Posts Tagged ‘carboxylic acid’
I’ve started so I’ll finish. Kinetic isotope effect models for a general acid as a catalyst in the protiodecarboxylation of indoles.Sunday, January 10th, 2016
Earlier I explored models for the heteroaromatic electrophilic protiodecarboxylation of an 3-substituted indole, focusing on the role of water as the proton transfer and delivery agent. Next, came models for both water and the general base catalysed ionization of indolinones. Here I explore general acid catalysis by evaluating the properties of two possible models for decarboxylation of 3-indole carboxylic acid, one involving proton transfer (PT) from neutral water in the presence of covalent un-ionized HCl (1) and one with PT from a protonated water resulting from ionised HCl (2).
I asked a while back whether blogs could be considered a serious form of scholarly scientific communication (and so has Peter Murray-Rust more recently). A case for doing so might be my post of about a year ago, addressing why borane reduces a carboxylic acid, but not its ester, where I suggested a possible mechanism. Well, colleagues have raised some interesting questions, both on the blog itself and more silently by email to me. As a result, I have tried to address some of these questions, and accordingly my original scheme needs some revision! This sort of iterative process of getting to the truth with the help of the community (a kind of crowd-sourced chemistry) is where I feel blogs do have a genuine role to play.
In the first part of the post on this topic, I described how an asymmetric sulfoxide could be prepared as a pure enantiomer using a chiral oxygen transfer reagent. In the second part, we now need to deliver a different group, cyano, to a specific face of the previously prepared sulfoxide-imine. The sulfoxide is now acting as a chiral auxilliary, and helps direct the delivery of the cyanide group to specifically one face of the imine rather than the other. After removal of the aluminum carrier for the cyano group and hydrolysis of the cyano group to a carboxylic acid group, we end up with an enantiomerically pure amino acid.