Nickel Catalysis: Synergy Between Method Development and Total Synthesis

Accounts of Chemical Research 48(5), 1503-1514, DOI: 10.1021/acs.accounts.5b00064

Nickel(0) catalysts have proven to be powerful tools for multicomponent coupling reactions in our laboratories over the past 15 years. This interest was originally sparked by the ubiquity of allylic alcohol motifs in natural products, such as (−)-terpestacin, which we envisioned assembling by the coupling of two π components (alkyne and aldehyde) with concomitant reduction. Mechanistic investigations allowed us to elucidate several modes of controlling the regioselectivity and stereoselectivity in the oxidative cyclization, and these insights enabled us to leverage combinations of alkenes and phosphine ligands to direct regioselective outcomes. The initial success in developing the first intermolecular reductive alkyne−aldehyde coupling reaction launched a series of methodological investigations that rapidly expanded to include coupling reactions of alkynes with other electrophilic π components, such as imines and ketones, as well as electrophilic σ components, such as epoxides. Aziridines proved to be more challenging substrates for reductive coupling, but we were recently able to demonstrate that cross-coupling of aziridines and alkylzinc reagents is smoothly catalyzed by a zero-valent nickel/phenanthroline system. Moreover, the enantioselective alkyne−aldehyde coupling and the development of novel P-chiral ferrocenyl ligands enabled the total synthesis of (−)-terpestacin, amphidinolides T1 and T4, (−)-gloeosporone, and pumiliotoxins 209F and 251D