Abstract Several B-allyl derivatives of 9-borabicyclo [3.3. 1] nonane (9-BBN) were prepared either by the allylation of B-methoxy-9-BBN with allylic aluminum re-agents or by the monohydroboration of certain dienes and allenes with 9-BBN. The 1 H NMR spectra of these derivatives were examined at various temperatures, revealing the presence of either permanent allylic rearrangements or cistrans isomerizations about the allylic double bond. ...