The present review offers an overview of the current approaches for the photochemical and photocatalytic generation of reactive intermediates and their application in the formation of carbon–carbon bonds. Valuable synthetic targets are accessible, including arylation processes, formation of both carbo- and heterocycles, alpha- and beta-functionalization of carbonyls, and addition reactions onto double and triple bonds. According to the recent advancements in the field of visible/solar light catalysis, a significant part of the literature reported herein involves radical ions and radicals as key intermediates, with particular attention to the most recent examples. Synthetic application of carbenes, biradicals/radical pairs and carbocations have been also reported.

Carbon-Carbon Bond Forming Reactions via Photogenerated Intermediates.

Photocatalysis for the formation of the C-C bond.

We report herein an operationally simple method for the direct conversion of benzylic C–H groups to C–F. We show that visible light can activate diarylketones to abstract a benzylic hydrogen atom selectively. Adding a fluorine radical donor yields the benzylic fluoride and regenerates the catalyst. The selective formation of mono- and difluorination products can be achieved by catalyst control. 9-Fluorenone catalyzes benzylic C–H monofluorination, while xanthone catalyzes benzylic C–H difluorination. The scope and efficiency of this new C–H fluorination method are significantly better than those of the existing methods. This is also the first report of selective C–H gem-difluorination.

Visible Light-Promoted Metal-Free C–H Activation: Diarylketone-Catalyzed Selective Benzylic Mono- and Difluorination

Publisher Summary This chapter describes the various aspects of the vibrational spectra of carbohydrates. Vibrational spectroscopy is one of the techniques most adapted techniques for the study of hydrogen bonding, which is the indicator of molecular interaction in the aqueous solutions of sugars. A polyatomic molecule, such as sugar, may be regarded as a system of masses joined by bonds having spring-like properties. The vibration of each of the masses (atoms) can be resolved into components parallel to the x, y, and z axis of a Cartesian system of coordinates. The harmonic approximation is applied in which any motion of the molecule is resolved in a sum of displacements parallel to the Cartesian coordinates and these are called “fundamental, normal modes of vibration.” The analysis of crystallographic results shows the important role played by anomeric center in the structure of sugars. Infrared dichroism in polysaccharides was applied to obtain information on the orientation of chemical groups in the crystalline structure. The computational calculation of the frequencies of carbohydrates' vibration is also elaborated in the chapter.

Vibrational spectra of carbohydrates.

Nucleophilic and organometallic displacement reactions of allylic compounds: stereo-and regiochemistry

Conjugate addition-alkylation reactions of lithium dialkyl cuprates to hex-2-enopyrano-4-ulosides (1), hex-3-enopyrano-2-ulosides (2), and hex-1-enopyrano-3-uloses (3) have been investigated. Extensive studies with 1 show that the homogeneous system using the soluble tri-n-butylphosphine copper(I) complex is less satisfactory than the heterogeneous medium in which copper(I) iodide is used. The use of Grignard reagents versus alkyl lithiums has also been investigated, the latter being found preferable. 1,2-Addition was observed in some cases, but conditions were developed to avoid formation of these side products.With α-enones 1 and 2 alkylation is completely stereoselective, the newly introduced alkyl group being in axial orientation. With 3 a complex mixture is obtained from which equatorial and axial adducts can be isolated in approximately equal amounts.

The stereochemistry of conjugate addition of lithium dialkyl cuprate reagents to some carbohydrate α-enones

Mokupalides, three novel hexaprenoids from a marine sponge

Alpha-oxygenated fatty acids occurring as amides of 2-methylene-β-alanine in a marine sponge

Highly functionalised branched-chain monosaccharides can be prepared by sensitised irradiation of conjugated enones (1) and (2) in an alcohol whereupon equatorial 1,4-addition of the carbinol is the major event, the adducts so obtained being correlated with the products of ground-state additions.

Ground and excited state 1,4-addition reactions of some carbohydrate enones

From a deep water Pacific zoanthid, Gerardia sp., we have isolated two new fluorescent nitrogenous pigments, derivatives of tetrazacyclopentazulene. The first was characterized by uv, 1H and 13C nmr data, and by X-ray diffraction; the second by interconversion.

Mark Bernard Yunker

Papers

The stereochemistry of conjugate addition of lithium dialkyl cuprate reagents to some carbohydrate α-enones

Mokupalides, three novel hexaprenoids from a marine sponge

Alpha-oxygenated fatty acids occurring as amides of 2-methylene-β-alanine in a marine sponge

Ground and excited state 1,4-addition reactions of some carbohydrate enones

Pseudozoanthoxanthins from gold coral