2021/08/05 by Sara Y. Howard, Michael J. Di Maso, Kristin Shimabukuro +6 · 1 citation
Biochemistry, Genetics and Molecular Biology · #Synthesis and Biological Activity #Marine Sponges and Natural Products #Phytochemical Studies and Bioactivities
paper · doi:10.1021/acs.joc.1c01163
openalex publication_date 2021/08/05 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
The mechanisms for the three- and four-component variants of the Castagnoli–Cushman reaction (CCR) have been investigated. A series of crossover experiments were conducted to probe the structure and reactivity of known amide-acid intermediates for the three- and four-component variants of the CCR (3CR and 4CR, respectively). Control experiments paired with in situ reaction monitoring with infrared spectroscopy for the 4CR align with a mechanism in which amide-acids derived from maleic anhydride can reversibly form free amine and cyclic anhydride. Although this equilibrium is unfavorable, the aldehyde present can trap the primary amine through imine formation and react with the enol form of the anhydride through a Mannich-like mechanism. This detailed mechanistic investigation coupled with additional crossover experiments supports an analogous mechanism for the 3CR and has led to the elucidation of new 3CR conditions with homophthalic anhydride, amines, and aldehydes for the formation of dihydroisoquinolones in good yields and excellent diastereoselectivity. This work represents the culmination of more than a decade of mechanistic speculation for the 3- and 4CR, enabling the design of new multicomponent reactions that exploit this novel mechanism.