Synthesis of C₆F₅-Substituted Aminoethanols via Acetate Ion Mediated C₆F₅-Group Transfer Reaction

Abstract

A new approach for the synthesis of N-(pentafluorophen­ylmethyl)aminoethanols is developed. The method includes alkyl­ation of imines with 2-tris(pentafluorophenyl)silyloxyethyl triflate, prepared from ethylene oxide and (C₆F₅)₃SiOTf, to give 2-silyloxyethyliminium ions. Their treatment with sodium acetate induces C-C bond formation proceeding as transfer of the C₆F₅ group from the five-coordinate silicate intermediate to the iminium center.

Key words

silicon - hypercoordination - amino alcohols - imines - tris(pentafluorophenyl)silyl derivatives

References

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8

When N-methyl-C-phenylimine (2a) was combined with (C₆F₅)₃SiOTf in CDCl₃ no silyl iminium ion was observed (¹H, ¹⁹F NMR control). Correspondingly, it is believed that silyl iminium ion from 2b and (C₆F₅)₃SiOTf is formed in small equilibrium concentration.

9

In the absence of pyridine lower yields of 4 were achieved, presumably owing to oligomerization of ethylene oxide by traces of triflic acid.

15

NaOAc is insoluble in THF. However, it dissolves in reaction mixture as C₆F₅ group transfer occurs, thereby allowing for convenient monitoring of reaction progress.

16

Crystallographic data (excluding structure factors) have been deposited with the Cambridge Crystallographic Data Centre, CCDC 275041 (for 4) and 275042 (for 3c) and are available free of charge at CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [fax: [phone] or e-mail: [e-mail]].