This study reports the cross-metathesis of bicyclic β-pinene, acyclic cis-3-
methylpent-2-ene terpenes and the natural rubber with functionalized olefins, a route for
the functionalization of the carbon-carbon double bond of natural products to obtain aliphatic
unsaturated esters. The production of unsaturated esters from β-pinene and cis-3-
methylpent-2-ene via cross-metathesis reaction with dimethyl maleate and diethyl maleate
in the presence of the ruthenium-alkylidene [Ru(Cl)2(=CHPh)(1,3-bis(2,4,6-
trimethylphenyl)-2-imidazolidinylidene)(PCy3)] (I), [Ru(Cl)2(=CH(o-isopropoxyphenylmethylene))(
1,3-bis(2,4,6-trimethylphenyl) -2-imidazolidinylidene)] (II) and rutheniumvinylidene
[RuCl2(=C=CH(p-C6H4CF3))(PCy3)2] (III) was carried out. Results showed that
the reaction of β-pinene with diethyl maleate using II catalyst produced unsaturated esters
with 43 % selectivity. I and III catalysts showed low activity toward the cross-metathesis of β-pinene and dimethyl
maleate. A survey about the cross-metathesis of acyclic cis-3-methylpent-2-ene with diethyl maleate by
II catalyst was also studied. The formation of ethyl but-2-enoate and ethyl-3-methylpent-2-enoate products was
highly selective by 63 %. The unsaturated esters formation from the cross-metathesis degradation of natural
rubber (99.9 % cis-polyisoprene) with dimethyl maleate and diethyl maleate using I-III catalysts was accomplished
as well. I and II catalysts showed high activity in the degradation of natural rubber with diethyl maleate
to produce the low molecular weight of oligomers unsaturated ester products (Mn = 1 x 103 g mol-1) with isoprene
units of m = 10 – 27 and yields ranging from 68 to 94 %.
Metathesis Transformations of Natural Products: Cross-Metathesis of Natural Rubber and Mandarin Oil by Ru-Alkylidene Catalysts
