Enantioselective rhodium-catalysed addition of allylboron reagents to cyclic imines and enantioselective nickel-catalysed Michael additions of 2-acetylazaarenes to nitroalkenes
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Enantioselective Rhodium-Catalysed Addition of Allylboron Reagents to Cyclic Imines Rhodium-catalysed enantioselective allylation reaction of imines in the presence of chiral diene ligands has been investigated. Under the optimised conditions, cyclic imines provided homoallylic amines in high yield and excellent enantioselectivities. The reaction most likely proceeds via allylrhodium(I) intermediates, and represents the first rhodium-catalysed enantioselective nucleophilic allylation of π-electrophiles with allylboron compounds. Furthermore, the allylations display a strong preference for carbon–carbon bond formation at the more substituted terminus of the allyl fragment of the allyltrifluoroborate. To demonstrate the utility of the allylation products, representative manipulations were conducted. Enantioselective Nickel-Catalysed Michael Additions of 2-Acetylazaarenes to Nitroalkenes An enantioselective Michael addition of acylazaarenes with α-substituted β-nitroacrylates in the presence of a chiral Ni(II)–bis(oxazoline) complexes has been developed. A range of azaaryl nucleophiles were shown to react with a variety of nitroalkenes to construct highly functionalised Michael addition products which contain a stereogenic all-carbon quaternary stereocentre with moderate to high yields and enantioselectivities. A possible mechanism for this reaction has been proposed.