1.3- Dioxanes 1.3- diols

Whilst some organic compounds can be investigated in aqueous solution, it is frequently necessary to add an organic solvent to improve the solubility suitable water-miscible solvents include ethanol, methanol, ethane-1,2-diol, dioxan, acetonitrile and acetic (ethanoic) acid. In some cases a purely organic solvent must be used and anhydrous materials such as acetic acid, formamide and diethylamine have been employed suitable supporting electrolytes in these solvents include lithium perchlorate and tetra-alkylammonium salts R4NX (R = ethyl or butyl X = iodide or perchlorate). 

Horseradish peroxidase Trypsin (protease) Subtilisin (protease) Phenol polymerization Transpeptidation Ester hydrolysis Ethylacetate Butan-l,4-diol Dioxane, chloroform, etc. 

Efficient acetalization of alkenes bearing various EWG with an optically active 1.3-diol 72 proceeds smoothly utilizing PdCN, CuCI. and O2 in DME to give the 1,3-dioxane 73[113], Methacrylamide bearing 4-t-butyloxazolidin-2-one 74 as a chiral auxiliary reacts with MeOH in the presence of PdCE catalyst... 

Treatment with acidic catalysts dehydrates i j -butenediol to 2,5-dihydrofuran [1708-29-8], C H O (100). Cupric (101) or mercuric (102) salts give 2,5-divinyl-l,4-dioxane [21485-51-8], presumably via 3-butene-l,2-diol. 

Acetals andKetals. Acetals of 1,3-diols are prepared by refluxing the diol with the aldehyde in the presence of an acid catalyst, even in an aqueous medium. The corresponding ketals are more difficult to prepare in aqueous solution, but cycHc ketals of neopentyl glycol, eg, 2-butyl-2-ethyl-5,5-dimethyl-l,3-dioxane (3), can be prepared if the water of reaction is removed azeotropicaHy (34). 

The first mechanistic studies of silanol polycondensation on the monomer level were performed in the 1950s (73—75). The condensation of dimethyl sil oxanediol in dioxane exhibits second-order kinetics with respect to diol and first-order kinetics with respect to acid. The proposed mechanism involves the protonation of the silanol group and subsequent nucleophilic substitution at the siHcone (eqs. 10 and 11). 

Boric acid is quite soluble in many organic solvents (Table 7). Some of these solvents, eg, pyridine, dioxane, and diols, are known to form boric acid... 

Monoprotection of a symmetrical diol can be effected by reaction with a polymer-supported phenylacetyl chloride. The free hydroxyl group is then converted to an ether and the phenylacetate cleaved by aqueous ammonia-dioxane, 48 h. ... 

The conversion of the intermediate bromo aldehyde to the dioxane proceeds readily owing to a favorable equilibrium position. However, the equilibrium for the reaction of the bromo ketone with the diol is unfavorable and requires removal of the by-product, water. This is done under mild conditions using... 

Prednisolone acetate (21-acetoxypregna-l,4-diene-ll3-17a-diol-3,20-dione) [52-21-1] M 402.5, m 237-239 , 240-242°, 240-243 , 244 , [a]], +116° (c 1, dioxane). Recrystd from EtOH, Mc2CO, Me2CO-hexane, and has UV 243nm in EtOH. [Joly et al. Bull Soc Chim Fr 366... 

The prevalence of diols in synthetic planning and in natural sources (e.g., in carbohydrates, macrolides, and nucleosides) has led to the development of a number of protective groups of varying stability to a substantial array of reagents. Dioxolanes and dioxanes are the most common protective groups for diols. The ease of formation follows the order H0CH2C(CHc,)2CH20H > H0(CH2)20H > H0(CH2)30H. 

The reaction of diacetylene with propane-1,3-diol gives 2-(prop-2-ynyl)-l,3-dioxane (39), 2-(propa-l,2-dienyl)-l,3-dioxane (40), and 2-(prop-l-ynyl)-l,3-dioxane (41) (74ZOR953). 

Unsaturated substituents of dioxolanes 36-38 and dioxanes 39-41 are prone to prototropic isomerization under the reaction conditions. According to IR spectroscopy, the isomer ratio in the reaction mixture depends on the temperature and duration of the experiment. However, in all cases, isomers with terminal acetylenic (36, 39) or allenic (37, 40) groups prevail. An attempt to displace the equilibrium toward the formation of disubstituted acetylene 41 by carrying out the reaction at a higher temperature (140°C) was unsuccessful From the reaction mixture, the diacetal of acetoacetaldehyde 42, formed via addition of propane-1,3-diol to unsaturated substituents of 1,3-dioxanes 39-41, was isolated (74ZOR953). 

The acid-catalyzed addition of an aldehyde—often formaldehyde 1—to a carbon-carbon double bond can lead to formation of a variety of products. Depending on substrate structure and reaction conditions, a 1,3-diol 3, allylic alcohol 4 or a 1,3-dioxane 5 may be formed. This so-called Prins reaction often leads to a mixture of products. 

In the presence of excess formaldehyde, the carbenium ion species 7 can further react to give a 1,3-dioxane 5. If only one equivalent of formaldehyde is used however, 1,3-diol 3 is formed as the major product ... 

Under appropriate conditions 1,3-dioxanes can be obtained in moderate to good yields. Below 70 °C the acid-catalyzed condensation of alkenes with aldehydes yields 1,3-dioxanes as major products, while at higher temperatures the hydrolysis of dioxanes to diols is observed. 

To the solution of (4S,5S, 5 S,)-5-(2-alkenylarnino)- or (4S,5S ,5 S )-5-(2-alkynylamino)-2,2,-dimethyl-4-phenyl-1.3-dioxane 9 obtained above in 30 raL of Et20 are added dropwise 30 mL of3N HC1 at 0 CC. Then the mixture is allowed to warm to r.t. over 12 h. The resulting precipitate is rccrystallizcd from CH2C12/Et20 (1 1) and treated with 2.5 N NaOH to provide the amino diol 10 which is extracted with 300 mL of Et,0 yield 81 87%. 

Compound types Aromatics Olefins Alcohols Nitriles Acids CHC12 CC13 CH2C1 NO, Diols Ketones Ethers Aldehydes N(Me), Esters Epoxides Nitromethane Nitrogroups Pyridine Dioxane Aromatic bases... 

The approx ratio used is diol, lg/diisocyanate, lg/catalyst, 0.0004g/dioxane, lml. Completion of the polymerization requires 258 hrs at 50°. 

The addition of an alkene to formaldehyde in the presence of an acid catalyst is called the Prins reaction.Three main products are possible which one predominates depends on the alkene and the conditions. When the product is the 1,3-diol or the dioxane, the reaction involves addition to the C=C as well as to the C=0. The mechanism is one of electrophilic attack on both double bonds. The acid first protonates the C=0, and the resulting carbocation attacks the C=C ... 

Diastereomerically pure 1,3-dioxanes are formed when optically pure l-aryl-2,2-dimethylpropan-l,3-diols react with phenylglyoxals only ketalisation is observed <96RTC407>. 

Alkylations of 4-cyano-l,3-dioxanes (cyanohydrin acetonides) represent a highly practical approach to syn-l,3-diol synthesis. Herein we present a comprehensive summary of cyanohydrin acetonide chemistry, with particular emphasis on practical aspects of couplings, as well as their utility in natural product synthesis. Both 4-acetoxy-l,3-dioxanes and 4-lithio-1,3-dioxanes have emerged as interesting anri-l,3-diol synthons. The preparation and utility of these two synthons are described. 

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