Aldehydes, adducts with thiazolium salts

Alcoxyalcene derivatives, of thiazolium salts, see Thiazolium salts Aldehydes, adducts with thiazolium salts, 35... 

The active aldehydes are derived from the reaction of 3-benzylthiazolium salts with o-tolualdehyde in the presence of DBU (l,8-diazabicyclo[5.4.0]undec-7-ene) via deprotonation of thiazolium salts, addition of the aldehyde and deprotonation of the adduct as shown in Scheme 33 [364], The anionic form of active aldehydes in Scheme 33 is confirmed by the direct detection of the one-electron oxidized species with use of ESR [364]. From the linewidth variations of the ESR spectra of the oxidized active aldehyde radicals were determined the rate constants [(5-7) x 10 s ] and the corresponding small reorganization energies (A = 12-13... 

NMR studies have revealed that under the reaction conditions, the tosyl amide 21 is in equilibrium with the iV-acylimine 22. The thiazolium salt 25 may be deprotonated by triethylamine then adds to the aldehyde 23 to provide the adduct 26. Deprotonation provides the reactive enamine tautomer 27. Reaction of this enamine with the A -acylimine 22 leads to the key C-C bond formation, which is followed by catalyst turnover to provide the desired product 24. 

To gain further evidence for mechanism 1 we prepared the proposed intermediate aldehyde thiazole adduct 26 (Figure 1) by deprotonating thiazole with LDA and adding the resulting anion to benzaldehyde. Alkylation of this nmterial with methyl iodide provided the corresponding salt, which was isolated and characterized. En loying a catalytic amount of this material in a reaction wifli a tosyl amide (21, Ar = Ar = Ph, R = c-hexyl) and benzaldehyde provided the keto-amide product 24 in 83% yield.. Thus the thiazolium salt 26 is a viable intermediate in this reaction and an evidence that supports the first mechanism. (Scheme 9). 

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