Abstract
1,3-Dipolar cycloaddition of stabilized azomethine ylides generated in situ from isatins and proline to 3-nitro-2-phenyl-2-trifluoromethyl-2H-chromenes in i-PrOH proceeds stereoselectively at room temperature and leads to the formation of hexahydro-6H-spiro[chromeno[3,4-a]pyrrolizine-11,3'-indolin]-2'-ones with the cis arrangement of the trifluoromethyl group and the nitro group. A similar reaction with the participation of thiaproline-based ylides at 50°С leads to mixtures of diastereomeric tetrahydro-6H,9H-spiro[chromeno[3',4':3,4]pyrrolo[1,2-c]thiazole-11,3'-indolin]-2'-ones with a predominance of the cis- or trans-isomer. The stereochemistry of the obtained products was confirmed by the NOESY experiment and X-ray structural analysis.
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