Substituent effects on the cyclization mode of 7-sulfonyl-3-hepten-1,5-diynes and 11-sulfonylundeca-3,7-dien-1,5,9-triynes

In probing of cycloaromatization of 7-phenylsulfonyl-3-hepten-1,5-diyne systems to generate biradical intermediates under an alkaline condition suggested that the aryl moiety on C3-C4 also plays an important role to switch the Myers cyclization to Schmittel cyclization in the allen-enyne system, although the aryl group on the alkyne terminus does not work in the proceeding of the cycloaromatization. For example, treatment of 1-phenyl-7-phenylsulfonyl-3-hepten-1,5-diyne (8) with triethylamine in the presence of 1,4-cyclohexadiene in benzene offered biphenyl 13 in 51% yield. Under the same reaction conditions, cyclization of 1-(2-phenylethynyl)-2-(3-phenylsulfonyl-1-propynyl) benzene (28) gave naphthalene 34 in 42% yield along with indene 35 in 32% yield. Moreover, the substituent effect also occurred in the cyclization of 11-phenylsulfonylundeca-3,7-diene-1,5,9-triyne (38), which provided indene 39 in 50% yield as the major product.