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