AbstractThe addition of acrolein to norcamphene leads to anexo‐oxa spiro compound (Scheme 1, VIa). The correspondingendo‐isomer VIb can be obtained from norbornanone X and methoxybutenyne XIIIviathe sequence of reactions outlined in Scheme 2. Because the steric course in some crucial steps is known, theendostructure of VIb can be established.An alternative route leading to theexo‐oxa. spiro compound IXa, starting with norbornanone is given in Scheme 3. Another route to predominantlyendo‐oxa compounds from norbornanone is given in S