On the reaction of (dibromomethyl)lithium with bicyclic and tricyclic ketones

Many literature examples show that the reaction of a simple cyclic ketone with (dibromomethyl)lithium at -78 o C, followed by low-temperature hydrolysis of the resulting lithium alkoxide 33, gives the corresponding dibromomethyl alcohol. We have found that the reaction of a bicyclic or tricyclic ketone with (dibromomethyl)lithium under comparable conditions provides a dibromomethyl alcohol and/or an α-bromo aldehyde. The latter product appears to result from an intramolecular displacement reaction in 33 to give a bromo epoxide, which then rearranges stereospecifically to the α-bromo aldehyde