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The free radical scavenging properties and possible antioxidant activity of 1,3-diphenylpropane-1,3-dione (1) are reported. Pulse radiolysis technique was employed to study the one-electron oxidation of 1 with various radicals viz. CCl3O2•, N3• and•OH in homogeneous aqueous solution. All these radicals reacted with 1 under ambient conditions at almost diffusion controlled rates producing transient species with an absorption maximum around 420 nm that decayed at first order rates. The transient absorption peak was shifted in the case of CCl3OO• radical reaction with 1 due to change in the polarity of the medium. Formation of a stable product with a broad absorption band starting from 400 nm and cut off at 230 nm was observed in the oxidation of 1 with•OH and•N3 radicals. In a biological system also, 1 showed significant inhibitory activity against Fe2+-mediatedlipidperoxidation. Based on these observations, a suitable mechanism for the oxidation of 1 has been proposed.

Plumbagin, a naphthoquinone occurring in the plants belonging to Plumbago sp. is known to have insect growth disrupting activities. In the present study, a comparative evaluation of bioactivities of related naphthoquinones, juglone and menadione and benzoquinones, 2,6-dimethylbenzoquinone and 2,3,6-trimethylbenzoquinone along with 2,6-dimethylhydroquinone have been undertaken using Dysdercus koenigii. The LD50 values of the compounds showed wide variation. Although all the test compounds disrupted the normal growth at sublethal doses, 2,6-dimethylbenzo- quinone and menadione showed activity at low doses.

A convenient mild protocol for oxidation of highly hindered electron rich benzhydrols using DDQ / PbO2 has been developed.

Intramolecular 1,2-arene-alkene photocycloaddition of 2-alkenyl-4-chromanones gave complex multicyclic oxatetracyclotetradecanediones which on internal photo- and microwave induced thermal rearrangements provided a diverse array of compounds with [3.3.0]bicyclooctane carbon frame work. The stereo- and regiochemical aspects as well as desymmetrization of alkenyl chromanones due to intramolecular 1,2-arenealkene photocycloaddition have also been discussed.

A novel transformation of 7-hydroxy-2-methyl-2-(4-methyl-3-pentenyl)-4-chromanone ( 1 ) to intramolecular 1,3-arene-alkene photocycloadduct, (1 S ,2 R ,5 S ,7 S ,10 S ,13 R )6,6,10-trimethyl-14-oxapentacyclo[8.3.1.0 1,7 .0 2,13 0 5,13 ] tetradecane-3,12-dione ( 3 ) via secondary photorearrangement of 1,2-arene-alkene photocycloadduct ( 2 ) has been described.

A convenient one-step synthesis of 2,2-dimethylchromans and chromenes using Amberlyst 15 as a catalyst is described.

On irradiation, 2-methyl-2-ethenyl naphtha-4-chromanone 1 undergoes an unusual intramolecular arene–alkene photocyclisation, followed by rearrangements to give a [5.3.1.06,1]benzotricycloundecene, 5.

The title compound, C16H20O3, was prepared by the photolysis of 7-hydroxy-2-methyl-2-(4-methyl-3-pentenyl)-4-chromanone. The H7 and H9 atoms are in an α configuration. The cyclobutane ring is non-planar, the cyclohexenone ring has a half-chair conformation, the pyranone ring has a sofa conformation and the cycloheptanone ring has a boat conformation. The groups of atoms C11, C12, C13, O14 and C12, C13, O14, C4 are both planar.

A novel intramolecular 1,2-arene-alkene photocycloaddition of 2-alkenyl-7-hydroxy-4-chromanone(1) and its alkyl ethers (2 and 3) to (4α, 7α, 9α)4,8,8-trimethyl-14-oxatetracyclo(6.5.14,13.01,9)tetradeca-12-ene-2,11-dione (4) is described.

The title compound, C16H20O3, was prepared by the photolysis of 7-hydroxy-2-methyl-2-(4-methyl-3-pentenyl)-4-chromanone. The H7 and H9 atoms are in an α configuration. The cyclobutane ring is non-planar, the cyclohexenone ring has a half-chair conformation, the pyranone ring has a sofa conformation and the cycloheptanone ring has a boat conformation. The groups of atoms C11, C12, C13, O14 and C12, C13, O14, C4 are both planar.

A novel method for the prenylation of phenols has been developed using 2-methyl-but-3-ene-2-ol as the prenylating agent in the presence of Amberlyst 15. The prenylated catechols and quinols showed better antioxidant activity than the corresponding non-prenylated compounds in the in vitro DPPH and lipid peroxidation assay. The resorcinol derivatives did not show significant antioxidant activity.

Condensation between 1-trimethylsilyloxy-3-butanone and trimethylsilyl [2-14C]acetate gave (±) [2-14C]mevalonolactone in one step.

A new method for cyclodehydration of o-hydroxyaryl-β-ketols to 4-chromanones using HMPT is described. The method has general applicability. It is particularly useful for the cyclisation of labile intermediates as exemplified by the synthesis of cannabinoid synthon, 2-methyl-2-(4-methyl-3-pentenyl)-7-methoxy-4-chromanone.

2-Hydroxy-4, 6-dimethoxycrotonophenone (1), isolated from the plant Dysophylla stellata Benth. by Joshi and Ravindranath,1 is the only example of an open chain form of chromanones. The co-occurrence of the crotonophenone (1) with chromone and butyrophenone1 suggests that these are biogenetically related in the same way as chalcones are to flavonoids.2 It is likely that more crotono-phenones and 2-methylchromanones will be discovered in nature.

Mevalonic acid lactone (MVA) labelled with stable as we11 as radioactive isotopes continuesto be one of the most widely used substrates in the biosynthesis of terpenoids. Elucidation of several intricate biochemical processes has been possible through the use of carefully chosen specifically 1abelled MVA.1 Attempts to develop new routes to its synthesis have, therefore, been continued and several elegant syntheses have been reported in recent years.2 Wedescribe here a short and efficient synthesis of MVA in which condensation between butan-1-01-3-one (2a) and acetic acid is brought about through their trimethylsilyl (TMS) derivative.3 Usual acidic work up of the reaction brings about cleavage of TMS groups thus obviating deprotection step used in most of the other syntheses.

A new method for cyclodehydration of o-hydroxyaryl-β-ketols to 4-chromanones using HMPT is described. The method has general applicability. It is particularly useful for the cyclisation of labile intermediates as exemplified by the synthesis of cannabinoid synthon, 2-methyl-2-(4-methyl-3-pentenyl)-7-methoxy-4-chromanone.

Thiols react with diimidazolylsulfide under mild conditions to give symmetrical trisulfides in good yield and high purity.