A new strategy for the synthesis of highly versatile cyclobutylboronates via the photosensitized [2 +2]-cycloaddition of alkenylboronates and alkenes is presented. The process is mechanistically different from other processes in that energy transfer occurs with the alkenylboronate as opposed to the other alkene. This strategy allows for the synthesis of an array of diverse cyclobutylboronates. The conversion of these adducts to other compounds as well as their utility in the synthesis of melicodenine C is demonstrated.
A modified Takemoto catalyst enabled the asymmetric Michael addition of carbazolones to 2-chloroacrylonitrile to afford 3,3-disubstituted carbazolones with excellent enantioselectivity. This method was successfully applied to total syntheses of three Kopsia alkaloids which featured an unprecedented Mn -mediated oxidative cyclization to create the caged ring system and a SmI -mediated reductive coupling as key steps.
A Ni-catalyzed silylacylation of alkenes is presented. The reaction combines alkenes, ClZnSiR 3 , and acid chlorides to provide rapid access to β-silyl ketones. Importantly, the method involves a [Ni]-SiR 3 complex as a catalytic intermediate, which is rarely described for three-component alkene functionalization. Finally, the synthetic utility of the products is demonstrated, and the mechanistic details are described.
Kopsinitarines A-E are complex octacyclic caged Kopsia alkaloids with strained cage skeletons and a unique cyclic hemiaminal bridge that makes total synthesis challenging. Herein, we disclose the first total synthesis of kopsinitarine E. The key synthetic features include a SmI 2-mediated radical cascade cyclization and a subsequent semi-pinacol rearrangement to install the key carbocyclic skeleton, a chemoselective hydrosilyl amide reduction to construct the hemiaminal ether bridge, and an intramolecular Mannich reaction to establish the highly strained cage system.
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