Ckellz over at New Reactions just posted the most awesome write-up about a new oxidant ‘affectionately dubbed Bobbitt’s Salt’ and its applications in simple, effective and selective oxidations of alcohols to aldehydes, among several other fantastic things. Before you read any further, I urge everyone to check out the original post. Amazing powder. Is that salt commercially available?
I’m a big fan of oxidations for several reasons. In real life, oxidations are generally much more challenging than what the typical text books suggests. Theoretically, many of the most common oxidations are elusive; we are not sure exactly how they do their job. I therefore welcome all efforts in nailing down oxidants’ modes of action, preferably in the form of curly arrows.
To be honest I haven’t had the time to read all the cited references in Ckellz’s post, but the mechanism he proposes… I don’t like it that much.
The main problem as I see it is the first step. The typical alcohol doesn’t kick out a hydride just like that. Some carboxylic acids, most notably formic acid, may expel a hydride if the conditions are right, but a straight alcohol? Improbable.
I started thinking that perhaps I could come up with an alternative that doesn’t include the spontaneous extrusion of a hydride as the key step. I soon realized that the accepted mechanism for the Swern oxidation had all the components I needed: a super-potent electrophile (check), alcohol as the nucleophile (check), an umpolung of the alcohol to turn it into a fantastic leaving group (check), and finally a concerted rearrangement to release the aldehyde (check). Like so:
Those who are not with me are against me! He-he. No but seriously, what does your gut feeling say? Which version do you like more?