A simple, convenient and green synthetic approach to diverse fused tricyclic xanthines has been developed via gold(I) complex-catalyzed intramolecular hydroamination or silver(I)-catalyzed isomerization-hydroamination of terminal alkynes under microwave irradiation in water. The first synthesis of N9-annelated xanthines has also been reported.

The dehydrogenation reaction mechanisms of methane catalyzed by a ligated transition metal MH(+) (M = Ru, Rh, and Pd) have been investigated theoretically. Activation of methane by MH(+) complexes is proposed to proceed in a one-step manner via one transition state: MH(+) + CH(4) --> MH(+)CH(4) --> [TS] --> (MCH(3)(+))H(2) -->MCH(3)(+) + H(2). Both high-spin and low-spin potential energy surfaces are characterized in detail. Our calculations indicate that the ground-states species have low electron spin and a dominant 4d(n) configuration for RuH(+), RhH(+), and PdH(+), and the whole reaction proceeds on the ground-states potential energy surfaces with a spin-allowed manner. The MH(+) (M = Ru, Rh, and Pd) complexes are expected from the general energy profiles of the reaction pathways to efficiently convert methane to metal methyl, thus RuH(+), RhH(+), and PdH(+) are likely to be excellent mediators for the activity of methane. In the reactions of MH(+) with methane, the H(2) elimination from the dihydrogen complex is quite facile without barriers. The exothermicities of the reactions are close for Ru, Rh, and Pd: 11.1, 1.2, and 5.2 kcal/mol, respectively.