Current Organic Chemistry - Volume 16, Issue 13, 2012

2-Mercaptobenzothiazole has found widespread industrial applications for the vulcanisation of rubber and, more recently, as a key component of the modified Julia olefination reaction. This review surveys the chemistry of 2-mercaptobenzothiazole, including its aromatic substitution reactions, redox chemistry and factors governing the regioselectivity of its alkylation reactions. In addition, the emerging synthetic uses of this heterocycle, including its application to the deoxygenation of epoxides, and the preparation of alkynes, are described.

One-pot synthesis of symmetrical and non-symmetrical spiro[oxindole]xanthenes was achieved by reacting excess of acid labile and stable p-substituted phenols with isatin in the presence of p-TsOH in refluxing p-xylene. The intermediary 3,3-bis(2-hydroxy-5- substitutedphenyl)oxindoles undergo ring forming dehydration, generating the targeted spiro compounds. Gaining mechanistic insight allowed the selection of suitable reaction times and conditions to optimize the yields of the more challenging non-symmetrical spiro[oxindole]xanthenes.

Allenes have been shown to be versatile building blocks in organic synthesis. However, the diversity of the allene chemistry offers a challenging and exquisite task for organic chemists bent on building the suitable allene substrates. A good solution might be propargyl-allenyl isomerization, which means to prepare readily available propargyl substrates. This review focuses on recent progress in the in situ propargyl-allenyl isomerization in organic synthesis, published in 1990 and later.

Organic carbamates represent an important class of compounds showing various interesting properties. They find wide utility in various areas as pharmaceuticals, agrochemicals (pesticides, herbicides, insecticides, fungicides etc.), intermediates in organic synthesis, protection of amino group in synthetic organic chemistry, as linkers in combinatorial chemistry etc. Classical synthesis of carbamates involves use of harmful reagents such as phosgene, its derivatives and carbon monoxide. Recently, carbon dioxide has frequently been employed as a green reagent in its various conditions and forms for the synthesis of organic carbamates employing diversity of starting materials, reagents and catalytic systems. In the present review, we would like to highlight the recent developments on the synthesis of organic carbamates using various conditions and forms of carbon dioxide.

New chiral bipyridyl alcohols and the corresponding N,N-dioxide derivatives were obtained with high enantiomeric excess by a chemo-enzymatic procedure. Metalation of commercial 6,6’-dimethyl-2,2'-bipyridine followed by reaction with acetaldehyde furnished an inseparable 1:1 mixture of dl- and meso- 6,6'-bis(2-hydroxypropyl)-2,2'-bipyridine ((±)-7a and meso-7b) that was subjected to lipasecatalysed enantioselective esterification with vinyl acetate in organic solvent. Immobilised Mucor Miehei lipase (Lipozyme® IM) displayed high stereoselectivity and unreacted alcohol (S,S)-7a, monoacetyl derivative (R,S)-6 and diacetate (R,R)-9 were obtained in high optical purities as the result of the simultaneous resolution of the racemate and desymmetrization of meso isomer. After separation, the chiral compounds were converted into the corresponding N,N-dioxide derivatives with additional axial chirality stereoselectively induced during the N,N-oxidation and some considerations about their stereochemistry and atropisomeric stability were deduced by circular dichroism spectroscopy.