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Unprecedented hydroxy-alkynylation and -alkenylation reactions of arylalkenes have been developed through electrochemically enabled addition of an organotrifluoroborate reagent and H2O across the double bond of the alkene. The use of electrochemistry to promote these oxidative alkene 1,2-difunctionalization reactions not only obviates the need for transition-metal catalysts and oxidizing reagents but also ensures high regio- and chemoselectivity to afford homopropargylic or homoallylic alcohols. The possibility of extending the electrochemical alkene difunctionalization strategy to other alkene carbo-heterofunctionalization reactions has been demonstrated.

An efficient visible light promoted metal-free dihydroxylation of styrenes with water and dioxygen has been developed for the construction of vicinal alcohols. The protocol was operationally simple with a broad substrate scope. The mechanistic studies demonstrated that one of the hydroxyl groups came from water and the other one came from molecular oxygen. Additionally, the β-alkyoxy alcohols could also be obtained using a similar strategy.

A new concept to access unsymmetrical 1,2-diols with high yields is reported. This new methodology is based on a retropinacol/cross-pinacol coupling process. This transformation is characterized by its operational simplicity and very mild reaction condi tions.

Visible light-induced photocatalytic fixation of CO2 into benzophenone (1) has been carried out in CO2-saturated DMF (N,N-dimethylformamide) using poly(p-phenylene) (PPP) as a heterogeneous photocatalyst and triethylamine as an electron donor. Diphenylglycolic acid (2) is produced as a CO2-fixed product together with benzhydrol (3), benzopinacol (4) and 1,1-diphenylpropane-1,2-diol (5). The presence of quaternary onium salts such as tetraethylammonium chloride (Et4NCl) increases the yield of 2 in the presence of CO2 and those of 3 and 5 in the absence of CO2. The soft onium cations from quaternary onium salts are proposed to stabilize diphenylcarbinol anion (9) as a common precursor of 2, 3 and 5 on the basis of the HSAB concept. Further, the enhanced formation of PPP dianions (7) through PPP radical anions (6) has been examined in the reduction of PPP with sodium metal in the presence of Et4NCl. Photocatalysis of PPP in the CO2 fixation is discussed in terms of onium salt effects and favorable photoformation of 6 and 7 as an electron pool in the presence of quaternary onium cations.

Photosensitized reaction of xanthinic compounds (XH) as caffeine (CF), theobromine (TB) and theophylline (TF) by benzophenone (BZ) in ethanol solution was investigated. In the three cases four main reaction products (benzopinacol; diphenylcarbinol; 1,1-diphenyl-1,2-propanediol and 8-[1-(1-hydroxyethyl)] xanthine) were identified and then characterized by melting point, 1H NMR, 13C NMR and mass spectrometry. The quenching of triplet BZ by the three XH was detected and a thorough kinetic analysis was performed. Caffeine produces mainly physical quenching, while TF reacts by N-H hydrogen abstraction. For TB both mechanisms are operative. Heats of reactions were calculated for chosen reactive steps of the mechanism by the PM3 method. They provide additional support to the proposed reaction scheme. We demonstrate that the mechanism leading to XP formation does not proceed through the X? radical directly obtained by H abstraction. An alternative reaction path through an intermediate radical originated on the addition of ethanol radical to XH is proposed. Redox potentials for the oxidation of XH were estimated by cyclic voltametry and by using the Rehm-Weller equation the redox quenching of triplet BZ by XH was discarded.

The ground state of the hydroxydiphenylmethyl radical (1) leads to benzpinacol (2) through head-to-head coupling and the diols 3 as cross-coupling product. In contrast, under the high-intensity conditions of the laser-jet photolysis, the excited radical 1* couples in the para position to afford the benzophenone derivatives 4 (head-to-tail coupling) (higher spin density at the para position/AM1 calculations). The major two-photon product is benzhydrol (5). The pronounced increase in hydrogen atom abstraction from MeOH to iPrOH by 1* is explained in terms of the greater electrophilic character of the electronically excited radical 1* versus its ground state.

In the laser-jet mode (argon ion laser) the excited hydroxydiphenylmethyl radical (3*) underwent H expulsion in inert solvents (benzene, acetonitrile) to produce benzophenone (two-photon product), besides dimerization of its ground state 3 to benzpinacol (one-photon product).In ethanol, the laser-jet photolysis of benzophenone afforded as new products (two-photon chemistry) benzhydrol, 4-(1-hydroxyethyl)benzophenone (1), together with benzpinacol and 1,1-diphenyl-1,2-propandiol (4), which are also observed in low-intensity photolyses (one-photon chemistry).Benzhydrol is formed through H abstraction from the excited radical 3* and ketone 1 possibly by coupling of an excited radical 3* at its para position (highest spin density) with a transient 1-hydroxyethyl radical.Photolysis of α-phenylbenzoin (2) produced benzpinacol, benzophenone, pinacol 4, benzhydrol, ketone 1, and the benzoyl-derived products benzil and benzaldehyde.Also benzhydrol was observed as a two-photon product.Key Words: Two-photon chemistry / Laser jet / Hydroxydiphenylmethyl radical / Hydrogen abstraction / Hydrogen atom expulsion

Ytterbium metal promoted cross-coupling reactions of diaryl ketones with a variety of electrophiles are described.Diaryl ketones treated with 1-2 equiv of Yb metal react smoothly with other ketones, nitriles, epoxides, CO2, etc., to give the corresponding unsymmetrical pinacols, α-hydroxy ketones, 1,3-diols, α-hydroxy carboxylic acids, etc., in good yields respectively.These reactions occur via nucleophilic addition of the intermediates 4a-c to electrophiles.Reaction of benzophenone (1a) with Yb metal is discussed in detail and some information on the composition of the intermediates of the reaction of diaryl ketones with Yb metal are also given.

New organic compounds containing a phosphorus heterocycle of the phosphonite type, in which the phosphorus atom is connected on the one hand to an oxygen atom and on the other hand to an oxygen, sulphur or nitrogen atom, characterized by comprising two of such heterocycles, the two phosphorus atoms being connected by a hydrocarbon group. Preparation of these diphosphonites by the action of a tetrahalogeno- or tetraminodiphosphine upon a diol or an alcohol carrying a phenol, thiol, enol, acid or amine function.

Irradiation of benzophenone in alcohol solutions produces unsymmetrical pinacols and para-coupled products as well as benzpinacol; the product composition depends on light intensity.

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