Synthesis of Functionally Substituted Olefins

The metathesis of olefins bearing functional groups provides potential routes to many valuable compounds. Metathesis catalysts, most of which contain a Lewis acid, are unfortunately poisoned by polar and basic compounds. As yet, only a few catalytic systems have proved to be active in metathesizing functionalized alkenes. In the homogeneous disproportionation of these substrates, the catalytic combination WCl —Sn(CH3)4 is still the best known [63]. In addition to its well known application in the conversion of unsaturated oxygen containing olefins, such as fatty acid esters and unsaturated ethers, its effectiveness for the homogeneous metathesis of unsaturated amines has also been described [64]. 

In fact, heterogeneous catalysts, such as ReOy—AI2O3 promoted by a small amount of an alkyltin compound, are better than homogeneous ones. This heterogeneous system is very active and selective in the metathesis of unsaturated esters [65]. 

At 50 C a conversion of 51% was reached within 1 h with very high selectivity (99%) using a molar ratio of ester/Re/Sn of 219/25/1. It was also reported that the catalyst Re207—AI2O3 alone showed no activity for the metathesis of polar compounds [65]. 

Of great potential value is the cometathesis of various unsaturated esters with ethylene to produce a,co-unsaturated esters. Thus, methyl-9-decenoate, a key intermediate in the synthesis of 0x0 ra 5-9-decenoic acid, was obtained by co-metathesis of ethylene and methyl oleate with two different catalyst systems, viz. WCl —(CH3)4Sn and Re207 AI2O3— (CH3)4Sn . Both catalyst systems show good activity at 70 C, the latter even at room temperature [66]. This substance is a honey bee phenomone. 

Allylethylether could be metathesized with the same system at 20 C. After 6 h, a conversion of 40% with a selectivity of 98% was obtained [67]. 

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