Catalysis Involving Metalacycles:

Late tranisition metals offer an opportunity to activate molecules for new bond formations under mild conditions. With appropriately designed substrates, one can envision accessing metalacyclic intermediates, which offer the distinct advantage of sp3-hybridized C-M bonds. We have developed catalytic anhydride cross-coupling reactions utilizing this strategy. The use of chiral ligands on the metal allows control of the backbone stereochemistry in the product via desymmetrization reaction(JACS 2002, 174; JACS 2004, 10248; JACS 2005, 247).

We have further extended this concept: metalacycles such as those above may be induced to extrude CO to generate a ring-contracted metalacycle. We have found that such intermediates undergo cross-coupling with organozinc reagents(JACS 2003,10498).

A complementary access to five-membered metalacycles involves the metal-mediated cycloaddition of alkenes and carbon dioxide. This strategy would convert a ubiquitous, widely-available greenhouse gas into value-added organic products. As a step towrads this goal, we have succeeded in utilizing isocyanates as CO2 surrogates in catalyzed cycloaddition reactions that form indolizidine and quinolizidine systems(JACS 2006, 2782; JACS 2006).