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Useful Asymmetric Organoligands for [3+2] Cycloaddition
No.156(January 2013)
IAP (1) and PyBidine (2) are asymmetric organoligands developed by Arai et al. The asymmetric organoligand 1 is found by using a novel high-throughput screening system1) for analyzing the asymmetric induction with circular dichroism as a detector.2) 2 is an asymmetric organoligand having two chiral imidazolidine moieties.3) The structure of an imidazoline, which is usually used as an N-heterocyclic ligand, is nearly planar, while 2 has imidazolidine moieties as ligands instead of imidazoline moieties, which affords a chiral asymmetrical field because of steric hindrance of sp3 carbon on the chiral imidazoline ligand
A copper(I) complex of 1 is highly effective in asymmetric Henry reactions and asymmetric Friedel-Crafts alkylations and the desired products are given in high enantiomeric excess.2) On the other hand, a complex of 2 and copper(II) acts as a catalyst of an asymmetric Mannich reaction.4) Furthermore, asymmetric [3+2]cycloaddition of iminoesters with alkenes can be performed by using the nickel(II) complex of 1, 5) or copper(II) complex of 23) and pyrrolidine cycles are formed with high enantioselectivities. In a case using 1 as a ligand, exo' product is formed, and in a case of 2, the endo one is formed each with high enantioselectivities.
References
- 1)Direct monitoring of the asymmetric induction of solid-phase catalysis using circular dichroism: diamine–CuI-catalyzed asymmetric Henry reaction
- 2)A library of chiral imidazoline–aminophenol ligands: discovery of an efficient reaction sphere
- 3)Chiral bis(imidazolidine)pyridine−Cu(OTf)2: catalytic asymmetric endo-selective [3+2] cycloaddition of imino esters with nitroalkenes
- 4)syn-Selective asymmetric Mannich reaction of sulfonyl imines with iminoesters catalyzed by the N,N,N-tridentate bis(imidazolidine)pyridine (PyBidine)–Cu(OTf)2 complex
- 5)Catalytic asymmetric exo' -selective [3+2] cycloaddition of iminoesters with nitroalkenes
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