Acetals reaction with triphenylmethyl

Di-O-methyl-D-glucose and thence the corresponding dimethyl-D-fruc-tose was produced from l,2-0-isopropylidene-6-0-triphenylmethyl-a-D-glucofuranose and purified by way of its a-1,2,6-triacetate, catalytic treatment of which, with sodium methoxide, gave the 6-acetate. Reaction with a stronger solution of this reagent afforded the fructose dimethyl ether. 1,6-Anhydro-... 

Support for the idea of a preliminary ionization in this transformation is to be found in the reaction of triphenylmethyl acetate with methyl magnesium iodide. l,l,l,Triphenylethane is formed in a yield of 68 per cent.22 A similar sequence may be written for this reaction ... 

Meerwein was the first to succeed in obtaining dioxolanylium ions of type 2, sufficiently stabilized as salts with non-polarizable anions that they could be isolated crystalline. The compounds can be prepared by splitting out of an anion from cyclic ortho esters or acetals wherein the required ring-system is already present. The ortho ester 1 reacts with antimony pentachloride or boron trifluoride, with splitting out of OR, to give 2. Acetals (3) from aldehydes can be converted, by hydride abstraction with triphenylmethyl or triethyl-oxonium fluorohorate, into salts (2) this reaction proceeds well only with acetals of the 1,3-dioxolane type (3) that have little steric hindrance. With acetals of the 1,3-dioxane type, formed from aldehydes, the reaction of hydride abstraction is not, as a rule, possible. In all such reactions, the anion involved is either SbClg or BF4 . 

A fluoroborate salt of the ion 43 can be obtained from the acetal 42 by treatment with triphenylmethyl fluoroborate. As indicated in the cycle of reactions, the cation 43 can rearrange successively, by neighboring-group reactions, into subsequent ions all of the ions are structurally identical with 43. The formula scheme indicates that, after each rearrangement step, the stereochemistry is so disposed that a new neighboring-group reaction can follow. The cycle is completed after ten steps, and the starting point is reached. 

The triphenylmethyl (trityl) group is removed under even milder conditions, and is an important hydroxyl-protecting group, especially in carbohydrate chemistry. This group is introduced by reaction of the alcohol with triphenylmethyl chloride via an SnI substitution. Hot aqueous acetic acid suffices to remove the trityl group. The ease of removal can be increased by addition of electron-releasing substituents. The p-methoxy derivatives have been employed for this purpose. ... 

Triphenylmethyl acetate67-84 and benzoate75 are solvolyzed with alkyl-oxygen fission even under neutral conditions, and the reaction is strongly acid-catalyzed in each case. The hydrolysis of triphenylmethyl acetate in 80% dioxan-water has been studied by Bunton and Konasiewicz 7. The reaction involves near-quantitative alkyl-oxygen fission in both acidic and initially neutral solution, as shown by the incorporation of l80 from enriched H20 into the triphenylmethyl alcohol produced, and by the lack of incorporation into the acetic acid. The rate of the acid-catalyzed reaction at 25°C is about 40% slower in 90% dioxan than in the more aqueous solvent. ... 

Ethyl 2,2,4-trimethyl-3-oxopentanoate. Add 24 g (28 ml, 0.21 mol) of ethyl 2-methylpropanoate b.p. 110-111 °C, to the solution of c. 0.21 mol of triphenylmethyl sodium in approximately 1400 ml of ether contained in the 2-litre twonecked flask. Stopper the flask, shake well to effect complete mixing and keep at room temperature for 60 hours. Acidify the reaction mixture by adding, with shaking, 15 ml of glacial acetic acid, and then extract with 100 ml of water. Wash the ethereal solution with 50 ml portions of 10 per cent sodium carbonate solution until free from excess acid, dry over anhydrous sodium sulphate remove the ether under reduced pressure with a rotary evaporator. Distil the residue under reduced pressure through a short fractionating column. Collect the ethyl 2,2,4-trimethyl-3-oxopentanoate at 95-96 °C/ 18mmHg the yield is 14.5 g (74%). The b.p. at atmospheric pressure is 201-202 °C. 

In a 25-mL Erlenmeyer flask place 8.75 mL of acetic anhydride, cool the tube, and add 0.44 g of fluoboric acid. Add 1 g of triphenylmethanol with thorough stirring. Warm the mixture to give a homogeneous dark solution of the triphenylmethyl fluoborate, then add 0.4 g of cycloheptatriene. The color of the trityl cation should fade during this reaction and the tropilium fluoborate begin to precipitate. Add 10 mL of anhydrous ether to the reaction tube, stir the contents well while cooling on ice, and collect the product by filtration on the Hirsch funnel. Wash the product with 10 mL of dry ether and then dry the product between sheets of filter paper. 

A detailed study of this dehydrogenative condensation in the presence of triphenylmethyl perchlorate or fluoroborate was made by Simalty-Siemiatycki and Fugnitto. The reaction is best carried out in refluxing acetic acid nitromethane or acetonitrile give less satisfactory results. Chalcone reacts in these conditions with phenylacet-aldehyde yielding 2,4-diphenylpyrylium with an unsubstituted a-position. This and similar 2-unsubstituted pyrylium salts prepared by this method are so reactive that they do not afford pyridines on treatment with ammonia in the usual conditions this behavior is similar to that of the unsubstituted pyrylium perchlorate. The reaction of... 

Triphenylmethane derivatives can be converted into triphenylmethanol derivatives by various oxidizing agents. Triphenylmethane itself with nitric acid or with chromic acid in glacial acetic acid gives triphenylmethanol, and with lead tetraacetate gives triphenylmethyl acetate. The principal importance of this reaction lies in the technical synthesis of triphenylmethane dyes from their leuco bases, for which purpose very varied oxidants such as arsenic acid, nitrobenzene, nitrous acid, and nitrosylsulfuric acid are used. 

Reaction of 3-bromo-3-methylbutan-2-one with triphenylmethylhydrazine and potassium thiocyanate in acetic acid gives 7,7,7a-trimethyl-2,3,5,6,7,7a-hexahydro-li/-imidazo[l,5-Z>][l,2,4]-tri-azole-2,5-dithione (381b) due to the facile hydrolysis the triphenylmethyl group. <95FES379>. 

Alcohols, Phenols, and Ethers. — Attempts to obtain evidence that l-(pentafluoro-phenyl)ethanoI or pentafluorobenzaldehyde ethyl acetal can act as a hydride ion donor towards triphenylmethyl fluoroborate have met with very limited success. The main products (82) and (83) of these reactions and the most likely routes to them are illustrated in Schemes 21 and 22, and although the traces of pentafluoro-... 

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