RhCl(PPh 3 ) 3 in the presence of excess hydrochloric acid and of 1 is first-order with respect to tolan and RhCl(PPh 3 ) 3 and exhibits activation parameters of ∆H ‡ = 94.7 ± 10 kJ mol -1 azobenzene in refluxing 1-pentanol catalyzes the cyclodimerization of arylalkynes to 1,2,3-substituted and ∆S ‡ = 36 ± 6 J K -1 mol -1 . Replacing HCl by HBr and HI decreases the rate by 28 and 55%, respectively. Although naphthalene derivatives. This enables an easy access to 1,2,3-triphenylnaphthalene
(1), 7-methoxy-1,2,3-tris(p-naphthalene formation occurs also in the absence of azobenzene, its presence stabilizes the catalyst, accelerates methoxyphenyl)naphthalene
(2), 7-methyl-1,2,3-tris(pmethylphenyl)naphthalene
(3), and 7-nitro-3-(p-the reaction, and inhibits formation of 1-chlorostilbene, which is the major by-product. When RhCl(PCy 3 ) 2 is used as nitrophenyl)-1,2-diphenylnaphthalene (4). A co-cyclodimerization of tolan with 4-octyne affords 3-phenyl-1,2-the catalyst, naphthalene formation even in the absence of azobenzene is highly selective, but proceeds much slower. dipropylnaphthalene (5). The structure of 4 was resolved by single-crystal X-ray structural analysis. The rate of formation No reaction is observed in non-protic solvents.
Cyclodimerization of Tolan by Various Catalysts