Oligosaccharide synthesis with trichloroacetimidates formation

Acid-catalysed alkylation of an alcohol with O-alkyl trichloroacetimidate prepared from allyl alcohol and trichloroacetonitrile is readily accomplished Scheme 4.233]440 as previously discussed for the preparation of benzyl and tert-butyl ethers.311 However, these conditions are not compatible with many of the protecting groups employed in oligosaccharide synthesis. For such cases, two methods for 0-allylation under essentially neutral conditions have been devised. The first method takes advantage of the mild conditions and regioselectivity of stannylene alkylations (see section 4.3.3). The method is illustrated by the selective O-allylation of o-lactal, which began with stannylene formation on an 0.8 mole scale [Scheme 4.234].441... 

Preparation of the Fmoc protected 6 was accomplished and used in oligosaccharide synthesis. After formation of the trichloroacetimidate donor and glycosylation, the Fmoc group was quantitatively cleaved using mild basic conditions.The synthesis of conandroside 7 was accomplished using conventional methods, with the key intermediate being 2-(3,4-di-0-benzyloxyphenyl)ethyl 2,6-di-0-acetyl-4-0-( ,Z)-3,4-0-benzylcafleoyl)-p-D-... 

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