TheVan Leusen reaction is the reaction of aketone withTosMIC leading to the formation of anitrile. It was first described in 1977 by Van Leusen and co-workers.^[1] Whenaldehydes are employed, the Van Leusen reaction is particularly useful to formoxazoles andimidazoles.

Thereaction mechanism consists of the initial deprotonation of TosMIC, which is facile thanks to the electron-withdrawing effect of bothsulfone andisocyanide groups. Attack onto thecarbonyl is followed by5-endo-dig cyclisation (followingBaldwin's rules) into a 5-membered ring.

If the substrate is an aldehyde, thenelimination of the excellenttosylleaving group can occur readily. Upon quenching, the resulting molecule is an oxazole.

If analdimine is used, formed from thecondensation of an aldehyde with anamine, then imidazoles can be generated through the same process.^[2]

When ketones are used instead, elimination cannot occur; rather, atautomerization process gives an intermediate which after a ring opening process and elimination of the tosyl group forms anN-formylated alkeneimine. This is then solvolysed by an acidic alcohol solution to give the nitrile product.

• Name reactions
• Nitrogen heterocycle forming reactions
• Oxygen heterocycle forming reactions

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