Search results for "Auxiliaries"
showing 5 items of 5 documents
Asymmetric Michael Addition in Synthesis of β-Substituted GABA Derivatives
2022
γ-Aminobutyric acid (GABA) represents one of the most prolific structural units widely used in the design of modern pharmaceuticals. For example, β-substituted GABA derivatives are found in numerous neurological drugs, such as baclofen, phenibut, tolibut, pregabalin, phenylpiracetam, brivaracetam, and rolipram, to mention just a few. In this review, we critically discuss the literature data reported on the preparation of substituted GABA derivatives using the Michael addition reaction as a key synthetic transformation. Special attention is paid to asymmetric methods featuring synthetically useful stereochemical outcomes and operational simplicity. This research was funded by the National Na…
Synthesis and Spectral and Structural Characterization of a New Series of Bis-Strapped Chiral Porphyrins Derived from L-Proline
2001
International audience; New chiral porphyrins were obtained in reasonable yields in three steps, starting from the áâáâ atropisomer of mesotetrakis(o-aminophenyl)porphyrin (TAPP). These potential catalysts for the enantioselective epoxidation of alkenes were obtained by the reaction of different linkers on the same Lprolinoyl-picket porphyrin. Their 1H NMR spectral characteristics, as well as the crystal structure of one of them, clearly indicate that the orientation of the proline cycle depends on the linker used to tether the two pickets on each side of the porphyrin. The same linker is employed for both sides of the porphyrin; hence the resulting D2-symmetric superstructure.
Auxiliaries
2014
The prototypical auxiliary in Ancient Greek is eimí “to be”, which is involved in some participial periphrases conveying aspectual value and variously interacting with the synthetic forms within the inflectional paradigm. However, many other verbs are involved in the Greek periphrastic constructions, although their status as auxiliaries is still a matter of debate. Resent research in grammaticalization allows to describe the entire range of such verbs in prototypical terms, that is, as a coherent category which includes more central and peripheral, i.e. less grammaticalized members.
Base-Dependent Stereodivergent Intramolecular Aza-Michael Reaction: Asymmetric Synthesis of 1,3-Disubstituted Isoindolines
2013
The nucleophilic addition (A(N)) / intramolecular aza-Michael reaction (IMAMR) process on Ellman's tert-butylsulfinyl imines, bearing a Michael acceptor in the ortho position, is studied. This reaction affords 1,3-disubstituted isoindolines with a wide range of substituents in good yields and diastereoselectivities. Interestingly, careful choice of the base for the aza-Michael step allows either the cis or the trans diastereoisomers to be exclusively obtained. This stereodivergent cyclization has enabled the synthesis of C2-symmetric bisacetate-substituted isoindolines. In addition, bisacetate isoindolines bearing two well-differentiated ester moieties are also noteworthy because they may a…