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Synthetic and Quantum Mechanical Studies into the N-Heterocyclic Carbene Catalyzed (4 + 2) Cycloaddition
Ist Teil von
Journal of organic chemistry, 2012-01, Vol.77 (2), p.1113-1124
Ort / Verlag
Washington, DC: American Chemical Society
Erscheinungsjahr
2012
Link zum Volltext
Quelle
Alma/SFX Local Collection
Beschreibungen/Notizen
The N-heterocyclic carbene catalyzed (4 + 2) cycloaddition between α,β-unsaturated acid fluorides and TMS dienol ethers provides cyclohexene fused β-lactone intermediates stable below −20 °C. These can be intercepted reductively or with organolithium reagents to produce diastereomerically pure cyclohexenes (>20:1 dr) with up to four contiguous stereocenters. The mechanism has been investigated using theoretical calculations and by examining secondary kinetic isotope effects. Together these studies implicate the formation of a diastereomerically pure β-lactone intermediate by a stepwise (4 + 2) cycloaddition involving Michael addition, aldol cyclization, and lactonization.