1,3-Dipolar addition of nitrones to symmetrically substituted allenes: for the determination of absolute configuration of chiral allenes by NMR spectroscopy

5-Methyl-5-phenylpyrroline N-oxide was proved to be a useful 1,3-dipole for determining the absolute configuration of chiral allenes by means of NMR spectroscopy.     

Palladium-catalyzed highly regio- and stereoselective addition of organoboronic acids to allenes in the presence of AcOH

The Pd(0)-catalyzed regio- and stereoselective addition of organoboronic acids to allenes leads to stereodefined tri- or tetrasubstituted alkenes. Furthermore, this method shows high substitutent-loading capability and tolerance of various substitutents. A hydropalladation-Suzuki coupling mechanism, which may account for the regio- and stereoselectivity, is proposed.     

Cobalt-Catalyzed C8-Dienylation of Quinoline-N-Oxides

An efficient Cp*Co^III-catalyzed C8-dienylation of quinoline-N-oxides was achieved by employing allenes bearing leaving groups at the α-position as the dienylating agents. The reaction proceeds by Co^III-catalyzed C−H activation of quinoline-N-oxides and regioselective migratory insertion of the allene followed by a β-oxy elimination, leading to overall dienylation. Site-selective C−H activation was achieved with excellent selectivity under mild reaction conditions, and 30 mol % of a NaF additive was found to be crucial for the efficient dienylation. The methodology features high stereoselectivity, mild reaction conditions, and good functional-group tolerance. C8-alkenylation of quinoline-N-oxides was achieved in the case of allenes devoid of leaving groups as coupling partners. Furthermore, gram-scale preparation and preliminary mechanistic experiments were carried out to gain insights into the reaction mechanism.     

C?C Fragmentation: Origins and Recent Applications

It has been 60 years since Eschenmoser and Frey disclosed the archetypal C? C fragmentation reaction. New fragmentations and several variants of the original quickly followed. Many of these variations, which include the Beckmann, Grob, Wharton, Marshall, and Eschenmoser–Tanabe fragmentations, have been reviewed over the intervening years. A close examination of the origins of fragmentation has not been described. Recently, useful new methods have flourished, particularly fragmentations that give alkynes and allenes, and such reactions have been applied to a range of complex motifs and natural products. This Review traces the origins of fragmentation reactions and provides a summary of the methods, applications, and new insights of heterolytic C? C fragmentation reactions advanced over the last 20 years.     

Computation of molecular parity violation using the coupled-cluster linear response approach

In memoriam, Nicholas C. Handy.

We report the implementation of a coupled-cluster linear response approach for the computation of molecular parity violation (in the framework of the PSI3 code, in particular). The approach is applied first to molecules such as hydrogen peroxide (HOOH), hydrogen disulfide (HSSH) and dichlorinedioxide (ClOOCl), which have been studied previously. The importance of including correlation is demonstrated for these examples, also including selected variations of geometry providing parity violation as a function of torsional angles. For the substituted allenes, 1,3 difluoroallene (CHF=C=CHF), 1,fluoro,3 chloroallene (CHF=C=CHCl) and 1,3 dichloroallene (CHCl=C=CHCl), we find that in particular the last molecule may be a suitable candidate for the experimental study of molecular parity violation.     

Metal-catalyzed cycloetherification reactions of β,γ- and γ,δ-allendiols: chemo-, regio-, and stereocontrol in the synthesis of oxacycles

Versatile routes that lead to a variety of functionalized enantiopure tetrahydrofurans, dihydropyrans, and tetrahydrooxepines are based on chemo-, regio-, and stereocontrolled metal-catalyzed oxycyclization reactions of β,γ- and γ,δ-allendiols, which were readily prepared from (R)-2,3-O-isopropylideneglyceraldehyde. The application of Pd(II), Pt(II), Au(III), or La(III) salts as the catalysts gives controlled access to differently sized oxacycles in enantiopure form. Usually, chemoselective cyclization reactions occurred exclusively by attack of the secondary hydroxy group (except for the oxybromination of phenyl β,γ-allenic diols 3b and 3d) to an allenic carbon atom. Regio- and stereocontrol issues are mainly influenced by the nature of the metal catalysts and substituents.