Kornblum oxidation

Mechanism

Similar to sulfonium-based oxidation of alcohols to aldehydes reactions, the Kornblum oxidation creates an alkoxysulphonium ion, which, in the presence of a base, such as triethylamine (Et3N), undergoes an elimination reaction to form the aldehyde or ketone.

Extensions

The first step is an SN2 reaction, so it is subject to the usual leaving group limitations of that reaction. While iodides work well, even bromides are often not reactive enough to be displaced by the DMSO. However, using an additive such as silver tetrafluoroborate allows the reaction to work on a wider range of substrates, as often seen for alkyl-halide substitutions, or they can be converted first to the corresponding alkyl tosylate. The reaction was initially limited to activated substrates, such as benzylic and α-halo ketones. To increase the range of viable substrates, Kornblum later added a preliminary conversion of the halide to a tosylate, which is a better leaving group, to the protocol, and using pyridine-N-oxide or similar reagents rather than DMSO. The Ganem oxidation built on this latter modification, expanding on the use of various N-oxide reagents.

References

References

1. (1959). "A New and Selective Method of Oxidation. The Conversion of Alkyl Halides and Alkyl Tosylates to Aldehydes". Journal of the American Chemical Society.
2. (1957). "A New and Selective Method of Oxidation". Journal of the American Chemical Society.
3. (1986). "An Improved Direct Oxidation of Alkyl Halides to Aldehydes". Synthetic Communications.
4. (1974). "Silver-Assisted Dimethylsulfoxide Oxidations: An Improved Synthesis of Aldehydes and Ketones". Tetrahedron Letters.
5. (2005). "Strategic Applications of Named Reactions in Organic Synthesis: Background and Detailed Mechanisms".