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This is a Working Paper and the author(s) would welcome any comments on the present text. Citations should refer to a Working Paper of the International Monetary Fund. The views expressed are those of the author(s) and do not necessarily represent those of the Fund WP/97/l2

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2,6-Dimethyl-5-heptenal (3) and 5-octenal (24) undergo concerted ene reactions with 1 equiv of Me2AlCl and cation-olefin cyclizations with 2 equiv of Me2AlCl, MeAlCl2, or EtAlCl2 to give a zwitterion which reacts to give several products including an ene adduct. 3,7-Dimethyl-6-octenal ( 12) and (Z)-and (E)-6-nonenal (18 and 19) undergo only ene reactions with all catalysts. The enones 31 and 32 formed by reaction of 3 and 12 with acetonylidenetriphenylphosphorane react analogously to 3 and 12 in the presence of Lewis acid. The effect of ring size on the nature of these cyclizations is explained on the basis of thermodynamic and kinetic data.

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