The First Practical Additive-Free 1,4-Conjugated Alkylation of Fluoro­alkylated Electron-Deficient Olefins with Various Organozinc Reagents

Abstract

1,4-Conjugated alkylation of fluoroalkylated olefins with organozinc reagents, such as RZnI and R₂Zn, was conducted smoothly to give the corresponding products in moderate yields without the use of either transition metals or Lewis acids. This reaction protocol allows not only a wide range of alkyl groups but also electron-withdrawing groups to be incorporated as 1,4-conjugated adducts.

Key words

1,4-conjugated alkylation - organozinc reagents - tri­fluoromethyl - electron-deficient olefin

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• 8 The alkylzinc halides, RZnI, were prepared according to the reported procedure; see ref. 4b.
• 9 The prepared dialkylzinc reagents were used without the removal of LiCl. For the detailed preparation procedure, see the experimental section.
• 10 The lithium zincate, (n-Bu)₃ZnLi, was prepared by mixing 3 equiv of n-BuLi (1.6 M hexane solution) and 1 equiv of ZnCl₂ (1.0 M, Et₂O solution) at 0 °C for 30 min.
• 11 The reactivity of dialkylzinc reagents is: salt-free R₂Zn > in situ generated R₂Zn.
• 12 The control experiments were conducted as follows. The 1,4-conjugated additions to (E)-1-phenylbut-2-en-1-one or chalcone with Et₂Zn were attempted under the same conditions as given in Table 1, entry 2; however, a quantitative amount of the starting alkene was recovered in both cases (methods A and B).