A new synthetic route to D3-trishomocubanone and oxa- D3-trishomocubane derivatives has been established by the rearrangement approach. A remotely located methyl substituent in the six-membered ring contributed to the acid-catalyzed rearrangement of the cage dione in an unusual fashion. This rearrangement approach provided an attractive route to extended D3-trishomocubanes, which are not accessible by the conventional multistep synthetic sequence. For the first time, two phenyl groups were incorporated from the solvent into the strained trishomocubane skeleton in an unprecedented manner via carbocation-mediated rearrangement with the aid of BF3·OEt2. Interestingly, an oxa-bridged trishomocubane skeleton was also formed during acid-promoted rearrangement.