Łowicki, D.; Baś, S.; Mlynarski, J.
Chiral Zinc Catalysts for Asymmetric Synthesis
Tetrahedron 2015 71 1339-1394 (link to page)
Zinc (Zn) is an essential mineral of exceptional biologic importance. The abundance of non-toxic zinc salts in the Earth’s crust make zinc an important candidate for cheap and environmentally benign catalysts and reagents. Recently, well-known applications of organozinc compounds in organic synthesis have been broadly expanded to asymmetric synthesis where chiral zinc complexes and covalently-bonded compounds play essential roles. The most common application of Zn in asymmetric synthesis involves the formation of C-C bonds in such reactions as aldol reaction, cyclopropanation, Diels-Alder reaction, Reformatsky reaction, Friedel-Crafts alkylation, alkynylation, organozinc addition to aldehydes including self-catalytic Soai reaction, and conjugate addition to unsaturated compounds. Another growing application of Zn is asymmetric C-O and C-H bond formation reactions. Studies on enantioselective C-P bond formations is also discussed. The last part of this review is devoted to stereoselective polymerisation catalysed by zinc complexes.
Szewczyk, M. Stanek, F.; Bezłada, A.; Mlynarski, J.
Zinc-Acetate-Catalyzed Enantioselective HYdrosilylation of Ketones
Adv. Synth. Catal. 2015 (link to page)
Bezłada, A.; Szewczyk, M.; Mlynarski, J.
Enantioselective Hydrosilylation of Imines Catalyzed by Chiral Zinc Acetate Complexes
J. Org. Chem. 2016 (link to page)
Zinc acetate complexes with chiral diphenyletylenediamine (DPEDA)-derived ligand have been proved to be highly efficient catalysts for enantioselective hydrosilylation of aryl ketones and imines. Replacing pyrophoric dialkyl zinc with readily available zinc salt simplifies the procedures and provides excellent conversions (up to >99%) and enantioselectivities (ees up to 97%) en route to the synthesis of chiral alcohols and amines.
Łowicki, D.; Bezłada, A.; Mlynarski, J.
Asymmetric Hydrosilylation of Ketones Catalyzed by Zinc Acetate with Hindered Pybox Ligands
Adv. Synth. Catal. 2014 356 591-595 (link to page)
A highly efficient asymmetric hydrosilylation (AHS) of a wide variety of prochiral aryl ketones catalyzed by zinc acetate with TPS-he-pybox (tert-butyldiphenylsilyl hydroxyethyl pybox) ligand has been successfully developed. Cheap and readily available chiral Lewis acid based on zinc salt have been used as promising catalyst for the reduction of aryl ketones under mild condition at room temperature leading to chiral alcohols in excellent yields and good to high enantioselectivities (up to 85% ee).
Molenda, M.; Baś, S.; El-Sepelgy, O.; Stefaniak, M.; Mlynarski, J.
Chemistry of Pyruvate Enolates: anti-selective Direct Aldol Reaction of Pyruvate Ester with Chiral Aldehydes Promoted by Dinuclear Zinc Catalyst
Adv. Synth. Catal. 2015 357 (link to page)
Chiral dinuclear zinc complex can effectively catalyse the direct aldol reactions of pyruvic acid ester with various chiral sugar aldehydes, thus functionally mimicking the pyruvate-dependent type II aldolases. Application of sterically hindered aryl esters allows for elusive aldol reaction of pyruvate donor with controlled anti-selectivity en route to the short and efficient synthesis of 3-deoxy-2-ulosonic acids. Pyruvic acid ester is here used as chemical equivalent of phosphoenolpyruvate (PEP) in imitation of the synthetic principle used in nature. Presented biomimetic methodologies use enol formation for the highly efficient and flexible formation of various C6-C9 ulosonic acids. Particularly, efficient and concise syntheses of 3-deoxy-D-erythro-hex-2-ulosonic acid (KDG, overall 50% yield), 3-deoxy-D-ribo-hept-2-ulosonic acid (DRH, overall 53% yield) and 3-deoxy-D-glycero-D-talo-non-2-ulosonic acid (4-epi-KDN, overall 78% yield) were described. Direct efficient application of pyruvic esters does not require additional damasking steps and thus surpass previously methodologies utilising masked pyruvic synthons such 2-acetylthiazole and pyruvic aldehyde dimethyl acetal.