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Hey Rojas, thanks alot for the great content, enjoying your educational work. For this one I was a little confused by your graphic depiction of the mechanism of the claisen condensation in the introduction part at around 1:36 - 2:10 that intermediate is missing a carbon, since if a 2 carbon enolate homolytically condensates with another 2 carbon ester, the intermediate should be a 4 carbon membered species (yours is a 3 Carbon member) or is my brain lagging there?

@rojaslab

Ай бұрын

I'm glad you're thinking about keeping track of the carbons! I can tell you've got this down! If you notice, the starting ester has 2 carbons, 1 at the carbonyl position and 1 as a methyl group. Notably, after the Claisen reaction, you still end up with 4 carbons, 2 at carbonyl positions, and 2 methylene carbons. If you take another look, I think you'll see all 4 carbons present and I appreciate you keeping me honest!

@gre7316

Ай бұрын

Hey thanks for the reply :) Im totally with you on the final beta-keto-ester! I was just a bit confused, as I thought, when the enolate attacks the other reactants ester carbonyl position, the intermidiate should have the carbonyl carbon binding to 4 substituents, namely its own methyl group, the negatively charged oxygen, the ester-oxygen and the newly formed carbon-carbon bond from the enolate, but in your intermediate Im missing the methyl group, just talking about the charged di-ester intermidiate structure :) As for further ideas: I work in drug development and I got a lab mate working on his bachelor thesis in route scouting, his first proposed step is claisen condensation with LDA of a 3-Chloro-propionate ester with a butylacetate (i guess its tertbutyl). first he prepares the enolate of the butylacetate and then he adds this mixture via dropping funnel to the chloro-propionate. after acidic workup and chromatography his reaction resulted in a range of products, reaching from elimination products, different beta-keto-esters, as well as starting material. I know its a difficult task, but can you give some general procedure to really stirr the reaction for better yield/purity if you have 2 different esters to start with, as well what is important to avoid or to keep close track of to avoid unwanted side products (e.g. i can imagine that unreacted residual LDA from the enolate preparation will mess up the claisen condensation, as it can react with the other ester to form another enolate... also the enolate can not only act as a nucleophile but also as a base...) is there a way to get rid of unreacted LDA, but keeping the enolate activated before adding the second ester, is there a way to avoid elimination reactions of the chloropropionate? thank you very much :)

13:36 Is there a mistake here?

@rojaslab

10 күн бұрын

Great question! The answer drawn is correct but I skipped several steps. To see the full mechanism, I presented it here at 1:45 and this will explain the loss of the OR group! My apologies for any confusion!

@marco5826

9 күн бұрын

@@rojaslab Thank you. I checked with Clayden's textbook. There is no error.

@rojaslab

9 күн бұрын

@@marco5826 Clayden's book is sooooo good! Probably the gold standard for intro organic chemistry courses. For advance organic, I highly recommend Modern Physical Organic Chemistry by Anslyn and Dougherty!