Trichloroacetimidate intermediate

Stereoselective transformation of allylic alcohol to allylic trichloroacetamide via trichloroacetimidate intermediate. 

Preparation of Trichloroacetimidates. The imidates derived from the addition of alcohols to trichloroacetonitrile have become important and versatile intermediates in synthetic chemistry. Consequently the principal synthetic use of trichloroacetonitrile has been in the formation of these useful trichloroacetimidate intermediates. The imidates are most often prepared by simple addition of a sodium or potassium alkoxide to the electron-deficient trichloroacetonitrile (eq l). In certain cases, slight modifications of the above procedure are utilized. The product imidates are isolable and, despite their propensity to rearrange, can in some instances be purified by distillation or chromatography. Typically the addition reaction is sufficiently clean to use the imidates without further purification. ... 

In addition, a novel fluorous support has been developed recently as an alternative to traditional polymer supports and applied successfully to oligosaccharide synthesis in combination with the trichloroacetimidate method [541]. Each intermediate in the fluorous oligosaccharide synthesis [542,543] could be obtained by simple fluorous-organic solvent extraction, and the reactions could be monitored by TLC, NMR and MS, in contrast to solid-phase reactions. Moreover, the new liquid-phase technique is anticipated to be easily applicable to the large-scale synthesis. 

Chiral nonracemic l-aryl-2-aminopropane-l,3-diols were converted to 2-trichloromethyl-5,6-dihydro-4/7-l,3-oxazine derivatives with complete diastereoselectivity via the corresponding bistrichloroacetimidate intermediates. In this transformation, one trichloroacetimidate participated as a leaving group, and the other as a nucleophile <20070L247>. 

The deprotonated alcohol ads to trichloroacetonitrile to give a trichloroacetimidate anion. As this latter intermediate can readily deprotonate the starting alcohol, only a catalytic amount of a strong base is needed. 

Glucolipsin A (21) is a macrocyclic dilactone natural product that exhibits glucokinase-activating properties. Fiirstner et al. employed an Evans aldol strategy to synthesize the syn -aldol intermediate 2310 (Scheme 2.1j). The aldol reaction of the boron enolate of 14 with 14-methylpentadecanal (22) delivered the yyn-aldol product 23 in essentially diastereomerically pure form (99% de) after purification. Subsequent glycosidation of the alcohol 23 with trichloroacetimidate (24) was facilitated by catalytic amounts of TMSOTf (20 mol %) to afford the key intermediate (25) in moderate yield. 

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