Microwave-Assisted Claisen Rearrangement/Diels–Alder Cascade reaction for the Synthesis of Caged Garcinia Natural Products and Analogues

Sequential Diels–Alder Reactions in a Conjugated Tetraene System

A sequence of two Diels–Alder reactions is observed for the reaction of bis-diene ( E)-3-[2-(furan-2-yl)vinyl]-5,5-dimethylcyclohex-2-en-1-one with two equivalents of N-phenylmaleimide. This study shows that the electron-deficient furanyl site, which is primarily “inactive” towards a [4 + 2] reaction, easily undergoes cycloaddition with the second equivalent of N-phenylmaleimide to produce the final bis-adduct. This is because the first Diels–Alder reaction between N-phenylmaleimide and the more reactive cyclohex-2-en-1-one site of the diene converts the 2-furanyl ring to a more electron-rich component, since the electron-withdrawing double bond attached to the furan ring changes to an electron-releasing alkyl group after the first cycloaddition. Consequently, the resulting furanyl diene is then able to undergo the second cycloaddition.

Microwave-assisted organic syntheses: microwave effect on intramolecular reactions – the Claisen rearrangement of allylphenyl ether and 1-allyloxy-4-methoxybenzene

We examined the possible effect microwaves may have on intramolecular reactions such as the Claisen-type rearrangement process carried out in DMSO solvent and in solvent-free microwave irradiation conditions.

Garcinia xanthones as orally active antitumor agents

Using a newly developed strategy whose key step is the regioselective propargylation of hydroxyxanthone substrates, 99 structurally diverse Garcinia natural-product-like xanthones based on gambogic acid were designed and synthesized and their in vitro antitumor activity was evaluated. A set of 40 related compounds was chosen for determination of their physicochemical properties including polar surface area, log D₇.₄, aqueous solubility, and permeability at pH 7.4. In the light of the in vitro antitumor activity and the physicochemical properties, two compounds were advanced into in vivo efficacy experiments. The antitumor activity of compound 112, administered po, showed more potent in vivo oral antitumor activity than gambogic acid.

Microwave-Assisted Condensation of Kojic Acid with Aldehydes

Kojic acid derivatives have been prepared in excellent yield by the condensation of two molecules of kojic acid and one molecule of an aldehyde using sodium carbonate as a base under microwave irradiation.