The directed ortho-lithiation of lithium phenylsulfide and lithium phenylselenide plus sigma-aromaticity and the hexakis(phenylseleno)benzene dication
The directed ortho-lithiation of lithium phenylselenide by reaction with $n$-butyllithium in cyclohexane with $N$,$N$,$N\sp\prime$,$N\sp\prime$-tetramethylethylenediamine gives almost quantitative conversion to lithium 2-lithiobenzeneselenolate and is estimated to be seven to eight times faster than the directed ortho-lithiation of lithium phenylsulfide to form lithium 2-lithiobenzenethiolate. Treatment of the lithium 2-lithiobenzeneselenolate with a variety of electrophiles (D$\sb2$O, carbon dioxide, selenium, methylene chloride, methyl iodide, thioxanthone, and dimethylcarbonate) form ortho-substituted products. The treatment of dilithium benzene-1,2-diselenolate with methylene chloride and 1,2-dibromoethane forms 1,3-benzodiselenole (70.4% yield) and dihydro-1,4-benzodiselenin (54.6% yield), respectively. The ortho-lithiation and $o,o\sp\prime$-dilithiation of dilithium benzene-1,2-diselenolate is presented. The adduct to thioxanthone is ring-closed to form the (1) benzoselenopyrano (2,3,4-kl) thioxanthylium cation and 13b$H$- (1) benzoselenopyrano (2,3,4-kl) thioxanthen-13b-ol (13.3% yield).
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign