Olefinated carbohydrates

Kuzina S.I., Demidov S.V., Denisov N.N., Mikhailov A.I. Synchronic reactions of free radicals formation at low-temperature chlorination of aromatic and olefinic carbohydrates. Izv. AN, Ser. Chem., 1999, 335. 

The research team of J. Tadanier prepared a series of C8-modified 3-deoxy-P-D-manno-2-octulosonic acid analogues as potential inhibitors of CMP-Kdo synthetase. One of the derivatives was prepared from a functionalized olefinic carbohydrate substrate by means of the Wohl-Ziegler bromination. The stereochemistry of the double bond was (Z), however, under the reaction conditions a cis-trans isomerization took place in addition to the bromination at the allylic position (no yield was reported for this step). It is worth noting that the authors did not use a radical initiator for this transformation, the reaction mixture was simply irradiated with a 150W flood lamp. Subsequently the allylic bromide was converted to an allylic azide, which was then subjected to the Staudinger reaction to obtain the corresponding allylic amine. 

The coupling partners, olefinated carbohydrates required for hydroboration are prepared via methylenation of the aldehyde or ketone moiety of the monosaccharides. 

Among other examples are unsaturated amines (190,191), carbohydrates (192,193), heterocycHc olefins (194), phosphoms and sulfur compounds (195,196), organometaUic compounds (148,197,198), functionalized iatermediates ia natural product syntheses (98—105,199,200), and many other compounds described ia reviews (5,6,8,9,13). 

Additions of the halogen fluorides to unsaturated steroids [62, 95, 96, 97, 98, 99] and carbohydrates [62, 75] are well known Typical reagent combinations include l,3-dibromo-5,5-dimethylhydantoin (DBH) or the Af-halosuccinimides with hydrogen fluoride Reversal of the expected regiochemistry can be observed with certain steroidal olefins [JOO, 101] (equation 7)... 

We will focus on the development of ruthenium-based metathesis precatalysts with enhanced activity and applications to the metathesis of alkenes with nonstandard electronic properties. In the class of molybdenum complexes [7a,g,h] recent research was mainly directed to the development of homochi-ral precatalysts for enantioselective olefin metathesis. This aspect has recently been covered by Schrock and Hoveyda in a short review and will not be discussed here [8h]. In addition, several important special topics have recently been addressed by excellent reviews, e.g., the synthesis of medium-sized rings by RCM [8a], applications of olefin metathesis to carbohydrate chemistry [8b], cross metathesis [8c,d],enyne metathesis [8e,f], ring-rearrangement metathesis [8g], enantioselective metathesis [8h], and applications of metathesis in polymer chemistry (ADMET,ROMP) [8i,j]. Application of olefin metathesis to the total synthesis of complex natural products is covered in the contribution by Mulzer et al. in this volume. 

Improved /V,/V-ligands, shown in Figure 103, have a chiral carbon closer to the coordinating atoms, i.e., a linkage between the carbohydrate Cl carbon and the N donor. This feature enhances the ability of the ligands to induce enantioselective coordination of prochiral olefins. 

A. Dondoni, M. Kleban, and A. Marra, The assembly of Carbon-linked calix-arene-carbohydrate structures (C-calixsugars) by multiple Wittig olefination, Tetrahedron Lett., 38 (1997) 7801-7804. 

Carbohydrate derivatives with a spiroisoxazoline moiety, present in psammap-lysins and ceratinamides (metabolites isolated from marine sponges) have been prepared in good yields and excellent regio- and diastereoselectivity by a route involving Wittig olefination and 1,3-dipolar cycloaddition as key steps (477). 

This chapter reviews the adsorptive separations of various classes of non-aromatic hydrocarbons. It covers three different normal paraffin molecular weight separations from feedstocks that range from naphtha to kerosene, the separation of mono-methyl paraffins from kerosene and the separation of mono-olefins both from a mixed C4 stream and from a kerosene stream. In addition, we also review the separation of olefins from a C10-16 stream and review simple carbohydrate separations and various acid separations. 

