Diels-Alder Cycloadditions Using Nucleophilic 3-(p-Tolylthio)-2-pyrone. Regiocontrolled and Stereocontrolled Synthesis of Unsaturated, Bridged, Bicyclic Lactones
Captodative 3-(tolylthio)-2-pyrone (1) is shown to be reactive as a nucleophilic diene undergoing 2 + 4-cycloadditions with various electrophilic alkenes under sufficiently mild thermal conditions (/= 90 deg C) so that the initial bicyclic lactone adducts can be isolated on gram scale in moderate to very good yields (42-82percent) without loss of CO2.These bicyclic adducts are formed regiospecifically and often with excellent stereoselectivity.These Diels-Alder cycloadditions are the first examples of a captodative unsturated sulfide acting as an enophile.NMR data ((13)C) are presented correlating the electron density in the pyrone diene systems with their Diels-Alder reactivity, and some transformations of the bicyclic lactone adducts are shown to illustrate the value and versatility of these richly functionalized synthetic intermediates.
Posner, Gary H.,Nelson, Todd D.,Kinter, Chris M.,Johnson, Neil
p. 4083 - 4088
(2007/10/02)
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