Sugar-derived cuprate

The photochemically induced radical addition of alcohols to enones has been described by Fraser-Reid [104-109]. Here again, the sense of addition depends on the steric effects of substituents, attack anti to the C-5 substituent being preferred [108,110]. Other uses of sugar-derived enones to trap radicals have been reported [111]. Enolone 77 gave interesting results in terms of selectivity [112]. In this instance, radical addition occurs with an equatorial selectivity, whereas cuprate addition occurs with an axial selectivity [9,62]. 

Resulting from Cuprates and Sugar-Derived Enones... 

In 1991, new syntheses of C-disaccharides incorporated Lewis acid mediated couplings with allylsilanes. Additionally, alkyllithium sugar derivatives were coupled to sugar lactones and electron deficient anions were added to sugar carbonates. Finally, complimentary to the anion chemistry used, sugar cuprates were utilized. 

Tributyltin cuprate has been prepared and used as a milder alternative to tributyltin lithium for application in sugar chemistry. Thus tin derivative 39 was prepared from the corresponding allylic bromide without any allylic rearrangement. (See Section 4 below for the use of this reagent in the preparation of acyclic alkenes). 

Derivatives of unsaturated sugars have been used as starting materials for the synthesis of a number of branched-chain sugars. Pyranosidic enones, for example, were shown to undergo 1,4-additions with lithium dimethyl cuprate, vinyl magnesium bromide, and 2-lithio-2-ethoxycarbonyl-l,3-dithiane, with the carbanion adding trans to the glycosidic substituent (Scheme 66). 4,6-Di-O-... 

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