Sulfonylations silver® oxide

Azaindoles are more stable to air oxidation than indoles, are stable to mild reagents like silver oxide and selenium dioxide, but are readily attacked by permanganate. In the structure proof of 7-aza-indole, Kruber oxidized the 1-benzenesulfonyl derivative with potassium permanganate in acetone solution to obtain 2-(benzene-sulfonyl)aminonicotinic acid. The 1-acetyl and 1-benzoyl derivatives gave inconsistent results, which Kruber attributed to their ease of hydrolysis. l-Benzoyl-2,5-dimethyl-4-azaindole and its 3-substituted derivatives give 3-benzamido-6-methylpicolinic acid with permanganate oxidation. ... 

Sulfonic esters are most frequently prepared by treatment of the corresponding sulfonyl halides with alcohols in the presence of a base. This procedure is the most common method for the conversion of alcohols to tosylates, brosylates, and similar sulfonic esters. Both R and R may be alkyl or aryl. The base is often pyridine, which functions as a nucleophilic catalyst, as in the similar alcoholysis of carboxylic acyl halides (16-61). Propylenediamines have also been used to facilitate tosylation of an alcohol. Silver oxide has been used, in conjunction with KI. Primary alcohols react the most rapidly, and it is often possible to sulfonate selectively a primary OH group in a molecule that also contains secondary or tertiary OH groups. The reaction with sulfonamides has been much less frequently used and is limited to A,A-disubstituted sulfonamides that is, R— may not be hydrogen. However, within these limits it is a useful reaction. The nucleophile in this case is actually RO . However, R may be hydrogen (as well as alkyl) if the nucleophile is a phenol, so that the product is RS020Ar. Acidic catalysts are used in this case. Sulfonic acids have been converted directly to sulfonates by treatment with triethyl or trimethyl orthoformate, HC(OR)3, without catalyst or solvent and with a trialkyl phosphite, P(OR)3. ... 

Pyridine A-oxides were converted to tetrazolo[l,5-a]pyridines 172 by heating in the presence sulfonyl or phosphoryl azides and pyridine in the absence of solvent <06JOC9540>. 3-R-5-Trinitromethyltetrazolo[l,5-a]-l,3,5-triazin-7-ones 173 have been prepared from the alkylation of 5-trinitromethyltetrazolo[l,5-a]-l,3,5-triazin-7-one silver salt with different alkylation agents <06CHE417>. The use of 2-fluorophenylisocyanide in the combinatorial Ugi-tetrazole reaction followed by a nucleophilic aromatic substitution afforded tricylic tetrazolo[l,5-a]quinoxaline 174 in good yields and with high diversity <06TL2041>. 

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