KHSO₄-Mediated Condensation Reactions of tert-Butanesulfinamide with Aldehydes. Preparation of tert-Butanesulfinyl Aldimines

Abstract

Optically pure tert-butanesulfinyl aldimines 1 were ­prepared by direct condensation of chiral tert-butanesulfinamide 3 with aldehydes 2 in high yields in the presence of KHSO₄. The main advantage of KHSO₄ is that it is applicable to the condensation ­reactions of a variety of aldehydes, including electron deficient and electron rich (hetereo)aromatic aldehydes, as well as aliphatic aldehydes.

Key words

tert-butanesulfinamide - aldehyde - tert-butanesulfinyl aldimines - potassium hydrogen sulfate - condensation

References

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8

General procedure: (S)-tert-Butanesulfinamide (1 mmol) was stirred with benzaldehyde (2 mmol) in toluene (10 mL) in the presence of KHSO₄ (2 equiv) for 24 h at 45 °C. KHSO₄ was then removed by filtration. The filtrate was concentrated to dryness. The residue was purified by flash chromato-graphy to afford (S)-tert-butanesulfinyl aldimine (1a) as a colorless liquid. [α]_D ²⁰ +105 (c 2.19, CHCl₃, Lit. [5] [10] [α]_D ²⁰ +104, CHCl₃). ¹H NMR and ¹³C NMR spectra were identical to that reported in the literature. [5] [10] The ee of synthesized aldimine 1, determined by HPLC analysis (Daicel Chiralcel OD column), was over 99%. [4] [5]