Triphenylmethyl chloride, conversion

A further example of conversion of a thiopyran into a thiopyrylium salt is offered by compound 123, which has been oxidized to the corresponding thiopyrylium cation 79 (R = H, n = 2) by triphenylmethyl chloride, tro-pylium tetrafluoroborate, silver nitrate, and l,3,5,7-tetramethyl-2-phenyl-2-azoniaazulene (127) (74IZV1831). 

It was Meerwein and van Emster who, in 1922, while studying the kinetics of the rearrangement of camphene hydrochloride (1) to isobomyl chloride (2) [Eq. (5.1)], noticed that the reaction rate increased in a general way with the dielectric constant of the solvent. Further, they found that metalhc chlorides such as SbCh, SnCb, FeCb, AlCb, and SbCf (but not BCh or SiCh), as well as dry HCl (all of which promote ionization of triphenylmethyl chloride by the formation of ionized complexes), also considerably accelerate the rearrangement of camphene hydrochloride. Meerwein concluded that the conversion of camphene hydrochloride to isobornyl chloride actually does not proceed by way of migration of the chlorine atom, but by a rearrangement of a cationic intermediate. Thus, the modern concept of carbocation intermediates was born. 

Unambiguously electrophilic C-alkylations of unactivated pyridine nuclei are unknown. A carbonium ion is presumably involved in the conversion of 2-hydroxypyridine into 2-hydroxy-5-triphenylmethylpyridine when it is heated with triphenylmethyl chloride, or with triphenylcarbinol and a little sulphuric acid. 2-Hydroxy-3-methylpyridine reacts similarly, but 2-hydroxy-6-methylpyridine is thought to give 2-hydroxy-6-methyl-3-triphenylmethyl-pyridine. Oddly, l-methyl-2-pyridone also gives 2-hydroxy-5-triphenyl-methylpyridine, the methyl group being lost. ... 

Ionic ring-expansions of 2-substituted thietanes in many cases probably proceed via the ion 106, which can open to a five-membered cyclic cation. The ring-expansion of 74 by such a mechanism has already been discussed in Section The conversion of 2-methylthietane to thiophene and di- and tetrahydro-thiophenes with triphenylmethyl cations, chloranil, and aluminum oxide also may occur via similar ions. 2-Methylthietane also yields 3-butenethiol when heated with alumina. ° The isomerization of hydroxy-benzodihydrothiophenes by aluminium chloride is believed to involve common thietane intermediates that subsequently undergo ring expansion. ... 

The conversion of A -aUcyl- or -aryl-pyridinium salts into the corresponding pyridine, i.e. the removal of the iV-substitutent, is generally not an easy process however triphenylphosphine or simply heating the iodide salt can work for metho-salts. l-Triphenylmethyl-4-dimethylaminopyridinium chloride and... 

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