Timothy J. Brocksom

The Diels-Alder reaction: an update

The last ten years have seen an explosive growth in synthetic applications of the Diels-Alder reaction, principally the intramolecular (IMDA) reaction but also the transannular (TADA) version. In this review we present these developments with special emphasis on the synthetic concepts and the experimental results and include related theoretical studies.

Porphyrins as Catalysts in Scalable Organic Reactions

Catalysis is a topic of continuous interest since it was discovered in chemistry centuries ago. Aiming at the advance of reactions for efficient processes, a number of approaches have been developed over the last 180 years, and more recently, porphyrins occupy an important role in this field. Porphyrins and metalloporphyrins are fascinating compounds which are involved in a number of synthetic transformations of great interest for industry and academy. The aim of this review is to cover the most recent progress in reactions catalysed by porphyrins in scalable procedures, thus presenting the state of the art in reactions of epoxidation, sulfoxidation, oxidation of alcohols to carbonyl compounds and C–H functionalization. In addition, the use of porphyrins as photocatalysts in continuous flow processes is covered.

A convenient deoxygenation of α,β-epoxy ketones to enones

Abstract A new and efficient methodology for the deoxygenation of α,β-epoxy ketones to enones has been developed, using aminoiminomethanesulfinic acid (thiourea dioxide) as the reducing agent under phase transfer conditions. The epoxides of mesityl oxide, isophorone, (−)-carvone, (+)-6-methyl-carvone, (+)-6-ethyl-carvone and (−)-myrtenal, were converted into their respectives enones in good to excellent yields.

A Simple and Efficient Synthesis of Thymoquinone and Methyl P-Benzoquinone

Abstract The Co(II) (salen) catalysed oxidations of thymol (1), carvacrol (2), o- and m-cresol, with molecular oxygen give high yields of the corresponding p-benzoquinones.

Enantiocontrolled total synthesis of (+)-bakkenolide-A

Abstract An efficient, stereoselective total synthesis of natural bakkenolide-A has been effected from (S)-1,6-dimethyl-1-cyclohexene, which can be obtained from 2-methyl-2-cyclohexen-1-one in 3 high-yield steps.

Sedative Effect of Monoterpene Alcohols in Mice: A Preliminary Screening

Many essential oils and monoterpenes are used therapeutically as relaxing drugs and tranquilizers. In this study, ten structurally related monoterpene alcohols, present in many essential oils, were evaluated in mice to investigate their pharmacological potential in the central nervous system. Isopulegol (1), neoisopulegol (2), (±)-isopinocampheol (3), (-)-myrtenol (4), (-)-cis-myrtanol (5), (+)-p-menth-1-en-9-ol (6) and (±)-neomenthol (8) exhibited a depressant effect in the pentobarbital-induced sleep test, indicating a sedative property. (-)- Menthol (7), (+)-dihydrocarveol (9), and (±)-isoborneol (10) were ineffective in this test. The results show that these psychoactive monoterpenes have the profile of sedative drugs, and this pharmacological effect is influenced by the structural characteristics of the molecules

Synthesis and antidepressant evaluation of three para-benzoquinone mono-oximes and their oxy derivatives.

A series of three para-benzoquinone mono-oximes and four oxy-derivatives were prepared and tested for their antidepressant properties. The (4E) oxime of 2-isopropyl-5-methyl-para-benzoquinone (4) and the corresponding 2-diethylamino-ethyl derivative (10) present antidepressant activities and were slightly more potent than the reference standard.

The stereoselective synthesis of terpene tetrahydrofurans using thallium triacetate

Abstract The reaction of diterpenes 1–3 and monoterpenes 9 , 10 with thallium triacetate leads stereoselectively to the tetrahydrofuran products 5–7 and 11 , 12 respectively, by 5-Endo-Trig cyclisation of the 3-alkenol system.

Enantiodivergent syntheses of cycloheptenone intermediates for guaiane sesquiterpenes

Abstract The syntheses of enantiomeric 6-isopropenyl-3-methyl-2-cycloheptenones 16 and 22 have been effected starting from ( R )-(−)-carvone. In the synthesis of 16 , ( R )-(−)-carvone was reduced and the resulting dihydrocarvone transformed regioselectively into silyl enol ethers. Cyclopropanation with dibromocarbene and in situ rearrangement gave an α-bromo-cycloheptenone which was reduced to the ( R )-(+)-cycloheptenone 16 . In the synthesis of 22 , ( R )-(−)-carvone was cyclopropanated with a sulfur ylide, followed by reduction with LiAlH 4 and acid-catalyzed cyclopropylcarbinyl rearrangement to afford a cycloheptenol. Oxidation and double bond conjugation led to the ( S )-(−)-cycloheptenone 22 in a partially racemized form. Four cycloheptenones have been obtained and are suitable intermediates for the enantiodivergent syntheses of guaiane sesquiterpenes.

Harvestman Phenols and Benzoquinones: Characterisation and Biosynthetic Pathway

Benzoquinones are usually present in arthropod defence exudates. Here, we describe the chemical profiles of 12 harvestman species belonging to the neotropical family Gonyleptidae. Nine of the studied species produced benzoquinones, while three produced alkyl phenols. Two benzoquinones and one phenol exhibited biological activity against bacteria and fungi. We also studied the biosynthesis of 2-ethyl-1,4-benzoquinone by feeding Magnispina neptunus individuals with 13C-labelled precursors; the benzoquinones were biosynthesised through a polyketide pathway using acetate and propionate building blocks.