Reactions of thianthrene cation radical tetrafluoroborate with aldehydes: formation of α-(5-thianthreniumyl)aldehyde tetrafluoroborates – a facile synthesis of α-ketols through Lobry de Bruyn–van Ekenstein rearrangement

Abstract

Reactions of thianthrene cation radical tetrafluoroborate with aldehydes, namely, butanal, pentanal, hexanal, heptanal, octanal, nononal, decanal, undecanal, dodecanal, tridecanal, and 3-phenylpropanal, led to the formation of α -(5-thianthreniumyl)aldehyde tetrafluoroborates (13a–k). Adducts (13a–k) are unstable and are converted to the corresponding hydrates (14a–k) when exposed to moisture or by deliberate addition of water to their solutions. Adducts (13a–k) and their hydrates (14a–k) were characterized with ¹H, ¹³C, and DEPT NMR spectroscopy. Interestingly, when solutions of adducts (13a–k) in acetonitrile were stirred with activated alumina, facile conversion to α -ketols (15a–k) occurred. It is proposed that the formation of α -ketols (15a–k) occurred through the Lobry de Bruyn–van Ekenstein rearrangement from the initially formed α -hydroxyaldehydes. α -Ketols 15a–j were isolated in good yield and their identities were confirmed with NMR spectroscopy.

Keywords:

• aldehydes
• thianthrene cation radical
• α-ketols

Acknowledgements

We thank the Welch Foundation for support (Grant D-0028) and Mr David W. Purkiss for the 500-MHz NMR spectroscopy.