Unsaturated carboxylic esters metathesis

Mo catalysts like 1 and 2 are also active in the metathesis of functionalized alkenes, such as unsaturated carboxylic esters. 

Table 1 shows some of the heterogeneous catalysts used for the metathesis of unsaturated carboxylic esters. These esters can be used as test substrates for functionalized olefin metathesis. 

Cp2TiMe2 and WOCI4 or WCle is an effective catalytic system for the metathesis of olefins. Importantly, the system tolerates carboxylic esters, and this enabled it to be used to effect the key steps in syntheses of civetone and other macrolides. Unsaturated ketones or acetals are not suitable substrates. 

A different task was pursued by the CM of CsA with various maleates 339 [ 148]. The CM demanded in this case the highly active Hoveyda catalyst D, that exhibits potency not reached by the phosphine-containing catalysts C and E. Under the conditions given in Scheme 65, metathesis with maleates 339 led (E)-selectively to the a,/J-unsaturated ester derivatives 340 in high yield. Compounds 340 still demonstrated activity comparable to that of CsA and are thus potential soft drugs via esterase-mediated biotransformation to the corresponding inactive carboxylic acids 341. 

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