Lionel Nicolas

Diastereoselective Metal‐Catalyzed Synthesis of C‐Aryl and C‐Vinyl Glycosides

Cobalt, the catalyst of choice: The diastereoselective cobalt-catalyzed cross-coupling of 1-bromo glycosides and aryl or vinyl Grignard reagents is described. A convenient and inexpensive catalyst, [Co(acac)(3)]/tmeda (acac = acetylacetonate, tmeda = N,N-tetramethylethylenediamine), gives full αu2005selectivity in the mannose and galactose series, and an αu2005selectivity in the glucose series with α/βu2005ratios of 1.3:1-3:1.

Cobalt-catalyzed diastereoselective synthesis of C-furanosides. Total synthesis of (-)-isoaltholactone.

An array of C-aryl and C-vinyl furanosides were prepared in good yields and diastereoselectivities from C-halogeno furanosides either with aryl Grignard or with vinyl Grignard using the convenient Co(acac)3/TMEDA catalytic system. This method is illustrated by the total synthesis of the (-)-isoaltholactone.

Lewis Basicity Modulation of N-Heterocycles: A Key for Successful Cross-Metathesis

Cross-metathesis involving N-heteroaromatic olefinic derivatives is disclosed. The introduction of an appropriate substituent on the heteroaromatic ring decreases the Lewis basicity of the nitrogen atom, thus preventing the deactivation of the ruthenium-centered catalyst. The reaction is quite general in terms of both N-heterocycles and olefinic partners.

Beyond catalyst deactivation: cross-metathesis involving olefins containing N-heteroaromatics

Summary Alkenes containing N-heteroaromatics are known to be poor partners in cross-metathesis reactions, probably due to catalyst deactivation caused by the presence of a nitrogen atom. However, some examples of ring-closing and cross-metathesis involving alkenes that incorporate N-heteroaromatics can be found in the literature. In addition, recent mechanistic studies have focused on the rationalization of nitrogen-induced catalysts deactivation. The purpose of this mini-review is to give a brief overview of successful metathesis reactions involving olefins containing N-heteroaromatics in order to delineate some guidelines for the use of these challenging substrates in metathesis reactions.

Synthesis of complex oxygenated heterocycles

Versatile and chemoselective preparation of substituted oxygenated heterocycles is described. Highly diastereoselective metal-catalyzed syntheses of trans-2,6- and cis-2,6-disubstituted tetrahydropyrans (THPs) are presented, along with an easy one-pot access to various ring size benzoannulated spiroketals.

Copper-catalysed amidation of 2-chloro-pyridines

The simple and inexpensive N,N-dimethylcyclohexane-1,2-diamine/CuI catalytic system provides a versatile, easy and efficient access to an array of N-(2-pyridin-2-yl)-amides from 2-chloro-pyridine derivatives.

Mining Parsing Results for Lexical Correction: Toward a Complete Correction Process of Wide-Coverage Lexicons

The coverage of a parser depends mostly on the quality of the underlying grammar and lexicon. The development of a lexicon both complete and accurate is an intricate and demanding task. We introduce a automatic process for detecting missing, incomplete and erroneous entries in a morphological and syntactic lexicon, and for suggesting corrections hypotheses for these entries. The detection of dubious lexical entries is tackled by two different techniques; the first one is based on a specific statistical model, the other one benefits from information provided by a part-of-speech tagger. The generation of correction hypotheses for dubious lexical entries is achieved by studying which modifications could improve the successful parse rate of sentences in which they occur. This process brings together various techniques based on taggers, parsers and statistical models. We report on its application for improving a large-coverage morphological and syntacic French lexicon, the Lefff.