On the Reaction of (Dibromomethyl)lithium with Bicyclic and Tricyclic Ketones

Article abstract of DOI:10.1021/jo00072a037

Many literature examples show that the reaction of a simple cyclic ketone with (dibromomethyl)lithium at -78 deg 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.The product ratios obtained in all of these reactions seem to be determined by the steric interactions in 33 between the alkoxide and dibromomethyl groups and the hydrogens that are syn to them at the carbons which are β to the original carbonyl carbon.As these steric interactions increase, the proportion of α-bromo aldehyde in the product mixture increases.If 33 obtained from any cyclic ketone is warmed to 10 deg C before it is hydrolyzed, then the only product isolated is the α-bromo aldehyde.