Ketal from ethylene glycol

Ketal from ethylene glycol, 39, 13 (3-Ketobutyraldehyde, dimethyl acetal,... 

A 17a-hydroxyl group reduces the reactivity of the 20-ketone but direct ketalization with ethylene glycol is not impeded, Ketalization can also be effected in the presence of 17a- and/or 21-hydroxy substituents. Thus the 3,20-biscycloethyleneketal (88) is obtained from (87) in high yield by the direct procedure, or better by distillation under vacuum without a diluent. A bromine atom at C-17 and a 21-acetoxy group even in the absence of a 17a-hydroxyl group strongly hinder ketalization at C-20. ... 

Incorporation of a carbonyl group into the alkyl side chain also proved compatible with biologic activity. The key intermediate (76) is obtainable by Michael addition of the anion from diethyl malonate to methylvinyl ketone followed by ketalization with ethylene glycol. Condensation of 76 with hydrazobenzene leads to the pyrazolodione hydrolysis of the ketal group affords ketasone (78). ... 

Since 2-acetylphenothiazine undergoes an autocondensation with sodamide, the introduction of a substituent in position 10 using this base as condensing agent requires protection of the keto group. This may be achieved by ketalization with ethylene glycol or by conversion into Schiff bases derivatives stable in alkaline medium are thus obtained, from which the ketones may be liberated by acidification after A-alkylation. 

Acetals and ketals of ethylene glycol are readily formed from bis-trimethylsilyl ethylene glycol, the aldehyde or ketone and trimethylsilyl triflate catalysis51 (equation 43). The reaction is quite selective for ketones over aldehydes (equation 44). 

Dials that bear two hydroxyl groups in a 1,2 or 1,3 relationship to each other yield cyclic acetals and ketals with aldehydes and ketones. The five-membered cyclic acetals derived from ethylene glycol are the most commonly encountered examples. Often the position of equilibrium is made more favorable by removing the water formed in the reaction by azeotropic distillation with benzene or toluene ... 

Cyclic acetal and ketal systems are susceptible to acidic hydrolysis and the protecting groups are usually removed in this way. The ease of acidic hydrolysis of a particular 1,3-dioxolan (60, derived from a 1,2-glycol) or a 1,3-dioxan system (61, derived from a 1,3-glycol) depends mainly on the 2-substituents (R and R ), but also on the other ring substituents. Thus the relative rates of hydrolysis of the 1,3-dioxolans derived from ethylene glycol and, respectively, formaldehyde, acetaldehyde and acetone (60 R=R = H R = CH3, R = H and... 

Acetoxyandrost-5-en-17-one (59) is converted into the ethylene ketal (60) by treatment with ethylene glycol, triethylorthoformate and p-toluenesulfonic acid. The ketal is brominated with pyridinium bromide perbromide in THF and then treated with sodium iodide to remove bromine from the 5 and 6 positions. This gives the 16a-bromo compound (61) which is hydrolyzed in methanol to the free alcohol (62). Dehydrobromination is effected with potassium Fbutoxide in DMSO to give the -compound (63). Acid catalyzed hydrolysis of the ketal in aqueous acetone gives the title compound (64). ... 

Ethylene ketals can be readily prepared by the ethylene glycol technique. 6-Ethylene ketals can also be prepared by exchange dioxolanation and suitable conditions have been described for the preparation of either the 3-mono-ketal (78), the 3,6-diketal (79) or 3,6,17-triketal (80) from the triketone... 

Scheme 3b). It is instructive at this point to reiterate that the furan nucleus can be used in synthesis as a progenitor for a 1,4-dicarbonyl. Whereas the action of aqueous acid on a furan is known to provide direct access to a 1,4-dicarbonyl compound, exposure of a furan to an alcohol and an acid catalyst should result in the formation of a 1,4-diketal. Indeed, when a solution of intermediate 15 in benzene is treated with excess ethylene glycol, a catalytic amount of / ara-toluenesulfonic acid, and a trace of hydroquinone at reflux, bisethylene ketal 14 is formed in a yield of 71 %. The azeotropic removal of water provides a driving force for the ketalization reaction, and the presence of a trace of hydroquinone suppresses the formation of polymeric material. Through a Finkelstein reaction,14 the action of sodium iodide on primary bromide 14 results in the formation of primary iodide 23, a substance which is then treated, in crude form, with triphenylphosphine to give crystalline phosphonium iodide 24 in a yield of 93 % from 14.

The signal molecule, 30,C6-HSL and number of its analogues, with variations in the acyl chain and the hetero-ring, have been prepared [15,56,57] to investigate the mechanism of induction of carbapenem and luminescence in Erwinia carotovora and V.fischeri respectively. Essentially, the acylation of l-HSL with 3-oxoalkanoic acid by the same method as outlined for the preparation of AT-acyl-L-HSL delivers the desired derivatives. However, as the p-keto acids are thermally labile, these were prepared from the corresponding p-keto ester after the initial protection of the p-keto function as ethylene glycol ketal (route a, Scheme 6). 

Ethylenedioxy-3(5,1 la.-dihydroxy-5a-pregnan-20-one.2 A solution of 3/ , 17a-dihydroxy-5a-pregnane-12,20-dione (8.75 g) dissolved in ethylene glycol (90 ml) containing boron trifluoride-ether complex (14 ml) is kept for 16 hr at room temperature. The solution is diluted with chloroform and washed to neutrality with water. The solution is evaporated to yield a crude ketal which is purified by crystallization from chloroform-ethyl acetate or methanol mp 255-259° (softens 252°) [a]D 74° (CHC13). 

Condensation of derivatives of phosphabicyclodecanones 119 with ethylene glycol in the presence of PTS/ZnCl2 gave cyclic ketals 120 of the phosphabicyclodecane series <1996RJC564> (Equation 24). Oximes and semicarba-zones were prepared from bicyclic ketones <1996RJC567>. 

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