Migration sulphonate groups

Mg has been studied in a polyelectrolyte system where the counterion is a phosphazene-bound sulphonate group. In this case the finite but low conductivity is due to Mg migration. A large increase in conductivity is noted when a bicyclic ligand, crypt [2.1.1.], is introduced (Hancock and Martell, 1988). Apparently, the cation-anion and cation-polymer interactions are reduced by complex formation, resulting in a more mobile cation, despite its larger effective radius. 

In a variation of these reactions, Grieco and Masaki used p-toluenesulfonyl groups to direct alkylation reactions in the formation of carbon chains and then cleaved the sulphones with lithium in ethylamine. This type of synthetic construction involving the use of sulphur-containing molecules has become a typical sequence in organic syntheses. In this case, the reactions formed part of successful syntheses of squalene and sesquifenchene and were carried out without any migration or loss of stereochemical integrity of the double bonds. Similar sequences have been reported by Trost (prenylation reactions) and Marshall (synthesis of a cembranoid precursor). 

The second major metabolite from T. inflation is structurally closely related to cyclosporin A, as can be deduced by elemental analysis, mass spectrum (m/z 1217), IR and NMR spectra. Furthermore, the presence of the double bond and OH group of the unusual MeBmt was established. Sulphonic acids in methanol or dioxane effected the typical rearrangement reaction by N, O-acyl migration to the iso-compound (13). Hydrolysis furnished the same amino acids as cyclosporin A with the exception of L-a-aminobutyric acid, which is replaced in cyclosporin C (12) by L-threonine. The amino-acid sequence could be deduced by conversion of cyclosporin C into cyclosporin A via the corresponding tosylate (14) and iodo derivatives (15) [7]. Position 2 for L-threonine as well as the assumed twisted -pleated sheet conformation of the molecule were confirmed by 13C-NMR spectra. 

A group of reactions involving 16,17-epoxy-pregnane derivatives illustrates the facility of C(is) methyl migration to an electron deficient C(i ). The i6a,i7a-epoxypregnan-20-ones (13) react with acetic anhydride and toluene- -sulphonic acid [24], hydrogen fluoride [23], and other acidic reagents [23,26], to form i7a-acetyl-i7/5f-methyl-i8-nor-olefins (14) and (15). The preferred position of the double bond apparently... 

The outcome of solvolysis of a sulphonic ester of a 19-hydroxy-steroid apparently depends upon functional groups in rings a and b. The 19-tosylates (501 3/3-OAc, 5a or SP-3-oxo) react by Wagner-Meerwein migration of C-1, giving the... 

Acylphosphonic acids (1-oxoalkylphosphonic acids) and their dialkyl esters undergo acid-catalyzed fission with the formation of carboxylic acids (or their alkyl esters) using a suiphonic acid as the catalyst the formation of an alkyl carboxylace is accompanied by that of an alkyl sulphonate. The reaction may be visualized as occurring through protonation on the carbonyl oxygen and migration of an alkoxy group from phosphorus... 

The nomenclature used here is chosen such that the migration of the sulphonic acid group is apparent. 

Dithiepins.—There are two new variations on the preparation of dithiepins by migration of a thio-group in 1,3-dithians. Treatment of the l,3-dithian-2-yl-methanols (164 R = C02Me or H) with methanesulphonyl chloride gave the 1,4-dithiepin (165), presumably by ring-expansion of the sulphonate ester. Another example is provided by the oxidation of the 2-ethylidene-l,3-dithian (166) with lead tetra-acetate the yields if R = alkyl or aralkyl varied between 34 and 67%, but if R = phenyl only (167) was produced, and not the thiepin enol acetate, as stated earlier by another group. ... 

Aromatic sulphonic acids (X = SO3H) for example, are isomerized in this way. The change of position in the aromatic ring of the tertiary alkyl groups and bromine likewise cannot be confined as intramolecular mechanism with successive 1,2-shifts of the migrating group. Thus, the interconversions of ortho- and para-disubstituted benzenes with substituents of the above type proceed faster than their conversion into a thermodynamically more stable meta isomer... 

An intramolecular electron-transfer/radical anion mechanism has been advocated for the Truce-Smiles-type rearrangement of t-butyl aryl sulphones by Bu"Li at —78 C, orf Ao-lithiation of the aryl moiety being followed by migration of the t-butyl group to the metallated site. Other methods of C—S bond cleavage that are covered in recent papers include photolysis and electrochemical reduction, ... 

A remarkably high rate accelaation by a y-sUyl group was found for the acyclic primary sulphonate 241, which is 218(X) times more reactive than its silicon-free analogue. In this case a 1,2-migration of Me3SiCH2 occurs after the rate-limiting formation of the carbocation 243, yielding the more stable tetiary carbocation 244 (equation 38). For the secondary sulphonate 242 a smaller kinetic y-silicon effect was detected . ... 

Certain a-hydroxyalkylthioketals eliminate benzenethiol under treatment with a sulphonic acid to provide a regiospecific approach to a-phenylthioketones (Scheme 31), On the other hand, j8-hydroxyalkyl phenyl sulphides eliminate water, with migration of the PhS group, to yield allyl sulphides. ... 

Further solvolytic studies from Winstein s group concern sulphonate esters of (472)—(482) products and rates are unexceptional. Acetolysis of (483) gives mainly the expected products (484) and (485), but with (486X (487) is the major product. Although simple acyl migration is stereoelectronically... 

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