Mechanism and absolute configuration of benzylidene derivatives of some acyclic C-Nucleosides

ABSTRACT

The mechanism of formation of benzylidene derivatives was deduced from the mode of the condition of benzylidenation as well as from their assigned structures. The absolute configuration has been assigned to the various isomeric forms for each diastereoisomer. The protection of hydroxyl groups in a polyhydroxymolecule can be achieved by various ways, e.g. by acylation and/or acetalization. The latter protecting groups possess the advantage, in most cases, of being stable towards, alkaline conditions but could be successively cleaved under acidic conditions, whereas, the acylated products possesses a reverse character. Acetalization may promise the direct protection of two hydroxyl groups out of three or more existing in the same molecule. Perprotection of the hydroxyl groups can be easily accomplished without much problems, whereas their partial protection needs much care and it is very important in organic synthesis: