Cobalt-catalyzed double hydroboration of pyridines

Cobalt(ii) complexes were prepared from a modular phosphinopyridonate platform and applied to the hydroboration of pyridines. The synthetically useful, yet challenging, double hydroboration toward tetrahydropyridine derivatives was successfully performed with high activity and regiocontrol. This new method enabled the direct synthesis of N-heterocyclic allylic boronates from commercial pyridines and pinacolborane (HBpin). One-pot acetylation afforded the bench-stable borylated N-acetyl tetrahydropyridines in good yields. The synthetic utility of this procedure was demonstrated by a gram-scale double hydroboration-acetylation sequence followed by chemical diversification. Mechanistic experiments indicated metal-ligand cooperativity involving ligand-centered C-H activation and the intermediacy of a cobalt(iii) hydride species.

Stereocontrolled Pericyclic and Radical Cycloaddition Reactions of Readily Accessible Chiral Alkenyl Diazaborolidines

In this paper is described an easily synthesized chiral diazaborolidine that is inexpensive, stable, and provides excellent stereoselection across a number of reaction classes. These versatile compounds possess utility in four different classes of cycloaddition reactions, offering good yield and stereoselectivity. X-ray structure analysis provides insight about the origin of stereocontrol.

Regiocontrolled synthesis of enantioenriched 2-substituted dehydropiperidines by stereospecific allyl-allyl cross-coupling of a chiral allylic boronate

The palladium-catalyzed cross-coupling of an optically enriched dehydropiperidinyl boronate with cinnamyl carbonates was optimized to minimize stereochemical erosion. Although the coupling of two unsymmetrical allyl fragments may generate four possible regioisomers, the optimal procedure using (p-CF₃C₆H₄)₃P as the ligand affords linear 2-allylated 3,4-dehydropiperidines exclusively (>98 : 2 rr) with enantiospecificity up to 99%.

Cyclopentyl Methyl Ether: An Elective Ecofriendly Ethereal Solvent in Classical and Modern Organic Chemistry

Solvents represent one of the major contributions to the environmental impact of fine-chemical synthesis. As a result, the use of environmentally friendly solvents in widely employed reactions is a challenge of vast real interest in contemporary organic chemistry. Within this Review, a great variety of examples showing how cyclopentyl methyl ether has been established as particularly useful for this purpose are reported. Indeed, its low toxicity, high boiling point, low melting point, hydrophobicity, chemical stability towards a wide range of conditions, exceptional stability towards the abstraction of hydrogen atoms, relatively low latent heat of vaporization, and the ease with which it can be recovered and recycled enable its successful employment as a solvent in a wide range of synthetic applications, including organometallic chemistry, catalysis, biphasic reactions, oxidations, and radical reactions.

N-Heterocyclic Carbene-Catalyzed Annulation of α-Chloroaldehydes with γ-/δ-Amino-α,β-Unsaturated Ketones: Enantioselective Synthesis of Pyrrolidones and Piperidones

The N-heterocyclic carbene-catalyzed [2+3] and [2+4] annulations of α-chloroaldehydes with γ-/δ-amino-α,β-unsaturated ketones were developed, giving the corresponding pyrrolidones and piperidones in good yields with exclusive trans-selectivities and excellent enantioselectivities.