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Highly Functionalized Cyclopentane Derivatives by Tandem Michael Addition/Radical Cyclization/Oxygenation Reactions.

Chemistry (Weinheim an der Bergstrasse, Germany) (2015-05-28)
Martin Holan, Radek Pohl, Ivana Císařová, Blanka Klepetářová, Peter G Jones, Ullrich Jahn
ABSTRACT

Densely functionalized cyclopentane derivatives with up to four consecutive stereocenters are assembled by a tandem Michael addition/single-electron transfer oxidation/radical cyclization/oxygenation strategy mediated by ferrocenium hexafluorophosphate, a recyclable, less toxic single-electron transfer oxidant. Ester enolates were coupled with α-benzylidene and α-alkylidene β-dicarbonyl compounds with switchable diastereoselectivity. This pivotal steering element subsequently controls the diastereoselectivity of the radical cyclization step. The substitution pattern of the radical cyclization acceptor enables a switch of the cyclization mode from a 5-exo pattern for terminally substituted olefin units to a 6-endo mode for internally substituted acceptors. The oxidative anionic/radical strategy also allows efficient termination by oxygenation with the free radical 2,2,6,6-tetramethyl-1-piperidinoxyl, and two C-C bonds and one C-O bond are thus formed in the sequence. A stereochemical model is proposed that accounts for all of the experimental results and allows the prediction of the stereochemical outcome. Further transformations of the synthesized cyclopentanes are reported.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Samarium(II) iodide solution, 0.1 M in THF, contains samarium chips as stabilizer
Sigma-Aldrich
Samarium(II) iodide, anhydrous, powder, ≥99.9% trace metals basis

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