- Study of the Oxidative Cleavage Proposed in the Biogenesis of Transtaganolides/Basiliolides: Pyran-2-one Aromaticity-Mediated Regioselective Control and Biogenetic Implications
-
The synthetic feasibility of the oxidative cleavage: epoxidation of 7-O-geranylscopoletin followed by electrocyclic ring-opening, proposed in the biogenesis of transtaganolides/basiliolides is studied. Unlike the proposed pericyclic reactions, this pathway has not yet been addressed. Three synthetic strategies have been tested consisting of: i) Baeyer–Villiger oxidation of p-quinoids, ii) hydrolysis of quinone monoketals, or iii) direct fragmentation by using oxygen donors. Oxidation of the benzene ring of hydroxylated coumarins has been achieved using peroxyacids, but cleavage took place between undesired positions. The aromaticity conservation of the pyran-2-one cycle during oxidation is the controlling factor of these observed regioselectivities. The use of a 4,5-dihydroxy-2-methoxycinnamate model, in which the pyran-2-one ring does not exert influence on oxidation, has allowed the design of a synthetic sequence toward an analogue of the natural pyran-2-one isolated from Thapsia transtagana, key in the biogenesis. Mechanistic proposals for the obtained results as well as their biogenetic implications are raised.
- álvarez, José María,Jorge, Zacarías D.,Massanet, Guillermo M.
-
-
- High-selectivity preparation method for 7-methoxy-6/8-hydroxy coumarin
-
The invention provides a high-selectivity preparation method for 7-methoxy-6/8-hydroxy coumarin and belongs to the field of synthesis of natural medicines. The method comprises the steps of subjecting a catechol coumarin compound to a high-selectivity methylation reaction with a methylation reagent in a proper base catalyst added organic reaction system, so as to obtain a 7-hydroxyl mono-methylate, wherein the mole ratio of a base to the catechol coumarin compound is (2.0 to 7.0): 1, the mole ratio of the methylation reagent to the catechol coumarin compound is (1.0 to 3.0): 1, the temperature of the organic reaction system is 0 DEG C to 30 DEG C, and the reaction time is 1.0 to 5.0 hours. The method has the characteristics of simplicity in operation, moderate conditions, good selectivity, high yield and the like and can be applied to the preparation of mono-methylates of coumarin catechols with different types of substituents.
- -
-
Paragraph 0032; 0033; 0034
(2017/08/28)
-
- Regioselective Mono-O-alkylation of some Pyrocatechoxide Dianions
-
In dimethyl sulphoxide the dianions derived from 2,3- or 3,4-dihydroxybenzaldehydes and 4-methylesculetin afford products corresponding to alkylation at the less acidic site while the monoanions give the isomeric phenols.
- Kessar, Satinder V.,Gupta, Yash P.,Mohammad, Taj,Goyal, Manju,Sawal, Kewal K.
-
p. 400 - 401
(2007/10/02)
-