Polymer-supported chiral molybdenum

More complex heterocyclic structures have been synthesized efficiently and with high stereoselectivities using tandem AROM-RCM sequences [85] similarly, application of tandem AROM/CM to functionalized norbomenes affords enantio-pure highly functionalized cydopentanes [86]. A polymer-supported chiral molybdenum catalyst for enantioselective metathesis effidendy promotes ARCM (kinetic resolution as well as desymmetrization) and AROM reactions and can be recycled [87]. 

Hoveyda and Schrock attached (97a) to polymer via attached styrene groups yielding the first reported supported chiral molybdenum olefin metathesis catalyst, (290) (Scheme 27). Supported complex (290) is less active than (97a), but it gives similar ranges of ees for enantioselective transformations like desymmetrization. The catalyst is recyclable and, even though the conversions have eroded, the enantioselectivity is still relatively high. Table 14. 

Another metal-catalyzed microwave-assisted transformation performed on a polymer support involves the asymmetric allylic malonate alkylation reaction shown in Scheme 12.4. The rapid molybdenum(0)-catalyzed process involving thermostable chiral ligands proceeded with 99% ee on a solid support. When TentaGel was used as as support, however, the yields after cleavage were low (8-34%) compared with the corresponding solution phase microwave-assisted process (monomode cavity) which generally proceeded in high yields (>85%) [30],... 

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