Approaches to substitute the chiral platform chemicals levoglucosenone and Cyrene
with aryl and alkylthiols have been developed via the α-haloketones. Substitution
of the 3-chloroalkene was catalyzed by Lewis acids, with the tropylium cation showing
excellent activity and yield. When thiolate was replaced with methoxide, an alkoxyoxirane
could be isolated, suggesting an analogous mechanism for the thiol substitution reaction.
Substitution of the 3-bromo derivative of Cyrene with thiolate nucleophiles proceeded
with retention of configuration in high yield, with an intermediate oxirane also demonstrated
when using methoxide. Computed LUMO energies for the α-haloketones support pathways
dependent on the type of halogen, with large contributions at the carbonyl, and a
sterically inaccessible σ* orbital due to the bicyclic ring system.
Keywords
Levoglucosenone - Tropylium - Oxirane - Cyrene - Thiols - Domino reaction
