Synthesis of Isopentenyiated 4-Hydroxy- 3-Methoxycoumarins and ω-Methyl-ω-Desacetyl Ripariochromene-B

Abstract

Abstract

Ω-Methoxyresacetophenone (5) reacted with either 3-methyl-but-2-enyl bromide in the presence of methanolic potash or with 2-methylbut-3-en-2-ol in the presence of boron trifluoride etherate to yield the same mixture of the 3-(6) and 5-(7)(3-methylbut-2-enyl) derivatives but in different proportions. In the former method, the 3-isomer (6) predominantes, whereas in the latter case the 5-isomer (7) does. The structures (6) and (7) and those of their methyl ethers (8 and 12) and 2,2-dimethylchroman derivatives (9, 10 and 11, 13) have been established by their NMR spectra. Both (6) and (7) have been converted into the corresponding 2,2-dimethylpyran derivatives (14 and 15) as established by their NMR spectra. The corpound (15) is the ω-methyl-ω-desacetyl derivative of riyariochromene-3 isolated from the Australian plant Eupatorium riparium Regel. (7), (14) and (15) have all been converted into