Ursula 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.

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.

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.

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.

Oxidation of mono-phenols to para-benzoquinones: a comparative study

A oxidacao de mono-fenois a para-benzoquinonas e assunto de interesse continuo devido a existencia de inumeros produtos naturais contendo esta unidade estrutural. As para-benzoquinonas possuem reatividade quimica importante como agentes oxidantes e como dienofilos na reacao de Diels-Alder. Usualmente nos preparamos as para-benzoquinonas pela reacao de oxidacao dos respectivos mono-fenois com oxigenio molecular e catalisada por [CoII(salen)]. Porem, foi necessario estudar estas oxidacoes utilizando-se outros oxidantes. Nos apresentamos aqui nossos resultados sobre esta importante reacao de oxidacao com uma variedade de oxidantes, utilizando onze mono-fenois como substratos. Os oxidantes utilizados foram cobalto, niquel, cobre e vanadio derivados com alguns ligantes do tipo salen. Tambem foram estudados peroxido de hidrogenio, OXONE®, dimetil dioxirano e acido iodoxibenzoico.

Cyclization of unsaturated monoterpenic alcohols mediated by thallium (III) salts

Abstract The reaction of thallium triacetate and thallium trinitrate with four monoterpenic unsaturated alcohols (isopulegol, neo-isopulegol, cis-carveol and α-terpineol), in AcOH:H2O (1:1, vol/vol) as solvent, led to the corresponding β-hydroxy-cyclic ethers with high regio- and stereoselectivity, in moderate to good yields. A mechanism of ring-contraction or ring-expansion of the oxythallated adduct is proposed, based on the substitution patterns of each double bond.

An Efficient Synthesis of Monoterpene α-Methylene-γ-Butyrolactones

Abstract The monoterpene trans- and cis- fused α-methylene-γ-butyrolactones (1) and (2) have been synthesised from the appropriate isopulegol epimers (3) and (4).

A síntese dos sesquiterpenos baquenolidas

The bakkenolide group of sesquiterpenes has been a focal point of synthetic efforts amongst several research laboratories all linked to our common origins at the Chemistry Institute at the State University in Sao Paulo. In this review we would like to present a historical perspective of this research, with unpublished background information, and a definitive retrosynthetic analysis of these molecules. This chemistry spans the time period from 1972 to 2006, and traces the initial steps with Prof. Dr. Helena Ferraz to the present day.