Quinoline Alkaloids. Synthesis of Khaplofoline, Ribalinine, and Flindersine

Pyranoquinoline alkaloids, which possess inter­ esting pharmacological properties are known [1, 2] to occur in the plant family Rutaceae. The alka­ loids, khaplofoline (1) and ribalinine (2), isolated respectively from Haplophyllum foliosum (Vved) [3] and Balfourodendron riedelianum [4], members of the rutaceae, are structurally proven to be of pyrano [2,3-b]quinoline systems. Several reports have appeared in the literature for the synthesis of 1 [3,5-9] and 2 [10-12], but the yields of 1 and 2 in these attempts were not quite appreciable and are often attended by the formation of their isomeric products. 0 R2 1: R1 = R2 = H 2 : R1 = CH3; R2 = OH I R1