Studies Related to the Synthesis of Chroman- And Quinoline-Based Heterocycles

Chromans and quinolines can be found in the core structures of many biologically active natural products. Recognizing new and efficient ways to synthesize these useful compounds is vital to modern drug design. Calyxin I, Calyxin J and Epicalyxin J are three natural products that have been shown to have antiproliferative activity against two cancer cell lines. The core tetrahydropyranochromene ring system that is common among all three compounds was synthesized. The preferred diastereomer in this synthesis was the syn conformer, which was confirmed by a 2-D NOESY experiment. Theoretical MP2 calculations showed that a favorable pi-pi stacking interaction could be responsible for the diastereoselectivity. A two-step synthesis of tetrahydro-2Hurochromenones was achieved. This synthesis involved the cyclopropanation of 2H-chromenes using diazo compounds or iodonium ylides and a rhodium catalyst. In the presence of a Lewis acid, the cyclopropane intermediate underwent acid-catalyzed rearrangement to a gamma-lactone. The stereochemistry of the lactones was based on X-ray crystallography. Lactonization of 2H-chromenes could be important in the construction of larger flavonoids or biflavonoids in the future. 4-Arylquinolines and 2,4-diarylquinolines were produced using a [4+2] cycloaddition reaction as the key step in their synthesis. An array of N-aryl and N-protected 1-azadienes were constructed from their corresponding cinnamaldehydes or chalcones. A 1,4-dihydroquinoline cycloadduct was prepared from a [4+2] cycloaddition reaction of a 1-azadiene with benzyne. Among the N-protected cycloadducts, the N-tosyl derivatives were used to generate various quinolines. Also, a short synthesis of 3-O-methylviridicatin from one of the N-tosyl cycloadducts is presented