ON THE REACTION OF (DIBROMOMETHYL)LITHIUM WITH BICYCLIC AND TRICYCLICKETONES

Many literature examples show that the reaction of a simple cyclic ket one with (dibromomethyl)-lithium at -78-degrees-C followed by low-temp erature hydrolysis of the resulting lithium alkoxide 33, gives the cor responding dibromomethyl alcohol. We have found that the reaction of a bicyclic or tricyclic ketone with (dibromomethyl)lithium under compar able conditions provides a dibromomethyl alcohol and/or an alpha-bromo aldehyde. The latter product appears to result from an intramolecular displacement reaction in 33 to give a bromo epoxide, which then rearr anges stereospecifically to the alpha-bromo aldehyde. The product rati os obtained in all of these reactions seem to be determined by the ste ric interactions in 33 between the alkoxide and dibromomethyl groups a nd the hydrogens that are syn to them at the carbons which are beta to the original carbonyl carbon. As these steric interactions increase, the proportion of alpha-bromo aldehyde in the product mixture increase s. If 33 obtained from any cyclic ketone is warmed to 10-degrees-C bef ore it is hydrolyzed, then the only product isolated is the alpha-brom o aldehyde