Carbohydrate nitroalkenes

Asymmetric tandem cycloaddition of a chiral carbohydrate nitroalkene with ethyl vinyl ether in the presence of electron-withdrawing alkenes produces a facile assembly of bicyclic systems, which can further be selectively cleaved to give homologated carbohydrates (Eq. 8.110).176... 

The asymmetric tandem cycloaddition of the chiral carbohydrate nitroalkene (35) with ethyl vinyl ether involves the initial formation of the nitronate (36) which reacts exclusively with electron-withdrawing alkenes by 3 -I- 2-cycloaddition to yield chiral bicycles (37) and (38) (Scheme 12). ... 

Nitroalkenes with Chiral Auxiliaries The use of carbohydrates as chiral auxiliary in Diels-Alder reactions for the stereoselective preparation of carbocyclic and heterocyclic chiral rings is well documented.48 For example, D-manno-nitroalkene reacts with 2,3-dimethyl-1,3-butadiene to give a 65 35 mixture of adducts, as shown in Eq. 8.29. The configurations at C-4 and C-5 have been determined to be (4R,5R) and (45,55), respectively. Hydrolysis of the product followed by degradative oxidation of the sugar side chains leads to enantiomerically... 

Nitroalkenes derived from galactose or other carbohydrates are converted directly into pyrroles substituted with such carbohydrates at the (3-position. They are important precursors for water-soluble porphyrins (Eq. 10.29).34 Such kinds of porphyrins are good candidates for photodynamic therapy of cancer and have been extensively studied. 

Figure 8. Formation of a carbohydrate nitrocyclopropane from a nitroalkenic sugar via a pyrazoline.

Figure 9. Preparation of some carbohydrate pyrazolines by cycloaddition of diazomethane to nitroalkenic sugars.

Borrachero et al. (180) prepared a number of sugar isoxazolidines by the reaction of carbohydrate-functionalized nitrones with nitroalkenes (Scheme 1.33). They found a matched pair of chiral sugar cycloaddition reaction partners to be... 

The study was intended to prove the intermediacy of nitroalkene 8 in the unexpected deacetona-tion-methoxylation of 1,2 3,5-diisopropylidene-6-deoxy-6-nitro-a-n-glucofuranose(ll), which occurred upon treating the latter carbohydrate with dilute methanolic sodium hydroxide60. In this reaction, deacetylated 9 and 10 were formed in a 4 1 ratio, too. Interestingly, under identical conditions, the cpimeric L-idose 12 was reversibly deprotonated and did not lose acetone. 

A domino nitro-Michael/Henry reaction was conceived by Seeberger et al. to afford a 2-nitropyranoside system 156, regarded as an excellent carbohydrate building block (Scheme 7.31) [84]. In this case, the reaction between hydroxyaldehyde 154 and nitroalkene 155 was investigated, with the base liHMDS performing well... 

Aminothiourea-prolinal dithioacetal (234), in the presence of PhC02H, can catalyse Michael addition of ketones R CH2COR and aldehydes to nitroalkenes at 3 mol% loading to afford the 3yn-configured products with <99 1 dr and <99% ee under solvent-free conditions at room temperature. The related carbohydrate-derived thiourea is believed to activate both 8-diketones and nitroalkenes via coordination (235) the Michael adducts were obtained in <89% ee " Another variant of the thiourea motif with a cinchona alkaloid scaffold exhibited higher stereocontrol in the same reaction (<98% ee), carried out in MeCN at —40°C ... 

The carbohydrate derived nitroalkene 351 undergoes Diels-Alder reaction with 1,3-butadiene to afford 352, while 354 leads to a reversal of the diastereoselec-tivity giving 355 as the major products. However, the diastereoselectivity was modest with ratios of 78 22 and 67 33 for these two reactions. Denitration, acidic deacylation, sodium periodate cleavage and final reduction provided the (5) and R) alcohols 353 and 356 respectively (Scheme 55). ... 

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