Because of their greater stability and unique conformational properties, unnatural amino acids are highly valued by pharmaceutical, biological, and organic chemists. This synopsis surveys the various catalytic methods used to access enantioenriched, acyclic α,α-disubstituted α-amino acids with a focus on the processes developed since 2007, when the last major reviews in this area were published.

Palladium-catalyzed cross coupling conditions were developed that efficiently afford 2-aryl-2-nitroacetates from aryl bromides and the very acidic nitroacetates.

Nitroarylacetates are useful small molecular building blocks that act as precursors to α-ketoesters and aryl nitromethanes as well as α-amino acids. Methods were developed that produce each of these compound types in good yields. Two different conditions for decarboxylation are discussed for substrates with neutral and electron-poor aryl groups versus electron-rich aryl groups. For formation of the α-ketoesters, new mild conditions for the Nef disproportionation were identified.

An axial chiral tetrachlorinated bisbenzo[a]phenazine has been discovered that undergoes an alkane-induced shift in the solid state from a disordered amorphous form to an ordered polycrystalline form. This phase transition is caused by the formation of pores that accommodate linear alkanes of varying lengths with a very strong affinity as judged by differential scanning calorimetry. Single crystal X-ray structure analysis revealed that a series of weak phenolic OH···Cl hydrogen bonds dictates the pore structure. These weak interactions can be disrupted mechanically, causing the material to revert to the amorphous form. Notably, the interchange between the amorphous and crystalline forms is readily reversible and is easily observed by characteristic colorimetric changes. Measurements via photoimage processing reveal that the degree of color change is dictated by the type of alkane employed.

This study describes the synthesis of a class of anion-binding catalysts based on a xanthene scaffold. Both unsymmetrical catalysts and C2-symmetrical catalysts were generated, and were examined in the cyclization of 3- and 2-substituted furans onto N-acyliminium ions. Good conversion for each reaction was observed with a variety of anion-binding catalysts (42–76%).

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Review: [71 refs.