Olefin-Methathese. XXII. Metathese von carbonyl-geschuetztem Allylaceton mit Monoolefinen an zinnalkylaktiviertem Re2O7/Al2O3

Article abstract of DOI:10.1016/0022-328X(89)87141-4

Olefin metathesis of allylacetone usually proceeds with little conversion.After the carbonyl group is protected by (i) silylation with ClSi(CH3)3 to give silylenolethers or (ii) by acetalisation with 1,2-ethanediol to the 1,3-dioxane derivative the reactivity increases significantly in the homometathesis reaction as well as in the co-metathesis with mono-olefins.Using Re2O7/Al2O3 + Sn(CH3)4 as catalyst the metathesis of allylacetone as its silylenolether or as 1,3-dioxolane proceeds with conversions of 46-53percent while the reaction of unprotected ketone only leads to a conversion of 14percent.Co-metathesis with the double-molar amount of symmetrical internal olefins (4-octene, 5-decene, 7-tetradecene, 9-octadecene) 75-90percent of the protected ketone is converted to give mainly the chain-prolonged silylenolethers or the 1,3-dioxolanes.Allylacetone silylated on a preparative scale was subjected to co-metathesis with 4-octene using MoO3-Re2O7/Al2O3 + Sn(CH3)4 as catalyst.After elimination of the protecting group the perfume substance 5-nonene-2-one was obtained in 61percent yield.