Theoretical and Experimental Investigation of Functionalized Cyanopyridines Yield an Anolyte with an Extremely Low Reduction Potential for Nonaqueous Redox Flow Batteries.

Cyanopyridines and cyanophenylpyridines were investigated as anolytes for nonaqueous redox flow batteries (RFBs). The three isomers of cyanopyridine are reduced at potentials of -2.2 V or lower vs. ferrocene+/0 (Fc+/0 ), but the 3-CNPy⋅- radical anion forms a sigma-dimer that is re-oxidized at E≈-1.1 V, which would lead to poor voltaic efficiency in a RFB. Bulk electrochemical charge-discharge cycling of the cyanopyridines in acetonitrile and 0.50 M [NBu4 ][PF6 ] shows that 2-CNPy and 4-CNPy lose capacity quickly under these conditions, due to irreversible chemical reaction/decomposition of the radical anions. Density-functional theory (DFT) calculations indicated that adding a phenyl group to the cyanopyridines would, for some isomers, limit dimerization and improve the stability of the radical anions, while shifting their E1/2 only about +0.10 V relative to the parent cyanopyridines. Among the cyanophenylpyridines, 3-CN-6-PhPy and 3-CN-4-PhPy are the most promising as anolytes. They exhibit reversible reductions at E1/2 =-2.19 and -2.22 V vs. ferrocene+/0 , respectively, and retain about half of their capacity after 30 bulk charge-discharge cycles. An improved version of 3-CN-6-PhPy with three methyl groups (3-cyano-4-methyl-6-(3,5-dimethylphenyl)pyridine) has an extremely low reduction potential of -2.50 V vs. Fc+/0 (the lowest reported for a nonaqueous RFB anolyte) and loses only 0.21 % of capacity per cycle during charge-discharge cycling in acetonitrile.

Ir-catalyzed reverse prenylation of 3-substituted indoles: total synthesis of (+)-aszonalenin and (-)-brevicompanine B.

The selective reverse prenylation of 3-substituted-1H-indoles at C3 is described. The iridium-catalyzed reaction proceeds with high branched to linear selectivity (>20:1) for a variety of indoles. In addition, a diastereoselective reverse prenylation of tryptophan methyl ester is disclosed, and its synthetic utility is demonstrated in the synthesis of (+)-aszonalenin and (-)-brevicompanine B.

Enantioselective Addition of Alkynes to α,α-Dichlorinated Aldehydes.

Enantioselective addition of terminal alkynes to α,α-dichlorinated aldehydes employing Zn(OTf)2/NME is disclosed. The propargylic alcohols obtained are accessed in good yields and high enantioselectivity from easily accessible α,α-dichloroaldehydes. The method opens new strategic opportunities for the synthesis of chlorinated natural products, such as the chlorosulfolipids.

Rh-Catalyzed Stereospecific Synthesis of Allenes from Propargylic Benzoates and Arylboronic Acids.

An enantiospecific approach to the synthesis of optically active, trisubstituted allenes from chiral propargylic benzoates and arylboronic acids has been developed. The transformation is catalyzed by a Rh-(P,olefin) complex formed in situ from [{Rh(cod)Cl}2] and a readily available phosphoramidite ligand. The method furnishes an assortment of diverse allenes in high yields and excellent enantiospecificity under mild conditions.