Cobalt catalysis Diels-Alder reactions

The application of alkynyl boron derivatives in cobalt-catalyzed Diels-Alder reactions was used by Hilt et al. for the synthesis of boron-functionalized cycloadducts such as 41, generated from 17 and isoprene under cobalt catalysis (Scheme 13.21). In a four-component reaction sequence, 41 could be converted in a thermal Diels-Alder reaction with dienophiles, such as A-phenylmaleimide, to form the tricyclic product 42 [26],... 

In the previous section efficient catalysis of the Diels-Alder reaction by copper(II)nitrate was encountered. Likewise, other bivalent metal ions that share the same row in the periodic system show catalytic activity. The effects of cobalt(II)nitrate, nickel(II)nitrate, copper(II)nitrate and zinc(ll)nitrate... 

Lewis-acid catalysis is effective in intermolecular as well as intramolecular /zomo-Diels-Alder reactions. Thus, complex polycyclic compounds 93 have been obtained in good yield by the cycloaddition of norbornadiene-derived dienynes 92 by using cobalt catalyst, whereas no reaction occurred under thermal conditions [91] (Scheme 3.18). 

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