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Abstract

The addition of acrolein to norcamphene leads to an exo-oxa spiro compound (Scheme 1, VIa). The corresponding endo-isomer VIb can be obtained from norbornanone X and methoxybutenyne XIII via the sequence of reactions outlined in Scheme 2. Because the steric course in some crucial steps is known, the endo structure of VIb can be established.

An alternative route leading to the exo-oxa. spiro compound IXa, starting with norbornanone is given in Scheme 3. Another route to predominantly endo-oxa compounds from norbornanone is given in Scheme 4.