Olefin-Metathese: XXII. Metathese von carbonyl-geschütztem Allylaceton mit Monoolefinen an zinnalkylaktiviertem Re2O7/Al2O3

Abstract Olefin metathesis of allylacetone usually proceeds with little conversion. After the carbonyl group is protected by (i) silylation with ClSi(CH 3 ) 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 cometathesis with mono-olefins. Using Re 2 O 7 /Al 2 O 3 + Sn(CH 3 ) 4 as catalyst the metathesis of allylacetone as its silylenolether or as 1,3-dioxolane proceeds with conversions of 46–53% while the reaction of the unprotected ketone only leads to a conversion of 14%. Co-metathesis with the double-molar amount of symmetrical internal olefins (4-octene,5-decene,7-tetradecene,9-octadecene) 75–90% 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 MoO 3 -Re 2 O 7 /Al 2 O 3 + Sn(CH 3 ) 4 as catalyst. After elimination of the protecting group the perfume substance 5-nonene-2-one was obtained in 61% yield.