The interesting yet poorly discovered potential of the cis-� geometry of chiral metal complexes in asymmetric catalysis has been exemplified by new entries in chromium-mediated chemistry; the derivatives of TBOx ligand have been successfully used in asymmetric Nozaki-Hiyama propargylation of aldehydes, which allowed preparation of a range of homopropargyl alcohols with up to 93% ee. A novel partially reduced H8-TBOx ligand was developed, which appeared to be superior to the parent system in the context of enantiocontrol. Compromise of enantioselectivity associated with the background process was detected, which was successfully overcome by the introduction of cobalt porphine co-catalysts (conventional cobalt additives appeared inefficient). TBOxCrCl was also used in the first example of enantioselective alkynylation of aldehydes with iodo- and bromoacetylenes (with cobalt co-catalysis being beneficial for the latter group of substrates). A range of propargyl alcohols were obtained with up to 92% ee.

Preparation of chiral propargyl and homopropargyl alcohols via Nozaki-Hiyama type reactions mediated by chromium complexes of TBOx family

243rd National Meeting (2012)

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