Current Organic Chemistry - Volume 11, Issue 2, 2007

Carbon-carbon bond forming reactions are simple and direct methods for synthesizing the various skeletons and the diverse structures of organic compounds. Even 100 years after the discovery of the Grignard reaction, organomagnesium, organolithium, and organoaluminum remain popular for carbon-carbon bond formation reactions in modern organic chemistry. Moreover, asymmetric alkyl- or aryl-additions to carbonyl compounds with organometal reagents is attractive due to the enantioselective synthesis of chiral secondary alcohols, which sharply contrasts the enantioselective reduction of carbonyl compounds. Herein, we review recent progress in the selective addition to carbonyl compounds with organometal reagents, particularly Li, Mg, and Zn from both a classic viewpoint using metal ate complexes and from a catalytic enantioselective viewpoint using new chiral ligands.

In the early 1950s Witkop described in a series of papers that oxidation of indoles with a variety of oxidation reagents leads to the formation of quinolones. The mechanism of this reaction involves the oxidative cleavage of the 2,3- double bond of the indole moiety (Witkop-oxidation) followed by a Camps-cyclization forming the quinolone ring. Winterfeldt identified conditions which allow a one pot Witkop-oxidation/Camps-cyclization sequence and applied this strategy for the synthesis of pyrrolo[2,3-c]quinolones starting from 1,2,3,4-tetrahydro-β-carbolines. This review gives a comprehensive description of all described examples of this reaction including a definition of scope and limitations and a discussion of the mechanism of this transformation.

Over the last 30 years, the use of diazocarbonyl compounds has been a very fertile field for the development of new synthetic methods for constructing C-C bonds and heterocyclic rings. The reactions of the carbenoids, derived from the diazocarbonyls, offer exciting new strategies for the construction of complex target molecules due to the range of unusual transformations and cascade sequences which can be utilized. This review provides an update of the significant advances in the field since the year 2000 in the synthesis of several heterocycles (pyrrole, aziridines, dihydrofurans, etc.) by inter- and intra-molecular insertions of carbenoid species, generated from α-diazo-β-keto compounds, into carbonhydrogen or heteroatom-hydrogen bonds. New methodologies and unusual synthetic transformations will be highlighted. Although heterocycles have very important uses, the focus of this survey will be directed not to their use but to the methods of preparation.

Oligopyridines connected through the 2- and 6- positions have long been the subject of continuing interest because of their high ability to interact with metal ions and/or other molecules, and their transition-metal complexes have been intensely studied for decades because of their characteristic photophysical properties. However, relatively few have been known in regard to the photophysical and photo-functional properties of oligopyridine derivatives. From the late 1990s, fluorescent oligopyridines have been of considerable interest as tunable fluorophores by intermolecular interaction, and the design and synthesis of novel oligopyridine derivatives and their application to fluorescent sensors has increasingly been studied. In this article, we will review recent developments of fluorescent oligopyridines and their photo-functionality.

Sulfonamide is an important functional group. Its cyclic version, sultam, has been successfully employed as a chiral auxiliary in controlling diastereoselectivities of numerous organic transformations. In this paper, the uses of chiral sultams that are not derived from camphor as chiral auxiliaries in asymmetric syntheses are reviewed.

The reactivators of acetylcholinesterase are very important components in the treatment of intoxications caused by organophosphate inhibitors such as tabun, sarin, soman, VX etc. and insecticides like echothiofat, metrifonat, chlorpyrifos etc. These inhibitors covalently bind on active site of mentioned enzyme and irreversibly inhibit its activity. The reactivator breaks the inhibitor-enzyme covalent bond and restores its activity. Unfortunately, there is no reactivator applicable for every type of inhibition; it means that every structural change in the molecule of inhibitor needs a specific structure of the reactivator. Therefore, development of more active acetylcholinesterase reactivators with broader spectrum is a major challenge actual from the point of view of war operations, accidents or terroristic attacks. Synthetic approaches, biological activity evaluation and structure-activity relationship studies of newly prepared acetylcholinesterase reactivators from 1990 to 2004 are summarized. Synthetic procedures used and the evaluation of antidotal efficacies are mentioned for individual types of reactivators. The main attention was paid to reactivators derived from pyridine carbaldoxime and imidazole carbaldoxime.