Uncatalyzed, highly stereoselective addition of α-morpholinostyrene to 3-nitro-2-(trihalomethyl)-2H-chromenes. Synthesis of trans–cis- and trans–trans-3-nitro-4-phenacyl-(2-trihalomethyl)chromanes

Add time:08/22/2019    Source:sciencedirect.com

Reactions of 2-R-3-nitro-2H-chromenes (R=CF3, CCl3, Ph) with α-morpholinostyrene in acetonitrile proceed diastereoselectively to give mainly trans–cis-2,3,4-trisubstituted chromane enamines at room temperature and trans–trans-chromane enamines at 60 °C as a result of nucleophilic addition at the C-4 atom of the chromene system. Acid hydrolysis of these compounds proceeded with retention of the configuration of the pyran ring and gave 4-phenacylchromanes. The stereochemistry of the products was established by X-ray diffraction analysis.

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