Advances in Stereoconvergent Catalysis from 2005 to 2015: Transition-Metal-Mediated Stereoablative Reactions, Dynamic Kinetic Resolutions, and Dynamic Kinetic Asymmetric Transformations.

Stereoconvergent catalysis is an important subset of asymmetric synthesis that encompasses stereoablative transformations, dynamic kinetic resolutions, and dynamic kinetic asymmetric transformations. Initially, only enzymes were known to catalyze dynamic kinetic processes, but recently various synthetic catalysts have been developed. This Review summarizes major advances in nonenzymatic, transition-metal-promoted dynamic asymmetric transformations reported between 2005 and 2015.

Rapid Room-Temperature 11C-Methylation of Arylamines with [11C]Methyl Iodide Promoted by Solid Inorganic Bases in DMF.

11[C]Methyl iodide is the most widely used reagent for labeling radiotracers with carbon-11 (t1/2 = 20.4 min) for molecular imaging with positron emission tomography. However, some substrates for labeling, especially primary arylamines and pyrroles, are sluggishly reactive towards [11C]methyl iodide. We found that insoluble inorganic bases, especially Li3N or Li2O, are effective in promoting rapid reactions (≤ 10 min) of such substrates with no-carrier-added [11C]methyl iodide in DMF at room temperature to give 11C-methylated products in useful radiochemical yields. In particular, we discovered that some primary arylamines in Li3N-DMF were converted into their formanilides, and that these were readily N-methylated with [11C]methyl iodide, preceding easy basic hydrolysis to the desired [11C]N-methyl secondary arylamines. Use of a solid base permitted selective reaction at an arylamino group and in some cases also avoided undesirable side reaction, such as ester group hydrolysis. An ultrasound device proved useful to provide remote and constant agitation of the radioactive heterogeneous reaction mixtures, but imparted no 'ultrasound-specific' chemical effect.

Formal total synthesis of (±)-cortistatin A.

A second-generation synthesis of the pentacyclic core of the cortistatins, a family of rearranged steroidal alkaloids that have recently attracted much attention, is reported. The improved sequence provides access to significant quantities of this key compound, which enabled a formal total synthesis of (±)-cortistatin A by conversion to the key Nicolaou/Hirama dienone. It is anticipated that this new, robust route to the pentacyclic core will facilitate the total synthesis of a range of natural products in the cortistatin family, as well as the construction of key structural analogs to probe the promising biological activity of these important compounds.