Isomerization methanesulfonic acid

In laboratory preparations, sulfuric acid and hydrochloric acid have classically been used as esterification catalysts. However, formation of alkyl chlorides or dehydration, isomerization, or polymerization side reactions may result. Sulfonic acids, such as benzenesulfonic acid, toluenesulfonic acid, or methanesulfonic acid, are widely used in plant operations because of their less corrosive nature. Phosphoric acid is sometimes employed, but it leads to rather slow reactions. Soluble or supported metal salts minimize side reactions but usually require higher temperatures than strong acids. 

On the basis of fundamental experiments (see Section IV,A,2) some indenobenzazepine alkaloids have been efficiently synthesized from the corresponding protoberberines via 8,14-cycloberbines. For example, the cycloberbine 428 derived from the protoberberine 427 was heated with methanesulfonic acid in aqueous tetrahydrofuran to afford a 2 1 mixture of cis- and trans-indenobenzazepines 429 in 92% yield (Scheme 85). The mixture was methylated with methyl iodide to give the cts-N-methyl derivative 430 and the unchanged trans secondary amine (21%), which was very difficult to methylate and which gave the /V-methyl derivative only in 6% yield even on treatment with dimethyl sulfate for 43 hr. Contrary to the ordinary cases (Section IV,A,2), the trans derivative did not isomerize to the cis isomer 430 under various acidic conditions. Debenzylation of 430 by hydrogenolysis afforded fumarofine (417), which was converted to O-methylfumarofine (316) by methylation with diazomethane (215). 

A reactor was charged with the step 3 product and mixture (64.9 g), methacrylic anhydride (36.0 g), methanesulfonic acid (5.3 g), and 325 ml toluene and then heated to 90°C for 3 hours. The mixture was then added to aqueous and treated with 500 ml of toluene. The organic layer was isolated and then washed with brine and additized with phenothiazine (0.33 g) and then concentrated and 63.2 g of product isolated as a colorless liquid. Analysis indicated it was a mixture of four isomers in an isomeric ratio of Isomer 1 (preferred) Isomer 2 Isomer 3 Isomer 4 of 38 34 17 11, respectively. 

Addition of methoxycarbonylnitrene generated photochemically from methyl azidoformate to methylenecyclopropane gave methyl l-azaspiro[2.2]pentane-l-carboxylate 1, which cannot be isomerized to the cyclobutane derivative like the isosteric oxaspiropentanes. " Treatment with acids such as hydrogen chloride or methanesulfonic acid cleaved the aziridine ring and gave l-(chloromethyl)-l-(methoxycarbonylamino)cyclopropane and l-(mesyloxymethyl)-l-(methoxycarbonylamino)cyclopropane. ... 

Perchloric acid (70%) is superior to sulfuric acid or methanesulfonic acid for the isomerization of oleic acid to y-stearolactone (2). The most satisfactory procedure is use of a 1 1 molar ratio and a temperature of 100° for 3 hrs.24e... 

The monoadduct of tetraene 11 and benzoquinone [107] can be reduced selectively into alcohol 37 (94%), the structure of which has been established by X-ray radiocrystaUography [163]. The corresponding mesylate 38 eliminates one equivalent of methanesulfonic acid in the presence of two equivalents of f-BuOH/THF giving a potassium phenolate 39 that is reacted with Mel to give the corresponding anisole 40 (99%). When an excess of base is used (4.3 equivalents of f-BuOK), the phenolate intermediate 39 is isomerized re-gioselectively (7 3) into the vinylphenolate 41. 

---