Reductive methylation dibenzothiophene

The reduction of three polynuclear aromatic compounds, namely, perylene, decacyclene, and dibenzothiophene, with potassium metal in tetrahydrofuran at 25 °C, followed by quenching with alkyl iodides, was investigated. With perylene, a dianion was obtained, which on reaction with methyl iodide added two methyl groups the main re-gioisomer had one methyl group on C-l and one methyl group on the adjacent nonprotonated carbon, C-14. The reductive alkylation of decacyclene also led to alkyl groups on quaternary carbon atoms. The reduction of dibenzothiophene led to a loss of sulfur and proton uptake from solvent to yield biphenyl as the product after 24 h of reduction. 

The half-wave reduction potentials (HWP) of dibenzothiophene and some of its derivatives have been measured for comparison with those of dibenzofuran and dibenzoselenophene. A shift to more negative HWP was observed for all of the methyl derivatives studied, the magnitude of which depended on the position of substitution. These shifts are in accord with LCAO molecular orbital theory predictions if the sulfur d orbitals are excluded from the calculations (Section III, A). ... 

Section III,B> ) The two methyl groups in 34 were formed from the corresponding methyl esters via reduction to the bis-hydroxymethyl compound followed by ditosylation and reduction with LAH. Both the intermediate diester and the derived dialcohol were separately cyclized to give the corresponding octahydrodibenzothiophenes (50% and 80%, respectively). However, no attempt to dehydrogenate these compounds to the dibenzothiophenes was made. This reaction obviously has considerable potential. 

The usual range of reactions has been recorded for the aldehydes of dibenzothiophene. Oxidation yields the corresponding acid, - reduction with LAH the corresponding alcohol, reduction under Huang-Minlon conditions the corresponding methyl compound, and two examples of the Cannizarro reaction have been described. ... 

Model reactions showed that 2-dodecyl-5-methyl thiophene, benzo[b]thiophene, 2-n-butyl benzo[b]thiophene and dibenzothiophene were unaffected by these reaction conditions after a 4-hour reflux. For the LiAlH4 reduction step the solvent dioxane (b.p. 100°C) is preferred to either diethyl ether or tetrahydrofuran since preferential reduction of certain sulfides in the latter solvents has been observed (2). The results of the sulfide analyses for several petroleums from Alberta are summarized in Table I. 

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