Formyl anion equivalents, 2- trimethylsilyl thiazole

A. Dondoni, G. Fantin, M. Fogagnolo, A. Medici, and P. Pedrini, Iterative, stereoselective homologation of chiral polyalkoxy aldehydes employing 2-(trimethylsilyl)thiazole as a formyl anion equivalent. The thiazole route to higher carbohydrates, J. Org. Chem. 54 693 (1989). 

Dondoni pioneered the use of 2-(trimethylsilyl)thiazole (71) as a formyl anion equivalent for the homologation of aldehydes. Extension of this reaction to ketones would be very useful, but has thus far been restricted to tritluoromethyl cases. However, it has now been widened to include several a, a -alkoxy ketones, as demonstrated in a new route to branched-chain monosaccharides. Aldehydes catalyse the reaction, although the scope is still limited electrophilic aldehydes, such as 2-fluorobenzaldehyde, promote the addition of (71) to electrophilic ketones. 

A. Dondoni, J. Orduna, and P. Merino, Construction of all 0-alkoxy D-tetrose and D-pentose stereoisomers from 2,3-0-isopropylidene-D-glyceraldehyde using 2-(trimethylsilyl)thiazole as a formyl anion equivalent. Synthesis p. 201 (1992). 

A key feature of the thiazole deprotonation chemistry is its potential as a latent formyl group in the assembly of tightly functionalized, chiral molecular architecture. The use of 2-(trimethylsilyl) thiazole (TST) as a formyl anion equivalent has been well investigated and popularized by... 

The compound 2-lithiothiazole like 2-(trimethylsilyl)thiazole (2-TST) has been used as a formyl anion equivalent used by Dondoni in the scheme below to prepare a chiral compound by a process called aminohomolgation of Gamer aldehyde. Propose stmctures for products A, B, C, and D below. ... 

In summary, 2-(trimethylsilyl)thiazole (1) appears to be a useful formyl anion equivalent. The advantages over other precursors to the formyl anion can be found in the stability of the thiazole ring to a wide range of reaction conditions and its ready conversion into the formyl group under mild and neutral conditions. Few of the many formyl anion equivalents have been demonstrated to be capable of producing labile a-alkoxy aldehydes without racem-ization. 

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