Glycoside stannyl

Compound 10 was converted into allyl glycoside 11 in 73 yield in two steps, (a) Bu2Sn0CH2CH=CH2—SnCl,(4), and (b) MeONa—MeOH. Treatment of 11 with dimethoxypropane and TsOH, and then with benzyl bromide— NaH—DMF afforded compound 12 in 51% yield. Solvolysis of compound 12 in MeOH—AcOH, and then monobenzylation by the stannylation— alkylation method(5) gave the desired glycosyl acceptor 8 in 67% yield. Acetylation of compound 8 and then deallylation with PdCl2— AcONa in aq.AcOH(6) afforded a 93% yield of hemiacetal 13, which was treated with (a) SOCI2—DMF in dichloroethane(7) and (b) AgF— CH CN(8) to give the desired fluoride 9 in 73% overall yield. 

Anionic nucleophiles provide valuable and versatile routes for the preparation of C-glycosides. However, the most extensively used technologies lie within the chemistry of Lewis acid-mediated reactions of carbohydrates with unsaturated hydrocarbons and derivatives thereof. In the next series of examples, reactions of sugars and sugar derivatives with olefins and their silyl-, stannyl-, and aluminum derivatives are discussed. 

If the 1,2 epoxide is used, the stannyl derivative obtained in this way may be applied in the synthesis of C-glycosides (e. g. 106) with the retention of the configuration at the anomeric center (O Scheme 29) [53]. 

Later work elaborating on the chemistry of glycals demonstrated the ease of formation of 1-stannyl glycals. These compounds, introduced in Scheme 3.1.1, are useful substrates for the direct formation of C-glycosides as well as for metal-metal exchanges with lithium to be discussed later in this chapter. As shown in Scheme 3.1.3, Hanessian, eta/.,4 utilized potassium tert-butoxide and butyllithium to effect the formation of 1-stannyl glycals. 

As already discussed in Scheme 3.1.3, Hanessian, etal.,8 prepared the Ci stannyl glycal shown. Further work by this group demonstrated the ability to transform this glycal analog to a lithiated species in preparation for coupling with an aldehyde. The reaction, shown in Scheme 3.1.7, produced a 68% yield of the C-glycoside as a mixture of isomers at the newly formed stereogenic center. 

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