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.

Abstract 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.