Nat. Commun. 2022, 13, 2335.
A modular and efficient method for constructing angular tri-carbocyclic architectures containing quaternary carbon center(s) from 1,3-dicycloalkylidenyl ketones is established. Substitution with R1 and R2 at the 4πe-system with electron-donating group favors this reaction, while that with electron-withdrawing group or proton disfavors. The electron-donating group as R1 directs the initial ring expansion at its own site, while the p-π- or n-π- associated substituent as R2 favors selectively the later ring expansion near its location because of the beneficial maintenance of an original conjugated system. The stereoselectivity has proved to be governed by either the steric effect of R3 and R4 at the expanded rings, or the migration ability of the migrating atom. Density Functional Theory calculation suggests the initial Nazarov cyclization would be the rate-determining step. It features high selectivity, mild conditions and convenient operation, wide scope (50 examples), up to 96% yield. A racemic total synthesis of the natural (±)-waihoensene is realized in 18 steps by use of this methodology.
In 2015, we developed an asymmetric tandem Nazarov cyclization/semipinacol rearrangement reaction, providing a key method for synthesis a series of chiral spiro[4.4]-nonane-1,6-diones with quaternary carbon center(s). (J. Am. Chem. Soc., 2015, 137, 8344-8347).
