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Synthesis of Unsaturated Esters by Cross-Metathesis of Terpenes and Natural Rubber Using Ru-Alkylidene Catalysts

[ Vol. 23 , Issue. 12 ]

Author(s):

Araceli Martínez*, Mikhail A. Tlenkopatchev, Selena Gutiérrez, Manuel Burelo, Joel Vargas and Enrique Jiménez-Regalado   Pages 1356 - 1364 ( 9 )

Abstract:


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 %.

Keywords:

Cross-metathesis, β-pinene, natural rubber degradation, terpenes, unsaturated esters, ruthenium-alkylidene, functionalized olefins.

Affiliation:

Escuela Nacional de Estudios Superiores, Unidad Morelia, Universidad Nacional Autonoma de Mexico, Morelia, Michoacan, Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, Ciudad de Mexico, Facultad de Quimica, Universidad Nacional Autonoma de Mexico, Ciudad de Mexico, Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, Ciudad de Mexico, Instituto de Investigaciones en Materiales, Unidad Morelia, Universidad Nacional Autonoma de Mexico, Morelia, Michoacan, Centro de Investigacion en Quimica Aplicada (CIQA), Saltillo, Coahuila

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