Thiazolium ylids

Benzilic acid rearrangement, 232 Benzoin condensation, 231 cyanide ion in, 231 thiazolium ylids in, 232... 

Thiazolium ylids (e.g., 30) undergo initial reaction with DMAD and dibenzoylacetylene in the expected way to give structures such as 31, but... 

Boekelheide and Fedoruk554 prepared the thiazolium ylid 40 and obtained the adduct formulated as 41. 

The organic product is a 1,4-diketone and the thiazolium ylid is released to continue with another cycle of the reaction. Like thiamine, the thiazolium ylid is catalyst. Processes like this, which copy nature, are called biomimetic. 

Decomposition of this product with the release of the thiazolium ylid also releases the product of coupling between the two keto-acids a l-hydroxy-2-keto-acid (in green). The original keto group of... 

On an industrial scale, methane, the main component of natural gas, can easily be converted to formaldehyde. An efficient catalytic condensation of formaldehyde to dihydroxyactone or glycolaldehyde would thus provide a route to C2- and C3-chemicals from methane. The tria-zolin-5-ylidene 94 turned out to be a powerful catalyst for the conversion of formaldehyde (95) to glycolaldehyde (96) in the formoin reaction (Teles et al. 1996). This reactivity is a useful complement to the catalytic properties of thiazolium salts which mainly afford 1,3-dihydroxy acetone as product (Scheme 23) (Castells et al. 1980 Mat-sumoto and Inoue 1983 Matsumoto et al. 1984). As triazolium ylides are much more stable than thiazolium ylids, the elimination of glycolaldehyde occurs faster than the addition of the third formaldehyde molecule. 

Michael addition of aromatic or heterocyclic aldehydes (via cyanohydrins) to a,p-unsaturated systems. Also addition of an aliphatic aldehydes catalyzed by thiazolium ylids (see 1st edition). 

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