem-dimethyl all carbon quaternary stereocenter beta to the remaining carbonyl. Prenyl esters under palladium catalyzed decarboxylative allylic alkylation tend to resist going at all (for instance the prenyl ester version of the 2-methylcyclohexenone derivative you have listed below, cannot be made to give product at any temperature with the same palladium catalyst), but when they do go, nulceophilic attack tends to occur on the less substituted side of the Pi-allyl complex greatly favoring prenylation over formation of the beta quaternary center. Thus the exact OPPOSITE allyl substitution product is preferred between these two reactions. (Under special conditions with specific substrates and very unique ligands, the palladium reaction can be made to slightly favor the Carrol like product of these reactions, but a mixture typically results)
Similarly with a crotyl ester, the Carrol rearrangement will perfectly transpose the stereochemistry of the crotyl methyl group while the palladium reaction will either cause complete scrambling, or with the proper asymmetric ligand framework, will scramble the methyl group to the thermodynamically preferred geometry before recombining via allyl alkylation with the beta carbonyl nucleophile.
Thus while in the original Tsuji papers the palladium reaction was refereed to as a "palladium catalyzed Carroll rearrangement" it was discovered shortly there after that it is most certainly NOT. Typically the shortest acceptable title for the palladium catalyzed decarboxylative allylic akylations is the "Tsuji Allylation", not to be confused with the "Trost Allylation" which is highly related but also distinct process, as again there are mechanistic and selectivity differences. Some people have roped the two together and call the body of relavent palladium catalyzed allylations the Tsuji-Trost allylation and then refer specifically to the decarboxylative versions, including the allyl enol carbonate verieties as well as the beta-keto ester substrates depicted on this page, the "Tsuji procedure" for the palladium catalyzed allylation. I believe Trost himself has done the later on a few of his relevant papers around 2006ish.
In conclusion I HIGHLY OBJECT to calling the palladium catalyzed decarboxylative allylic alkylation reactions Carroll rearrangements as the Tsuji Allylation is an important and distinct process even though on the simplest possible substrates it gives identical products to the Carroll rearrangement. Vast mechanistic differences are key to this distinction and are apparent with more complicated substrates and products. 131.215.40.141 (talk) 00:10, 15 December 2009 (UTC) by Nat (Guest)
- fair critisism, the Tsuji Allylation article should be created V8rik (talk) 21:17, 15 December 2009 (UTC)