Intramolecular imino Diels-Alder reaction of a 3-vinyl indole: Applicationto a total synthesis of (+/-)-eburnamonine

The intramolecular [4 + 2] cycloaddition of imine 1 has been examined under a variety of conditions including thermal; catalysis by acid, lithium cati on, and Florisil; and the use of 5.0 M lithium perchlorate in diethyl ether . Cycloadduct 2 was transformed into (+/-)-eburnamonine 3 using acid cataly sis. Substrate 1 was prepared by coupling indole-3-carboxaldehyde 7 with th e activated p-nitrophenyl ester 9. Subsequent methylenation of 10 gave rise to 11, which upon exposure to fluoride ion provided imine 1.