Solvent-triggered stereoselectivity of α,α-cyclopropanation of amino acids in the Ni(ii) chiral coordination environment

Reductive opening of a cyclopropane ring in the Ni(II) coordination environment: a route to functionalized dehydroalanine and cysteine derivatives

The involvement of an α,α-cyclopropanated amino acid in the chiral Ni(II) coordination environment in the form of a Schiff base is considered as a route to electrochemical broadening of the donor-acceptor cyclopropane concept in combination with chirality induction in the targeted products. A tendency to the reductive ring-opening and the follow-up reaction paths of thus formed radical anions influenced by substituents in the cyclopropane ring are discussed. Optimization of the reaction conditions opens a route to the non-proteinogenic amino acid derivatives containing an α-β or β-γ double C=C bond in the side chain; the regioselectivity can be tuned by the addition of Lewis acids. One-pot combination of the reductive ring opening and subsequent addition of thiols allows obtaining the cysteine derivatives in practical yields and with high stereoselectivity at the removed β-stereocenter.

Ni(II) Schiff-Base Complexes as Chiral Electroauxiliaries and Methodological Platform for Stereoselective Electrochemical Functionalization of Amino Acids

The concept of chiral electroauxiliary based on the redox active chiral platform to perform transformations of a redox inactive substrate is suggested and discussed in the context of the targeted stereoselective electrochemical functionalization of amino acids. Tailor-made amino acids are essential structural features of modern medicinal chemistry and drug design; the development of efficient synthetic approaches to these compounds is of topical interest. The modified substrate (an amino acid) is included as a structural motif in the redox active complex (with a possibility to be released after modification) that integrates "a bifunctional linker" (the structural motif capable to "catch" a substrate) and a chiral moiety responsible for asymmetry induction. The amino acid, being included as a part of such ensemble, becomes stable towards redox destruction and its targeted electrochemical modification saving the amino acid skeleton is possible, thus developing new modes of reactivity for well-known compounds.