The decay of electronically excited allopurinol riboside was studied through the fluorescence up-conversion technique and high level ab initio calculations. For the allopurinol system with a pyrazolic five-membered ring, we observed an ultrafast decay of the fluorescence signal in water (τ < 0.2 ps), similar to what has been observed for hypoxanthine and inosine (with an imidazolic five-membered ring). These results show that the S(1) dynamics in this type of heterocyclic systems are general and dominated by the distortion in the pyrimidinic six-membered ring with a negligible influence of the rest of the heterocycle. The measurements are consistent with the presence of a highly accessible conical intersection between the S(1) (π-π*) excited state and S(0), as calculated by MR-CIS/CASSCF computations. Our calculations show that the loss of planarity of the six-membered ring is responsible for direct access to the S(1)-S(0) degeneracy region without requiring distortions in the rest of the molecule.

An air-stable phosphinito palladium(ii) complex has been found to be an efficient catalyst in the formation of C–C bonds.

In this paper, we describe the catalytic hydrophosphonylation of several aromatic nitriles used to synthesize α‐aminophosphonates (α‐APs) using commercially available trialkyl phosphites (P(OR)3, R=Et, iPr, Bu,) and simple and inexpensive nickel chloride (NiCl2.6H2O) as the catalytic precursor. The use of triethylborane (Et3B) as a Lewis acid (LA) was mandatory in order to successfully perform H‐phosphite moiety incorporation at the CN bond of non‐activated benzonitriles (BN) derivatives. Interestingly, when a highly activated BN such as 2,3,4,5,6‐pentafluorobenzonitrile (BN‐g) was employed, it was possible to perform the reaction in the absence of an LA using milder reaction conditions. Also, we found that using HP(O)(OiPr)2 as a starting material afforded the aminobisphosphonate derivative with better selectivity than using the method involving P(OiPr)3 as the initial reagent. Remarkably, when using HP(O)(OiPr)2 with an excess of Et3B, the reaction's selectivity completely changed to yield N‐benzyl‐ benzylimine (BBI) and 2,4,5‐triphenylimidazole.

The use of simple and inexpensive NiCl2⋅6 H2O as a catalyst precursor for C−P bond formation in the presence of commercially available trialkyl phosphites (P(OR)3, R=Et, iPr, Bu, SiMe3) along with several alkynes is presented. Control experiments showed the in situ formation of (RO)2P(O)H as the species that undergo the addition into the C≡C bond at the alkynes to yield the product of P−H addition. The hydrophosphonylation of diphenylacetylene with P(OEt)3, P(OiPr)3, and P(OSiMe3)3 proceeds in high yields (>92 %) without the need of a specific solvent or ligand. This method is useful for the preparation of organophosphonates for both phenylacetylene as a terminal alkyne model and internal alkynes in yields that range from good to modest.