Erythrose, trimethylsilyl derivatives

Ribosidation of the trimethylsilyl derivative of 2-hydroxypyrazine (69) (prepared with trimethylsilyl chloride and bistrimethylsilylamine) with 1,2,3,5-tetra-O-acetyl-/J-D-ribofuranose and titanium tetrachloride in 1,2-dichloroethane, followed by deacetylation with sodium methoxide, gave 2-oxo-l-( -D-ribofuranosyl)-l, 2-dihydropyrazine and its 4-oxide was prepared similarly (1035). A similar reaction occurred with the trimethylsilyl derivative of 3-hydroxypyrazine 1-oxide and 1,2,3-tri-<3-acetyl-D-erythrose (1110). 

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]. 

An alternative method (Scheme 13.29) for the homologation of the D-glyceraldehyde derivative (7 )-24 to derivatives of D-erythrose 60 and D-threose 61 was proposed by Kusakabe and Sato [68]. Reaction of (7 )-24 with appropriate l-(trimethylsilyl)vinyl-copper reagents lead to either anti or... 

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