B P Joshi

Microwave-Assisted Mild Conversion of Natural Dihydrotagetone into 5-Isobutyl-3-methyl-4,5-dihydro- 2(3H)-furanone, an Analogue of Whisky Lactone*

A microwave-assisted mild protocol is developed for the synthesis of 5-isobutyl-3-methyl-4,5-dihydro-2(3H)-furanone, an analogue of whisky lactone, from dihydrotagetone, an acyclic monoterpenoid obtained from Tagetes minuta. The methodology involved oxidation of dihydrotagetone in the presence of sodium metaperiodate/potassium permanganate/alumina to give 2,6-dimethyl-4-oxo-heptanoic acid, which upon reduction and subsequent lactonization provided 5-isobutyl-3-methyl-4,5-dihydro-2(3H)-furanone. The reaction is also conducted under conventional conditions and is compared with the microwave method.

One step conversion of toxic beta-asarone from Acorus calamus into 1-(2,4,5-trimethoxyphenyl)-1,2-dihydroxypropane and asaronaldehyde occurring in Piper clusii.

Abstract 1-(2,4,5-Trimethoxyphenyl)-1,2-dihydroxypropane (2), a natural phenylpropanoid occurring in Piper clusii, has been synthesized for the first time from toxic β-asarone (1) of Acorus calamus with osmium tetroxide, while 1 with osmium tetroxide (catalytic amount) in presence of sodium metaperiodate furnished the asaronaldehyde (3) in high yield.

Microwave-assisted minutes synthesis of bioactive phenylbutanoids occurring in Zingiber cassumunar

Microwave-assisted condensation of benzaldehyde (3a,b) with acetone in aqueous sodium hydroxide adsorbed on basic alumina provides phenylbutenone (4a–4b) in 68–71% yield within 4 min, which upon further reduction with sodium borohydride and basic alumina gives phenylbutenol (5a,b) in 91–94% yield within 2 min. Dehydration of 5 with anhydrous copper (II) sulfate gives phenylbutadiene (1a,b), a metabolite of Zingiber cassumunar, within 3 min in 42–48% yield, respectively. All the steps involve environmental friendly solvents and reagents, mild reaction conditions, and overall formation of product 1a,b from 3a,b in 34–38% yield within 9 min under microwave irradiation.

Microwave-assisted rapid synthesis of methyl 2,4,5-trimethoxyphenylpropionate, a metabolite of Cordia alliodora.

Microwave assisted condensation of asaronaldehyde (2) with malonic acid in piperidine-AcOH provides 2,4,5-trimethoxycinnamic acid (3) in 87% yield within 4 min, which upon further reduction with PdCl2-HCOOH-aq. NaOH gives 3-(2,4,5-trimethoxy)phenyl propionic acid (4) in 88% yield within 3 min. Esterification of 4 with MeOH-H+ gives methyl 2,4,5-trimethoxyphenylpropionate (1), a metabolite of Cordia alliodora, in 94% yield within 3 min (overall 69% yield).

Ultrasound-assisted conversion of toxic beta-asarone into nontoxic bioactive phenylpropanoid: Isoacoramone, a metabolite of Piper marginatum and Acorus tararinowii

Ultrasound-assisted synthesis of bioactive isoacoramone (1), a metabolite of Piper marginatum and Acorus tararinowii, has been achieved by oxidation of toxic β-asarone (2) with potassium permanganate/copper sulphate/alumina into asaronaldehyde (3) followed by treatment with ethylmagnesium iodide to provide 1-(2,4,5-trimethoxy)phenyl-1-propanol (4) which upon further oxidation with potassium permanganate/copper sulphate afforded 1 in 64% yield (overall 32%). Toxicological evaluation of 1 reveals it to be nontoxic up to 60u2009mg/kg b.w.