Allylbenzene cross-metathesis

An alternative approach to phosphine-free ruthenium precatalysts is based on pyridine complex 70 [48], which has been established by Grubbs et al. as a valuable precursor for other mixed NHC-phosphine complexes (cf. Scheme 15). Complex 70 is only moderately active in the cross metathesis of allylbenzene... 

Figure 7 Cross metathesis of allylbenzene and CDAB with common metathesis catalysts. Adapted from [22],...

Scheme 7 Cross metathesis of allylbenzene and acrylonitrile with catalysts bearing N-aryl, N -alkyl NHCs...

In a subsequent report, the CAAC-based metathesis catalysts were examined for selectivity in the formation of Z E olefins, as well as their activity for ethenolysis [12]. Both of these processes require kinetic selectivity to produce the thermodynamically less-favored Z and terminal olefins, respectively. It was discovered that the CAAC catalysts displayed improved conversion to the Z olefin EIZ= 1.5—2.5 after 70% conversion) for the cross metathesis of cis-l,4-diacetoxy-2-butene with allylbenzene, relative to that observed using the classical NHC- and phosphine-based systems ElZ = 3-4) at comparable conversion (Scheme 4.3). 

Scheme 4.3 Cross metathesis of c s-1,4-diacetoxy-2-butene with allylbenzene.

The kinetic selectivity of the CAAC-based catalysts was investigated by probing the EjZdiastereoselectivity in the cross-metathesis of cA-l,4-diaceto-2-butene with allylbenzene (Equation (5.4)). Compared to the commercially available Grubbs catalysts, 66-68 afforded lower EjZ ratios (3 1 at 70%... 

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