Olefin cross

Olefin cross metathesis starts to compete with traditional C=C bondforming reactions such as the Wittig reaction and its modifications, as illustrated by the increasing use of electron-deficient conjugated alkenes for the ( )-selective construction of enals and enoates. 

The alkene groups in TsICH = CH2]s have allowed a wider variety of chemistry to be carried out than for either TsHs or TsPhs. For example, Feher s group have prepared a variety of unsaturated POSS molecules via olefin cross-metathesis... 

The reactivity of T8[OSiMe2CH = CH2]s is, as expected, often similar to that described for T8[CH = CH2]s. Initially, Feher et al. performed olefin cross-metathesis... 

The olefin cross metathesis (CM) can be described as the intermolecular metathesis of alkylidene fragments between two different olefins [133]. It can be farther divided into three main subtypes cross metathesis, ring opening cross metathesis (ROCM) and enyne cross metathesis (ECM) (Scheme 3.9). 

Scheme 5.13 Cleavage of an octenediol linker by olefin cross-metathesis to yield NPG63.69...

In general, electronically mismatched systems undergo cross metathesis more effectively, see New Approaches to Olefin Cross-Metathesis, H.E. Blackwell, D.J. O Leary, A.K. Chatterjee, et al, J. Am. 

Synthesis of Trisubstituted Alkenes via Olefin Cross-Metathesis, A. K. Chatter-JEE, R.H. Grubbs, Org. Lett. 1999, 1,... 

McNaughton, B. R. Bucholtz, K. M. Camaano-Moure, A. Miller, B. L. Self-selection in olefin cross metathesis The effect of remote functionality. Org. Lett. 2005, 7, 733-736. 

The use of menthol in the synthesis of important synthons for optically active methyl branched insect pheromones is discussed briefly. Applications of olefin cross metathesis in production of commercial products, including insect pheromones has been discussed. ... 

As described above in Eq. 43, simple allylboronates can be transformed into more elaborated ones using olefin cross-metathesis. " Treatment of pinacol allylboronate 31 with a variety of olefin partners in the presence of Grubbs second-generation catalyst 142 smoothly leads to formation of 3-substituted allylboronates 143 as cross-metathesis products (Eq. 104). Unfortunately, these new allylic boronates are formed as mixtures of geometrical isomers with modest E/Z selectivity. They are not isolated but rather are treated directly with benzaldehyde to give the corresponding homoallylic alcohol products in good yields (Table A). 

Table A. Functionalized homoallylic alcohols from olefin cross metathesis and subsequent allylboration reactions with benzaldehyde...

Figure 9.13 Templated olefin cross-metathesis of two groups of olefins tethered to the two duplex strands.

M.M. Vasbinder, S.J. Miller, Synthesis of the Pro-Gly dipeptide alkene isostere using olefin cross-metathesis, J. Org. Chem. 67 (2002) 6240-6242. 

As olefin CM is a thermodynamically controlled intermolecular reaction, there are several inherent challenges toward achieving product selectivity. First and foremost, if a catalyst cannot distinguish between the two olefin crosspartners, a statistical mixture of products will result (Scheme 2). In this situation, one of the olefin cross-partners would need to be added to the reaction in excess to achieve a synthetically useful yield (e.g., 10 equiv. required to attain a 91% yield). 

The statistical distribution scenario in Scheme 2 assumes that complete conversion of the starting terminal olefins is achieved and that any internal olefins formed over the course of the reaction react equally with the catalyst. However, in cases where low catalytic activities do not ensure complete conversion, CM reactions become increasingly difficult to execute, as the desired product must now be separated from a reaction mixture containing five distinct olefins. The use of excess olefin cross-partner compounds this problem by lowering the effective catalyst... 

As illustrated above, various possible alkylidene intermediates and numerous primary and secondary pathways are involved in olefin CM. To simplify selective reaction design, an empirical product selectivity model was recently developed by Grubbs and co-workers, in which some degree of orthogonality amongst olefin cross-partners was established by categorizing the relative capacity of olefins to homodimerize in the presence of a given metathesis catalyst. ... 

Scheme 4 Equilibria involved in olefin cross-metathesis.

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