New aspects of hydrogallation reactions with alkynes : Simple addition versus formation of cyclophanes

Treatment of 1,4-bis(3,3-dimethyl-1-butynyl)benzene C 6 H 4 (C≡C-CMe 3 ) 2 with 2 equiv of diethylgallium hydride resulted in addition of one Ga-H bond to each triple bond of the starting compound. Whereas in that case products of secondary reactions could not be isolated, dineopentylgallium hydride afforded a [3,3]-cyclophane derivative with two bridging Ga-CH 2 -CMe 3 groups, which may be derived from the simple addition product by condensation and release of trineopentylgallium. A cis-arrangement of Ga and H was observed in all cases.