Condensation with secondary alcohol group

Cyclopentanone and cyclohexanone contain four active hydrogen atoms and condense with formaldehyde to form substances which contain four —CH2—OH groups. The latter may be converted directly into explosive tetranitrates or they may be reduced, the carbonyl groups yielding secondary alcohol groups, and the products then may be nitrated to pentanitrates. 

To test whether urea could condense with a simple secondary alcohol group under acid-catalysis conditions, cyclohexanol, a simple high-boiling (bp 161 °C) alcohol, was substituted for carbohydrate in a reaction flask with urea (1 0.5 mole ratio) and acid. The mixture was heated at 65 to 122 °C for 2.5 hours. 

Tin(II) triflate has been used to catalyse the condensation between tetra-O-acetyl-a-D-glucopyranosyl bromide and primary and secondary alcohol groups on other monosaccharide derivatives. The products had the 3-configuration exclusively but the yields were modest (30-65%). In a related study the influences of catalyst, solvent, and temperature on the reaction of 0-(tetra-O-benzyl-a-D-glucopyranosyDtrichloroacetimidate with primary and secondary sugar alcohols were examined. With boron trifluoride in dichloro-methane at -I8—good yields (e.g. 80 for a secondary alcohol) and anomeric ratios (a,3, ca. 1 4) were obtained. 

Chemical reactions involved in the sol-gel process are similar to those that lead to standard polyurethanes [24, 25]. Precursors are polyols (sometimes natural polyols like pen-taerythritol or saccharose) and cross-linking is induced by using polyfunctional isocyanates (Figure 10.4). Condensation kinetics depends dramatically on the alcohol. Primary polyols react approximately ten times faster than polyols with secondary hydroxyl groups [24, 25]. 

The fact that the polysaccharides as a class have no sweet taste suggests that the secondary alcohol groups, —CH.OH, that confer sweetness and solubility on organic compounds, have been combined in some way during polymerisation of the sugar units. This polymerisation is different from condensation, such as occurs in the formation of ethers and esters, since polysaccharides, with the exception of lignose and cellulose, are easily depolymerised by dilute acids. 

A synthesis of 2-alkyl-2,3-dihydro-y-pyrones (187) from methoxybutenyne and aldehydes has been described (83TL4551). The condensation of lithiomethoxy-butenyne (184) with aldehydes at -78°C leads to the secondary alcohols 185, which form the dihydropyrones 187 via hydration of the acetylenic bond and hydrolysis of the methoxyethenyl group to the ketoenol 186 (0°C, p-TSA, THF, H2O or 30% HCIO4, 20 min) folowed by intramolecular cycloaddition. 

Condensation of piperazine with 2-methoxytropone gives the addition-elimination product 12 [2]. Alkylation of the remaining secondary amino group with bromoketone 13, itself the product from acylation of dimethyl catechol, gives aminoketone 14. Reduction of the carbonyl group with sodium borohydride leads to secondaiy alcohols 15 and 16. Resolution of these two enantiomers was achieved by recrystallization of their tartrate salts to give ciladopa (16) [3],... 

The Guerbet reaction is an important industrial process for increasing the carbon numbers of alcohols. Thus, a primary or secondary alcohol reacts with itself or another alcohol to produce a higher alcohol (Scheme 23). Alkaline earth metal oxides have been used as catalysts for the condensation of alcohols. Ueda et al. (158,159) reported the condensation of methanol with other primary or secondary alcohols having a methyl or methylene group at the )S-position they used MgO, CaO, and ZnO as catalysts. The reactions were performed with gas-phase reactants at 635 K only MgO was found to be both active and selective (>80%). 

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