Triphenylmethyl Trityl Cation

Triphenylmethyl (Trityl) Cation The highly stable triphenylmethyl cation (85) is found to undergo a wide variety of photoreactions depending on such variables as the nature of the solvent, the pH of the medium, and the presence or absence of 

Dependence of Product Formation on Solvent Composition in the Irradiation of the Trityl Cation (Inert Atmosphere) 

for example, ion 85 was photolyzed in 96% sulfuric acid, 9-phenylfluoren-9-ol (86) was generated as the single product. 

However in 72% H2SO4 no 86 was observed, but rather dimers 87, 88 and 89 were formed. The mechanism for the dimerization reaction is 

---

An interesting X-ray structure of the highly strained, sp hybridized vinyl cation 8 was recently reported by Muller et al. The synthesis of 8 was accomplished by the reaction of alkynylsilane 7 and triphenylmethyl (trityl) cation. 

A general method for the synthesis of pyrylium salts is the cyclodehydration of 1,5-dicarbonylalkanes (Scheme 4.4). Acetic anhydride is commonly used as both solvent and reagent, but since the initial product is a 4/f-pyran, an oxidant such as the triphenylmethyl (trityl) cation in the form of triphenylmethyl hexachloroantimonate is added (Ph3C + [H ] -> Ph3CH). In certain cases, however, it is advantageous to isolate the pyran and to oxidize it in a separate step. 

The first stable, long-lived carbocation observed was the triphenylmethyl (trityl) cation 135.6 y... 

Initiation with Triphenylmethyl Cation. Triphenylmethyl (trityl) cation derives its stability (7, 30) from resonance between the electro-... 

Although the reaction can be envisaged as catalytic in the Lewis acid, in practice only certain Lewis acids are effective in a catalytic sense. Notable among these are triphenylmethyl (trityl) cation (65), trimethylsilyl triflate (66), and trimethylsilyl chloride-tin(I I) chloride (61 a), which efficiently promote the reaction using as little at 2-3 mol% catalyst. 

One of the most stable carbocation structures is the employing all three rings. Trityl chloride ionizes read-triphenylmethyl cation (trityl cation). In this struc- ily, and can capture an available nucleophile, ture, the positive charge is stabilized by resonance... 

Triphenylmethyl (trityl) tetrafluoroborate, on the other hand, is sp2 hybridized but it is also extremely reactive toward electron donors. The acceptor orbital of the trityl cation is an unfilled 2p atomic orbital on the charged carbon. These carbon electrophiles are isolable compounds, but they are extremely reactive with any sort of electron donor (H2O vapor is a common culprit). 

Allyl halides heterolyze just as easily as benzyl halides because they also produce a resonance-stabilized carbenium ion. Even faster heterolyses are possible when the charge of the resulting carbenium ion can be delocalized by more than one unsaturated substituent and can thereby be stabilized especially well. This explains the remarkably high SN1 reactivities of the benzhydryl halides (via the benzhydryl cation) and especially of the triphenylmethyl halides (via the trityl cation) ... 

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. 

Triphenylmethyl (trityl) groups can be cleaved under very mild acidic conditions and the resulting trityl cations display a lower electrophilicity than ferf-butyl cations therefore, trityl side-chain protection is especially useful in SPPS of sensitive peptides containing Met and Trp. In a recent comparative study, crude products of higher purity were obtained using side-chain-trityl-protected amino acids compared to standard Fmoc/tBu amino acid derivatives,... 

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. 

Organometallic tr complexes having hydrogen ona. p carbon commonly react with triphenylmethyl (or trityl) cation. While main-group alkyls fragment to alkene, metal cation and triphenylmethane, comparable transition-metal derivatives produce rearranged cationic olefin n complexes and triphenylmethane ... 

The acidic conditions produce the hydrolysis of the trityl (triphenylmethyl) ether. Normally, the acidic hydrolysis of ediers is very difficult. In this case, the hyth-olysis can be done rnider very mild conditions, due to the stability of the intermediate trityl cation. 

Initiation with Triphenylmethyl Cation. When tetrahydrofuran (THF) is used to dissolve triphenylmethyl hexachlorantimonate at room temperature, there is almost immediate decomposition of the triphenylmethyl cation (6). On the other hand, solutions of the trityl salt in THF can be prepared and stored as deep yellow solutions if maintained at temperatures around — 80°C. At room temperature the initial decoloration of the catalyst is followed rapidly by polymerization of the monomer to poly(tetramethylene oxide), and the actual percentage conversion depends markedly on the temperature. This behavior is typical of systems exhibiting monomer-polymer equilibria (28), and Table III shows values for the equilibrium conversion of monomeric THF to polymeric THF obtained with a variety of catalysts. As for vinyl ether polymerization, it is most convenient to use the trityl hexachlorantimonate salt however, recourse to Table III shows clearly that above room temperature this anion yields less than the expected equilibrium conversion monomer... 

Now we can strip away the protecting groups one by one and it is instructive to see how selective these methods are. The trityl group comes off in aqueous acetic acid by another SN1 reaction in which water captures the triphenylmethyl cation, and the benzyl group is removed by hydrogenoly-sis—hydrogen gas over a 10% palladium on charcoal catalyst in ethanol. 

The glycosidation reaction which depends upon the condensation of sugar 1,2-0-cyanoalkylidene derivatives and tritylated acceptors continues to attract the attention of Kotchetkov and colleagues. The rate-determining step of the condensation has been shown to be the reaction between the donor and the triphenylmethyl cation. The stereochemical outcome of the reaction is dependent upon the concentration of trityl perchlorate used as catalyst. A new mechanism for 1,2-cw-glycoside formation by this method was proposed. The nature of the O-protecting groups used in the acceptor also has an effect on the anomeric ratio produced. ... 

---