Quantitative prediction of excited-state decay rates for radical anion photocatalysts.

We present a computational approach for predicting key properties of organic radical anions, including excited-state lifetimes and redox potentials. The approach shows good agreement with experimental data and has potential for in silico screening to facilitate the rational design of photocatalysts.

Unravelling the Effect of Water Addition in Consecutive Photocatalysis with Naphthalene Diimide.

We describe the effect of water addition in the catalyst performance for a C-H functionalization of benzene. Improved yields and selectivity were achieved in a consecutive photoredox catalysis in contrast to the reaction without water. Mechanistic analysis demonstrated this is due to a better catalyst stability and faster kinetic rather than a change in the different steps of the mechanism. The addition of water constitutes a convenient approach to improve catalyst performance, and it was also observed with other catalysts.

Initiation in Photoredox C-H Functionalization Reactions. Is Dimsyl Anion a Key Ingredient?

Previous studies have reported the arylation of unactivated arenes with ArX, base (KOtBu or NaOtBu), and an organic additive at high temperatures. Recently, we showed that this reaction proceeds in the absence of additives at rt but employs UV-vis light. However, details of mechanisms that can use a photoinduced base-promoted homolytic aromatic substitution reaction (photo-BHAS) have remained elusive until now. This work examines different mechanistic routes of the essential electron-transfer step (ET) of this reaction in order to identify a possible path for the formation of 1-adamantyl radicals from 1-haloadamantanes (initiation step). On the basis of photochemical and photophysical experiments and computational studies, we propose an unprecedented initiation step that could also be applied to other ET reactions performed in DMSO. For the first time, it is reported that dimsyl anion, formed from a strong base and DMSO (solvent), is responsible for inducing the initiation by a photo-BHAS process on alkyl halides.

Reduction of aryl halides by consecutive visible light-induced electron transfer processes.

Biological photosynthesis uses the energy of several visible light photons for the challenging oxidation of water, whereas chemical photocatalysis typically involves only single-photon excitation. Perylene bisimide is reduced by visible light photoinduced electron transfer (PET) to its stable and colored radical anion. We report here that subsequent excitation of the radical anion accumulates sufficient energy for the reduction of stable aryl chlorides giving aryl radicals, which were trapped by hydrogen atom donors or used in carbon-carbon bond formation. This consecutive PET (conPET) overcomes the current energetic limitation of visible light photoredox catalysis and allows the photocatalytic conversion of less reactive chemical bonds in organic synthesis.

Synthesis of 6-substituted 2-pyrrolyl and indolyl benzoxazoles by intramolecular O-arylation in photostimulated reactions.

The synthesis of a series of 6-substituted 2-pyrrolyl and 2-indolyl benzoxazoles by photostimulated C-O cyclization of anions from 2-pyrrole carboxamides, 2-indole carboxamides, or 3-indole carboxamides has been found to proceed in good to excellent yields (41-100%) in DMSO and liquid ammonia. The pyrrole and indole carboxamides are obtained in good to very good isolated yields by an amidation reaction of different 2-haloanilines with 2-carboxylic acid of pyrrole and 2- or 3-carboxylic acid of indole. To explain the regiochemical outcome of these reactions (C-O arylation vs C-N or C-C arylation), a theoretical analysis was performed using DFT methods and the B3LYP functional.

Short access to 6-substituted pyrimidine derivatives by the S(RN)1 mechanism. Synthesis of 6-substituted uracils through a one-pot procedure.

The synthesis of 6-substituted 2,4-dimethoxypyrimidines with different nucleophiles was accomplished with good to excellent yields (50-95%) through S(RN)1 reactions, starting from commercially available 6-chloro-2,4-dimethoxypyrimidine (1). Hydrolysis of these derivatives gave access to 6-substituted uracils with good yields and short times by the use of microwave irradiation. The preparation of uracils from 1 without the isolation of 2,4-dimethoxypyrimidine derivatives affords a rapid access to these compounds in good yields and excellent purity by avoiding an unnecessary step of purification.

A novel approach to the synthesis of 6-substituted uracils in three-step, one-pot reactions.

From the commercial 6-chloro-2,4-dimethoxypyrimidine (1) and by a photostimulated reaction with Me(3)Sn(-) ions, 2,4-dimethoxy-6-(trimethylstannyl)pyrimidine (2) was obtained in 95% yield. By the cross-coupling reaction of 2 with 1-iodonaphthalene as electrophile catalyzed by Pd (Stille reaction), 2,4-dimethoxy-6-(naphthalen-1-yl)pyrimidine (9) was obtained in 76% yield. By hydrolysis of 9, 6-(1-naphthyl)uracil was obtained in 98% of isolated yield. When the three steps (S(RN)1 reaction-cross coupling reaction-hydrolysis) were performed in a one-pot reaction, 6-substituted uracils (1-naphthyl, 4-chlorophenyl, 3-chlorophenyl, 2,3,4,5,6-pentafluorophenyl) were obtained (43-57%) of isolated pure products. When the electrophile was a benzoyl chloride, 6-benzoyl uracil (54%) and 6-(2-chlorobenzoyl) uracil (49%) were obtained in isolated pure products.