As promised, this chapter outhnes numerous liquid-phase non-aromatic adsorption processes that enable one to economically separate a commercially desirable component from a mixture when the separation is impossible (given the closeness of their relative volatilities) by conventional means such as distillation. We review process that can separate a wide range of normal paraffins from a mixture of their corresponding feedstocks. In addition to this, we also review how to separate mono branched paraffins and olefins from similar feedstocks. Finally we review liquid-phase adsorption processes to isolate desired carbohydrates, fatty acids and citric acid from their feed source and for each separation we reveal insight on the corresponding operating conditions, process configuration and adsorbent necessary to achieve the separation. 

Carbohydrate anisyl tellurides are easily prepared by treatment of the corresponding mesylates or tosylates with the anisyl teUurolate anion. By irradiation of these tellurocarbohy-drates in the presence of M-acetoxythiopyridone and the electrophilic olefin, the tandem addnct is formed. The oxidative elimination of the thiopyridine moiety leads to the trans-olefms. ... 

Radical addition (general procedure)d To the tellurocarbohydrate (1 mmol) and the appropriate olefin (5 mmol) in dry CH2CI2 (4 mL) under argon at 5°C is added acetoxy-2-thiopy-ridone (0.5 mmol). Photolysis with a 150 W tungsten lamp for 10 min is followed by further addition of the reagent (0.25 mmol). This is repeated until all the carbohydrate disappears (TLC -1.5 mmol of the reagent is usually required). 

After these results had established the feasibility of generating and utilizing a carbohydrate phosphorane, the two systems that had been reported earlier were examined in order to determine if similar conditions would allow them to undergo the Wittig reaction. The ylide derived from phosphonium salt I condensed with both benz-aldehyde and U-chlorobenzaldehyde to produce good yields of olefinic products Villa and Vlllb. The ylide derived from phosphonium salt II also was successfully condensed with benzaldehyde, but the yield of IX was only 30 , presumably because of its extremely poor solubility even in an HMPA-THF solvent mixture. Both of these systems supported the tenet that it was possible to use unstabilized carbohydrate phosphoranes if the conditions are proper and if the g-oxygen is attached to the carbohydrate through another set of bonds. 

Condensation of the ylide derived from X with carbohydrate aldehyde X proceeded smoothly to afford only the Z-isomer XIII. Proof of the olefinic configuration was garnered by photochemical isomeri-... 

Carbenes, dioxirane preparation, 1132 Carbocations, antimalarial endoperoxides, 1309 Carbohydrate hydroperoxides, Mo-catalyzed olefin epoxidation, 432, 436 Carbohydrates, TBARS assay, 669 Carbonate esters, oxidative ozonolysis, 737, 738... 

Optically active aldehydes are available in abundance from amino and hydroxy acids or from carbohydrates, thereby providing a great variety of optically active nitrile oxides via the corresponding oximes. Unfortunately, sufficient 1,4- or 1,3-asymmetric induction in cycloaddition to 1-alkenes or 1,2-disubstituted alkenes has still not been achieved. This represents an interesting problem that will surely be tackled in the years to come. On the other hand, cycloadditions with achiral olefins lead to 1 1 mixtures of diastereoisomers, that on separation furnish pure enantiomers with two or more stereocenters. This process is, of course, related to the separation of racemic mixtures, also leading to both enantiomers with 50% maximum yield for each. There has been a number of applications of this principle in synthesis. Chiral nitrile oxides are stereochemicaUy neutral, and consequently 1,2-induction from achiral alkenes can fully be exploited (see Table 6.10). 

From among the variety of non-carbohydrate precursors, acetylenes and alkenes have found wide application as substrates for the synthesis of monosaccharides. Although introduction of more than three chiral centers having the desired, relative stereochemistry into acyclic compounds containing multiple bonds is usually difficult, the availability of such compounds, as well as the choice of methods accessible for their functionalization, make them convenient starting-substances for the synthesis. In this Section is given an outline of all of the synthetic methods that have been utilized for the conversion of acetylenic and olefinic precursors into carbohydrates. Only reactions leading from dialkenes to hexitols are omitted, as they have already been described in this Series.7... 

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