Kee-Yong Jung, M. Koreeda*
Nov 24, 1989
Citations
0
Influential Citations
54
Citations
Journal
Journal of Organic Chemistry
Abstract
A mild, efficient synthesis of the carcinogen 1,4-dimethylphenanthrene (2) and its bay-region methyl-bearing regioisomers 2,4-dimethyl- and 3,4-dimethylphenanthrenes (3 and 4) is described. The synthesis involves a generally applicable strategy that features a furan/dimethyl-1-naphthyne cycloaddition reaction followed by a convenient direct deoxygenation of the resulting enooxide with excess trimethylsilyl iodide generated in situ. The Friedel-Crafts cyclization of p-xylene with {gamma}-butyrolactone/AlCl{sub 3} or {gamma}-(2,5-dimethylphenyl)butyric acid via its trifluoromethanesulfonic anhydride derivative results in the formation of a mixture of 5,8-, 6,8-, and 5,7-dimethyl-1-tetralones (17, 20, and 21, respectively) through migration of aromatic methyl groups. The precursor to 6,8-dimethyl-1-naphthyne (10) was prepared from tetralone 20, isolable only as a 5:1 inseparable mixture with 17 from the direct Friedel-Crafts cyclization of p-xylene with {gamma}-butyrolactone, by {alpha}-dibromination with CuBr{sub 2}, dehydrobromination, and tosylation. The precursors to 5,8-dimethyl-1-naphthyne (9) and 7,8-dimethyl-1-naphthyne (11) were synthesized from the corresponding 1-naphthols 15 and 31, respectively. The synthesis of these naphthols involved cycloaddition between the corresponding dimethylated benzyne and furan followed by acid-catalyzed isomerization.