Alkyl carbohydrate esters

Description. The common aspect among the surfactants grouped in this class and the sorbitan esters and alkyl carbohydrates esters classes is that they all derive from the condensation reaction of a polyhydroxyl compound (glycol, glycerol, sorbitol, sucrose, etc.) with a fatty acid. Some of them can be directly extracted from natural sources. 

Polyethers, alkanolamides, alkyls, alkylethoxylates, amines, benzyls, carbohydrates, esters, perfluoroalkyls Alkyl-, amidoimidazoline- and carboxy-quaternary ammonium salts Betaines, phosphobetaines, sulfobetaines... 

The alkylation of enolates constitutes a very powerful method for the formation of C-C bonds. Several methods have been developed in order to control the stereoselectivity of this process. First applications of carbohydrate auxiliaries in stereoselective alkylations of ester enolates were described by Heathcock et al. [152] in 1981. 

Kuhn, C, Florent, J-C, A carbohydrate approach to 4-hydroxy-2-cyclopentenone moiety of antitumor prostanoid punaglandin IV via alkylation of ester uronate, Tetrahedron Lett., 39, 4247-4250, 1998. 

Multifunctional carbohydrate derivatives have been used widely as chiral synthons [240], and they have more recently found application as chiral auxiliaries [241], In this chapter, examples of carbohydrates in which an alcohol functional group is the point of attachment to the reagent wall be presented. Alkylations of ester etiolates of the D-allofiiranose derivative 1.47 or of the diacetoneghicose... 

Polyhydroxy(cyclo)alkyl phosphonic esters in the /nyo-inositol series have been prepared through a simple application of the Michaelis-Arbuzov reaction, and the displacement of methanesulphonyl groups from (137) occurs in reactions with simple trialkyl phosphites to give, for example, (138). Interest continues in carbohydrate-like... 

Further applications of coupled h.p.l.c.-m.s. systems have appeared. The efficacy of adding ammonium acetate to the mobile phase to enhance MH and [M+NH, ] ion intensities was tested with a variety of underivatized, per-Q-acetylated, and per-Q-alkylated carbohydrates. Qualitative analysis of crude saponins containing oligoglycoside and oligoglycosyl ester moieties was performed on a system with a new FRIT-FAB interface. ... 

Medium reactivity contaminants alcohols, ketones, organic acids, esters, alkyl-substituted aromatics, nitro-substituted aromatics, carbohydrates. 

Scheme 10.17 illustrates allylation by reaction of radical intermediates with allyl stannanes. The first entry uses a carbohydrate-derived xanthate as the radical source. The addition in this case is highly stereoselective because the shape of the bicyclic ring system provides a steric bias. In Entry 2, a primary phenylthiocar-bonate ester is used as the radical source. In Entry 3, the allyl group is introduced at a rather congested carbon. The reaction is completely stereoselective, presumably because of steric features of the tricyclic system. In Entry 4, a primary selenide serves as the radical source. Entry 5 involves a tandem alkylation-allylation with triethylboron generating the ethyl radical that initiates the reaction. This reaction was done in the presence of a Lewis acid, but lanthanide salts also give good results. 

Covalently bonded chiral auxiliaries readily induce high stereoselectivity for propionate enolates, while the case of acetate enolates has proved to be difficult. Alkylation of carbonyl compound with a novel cyclopentadienyl titanium carbohydrate complex has been found to give high stereoselectivity,44 and a variety of ft-hydroxyl carboxylic acids are accessible with 90-95% optical yields. This compound was also tested in enantioselective aldol reactions. Transmetalation of the relatively stable lithium enolate of t-butyl acetate with chloro(cyclopentadienyl)-bis(l,2 5,6-di-<9-isopropylidene-a-D-glucofuranose-3-0-yl)titanate provided the titanium enolate 66. Reaction of 66 with aldehydes gave -hydroxy esters in high ee (Scheme 3-23). 

As far as propargyl thioethers are concerned, the substrates in this section follow all the principles discussed for propargyl ethers and propargylamines in the two preceding sections. For alkyl propargyl thioethers typical bases used are sodium amide in liquid ammonia, alcoholate or alkali metal hydroxide [178, 186-189, 191, 287-291], and again some derivatives of carbohydrates have been used successfully [292, 293], If an ester group is also present in the molecule, the reaction can be accompanied by a hydrolysis to the carboxylate [294]. 

O. Varela, G. M. de Fina, and R. M. de Lederkremer, The reaction of 2-hydroxyglycal esters with alcohols in the presence of N-iodosuccinimide, stereoselective synthesis of a anomers of alkyl 3-deoxyhex-2-enopyranosides and 3,4-dideoxyhex-3-enopyranosid-2-uloses, Carbohydr. Res., 167 (1987) 187-196. 

Examples of radical-mediated C-alkylations are listed in Table 5.4. In these examples, radicals are formed by halogen abstraction with tin radicals (Entries 1 and 2), by photolysis of Barton esters (Entry 3), and by the reduction of organomercury compounds (Entry 4). Carbohydrate-derived, polystyrene-bound a-haloesters undergo radical allylation with allyltributyltin with high diastereoselectivity (97% de [41]). Cleavage from supports by homolytic bond fission with simultaneous formation of C-H or C-C bonds is considered in Section 3.16. 

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