Synthetic and quantum mechanical studies into the N-heterocyclic carbene catalyzed (4 + 2) cycloaddition |
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Authors: | Ryan Sarah J Stasch Andreas Paddon-Row Michael N Lupton David W |
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Affiliation: | School of Chemistry, Monash University, Clayton 3800, Victoria, Australia. |
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Abstract: | 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. |
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