Glycols, cyclic aldehydes

A soln. of cinnamaldehyde ethylene glycol cyclic acetal (prepared from the aldehyde and ethylene glycol) in ethyl acetate hydrogenated with 5%-Pd-on-carbon until uptake of 1 equivalent Hg ceases after 10 min., and the intermediate acetal refluxed 1 hr. with 5%-HCl soln. in benzene-dioxane hydrocinnamaldehyde. Y 89%. F. e. s. J. H. Billman, J. I. Stiles, and J. Tonnis, Synth. Commun. 1, 127 (1971). 

Derived from an aldehyde or ketone and an alcohol using an acid catalyst. Ethylene glycol or 1,3-dihydroxypropane are frequently used to give 5-or 6-member cyclic products. 

Diols that bear two hydroxyl groups m a 1 2 or 1 3 relationship to each other yield cyclic acetals on reaction with either aldehydes or ketones The five membered cyclic acetals derived from ethylene glycol (12 ethanediol) are the most commonly encoun tered examples Often the position of equilibrium is made more favorable by removing the water formed m the reaction by azeotropic distillation with benzene or toluene... 

Show all the steps in the acid-catalyzed formation of a cyclic acetal from ethylene glycol and an aldehyde or ketone. 

Conversion to acetals is a very general method for protecting aldehydes and ketones against nucleophilic addition or reduction.245 Ethylene glycol, which gives a cyclic dioxolane derivative, is frequently employed for this purpose. The dioxolanes are usually prepared by heating a carbonyl compound with ethylene glycol in the presence of an acid catalyst, with provision for azeotropic removal of water. 

Considerable interest remains in catalyzed hydrogen-transfer reactions using as donor solvents alcohols, glycols, aldehydes, amides, acids, ethers, cyclic amines, and even aromatic hydrocarbons such as alkylben-... 

SAQ 4. 12 The simple aldehyde ethanal (VII) reacts with the di-alcohol ethylene glycol (VIII) to form a cyclic acetal (IX) ... 

In classical Hantzsch procedure, an enaminocarbonyl is formed in sim by condensation of ammonia source onto the 1,3-dicarbonyl substrate. But many groups have used a three-component modified-Hantzsch protocol in which the preformed enamine is introduced as a partner. Thus, utilization of cyclic or acyclic 1,3-dicarbonyl compounds, aldehydes, and acyclic or cyclic enamines has been reported, leading regioselectively to diversely substituted 1,4-DHP derivatives (Scheme 7). The sequence involving such starting materials was performed in numerous efficient systems, and more particularly in the following (1) microwave-assisted reaction in acetic acid [50], DMF [51], or an acetic acid/DMF system [52] (2) sonification in ethylene glycol [53] and (3) use of ionic liquids such as [bmim]BF4 [54]. 

We developed a method for the synthesis of a variety of cyclic acetals that utilizes bismuth triflate as a catalyst and does not require the use of a Dean-Stark trap for removal of water [102]. In this method, an aldehyde or ketone is treated with 1,2-bis (trimethylsiloxy)ethane in the presence of bismuth triflate. A comparison study using o-chlorobenzaldehyde showed that with ethylene glycol a low conversion to the dioxolane was observed after 2 h whereas the use of the 1,2-bis(trimethylsiloxy) ethane afforded the corresponding dioxolane in good yields. (Scheme 9). 

Aldehyde 82 was extremely reactive and was best isolated as the hydrate 84a. Indeed, recrystallization of the aldehyde 82 from ethanol gave 3-(l-ethoxy-l-hydroxymethyl)fervenulin 84b, while reaction with ethylene glycol gave the cyclic acetal 76a. The reactivity of the aldehyde 82 was exploited by easy Schiff base formation upon reaction with /i-aminobenzoylglutamic acid, a process that was followed by reduction to give the fervenulin-based folic acid analogue 85 <1996JHC949>. 

Carbonyl compounds react with glycols in anhydrous acid to form 1,3-cyclic ethers. These are called acetals if formed from aldehydes, and ketals if formed from ketones. 

The lower members of the homologous series of 1. Alcohols 2. Aldehydes 3. Ketones 4. Acids 5. Esters 6. Phenols 7. Anhydrides 8. Amines 9. Nitriles 10. Polyhydroxy phenols 1. Polybasic acids and hydro-oxy acids. 2. Glycols, poly-hydric alcohols, polyhydroxy aldehydes and ketones (sugars) 3. Some amides, ammo acids, di-and polyamino compounds, amino alcohols 4. Sulphonic acids 5. Sulphinic acids 6. Salts 1. Acids 2. Phenols 3. Imides 4. Some primary and secondary nitro compounds oximes 5. Mercaptans and thiophenols 6. Sulphonic acids, sulphinic acids, sulphuric acids, and sul-phonamides 7. Some diketones and (3-keto esters 1. Primary amines 2. Secondary aliphatic and aryl-alkyl amines 3. Aliphatic and some aryl-alkyl tertiary amines 4. Hydrazines 1. Unsaturated hydrocarbons 2. Some poly-alkylated aromatic hydrocarbons 3. Alcohols 4. Aldehydes 5. Ketones 6. Esters 7. Anhydrides 8. Ethers and acetals 9. Lactones 10. Acyl halides 1. Saturated aliphatic hydrocarbons Cyclic paraffin hydrocarbons 3. Aromatic hydrocarbons 4. Halogen derivatives of 1, 2 and 3 5. Diaryl ethers 1. Nitro compounds (tertiary) 2. Amides and derivatives of aldehydes and ketones 3. Nitriles 4. Negatively substituted amines 5. Nitroso, azo, hy-drazo, and other intermediate reduction products of nitro com-pounds 6. Sulphones, sul-phonamides of secondary amines, sulphides, sulphates and other Sulphur compounds... 

Ethylene glycol in the presence of an acid catalyst readily reacts with aldehydes and ketones to form cyclic acetals and ketals (60). 1,3-Dioxolane [646-06-0] is the product of condensing formaldehyde and ethylene glycol. Applications for 1,3-dioxolane are as a solvent replacement for methylene chloride, 1,2-dichloroethane, 1,1,1-trichloroethane, and methyl ethyl ketone as a solvent for polymers as an inhibitor in 1,1,1-trichloroethane as a polymer or matrix interaction product for metal working and electroplating in lithium batteries and in the electronics industry (61). 1,3-Dioxolane can also be used in the formation of polyacetals, both for homopolymerization and as a comonomer with formaldehyde. Cyclic acetals and ketals are used as protecting groups for reaction-sensitive aldehydes and ketones in natural product synthesis and pharmaceuticals (62). 

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 cyclic ketals of neopentyl glycol, eg,... 

In this review, the term acetal will be used to connote a cyclic compound (I) formed, together with one mole of water, by the condensation of an aldehyde with an equimolecular proportion of a glycol, and not, as is more usual, an acyclic compound derived from one mole of an aldehyde and two moles of a monohydric alcohol. A compound which contains more than one such ring system will be termed a diacetal, triacetal, etc. In an analogous fashion, cyclic condensation products (II) obtained from ketones will be called ketals. ... 

Fig. 8 (a) Reversible formation of cyclic and linear acetal oligomers from triethylene glycol and 4-nitrobenzaldehyde. (b) Reversible formation of hemithioacetal (HTA) from reaction between a thiol and an aldehyde derivative... 

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