Aldehydes lithiated oxazoles

The additives (MeaSiCl or BF3 Et20) may activate the carbonyl compound or stabilize the intermediate. BF3 Et20 has been used as an activator in the reaction of aldehydes with lithiated phenylsulfones [111] although its fimc-tion remains vague. It may be noted that acyclic products were formed on silylation of the hydroxy sulfides obtained in the reaction of oxazol-2-yl sulfides with aldehydes [80]. 

Conformationally-locked C-nucleosides such as 147 have been reported from Imanishi s laboratory. These were prepared by formation of the C-T-O bond in Mitsunobu reactions, the necessary diols being formed by stereoselective addition of Grignard derivatives of the heterocycles to an aldehyde. Use of lithiated heterocycles gave substantially more of the other epimers of the diols, thus permitting access to the a-anomers after Mitsunobu reaction. The oxazole 147 and the compound without the phenyl group were incorporated into oUgonuc-leotides, and the triplex-forming ability of the these towards a purine sequence of duplex DNA was studied. ... 

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