Having established a viable model for the unexpected isomerism of oxetane carboxylic acids to lactones[cite]10.1021/acs.orglett.2c01402[/cite], and taken a look at a variation in the proton transfer catalyst needed to accomplish the transformation, I now investigate the substrate itself.
Previously, a mechanism with a reasonable predicted energy was modelled for the isomerisation of an oxetane carboxylic acid to a lactone by using two further molecules of acid to transfer the proton and in the process encouraging an Sn2 reaction with inversion to open the oxetane ring. We are now ready to explore variations to this mechanism to see what happens.
In 2006[cite]10.1021/ic0519988[/cite] we published an article illustrating various types of pseudorotations in small molecules. It’s been cited 20 times since then, so reasonable interest! We described rotations known as Lever and Turnstile as well as the better known Berry mode. Because the differences between these rotations are quite subtle, we included an interactive electronic supporting information to illustrate them.
In the previous post, I looked at the intramolecular rearrangement of the oxetane carboxylic acid to a lactone, finding the barrier to the Sn2 reaction with retention was unfeasibly high. Here I explore alternatives. This first attempt uses a second molecule of a carboxylic acid (modelled as formic acid for simplicity) to see if it can catalyse the reaction.
Derek Lowe’s blog has a recent post entitled A Downside to Oxetane Acids which picks up on a recent article[cite]10.1021/acs.orglett.2c01402[/cite] describing how these acids are unexpectedly unstable, isomerising to a lactone at a significant rate without the apparent need for any catalyst. This is important because these types of compound occur frequently in the medicinal chemistry literature.
WATOC 2020 was just held in 2022 in Vancouver Canada, over one week. With many lectures held in parallel, it is not possible for one person to cover anything like the topics presented, so this is a personal view of some of those talks that I attended. As happens with many such events, common themes gradually emerge and here I highlight just two that struck me as important for the future of computational chemistry.
I have long been fascinated by polymers of either carbon dioxide, † or carbon monoxide, or combinations of both. One such molecule, referred to as dioxane tetraketone when it was featured on the ACS molecule-of-the-week site and also known as the anhydride of oxalic acid, or more formally 1,4-dioxane-2,3,5,6-tetraone, has been speculated upon for more than a century.[cite]10.1002/cber.19080410335[/cite] The history of
Minds (and memories) can work in wonderful ways. In 1987[cite]10.1021/jo00389a050[/cite] we were looking at the properties of “stable” tetrahedral intermediates formed in carbonyl group reactions. The reaction involved adding phenylhydroxylamine to acetyl cyanide.
Previously, I explored the unusual structure of a molecule with a hydrogen bonded interaction between a phenol and a pyridine. The crystal structure name was RAKQOJ and it had been reported as having almost symmetrical N…H…O hydrogen bonds. This feature had been determined using neutron diffraction crystallography, which is thought very reliable at determining proton positions.
Proton transfers are amongst the most common of all chemical reactions.
The previous examples of four atom systems displaying two layers of aromaticity illustrated how 4 (B 4 ), 8 (C 4 ) and 12 (N 4 ) valence electrons were partitioned into 4n+2 manifolds (respectively 2+2, 6+2 and 6+6). The triplet state molecule B 2 C 2 with 6 electrons partitioned into 2π and 4σ electrons, with the latter following Baird’s aromaticity
