Dondoni homologation

DOEBNER - MILLER Quinoline synthesis 98 DOERING - LA FLAMME Aliens synthesa 99 DONDONI Homologation 100 DOTZ Hydroqumone synthesis 101 Drechset 123 Drewson 12... 

A. Dondoni and P. Merino 21 DIASTEREOSELECTIVE HOMOLOGATION OF D-(R)-GLYCERALDEHYDE ACETONIDE USING 2-(TRIMETHYLSILYL)-THIAZOLE 2-O-BENZYL-3,4-ISOPROPYLIDENE-D-ERYTHROSE... 

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 and P. Merino, Diastereoselective homologation of D-(ft)-glyceraldehyde acetonide using 2-(trimethylsilyl)thiazole 2-0-benzyl-3,4,-0-isopropylidene-D-erythrose, Org. Synth. 72 21 (1993) The procedure has been checked by A. I. Meyers and G. P. Brengel, Colorado State University, USA. 

A. Dondoni, G. Fantin, M. Fogagnolo, and A. Medici, Stereospecific homologation of d-xylo and D-galacto dialdoses, Tetrahedron 43 3533 (1987). 

The results described in the following, part of which have been presented as a preliminary communication, are collected in a full paper. A. Dondoni, S. Franco, F. Junquera, F. L. Merch n, P. Merino, T. Tejero, and V. Bertolasi, Stereoselective homologation-amination of aldehydes by addition of their nitrones to C-2 metalated thiazoles. A general entry to a-amino aldehydes and amino sugars, Chem. Eur. J. 1 505 (1995). 

A. Dondoni, G. Fantin, and M. Fogagnolo, 2-Acetylthiazole as a three-carbon homologating reagent of aldehydes. Application toward the synthesis of amino hexoses from L-serinal, Tetrahedron Lett. 30 6063 (1989). 

Dondoni and coworkers [63] have shown that homologation of a-hydroxycarbaldehydes can be achieved with high antiselectivity by addition of 2-(trimethylsilyl)thiazole (42) (Scheme 13.25). For instance, D-glyceraldehyde acetonide (R)-24 reacts with 42 giving 43 in 96% yields with the anti vs. syn diastereoselectivity better than 95 5. Release of the aldehyde requires protection of the alcohol as a benzyl ether, methylation of the thiazole generates intermediate 43 Me that is not isolated but reduced in situ with NaBH4 to give thiazoline 43 H. Mercury(II)-catalyzed hydrolysis liberate the semiprotected D-erythrose derivative d-45 in 62% overall yield [64]. Methylation of the thiazole moiety can also be achieved with methyl triflate instead of Mel, and copper(II)chloride can be used instead of mercury(II)chloride [65]. 

SCHEME 13.27 Examples of syntheses of aldoses by Dondoni s one-carbon chain homologation. 

Dondoni and co-workers [197,198,199,200,201,202,203,204,205,206] have shown that homologation of a-hydroxycarbaldehydes and a-hydroxylactones can be achieved with high... 

A. Dondoni, D. Perrone, P. Merino, Homologation of L-threonine to a-epimer p-amino-a,7-dihy-droxy aldehydes and acids via stereoselective reduction of 2-thiazolyl amino ketones, /. Chem. Soc., Chem. Commun. (1991) 1313. 

Dondoni A, Perrone D, Semola T (1995) Synthesis of Taxol and Taxotere Side chains by 2-(Trimethylsilyl)thiazole Based Homologation of L-Phenylglycine. Synthesis 181... 

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