2-phenyl-1-boraadamantane complexes. Synthesis and intramolecular dynamics

The reaction of triallylborane with 3-phenylprop-1-yne at 135-140 degrees C followed by treatment of the reaction mixture with MeOH afforded 7-benzyl- 3-methoxy-3-borabicyclo[3.3. 1]non-6-ene (1) in 81% yield. Hydroboration of compound 1 with a solution of BH3 in THF yielded the tetrahydrofuran compl ex of 2-phenyl-1-boraadamantane (2). The reactions of trimethylamine or pyr idine with compound 2 afforded the trimethylamine (3) or pyridine (4) compl exes of 2-phenyl-1-boraadamantane, respectively. Hindered rotation about th e C(2)-Ph bond in adduct 3 was observed by H-1 and C-13 NMR spectroscopy. T he activation energy of this process is 58.6 kJ mol(-1) (determined by 2D H -1-H-1 EXSY spectroscopy).