Sulfones, alkylation rearrangement

Compounds 45 exhibit, in addition to sulfone-sulfinate rearrangements " ", alkyl sulfone cleavages , intramolecular Smiles-type rearrangements and extrusion of SOj , an exceptional mode of remote group interaction which leads to the loss of... 

The Niki reaction474 (alkylation of dimedone by l,4-dibromo-2-methyl-2-butene, with formation of compound 218), applied to phloro-acetophenone and to 3-isopentyl-2,4,6-trihydroxyisobutyrophenone, leads respectively to 2,3-dihydrobenzofurans 219a and 219b. Furan 219b with toluene- >-sulfonic acid rearranges to the benzofuran 220b.475... 

When polyalkyl- or polyhalobenzenes are treated with sulfuric acid, the ring is sulfonated, but rearrangement also takes place. The reaction, known as the Jacobsen reaction, is limited to benzene rings that have at least four substituents, which can be any combination of alkyl and halogen groups, where the alkyl groups can be... 

Oxime sulfonates were rearranged in the presence of diisobutylaluminum methyl sulfide to produce methylthioimidates, e.g. (291 equation 155), and methylthiolactim ethers in good yields. The adducts formed in the reaction of Grignaid reagents with trimeAylsilylmethyl isothiocyanate can be alkylated to furnish the A(-trimethylsilylmethylthioimidates (292 equation 156). ... 

Fragmentation Loss of alkyl by fragmentation of the C-O bond with concomitant double H rearrangement to form the protonated sulfonic acid ion (m/z 97 for methanesulfonates), which then loses water. Loss of the alkoxyl residue (fragmentation of the S-O bond). Formation of an alkene ion from the sulfonate alkyl by a McLafferty-type rearrangement. In aryl esters, the phenoxy ion and the phenol radical cations dominate the spectrum. 

Such reductive ring contractions of sulfones are formally similar to two other methods capable of supplanting a sulfur atom by a carbon-carbon double bond the Ramberg-Backlundand Stevens rearrangements. The distinguishing feature of this novel approach to cyclobutenes consists in the resultant higher level of alkyl substitution at the sp -hybridized centers. 

Many variations of the reaction can be carried out, including halogenation, nitration, and sulfonation. Friedel-Crafts alkylation and acylation reactions, which involve reaction of an aromatic ling with carbocation electrophiles, are particularly useful. They are limited, however, by the fact that the aromatic ring must be at least as reactive as a halobenzene. In addition, polyalkylation and carbocation rearrangements often occur in Friedel-Crafts alkylation. 

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