Alkoxide aliphatic

The extreme hydrophobicity, or in other words, the low water solubility, of the carborane cage is a major disadvantage in terms of biodistribution. However, 0-C2B10 can be readily converted into a water-soluble degradation product. 0-C2B10 reacts with strong nucleophiles such as alkoxides, aliphatic amines and fluoride anion to... 

Other bases found to react with 1,1,1-trinitroethane via formation of 1,1-dinitroethene include trimethylamine, guanidine and diethylmalonate anion (152), the latter forming (153) in 36 % yield. Shechter and Zeldin found no correlation as to why some bases react with 1,1,1-trinitroethane so differently to others but noted that simple alkoxides, aliphatic amines, guanidine, cyanide and malonate anions reacted via the 1,1-dinitroethene pathway. 

As cations, the rf-complexes are more electrophilic than the corresponding T -diene complexes and react with a wide range of nucleophiles (Scheme 10.26), in a manner similar to the T -allyl complexes (Section 9.1). Alkoxides, aliphatic amines, aromatic amines, phthalimide, stabilized enolates, ... 

Even polyalkoxy-s-triazines are quite prone to nucleophilic substitution. For example, 2,4,6-trimethoxy-s-triazine (320) is rapidly hydrolyzed (20°, dilute aqueous alkali) to the anion of 4,6-dimethoxy-s-triazin-2(l )-one (331). This reaction is undoubtedly an /S jvr-4r2 reaction and not an aliphatic dealkylation. The latter type occurs with anilines at much higher temperatures (150-200°) and with chloride ion in the reaction of non-basified alcohols with cyanuric chloride at reflux temperatures. The reported dealkylation with methoxide has been shown to be hydrolysis by traces of water present. Several analogous dealkylations by alkoxide ion, reported without evidence for the formation of the dialkyl ether, are all associated with the high reactivity of the alkoxy compounds which ai e, in fact, hydrolyzed by usually tolerable traces of water. Brown ... 

From the preceding discussion, it is easily understood that direct polyesterifications between dicarboxylic acids and aliphatic diols (Scheme 2.8, R3 = H) and polymerizations involving aliphatic or aromatic esters, acids, and alcohols (Scheme 2.8, R3 = alkyl group, and Scheme 2.9, R3 = H) are rather slow at room temperature. These reactions must be carried out in the melt at high temperature in the presence of catalysts, usually metal salts, metal oxides, or metal alkoxides. Vacuum is generally applied during the last steps of the reaction in order to eliminate the last traces of reaction by-product (water or low-molar-mass alcohol, diol, or carboxylic acid such as acetic acid) and to shift the reaction toward the... 

A similar reducing system is created by combining dilithium catecholate and trichlorosilane at —78° in tetrahydrofuran. It is speculated that the relatively unstable pentacoordinate bis(l,2-benzenediolato)hydridosilicate (61) is formed in situ and that it is this species that can reduce aldehydes and ketones, but not esters, to alcohols when they are added to the reaction mixture at 0° (Eq. 168).93 In a like manner, the dilithium salt of 2,2/-dihydroxybiphenyl, which forms a pentacoordinate intermediate that is stable enough to react at room temperature, can also be used to promote the reduction reaction. The alkoxides of aliphatic diols... 

Although transition metal-catalyzed allylic alkylation has become one of the most powerful methods in chemical synthesis, the formation of ether bonds using this process has been slow to evolve.119-121 The main reasons for this disparity are the lower nucleophilicity and higher basicity of oxygen nucleophiles, particularly those derived from aliphatic alcohols, compared to their carbon or nitrogen analogs. However, this notion has rapidly been revised, as recent advances in the O-allylation area have largely addressed the issue of the reactivity mismatch between the hard alkoxide and the soft 7r-allylmetal species to provide a considerable body of literature. 

While the notion that the alkoxides derived from aliphatic alcohols are poor nucleophiles toward 7r-allylmetal complexes has prevailed over the years, much progress made in the recent past has rendered the transition metal-catalyzed allylic alkylation a powerful method for the O-allylation of aliphatic alcohols. In particular, owing to the facility of five- and six-membered ring formation, this process has found extensive utility in the synthesis of tetrahydrofurans (THFs) (Equation (29))150-156 and tetrahydropyrans (THPs).157-159 Of note was the simultaneous formation of two THP rings with high diastereoselectivity via a Pd-catalyzed double allylic etherification using 35 in a bidirectional synthetic approach to halichondrin B (Equation (30)).157 The related ligand 36 was used in the enantioselective cyclization of a Baylis-Hillman adduct with a primary alcohol (Equation (31)).159... 

Due to the poor nucleophilicity of aliphatic alkoxides, the intermolecular O-allylation of aliphatic alcohols has been performed, for the most part, using a large excess of structurally simple primary alcohols (Equation (37))165 and/or unsubstituted allylic substrates.166,167 When allylic systems activated with an electron-withdrawing substituent were employed, only a slight excess of the alcohol was necessary to achieve complete stereospecificity, as exemplified by Equation (38).168,169... 

Another Rh-catalyzed protocol that has potentially broad utility has come from the reactions of Cu(i) alkoxides with allylic carbonates.190,191 Under the action of Wilkinson s catalyst modified by P(OMe)3, a variety of primary, secondary, and even tertiary aliphatic alcohols undergo an allylic etherification process with a high degree of retention of regio- and stereochemistry, thus providing expeditious access to a and/or ct -stereogenic ether linkages (Scheme 5).192... 

See also Alkenylsuccinic anhydrides production of, 17 726 Alkenylsuccinic anhydrides, 15 490 Alkoxidation, higher aliphatic alcohols, 2 5 Alkoxide catalysts, 10 683 Alkoxide-derived silica gels, structure of, 23 73... 

The first stage of Kolbe s synthesis is analogous to the well-known aliphatic synthesis of alkyl carbonates from alkoxides and carbon dioxide ... 

As shown in Scheme 1, aliphatic phosphines such as P(n-Bu)3 catalyze the addition of alcohols (2) to methyl propiolate (3) [35]. The mechanism is believed to involve an initial addition of the phosphine to the C = C moiety to give a zwitterionic allenolate (I), which then deprotonates the alcohol, yielding a vinyl phosphonium salt (II). An alkoxide addition to give an enolate (III), followed by phosphine elimination gives the product 4 and regenerates the catalyst. Several experiments suggest that when alcohols are used in excess, the catalyst rests as the original phosphine [34]. 

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