Journal
JOURNAL OF ORGANIC CHEMISTRY
Volume 71, Issue 1, Pages 70-74Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jo051539o
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Diels-Alder reactions of 3-substituted cournarins 1a-g with methyl-1,3-butadienes 2a-c carried out in water alone and in CH2Cl2 under 9 kbar pressure are reported. In aqueous medium satisfactory results were obtained by operating at 150 degrees C, whereas under high pressure the cycloadditions were complete at 60-70 degrees C with excellent yields (85-95%). The reactions with isoprene (2b) always resulted in the exclusive formation of para cycloadducts, whereas with (E)-piperylene (2c) only ortho products were detected. The cycloaddition of 3-phenylsulfonylcoumarin (1a) with (E)-piperylene (2c) allowed the endo adduct to be obtained exclusively, whereas 3-carboxycoumarin (1b) reacted with 2c to give a mixture of the corresponding endolexo adducts in a 58:42 ratio in water and in a 45:55 ratio under high-pressure condition.
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