Development of New Synthetic Reactions by Use of Acylzirconocene Complexes

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Nucleophilic reactions of acylzirconocene chloride and alkenyl zirconocene chloride complexes under a variety of catalytic conditions have been investigated. Direct access of α-amino ketone derivatives through reaction of acylzirconocene chlorides with N-benzylideneaniline derivatives in which acylzirconocene chlorides react as an "unmasked" acyl anion donor, was carried out under Yb(OTf)_3/TMSOTf-catalyzed conditions. The same above reactions were also carried out with the use of Bronsted acid as a catalyst in place of Yb(OTf)_3/TMSOTf. The operationally simple three-component reaction comprised of aldehyde, aniline and acylzirconocene chloride affords α-amino ketone derivatives essentially in the absence of a catalyst. Acylzirconocene chloride complex reacts with ω-unsaturated α,β-enones and -ynones under Pd-Me_2Zn(Me_2AlCl) catalyzed conditions to give stereoselectively bicyclo[3.3.0]compounds. The 1,4-conjugated addition of alkenylzirconocene chloride complexes to α,β-enones, α,β-enoic acid esters, and α,β-enoic acid amides can be efficiently achieved by the use of [RhCl(cod)]_2 catalyst. A high diastereoselectivity was obtained through the reaction of α,β-enoic acid amide derived from Oppolzer's sultam and 2-butenoyl chloride, while the use of Evans' chiral oxazolidinone as a chiral auxiliary in place of Oppolzer's sultam gave a poor diastereoselectivity. [RhCl(COD)]_2 (2mol%)-catalyzed reactions of alkenylzirconocene chloride complexes to N-Ts, -PO(OEt)_2 and COOR aldimine derivatives also proceeded efficiently in dioxane at room temperature to give allylic amine derivatives in excellent yields. This was the first example of the catalytic addition reactions of alkenylzirconocene chloride complexes to aldimine derivatives.