ASYMMETRIC SEQUENTIAL MICHAEL ADDITION-N-HETEROCYCLIZATION REACTIONS INVOLVING CHIRAL IMINES

The reaction of chiral imines ent-14, 27, and 31 with alpha-chloroacry lonitrile 6, maleic anhydride 9, and citraconic anhydride 35 has been investigated. Addition of imine 27 to 6 furnished, after NaBH3CN-reduc tion of the crude product, the bicyclic derivative 28 as a single isom er. When the same protocol was applied to imine ent-14, a mixture of a dducts 29 and 30 was obtained. Addition of imine 31 to 6 gave the annu lated pyrrole 32. Condensation of imine 27 with maleic anhydride 9 aff orded compound 33 as a single isomer. Addition of imine ent-14 to citr aconic anhydride 35 led, after esterification of the crude product wit h CH2N2, to a mixture of adducts 36 and 37. The mechanism of these aza -annulations was discussed on the basis of the regio- and stereoselect ivities observed.