Trityl chloride , reaction with primary

The most widely recognized method of selective etherification of sugars and polysaccharides involves the reaction of primary alcohol groups with triphenylmethyl (trityl) chloride. Helferich60 has described the selective character of this reagent, whose rate of reaction with primary hydroxyl groups is many fold that with secondary groups. 

Trityl (triphenyl methyl) ethers are formed by reaction of the carbohydrate, usually dissolved in pyridine, with trityl chloride (triphenylchloromethane). This reagent shows a high degree of regioselectivity for reaction with primary hydroxyl groups in the presence of secondary hydroxyl groups, due to the high de-... 

In subsequent studies,22 Sheehan et al. demonstrated that the action of diisopropylcarbodiimide on penicilloate 24, prepared by protection of the free primary amino group in 23 with trityl chloride (see Scheme 6b), results in the formation of the desired -lactam 25 in a very respectable yield of 67 %. In this most successful transformation, the competing azlactonization reaction is prevented by the use of a trityl group (Ph3C) to protect the C-6 amino function. Hydrogenolysis of the benzyl ester function in 25, followed by removal of the trityl protecting group with dilute aqueous HC1, furnishes 6-aminopenicillanic acid (26), a versatile intermediate for the synthesis of natural and unnatural penicillins. 

The bulky triphenylmethyl or trityl (Tr) group is often employed for the regioselective protection of a primary sugar alcohol. It is conveniently introduced into partially protected sugar derivatives by treatment with trityl chloride (TrCl) in pyridine (Scheme 2.8).19 The protection can be slow but the addition of 4-(dimethyl)aminopyride (DMAP) or 1,8-diazobicyclo[5.4.0]undec-7-ene (DBU) can accelerate the reaction. 

Sommer and Bauman investigated the reaction of optically active a-naphthylphenylmethylsilyl hydride with trityl chloride and found that the stereochemical course was retention in benzene solution, inversion in methylene chloride, and full racemization in methylene chloride (93). The result in CH2C12 was explained as consistent with an exchange in which electrophilic attack on the silicon hydride by a triphenyl cation is of primary importance however, the counterion appears in the transition state [Eq. (16)]. Racemization of the unreacted R3SiH could arise from... 

An exceptionally stable cation is formed when three benzene rings can help to stabilize the same positive charge. The result is the triphenylmethyl cation or, for short, the trityl cation. The symbol Tr (another of these organic elements ) refers to the group Ph3C. Trityl chloride is used to form an ether with a primary alcohol group by an SnI reaction. Here is the reaction. 

Tiitylation silylation. This amine is an efficient catalyst for tritylation of hydroxyl groups with trityl chloride and triethylamine. The method permits use of solvents other than pyridine, such as DMF or CHjClj. The same conditions can be used to prepare t-butyldimethylsilyl ethers. Yields are comparable to those obtained with imidazole (4, 57-58). A further advantage is that the selectivity for reaction with a primary hydroxyl group is enhanced in this new procedure. ... 

On the other hand, experience has shown that in polyhydroxy compounds containing both primary and secondary hydroxyl groups, the primary hydroxyls react preferentially. As a rule, particularly in the absence of a significant excess of trityl chloride, only the trityl ethers of primary hydroxyl groups are isolated. This fact has led to the assumption that the reaction with trityl chloride in pyridine may be used for establishing the presence of primary hydroxyl groups in polyhydroxy compounds. The formation of a trityl ether was thought to be conclusive... 

In 1933, Bredereck discovered that adenosine reacts with trityl chloride to give a raonotrityl-adenosine which, without direct experimental evidence, he assumed to be 5-trityl-adenosine. In support of this formulation he presented the observation that no reaction between trityl chloride and a mixture of a- and 8-methyl ribopyranosides (having no primary hydroxyl group) could be detected polarimetrically. 

Selective protection of the primary hydroxy group in polyols by the trityl group can generally be accomplished by the reaction with trityl chloride in pyridine. TTie use of DMAP (0.04 equiv.) and EtsN (1.5 equiv.) facilitates the reaction. " Selective phenylation of one hydroxy group of diols can be carried out by the reaction with triphenylbismuth diacetate. While regioselectivity for primary-secondary vicinal diols is poor, only secondary alcoholic functions are converted to the phenyl ether in secondary-tertiary vicinal diols. Although phenylation of glycols occurs smoothly, monohy oxy alcohols are left essentially intact. ... 

An infrared method for the analysis of primary alcohols in polyglycols based on the reaction of the polyol with triphenylchloromethane is where the reagent consists of trityl chloride, with tris(dimethyl amino)phosphine oxide in quinoline as a solvent. This reagent is added to the sample, scanned from 3700 to 3100 cm to establish the total hydroxyl absorbance, and the reaction is then carried out in a glass-stoppered flask in a thermostatted bath at 75°C. At appropriate times, aliquots are removed and scanned, the absorbance being measured at 3280cm... 

The rates of reaction of triphenylmethyl chloride with several characteristic compounds are given ( 7) in Table I, which also illustrates the effect of the trityl chloride concentration. For the 8-fold excess, the primary alcoholic group of the galactose derivative reacts 226 times as rapidly as the secondary alcoholic group of the glucose derivative. However, the difference between the primary alcoholic group of the sorbose derivative and the secondary hydroxyl of the glucose derivative is only 34 times. 

The formation of triphenylmethyl (trityl) ethers from trityl chloride and primary or secondary alcohols is another reaction now found to be catalysed by DMAP. In this procedure, as with the silylation reported above, stoicheiometric triethylamine is used to regenerate the DMAP. Tritylone ethers (60) are more... 

The hydroxy groups of sugars can be further alkylated, tosylated (reaction with p-toluenesulfonyl chloride (79), or tritylated. In the latter case only primary hydroxy groups react (80). 

For example, the bulky trityl chloride selectively reacts with primary alcohol groups (see section 4.3b). The secondary alcohol groups can then be protected by acetylation or benzoylation, and the trityl group selectively removed by mild acid hydrolysis (see reaction 4.16). The reaction of tosyl chloride has also been used to selectively derivatize the primary alcohols [6]. The tosyl group can then be displaced by various nucleophiles such as halides or azide (reaction 4.14). 

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