Glycoside nitroalkyl

The conjugate addition of protected pyranose alkoxides to 1-nitro- and 1-nitrosoalkenes gave 2-nitroalkyl and 2-oximinoalkyl glycosides. In several cases, the reaction proceeded with preferential formation of the a-glycoside (a /3 < 4 1).190... 

The formation of nitroalkyl glycosides, illustrated in Figure 7.12, is limited in scope and few examples have been reported. The problems associated with this reaction involve the acidity of nitromethyl groups. Specifically, after formation of the C-glycoside, nitromethyl anions are easily formed. Moreover, when acetyl protecting groups are used, nitronates readily form. The few examples illustrated in this section are intended to convey the relatively limited accessibility of these compounds. 

Unlike nitroalkylation reactions, employing allylic ethers as reagents in C-glycoside chemistry has proven to be substantially more useful. These reactions, illustrated in Figure 7.13, show a propensity for a selectivity and are able to provide additional asymmetric centers. However, these... 

In 1990, additional research into the conformational features of C-disaccharides was reported.24 In addition to the insights provided by this study, significant developments in the synthetic methodology surrounding these compounds became apparent. Of notable interest are the use of C-nitroalkyl glycosides and palladium mediated coupling reactions. 

Chemistry involving the use of C-nitroalkyl glycosides has already been discussed in Chapter 2 and presented in Schemes 8.2.1 and 8.2.2. Complimentary to the dimerization reaction presented in Scheme 8.2.2 is the ability to apply similar chemistry to the unsymmetrical coupling of two different sugar units. Unlike the dimerization, the unsymmetrical couplings center around the addition of stabilized anions to aldehydes. As shown in Scheme 8.8.2, Martin, et al.,2(> reported the incorporation of this chemistry into the preparation of C-disaccharides. As illustrated, the actual coupling proceeded in a 52% yield with the subsequent elimination giving the olefin in a... 

---