One-pot Negishi cross-coupling reactions of in situ generated zinc reagents with aryl chlorides, bromides, and triflates

In situ generated aryl, heteroaryl, alkyl, or benzylic polyfunctional zinc reagents obtained by the addition of zinc and LiCl to the corresponding organic iodides undergo smooth Pd(0)-catalyzed cross-coupling reactions with aryl bromides, chlorides, and triflates in the presence of PEPPSI as a catalyst. This procedure avoids the manipulation of water and air-sensitive organozinc reagents and produces cross-coupling products in high yields.     

Generalized weighted Morrey spaces and classical operators

We introduce the notion of generalized weighted Morrey spaces and investigate the boundedness of some operators in these spaces, such as the Hardy–Littlewood maximal operator, generalized fractional maximal operators, generalized fractional integral operators, and singular integral operators. We also study their boundedness in the vector‐valued setting.     

Nonradiative decay mechanisms of the biologically relevant tautomer of guanine

We present the excited-state potential energy profiles of the biologically relevant 9H-keto-amino tautomer of guanine with respect to the radiationless decay via the out-of-plane deformation of the six-membered ring as well as the dissociation of NH bonds. The CASPT2//CASSCF method is employed for the reaction-path calculations. The reaction path for the out-of-plane deformation in the (1)pi pi* state leads in a barrierless way to a conical intersection with the electronic ground state. For the NH dissociation via the (1)pi sigma* state, the 9H-keto-amino tautomer is shown to have lower energy barriers than the 7H tautomers which we have studied recently. These two radiationless decay mechanisms explain the unexpected missing of the biologically relevant form in the resonant two-photon ionization spectrum of guanine in a supersonic jet. It is suggested that these ultrafast deactivation processes provide the biologically relevant tautomer of guanine with a high degree of photostability.     

Nonradiative deactivation mechanisms of uracil, thymine, and 5-fluorouracil: a comparative ab initio study

The mechanisms of the ultrafast nonradiative deactivation of uracil and its substituted derivatives thymine (5-methyluracil) and 5-fluorouracil after absorption of UV light are explored and compared by means of ab initio multistate (MS) CASPT2 calculations. The MS-CASPT2 method is applied for the calculation of potential energy profiles, especially for the geometry optimization in the electronically excited state, with the aim of an accurate prediction of deactivation pathways. The resulting energy curves of each molecule exhibit that the conical intersection between the (1)ππ* and ground states is accessible via small energy barriers from the minimum in the (1)ππ* state as well as from that in the (1)nπ* state. The barrier of 5-fluorouracil in the (1)ππ* state is calculated to be definitely higher than those of uracil and thymine, which is consistent with experiments and suggests that the elongation of the excited-state lifetime of uracil by fluorine substitution is significantly contributed from intrinsic electronic effect of the molecule. However, no evidence of the experimentally observed longer excited-state lifetime of thymine than uracil is found in the presently calculated MS-CASPT2 potential energy curves in the (1)ππ* and (1)nπ* states, implying nonnegligible contribution of other factors such as solvation effect and substituent mass to the photoinduced dynamics of uracil derivatives.     

Isotope effect in the carbonyl sulfide reaction with O(3P)

The sulfur kinetic isotope effect (KIE) in the reaction of carbonyl sulfide (OCS) with O((3)P) was studied in relative rate experiments at 298 ± 2 K and 955 ± 10 mbar. The reaction was carried out in a photochemical reactor using long path FTIR detection, and data were analyzed using a nonlinear least-squares spectral fitting procedure with line parameters from the HITRAN database. The ratio of the rate of the reaction of OC(34)S relative to OC(32)S was found to be 0.9783 ± 0.0062 ((34)ε = (-21.7 ± 6.2)‰). The KIE was also calculated using quantum chemistry and classical transition state theory; at 300 K, the isotopic fractionation was found to be (34)ε = -14.8‰. The OCS sink reaction with O((3)P) cannot explain the large fractionation in (34)S, over +73‰, indicated by remote sensing data. In addition, (34)ε in OCS photolysis and OH oxidation are not larger than 10‰, indicating that, on the basis of isotopic analysis, OCS is an acceptable source of background stratospheric sulfate aerosol.     

Theoretical study of the excited‐state double proton transfer in the (3‐methyl‐7‐azaindole)‐(7‐azaindole) heterodimer

Excited‐state double proton transfer (ESDPT) in the (3‐methyl‐7‐azaindole)‐(7‐azaindole) heterodimer is theoretically investigated by the long‐range corrected time‐dependent density functional theory method and the complete‐active‐space second‐order perturbation theory method. The calculated potential energy profiles exhibit a lower barrier for the concerted mechanism in the locally excited state than for the stepwise mechanism through the charge‐transfer state. This result suggests that the ESDPT in the isolated heterodimer is likely to follow the former mechanism, as has been exhibited for the ESDPT in the homodimer of 7‐azaindole. © 2012 Wiley Periodicals, Inc.     

Cu(I)-catalyzed α-alkylation of ketones with styrene derivatives

α-Alkylation of ketones with styrene derivatives was developed using a mesitylcopper-dppp complex as a soft Brønsted base catalyst. No waste derived from the alkylating reagent was produced in this catalytic alkylation reaction. The bisphosphine ligand structure, as well as the reaction solvent, had profound effects on catalyst activity. The reaction proceeded under mild conditions from a range of ketones and styrene derivatives. The present catalysis is especially useful for the selective mono-alkylation of ketones.     

Novel catalyst system for the synthesis of poly(alkylene oxide) with controlled molecular weight

An organoaluminum compound with bulky phenoxide groups as a Lewis acid can accelerate much the living polymerization of alkylene oxide initiated with aluminum porphyrin by the coordinative activation of the monomer. This concept can be extented to the polymerization initiated with aluminum Schiff base and tetraazaannulene complexes.