O-alkyl moiety

The three most prevalent fatty alcohols present in the 1-O-alkyl moiety of the ether lipids are C16 o, C18 0 and Cm, corresponding to chimyl 4, batyl 5 and selachyl 6 alcohols, respectively, the last one being the most abundant. As implied by the -terminology their natural absolute configuration is S (see Fig. 24.3). 

Deprotonation of the amide moieties in dibenzodiazocinediones and trapping with electrophiles always leads to iV-substituted derivatives 2 5,58 no O-alkylation has been described. 

Starting from n-butane, 2-butoxides that rapidly convert to 2-butanone are found over MgCr204 [24]. However, the further oxidation of adsorbed 2-butanone only gives rise to the acetate species, while starting from n-butane, formate species are also observed. This can be explained assuming that sec-butoxides can partly isomerize to rert-butoxides before further oxidation. This implies that the C-O bond formed is partly ionic and the alkyl moiety has the... 

The alkyl complexes [TpBut]MgR (R = Me, Et, Pr , Bul) react with excess 02 at room temperature to give alkylperoxo complexes [TpBut]-MgOOR (Scheme 5), which have been characterized by 170 NMR spectroscopy. Each complex exhibits two 170 NMR resonances in the ranges 8 102-183 and 8 323-427 for the two distinct oxygen atoms of the alkylperoxo (Mg-O-O-R) moiety (Table IV). Organometallic derivatives generally react with oxygen to produce complex mixtures (69,... 

The modulation of the chiral pocket, possible by O-alkylation of the hydroxylic moiety, was found to be in line with the observed experimental variations of enantio-discrimination when O-alkyl-modified cinchonidine was used as surface modifier. 

Schwesingefs phosphazene base 2-tert-butylamino-2-diethylamino-l,3-dimethyl-perhydro-l,3,2-diazaphosphorine (PS-BEMP has a pKb = 27.5 in MeCN) has been immobilized and shown to have immense utility in the N- and O-alkylation of many weakly acidic heterocycles. Kim et al. has made extensive use of this reagent in the multi-step synthesis of a small collection of guanines possessing potential antiviral activity [90]. The generic procedure involved the direct alkylation of the purine moiety (20) (Scheme 2.64), promoted by PS-BEMP, resulting in a mixture... 

Changing the base to triethylamine improves the yield of benzoylhydroxamic acid (96a) up to 91% the purification required column chromatography. Independently of the substituent in both Af-acylbenzotriazole and hydroxylamine, the desired O-alkyl, N-alkyl and 0,A-dialkyl hydroxamic acids were obtained as sole products as a result of nucleophilic displacement of the benzotriazolyl moiety by the hydroxylamine nitrogen. 

In 2003, Banerjee et al. designed an efficient photoremovable protecting group for the release of carboxylic acids based on similar p-elimination from photoenols (Scheme 14). They showed that o-alkyl acetophenone derivatives with various ester groups in the p-position release their ester moiety in high chemical yields. The authors proposed that the photorelease took place as shown in Scheme 14 but did not support the mechanism with transient spectroscopy. Formation of 21, which is expected to be the major product in the reaction, was not confirmed, and thus, the authors speculated that 21 undergoes polymerization to yield oligomers. 

While 1,2-diazinones usually give N-alkylation, O-alkylation can be achieved by first transforming them into the trimethylsilyloxy-l,2-diazines or silver salts <1996CHEC-II(6)1>. This approach has been used by El Ashry to attach sugar moieties to the oxygen atom of phthalazin-l(2//)-one <2003CAR2291 >. 

Reaction at the C atom of nitronate salts is known with a variety of electrophiles, such as aldehydes (Henry reaction) and epoxides (191-193). Thus the incorporation of the nitro moiety and the cyclization event can be combined into a tandem sequence. Addition of the potassium salt of dinitromethane to an a-haloaldehyde affords a nitro aldol product that can then undergo intramolecular O-alkylation to provide the cyclic nitronate (208, Eq. 2.17) (59). This process also has been expanded to a-nitroacetates and unfunctionalized nitroalkanes. Other electrophiles include functionalized a-haloaldehydes (194,195), a-epoxyaldehydes (196), a-haloenones (60), and a-halosulfonium salts (197), (Chart 2.2). In the case of unsubstituted enones, it is reported that the intermediate nitronate salt can undergo formation of a hemiacetal, which can be acetylated in moderate yield (198). 

Selective alkylation of 5,6-O-isopropylidene-L-ascorbic acid (152) at 0-3 has been performed with K2C03-acetone-alkyl halides. With an excess of alkyl halide, the 2,3-di-O-alkylated derivatives could be obtained, but by stepwise alkylation different alkyl moieties could be introduced at 0-3 and 0-2.349... 

The photocyclization of o-alkoxy phenyl ketones to yield benzofuranols (57 and 58) represents one of the earliest example of 8-H-abstraction from the lowest n, n triplet Wagner et al. [18] have provided detailed photokinetic data studying the photocyclization of a variety of o-alkoxyphenyl ketones 56, and have revealed that quantum efficiency for cyclization for 56d was the lowest (0.023) and that for 56f the highest (1.00). The diastereoselectivity for cyclization of 56 was found to be higher in benzene and lower in polar solvents. From the estimated kH values (0.6-25 x 106 s 1), it was inferred that the low rate constant for 56e (8 x 106 s ) compared to that for 56g (25 x 106s 1) i s due to the alkyl chain in the alkoxy groups that points away from the o-carbonyl moiety in the most populated equilibrium conformations (Table 8.1). 

The construction of the 2,3-dihydrofuran moieties of breviones was reported in which the epoxide and the a-pyrone depicted in the following scheme underwent both C-alkylation and consecutive O-alkylation presumably via rc-allylpalladium complexes <02TL1713>. 

To deduce the location of the double bond within the lipid backbone, the mixture (500 ng) was subjected to consecutive bisthiomethylation of the alkene85 and O-methyloxime formation (Equation 3). GC—MS study of the fragmentation of these derivatives (e.g., see 31, derived from 24) allowed simultaneous determination of the cleavage site (between C24 and C25) and of which portion contained the original ketone (i.e., the odd versus even mass fragments of 17 3 and 426 for 31). All of the monounsaturated lipid ketones had the alkene in the same downstream location in other words, they varied in the number of methylene units between the ketone and alkene functional groups but were constant in their -octyl terminal alkyl moiety. The four most major components (24, 25, 27, and 28) were prepared by chemical synthesis and used to confirm their identity in the natural pheromone and their pheromonal activity both alone and in admixtures. 

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