Mini-Reviews in Organic Chemistry - Volume 3, Issue 2, 2006

Aromatic sulfonic acids have been found in Nature only rarely as bacterial metabolites, mostly with the sulfonate group located on an oxygenated benzene ring. This suggests a mechanism of formation as it is discussed for the first step of a Bucherer reaction.

Fluorine atom has been used extensively to modulate the properties of various peptide-like compounds to modulate enzyme activities such as proteases. Fluorinated functionalities such as trifluoromethyl group, difluoromethyl group, fluoromethyl moiety and recently -CHF-S- were investigated. This article discusses important fluorine containing peptidomimetics, synthetic strategies, and the modulation of enzymic activities.

The lowest lying triplet excited states of diaryl ketones are usually long lived and can be photochemically generated with high quantum yields. Hence, compounds of this type are efficient triplet photosensitizers. Three major mechanisms, namely hydrogen abstraction, energy transfer and electron transfer, can be involved in the photosensitized processes. This paper reviews recent examples on the relevance of diaryl ketones as triplet photosensitizers in synthesis. In addition, a number of applications are also presented. In general, the literature coverage has been limited to the publications that appeared during the last five years.

The present review highlights our recent research findings in the field of asymmetric Baylis-Hillman reaction. In particular, it elaborates on the following efficient aids: 1) utilization of sugar-derived acrylates as chiral auxiliary for diastereoselective Baylis-Hillman reaction; 2) use of novel chiral electrophiles such as sugar-derived aldehydes and chiral 2,3-epoxy aldehydes for the diastereoselective Baylis-Hillman reaction to obtain valuable chiral adducts; 3) a novel prolinol derivative promoted enantioselective Baylis-Hillman reaction and 4) intramolecular Baylis-Hillman reaction wherein both the aldehyde and acrylate component are part structure of the same molecular framework to afford high de's. This review also covers the related research work from other groups on asymmetric Baylis-Hillman reaction.

The oxidation of alcohols is a fundamental transformation in organic synthesis and a large number of reagents have been developed for this purpose. In spite of the different methodologies, the modern organic synthesis still requires more efficient oxidant reagents. In this context, TEMPO (2,2,6,6-tetramethylpiperidine- N-oxyl) has emerged as the chosen reagent. The aim of this review is to highlight the TEMPO oxidation as a very important procedure in the synthesis of natural products accomplished between 2000 and 2004.

The chemistry and applications of aminomethylated pyrroles are extensively reported by the present review. An overall account of the synthetic approaches to pyrrole Mannich bases is offered, with an emphasis on topics such as regioselectivity (α-aminomethylation over α-aminomethylation, C-Mannich reaction versus N-Mannich reaction), mono- and bis-aminomethylation, influence of substituents in the pyrrole ring, chemoselectivity, or the special mention of N-tert-butoxycarbonyl-2-[(tert-butyldimethylsilyl)oxy]pyrrole as a substrate. The scope and limitations of the aldehyde component and amine reagents in the Mannich reaction of pyrroles have been explored, the use of preformed aminomethylation reagents and catalysts with the view to improve yields or stereoselectivity has been surveyed, and the mechanism and by-products arising from the aminomethylation of pyrroles have been outlined. Pyrrole Mannich bases have been portrayed as excellent H-, C-, N-, O-, S-, and P-alkylating agents as a direct consequence of their ability to replace the easily leaving dialkylamino group with other nucleophiles, and the involvment in ring closure processes leading to porphyrins, or other miscellaneous reactions have also been included in the broad coverage of these compounds' reactivity. A particular attention has been paid to the contribution of pyrrole Mannich bases to drug discovery and advances in medicinal chemistry.