Bismuth Triflate as a Safe and Readily Handled Source of Triflic Acid: Application to the Oxa–Pictet–Spengler Reaction

Abstract

The oxa–Pictet–Spengler reaction with various aldehydes and β-arylethanol yields 1-substituted-isochromans in the presence of bismuth triflate as catalyst in good yields. The method was extended to O,O-acetals to afford the corresponding 1,1-disubstituted-isochromans in good yields. These studies also provide insights into the catalytic role of triflic acid generated upon hydrolysis of Bi(OTf)₃ by residual water. The low toxicity and easy handling of Bi(OTf)₃ by comparison with triflic acid make these procedures an attractive method to provide isochromans in good to excellent yields.

Keywords:

• β-Arylethanol
• bismuth triflate
• isochroman
• oxa–Pictet–Spengler
• triflic acid

ACKNOWLEDGMENT

The authors gratefully acknowledge the Ministère de l'Enseignement et de la Recherche Scientifique for financial support (B. B.).

Notes

^a Yields for the isolated product (characterized by ¹H, ¹³C NMR, and mass spectrometry).

^b Molecular sieves (MS) were activated at 150 °C on high vacuum.

^c 100 μL water (2.5% volume).

^a Yields for the isolated products (characterized by ¹H, ¹³C NMR, and MS).

^b Physical and spectral data are in accordance with the literature.

^a Yields for the isolated products (characterized by ¹H, ¹³C NMR, and MS).

^b 2 eq 2,2-dimethoxypropane were used.

^c Percent conversion observed by ¹H NMR.

^d Physical and spectral data are in accordance with the literature.