A three-component hydrocarboxylation of an olefin with CO2 and H2 could be regarded as a dream reaction, since it would provide a straightforward approach for the synthesis of aliphatic carboxylic acids in perfect atom economy. However, this transformation has not been realized in a direct manner under mild conditions, because boosting the carboxylation with thermodynamically stable CO2 while suppressing the rapid hydrogenation of olefin remains a challenging task. Here, we report a rhodium-catalysed reductive hydrocarboxylation of styrene derivatives with CO2 and H2 under mild conditions, in which H2 served as the terminal reductant. In this approach, the carboxylation process was largely accelerated by visible light irradiation, which was proved both experimentally and by computational studies. Hydrocarboxylation of various kinds of styrene derivatives was achieved in good yields without additional base under ambient pressure of CO2/H2 at room temperature. Mechanistic investigations revealed that use of a cationic rhodium complex was critical to achieve high hydrocarboxylation selectivity.

A highly useful, visible-light-driven carboxylation of aryl bromides and chlorides with CO2 was realized using a combination of Pd(OAc)2 as a carboxylation catalyst and Ir(ppy)2(dtbpy)(PF6) as a photoredox catalyst. This carboxylation reaction proceeded in high yields under 1 atm of CO2 with a variety of functionalized aryl bromides and chlorides without the necessity of using stoichiometric metallic reductants.

A meta -selective C−H carboxylation reaction of 1,1-diarylethylene derivatives with CO 2 by using a rhodium catalyst with NaO i Pr as a stoichiometric reductant has been achieved. Together with hydrogenation of the ethylene moiety, a carboxyl group was introduced to the meta -position of the aryl ring with high selectivity over the ortho -positions. Experimental and computational mechanistic studies indicate that this carboxylation reaction proceeds via hydrorhodation on the ethylene moiety, followed by 1,4-rhodium migration and successive 1,2-rhodium migration on the aryl ring. The use of a bulky phosphine ligand seems to be the key to this unusual aryl-to-aryl 1,2-rhodium shift.

This chapter describes the development of catalytic systems for the transition-metal-catalyzed direct carboxylation of Csp2─H and Csp3─H bonds, their substrate scope, and limitations, and some mechanistic aspects of those transformations are also discussed. First, we start with the Csp2─H carboxylation of electron-deficient arenes and heteroarenes mediated by basic Au(I)-OH and Cu(I)–OH complexes; then continue with the reactivity of Rh(I), Rh(II), and Pd(II) catalytic systems for the direct C–H carboxylation of inert Csp2─H bonds; and conclude with the pioneering efforts toward the Csp3─H carboxylation of allylic compounds.

A visible-light-driven carboxylation of aryl and alkenyl triflates with CO2 is developed by using a combination of Pd and photoredox catalysts. This reaction proceeds under mild conditions and can be applied to a wide range of substrates including acyclic alkenyl triflates.

We report herein a regio- and stereoselective photocatalytic hydrogenolysis of allylic alcohols to form unsaturated hydrocarbons employing a palladium(II)-loaded titanium oxide; the reaction proceeds at room temperature under light irradiation without stoichiometric generation of salt wastes. Olefin and saturated alcohol moieties tolerated the reaction conditions. Hydrogen atoms were selectively incorporated into less sterically congested carbons of the allylic functionalities. This protocol allowed a short-step synthesis of (S)-(+)-lavandulol from (R)-(-)-carvone by avoiding otherwise necessary protection/deprotection steps.

Abstract A brief account of our recent work on the chemo-, regio- and stereoselective photocatalytic hydrogenolysis of allylic alcohols to alkenes promoted by palladium-loaded titanium oxide (Pd/TiO2) photocatalysts is presented. Since methanol is employed as the reducing agent, the method does not involve stoichiometric generation of salt waste. The photocatalytic hydrogenolysis proceeds at room temperature, and is compatible with the presence of functional groups such as C=C double bonds and hydroxyl groups at non-allylic positions. The regioselectivity is predictable: the hydrogen atom is predominantly incorporated into the sterically less hindered carbon atom of the allylic moiety. This protocol should provide straightforward green access to a range of platform chemicals (exemplified by the two-step synthesis of propylene from glycerol) and fine chemicals [e.g. (S)-(+)-lavandulol from (R)-(–)-carvone] without the need for protection/deprotection steps.

