Amines, tritylated

Me3SiI, CH2CI2, 25°, 15 min, 85-95% yield.Under these cleavage conditions i,3-dithiolanes, alkyl and trimethylsilyl enol ethers, and enol acetates are stable. 1,3-Dioxolanes give complex mixtures. Alcohols, epoxides, trityl, r-butyl, and benzyl ethers and esters are reactive. Most other ethers and esters, amines, amides, ketones, olefins, acetylenes, and halides are expected to be stable. 

The bulky triphenylmethyl group has been used to protect a variety of amines such as amino acids, penicillins, and cephalosporins. Esters of N-trityl a-amino acids are shielded from hydrolysis and require forcing conditions for cleavage. The a-proton s also shielded from deprotonation, which means that esters elsewhere in the molecule can be selectively deprotonated. 

Attempts to prepare 2-aminoazepinium cations by the action of trityl tetrafluoroborate on 3//-azepin-2-amines have failed,64 as have attempts to Ar-methylate 2,5,7-trimethyl-3/f-azepine with an excess of iodomcthanc in a scaled tube at 100°C for seven hours.77 In contrast, the unstable Ar,Ar-dialkyl-6-(methylsulfanyl)-3//-azepin-2-amines, e. g. 1, with trityl tetrafluoroborate, or the corresponding nitrosonium salts, yield their tetrafluoroborate salts, e.g. 2s4 (see also Section 3.1.1.5.4.). 

The C6 position of a V,./V-dialkyl-3//-azepin-2-amine, e.g. 1, displays remarkable reactivity towards electrophilic substitution, and with dimethyl(methylsulfanyl)sulfonium tetrafluorobor-ate undergoes methylsulfanylation and quaternization to yield 6-(methylsulfanyl)-3//-azepin-ium tetrafluoroborates, e.g. 2, identical to those obtained by quaternization of the free bases with trityl tetrafluoroborate.64 Basification of the salts with potassium carbonate yields the free bases, e.g. 3, which decompose during distillation or on exposure to air. 

Attempts to prepare 2-aminoazepinium salts by the action of trityl tetrafluoroborate on azepin-2-amines, e.g. 18, resulted in ring contraction to stable 2-azabicyclo[4.1.0]hepta-2.4-dienium salts, e.g. 3-(pyrrolidin-l-yl)-7-trityl-2-azabicyclo[4.1,0]hcpta-2,4-dicnium tetrafluoroborate (19), the valence isomers of 7-(dialkylamino)-3-trityl-3//-azepinium tetrafluoroborates 64 with Meerwein s reagent the 2-ethyl derivative (77%) is formed. 

The intermediate N-acylpyridinium salt is highly stabilized by the electron donating ability of the dimethylamino group. The increased stability of the N-acylpyridinium ion has been postulated to lead to increased separation of the ion pair resulting in an easier attack by the nucleophile with general base catalysis provided by the loosely bound carboxylate anion. Dialkylamino-pyridines have been shown to be excellent catalysts for acylation (of amines, alcohols, phenols, enolates), tritylation, silylation, lactonization, phosphonylation, and carbomylation and as transfer agents of cyano, arylsulfonyl, and arylsulfinyl groups (lj-3 ). 

Hydroxamic acids are an important class of compounds targeted as potential therapeutic agents. A-Fmoc-aminooxy-2-chlorotrityl polystyrene resin 61 allowed the synthesis and subsequent cleavage under mild conditions of both peptidyl and small molecule hydroxamic acids (Fig. 14) [70]. An alternative hydroxylamine linkage 62 was prepared from trityl chloride resin and tV-hydroxyphthalimide followed by treatment with hydrazine at room temperature (Scheme 30) [71]. A series of hydroxamic acids were prepared by the addition of substituted succinic anhydrides to the resin followed by coupling with a variety of amines, and cleavage with HCOOH-THF(l 3). 

To create the free secondary amine group (N-H) fulleropyrrolidine, an amine-protected starting material can be used in the reaction (Cai et al., 2006). For instance, a trityl-oxazolidinone (using either triphenylmethyl- or better, 4-methoxytriphenylmethyl-protecting groups) can be reacted with C60 to yield the trityl-protected pyrrolidine (Figure 15.5). 

Figure 15.5 A trityl-protected pyrrolidine derivative of Cgg can be prepared by the reaction of N-trityl-oxazolidinone with a fullerene. Deprotection of the trityl group using methanesulfonic acid gives the secondary amine, which can be used in further conjugation reactions.

C1 Trityl Chloride resin (17.33 g, NovaBiochem, Lot A20915, 200 - 400 mesh, 1 % DVB, 1.33 mmol / g, 23.0 mmol) was placed in a 500-mL round-bottom flask. /V,/V-Dimcthylformamide (200 mL) was added, which caused the resin to swell this suspension was gently stirred by a magnetic stir bar. Propargyl amine (10 g,... 

FIGURE 6.16 Protecting groups for carboxamides. Derivatives are obtained by reaction of the carboxamide with an alcohol or the acid with an amine. Mbh = 4,4 -dimethoxybenzhydryl64 Trt = trityl [Sieber Iselin, 1991] Xan = 9-xanthenyl63 Dmb = 2,4-dimethoxybenzyl66 Tmb = 2,4,6-trimethoxybenzyl65 BHR = benzhydryl-resin.68... 

The immobilization of nucleophilic substrates such as acids, alcohols, thiols and amines is realized by the Trityl resin (16), which is reasonably acid sensitive [28-30]. 

Figure 5. Synthetic route to site-isolated 3-aminopropyl groups functionalized on mesoporous silica through use of 3-arninopropyltrimethoxysilane with bulky trityl group protected amine that serves as spacer [20].

In contrast, the use, in chromatography, of poly(trityl methacrylate) appears much more promising. Both the insoluble polymer and macroporous silica gel coated with a soluble polymer have been used. The latter system gives better results, especially with regard to elution time. The columns have proved quite efficient in resolution of a great variety of chiral organic compounds (365, 388). Other examples of usefiil chiral polymer supports are the substituted polyacrylamides (389). Earlier used adsorbents obtained by reacting optically active amines with polyacryloyl chloride have been superseded by new chiral phases prepared by direct polymerization of optically active acrylamides. 

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