Catalytic Ring Expansions of Cyclic Alcohols Enabled by Proton-Coupled Electron Transfer
We report here a catalytic method for the modular ring expansion of cyclic aliphatic alcohols. In this work, proton-coupled electron transfer activation of an allylic alcohol substrate affords an alkoxy radical intermediate that undergoes subsequent C-C bond cleavage to furnish an enone and a tethered alkyl radical. Recombination of this alkyl radical with the revealed olefin acceptor in turn produces a ring-expanded ketone product. The regioselectivity of this C-C bond-forming event can be reliably controlled via substituents on the olefin substrate, providing a means to convert a simple N-membered ring substrate to either n+1 or n+2 ring adducts in a selective fashion.
Zhao, Kuo,Yamashita, Kenji,Carpenter, Joseph E.,Sherwood, Trevor C.,Ewing, William R.,Cheng, Peter T. W.,Knowles, Robert R.
AN EFFICIENT SYNTHESIS OF 2-SUBSTITUTED 3,3-DIMETHYLCYCLOHEXAN-1-ONES. A SIMPLE SYNTHETIC ROUTE TO PODOCARPA-8,11,13-TRIENE INTERMEDIATES.
2-Substituted 3,3-dimethylcyclohexan-1-ones are conveniently prepared from the respective 2-substituted 3-methylcyclohex-2-en-1-ones through boron trifluoride-ether-mediated conjugate addition of a methyl group with lithium dimethylcuprate and those incorporating 2β-phenylethyl substituents have been further transformed to podocarpa-8,11,13-triene intermediates in excellent yields.
Banik, Bimal K.,Chakraborti, Asit K.,Ghatak, Usha Ranjan
p. 3391 - 3397
(2007/10/02)
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