AbstractThe title reaction undergoes under UV‐vis light irradiation using Ag/TiO2 as photocatalyst.

N-Methylation of amines with methanol proceeds at room temperature in the presence of a silver-loaded titanium dioxide (Ag/TiO2) photocatalyst under UV-vis light irradiation. This method allows facile synthesis/isolation of N-methylamines bearing various functional groups including N-benzyl, N-allyl, N-Boc, hydroxyl, ether, acetal, carboxamide, formamide, and olefin groups.

Photochemical transformation of biomass-derived or renewable substances with promising scalability is an important challenge for promoting green and sustainable chemistry. We report here that photocatalytic transfer hydrogenolysis of allyl alcohol (obtained from glycerol) gives potentially sustainable propylene with high chemo-and redox selectivity, promoted by powdered Pd/TiO2 in CH3OH (obtained from CO2) under near-ultraviolet-visible light irradiation (lambda > 365 nm) at ambient temperature.

Photosynthetic dehydrogenation: Potential usefulness of visible-light-induced dehydrogenation of alcohols in organic synthesis was demonstrated, in which aldehydes and H2 were afforded by using Ru/SrTiO3:Rh and water (see scheme). Water was essential for the reaction. High efficiency (TON: up to 15 400 based on Rh; H2 and aldehyde evenly generated) and high selectivity were achieved.

AbstractA new method for the protection of different heterocyclic compounds is presented.

Additions of lactams, imides, (S)-4-benzyl-1,3-oxazolidin-2-one, 2-pyridone, pyrimidine-2,4-diones (AZT derivatives), or inosines to the electron-deficient triple bonds of methyl propynoate, tert-butyl propynoate, 3-butyn-2-one, N-propynoylmorpholine, or N-methoxy-N-methylpropynamide in the presence of many potential catalysts were examined. DABCO and, second, DMAP appeared to be the best (highest reaction rates and E/Z ratios), while RuCl3, RuClCp*(PPh3)2, AuCl, AuCl(PPh3), CuI, and Cu2(OTf)2 were incapable of catalyzing such additions. The groups incorporated (for example, the 2-(methoxycarbonyl)ethenyl group that we name MocVinyl) serve as protecting groups for the above-mentioned heterocyclic CONH or CONHCO moieties. Deprotections were accomplished via exchange with good nucleophiles: the 1-dodecanethiolate anion turned out to be the most general and efficient reagent, but in some particular cases other nucleophiles also worked (e.g., MocVinyl-inosines can be cleaved with succinimide anion). Some structural and mechanistic details have been accounted for with the help of DFT and MP2 calculations.

Pd-catalysed reactions of 2-Cl, 2-Br and 2-I derivatives of a 6-chloropurine nucleoside with benzamide have been compared, using Pd2dba3, Xantphos and Cs2CO3 in toluene, between 20 and 80°C. The reactivity order was 2-I>2-Br>6-Cl≫2-Cl. The 2-I substituent could be replaced even at 0°C, under conditions disclosed here for the first time. On the other hand, the replacement of the chlorine atom at position 2 (2-Cl) required 110°C.

AbstractThe replacement of halogen substituents by different N‐nucleophiles is investigated.

[N,1-(15)N(2)]-Guanosine, or [1,NH(2)-(15)N(2)]-guanosine, and derivatives were prepared from tri-O-acetylinosine, via N-nitration and reaction with (15)NH(2)OH, followed by conversion of the (15)N-labeled 1-hydroxyinosine to the corresponding 2,6-dichloropurine riboside. The sequential one-pot C-O and C-N key couplings of this dichloro derivative with PhCH(2)OH and PhCO(15)NH(2) or (i)PrCO(15)NH(2) was achieved in good overall yields, with Pd(0)-Xantphos as the best choice of five different catalytic systems examined.

A general approach to enantiopure C-glycofuranoside-based hybrid α/β-amino acids and nitrones, among other valuable building blocks, has been established via formyl C-glycofuranosides, easily available from hexose-derived equatorial-2-OH-glyco-pyranosides by DAST-promoted ring contraction.