Search results for "synthesis"
showing 10 items of 2844 documents
Total Synthesis of Stemoamide, 9a-epi-Stemoamide, and 9a,10-epi-Stemoamide: Divergent Stereochemistry of the Final Methylation Steps
2020
Total syntheses of stemoamide, 9a-epi-stemoamide, and 9a,10-epi-stemoamide by a convergent A + B ring-forming strategy is reported. The synthesis required a diastereoselective late-stage methylation of the ABC stemoamide core that successfully enabled access to three of the four possible diastereomeric structures. For the natural stemoamide series, the diastereoselectivity can be rationalized both by kinetic and thermodynamic arguments, whereas for the natural 9a-epi-stemoamide series, the kinetic selectivity is explained by the prepyramidalization of the relevant enolate.
Proline-Modified Porphyrin Catalysts for Enantioselective Epoxidations: Design, Synthesis, and Reactivity
2004
International audience; The syntheses of various strapped and −picket-fence× chiral porphyrins are described, and their reactivities towards the enantioselective epoxidation of alkenes are reported. Four L-proline residues provide the chiralityfor the various meso-substituted catalysts, which differ by either the spatial arrangement of the stereogenic centers or the nature and length of the straps. The resulting bridged structures possess four amide linkages ineach strap, leading to highly rigid molecules with well-defined geometries whereas the strapped Fe catalysts gave rise to only moderate enantioselectivities, the C2-symmetrical ones being superior to the D2-symmetrical compounds. The …
Total Synthesis of (±)-Scopolamine: Challenges of the Tropane Ring
2016
Scopolamine was synthesized using 6,7-dehydrotropine as a key intermediate. Rhodium-catalyzed [4 + 3] cycloaddition chemistry and a modified Robinson–Schopf reaction were each independently evaluated for their utility in constructing the tropane core. Both synthetic approaches gave comparable overall yields.
Asymmetric Synthesis of Spiro β-Lactamsviaa Squaramide- Catalyzed Sulfa-Michael Addition/Desymmetrization Protocol
2016
An efficient asymmetric synthesis of spirocyclohexenone β-lactams bearing three contiguous stereocenters has been achieved in moderate to good yields and high stereoselectivities. The protocol involves the combination of a squaramide-catalyzed sulfa-Michael addition under desymmetrization via a dynamic kinetic resolution of racemic 2,5-cyclohexadienones.
Fluorine-Containing Drugs Approved by the FDA in 2018
2019
Over the last two decades, fluorine substitution has become one of the essential structural traits in modern pharmaceuticals. Thus, about half of the most successful drugs (blockbuster drugs) contain fluorine atoms. In this review, we profile 17 fluorine-containing drugs approved by the food and drug administration (FDA) in 2018. The newly approved pharmaceuticals feature several types of aromatic F and CF3 , as well as aliphatic (CF2 ) substitution, offering advances in the treatment of various diseases, including cancer, HIV, malarial and smallpox infections.
Squaramide-Catalyzed Asymmetric aza-Friedel-Crafts/N,O-Acetalization Domino Reactions Between 2-Naphthols and Pyrazolinone Ketimines
2017
N-Boc ketimines derived from pyrazolin-5-ones were explored to develop an unprecedented domino aza-Friedel-Crafts/N,O-acetalization reaction with 2-naphthols. The novel method requires a catalyst loading of only 0.5 mol % of a bifunctional squaramide catalyst, is scalable to gram amounts, and provides a new series of furanonaphthopyrazolidinone derivatives bearing two vicinal tetra-substituted stereogenic centers in excellent yields (95-98 %) and stereoselectivity (>99:1 d.r. and 97-98 % ee). A different reactivity was observed in the case of 1-naphthols and other electron-rich phenols, which led to the aza-Friedel-Crafts adducts in 70-98 % yield and 47-98 % ee.
Electron Accumulative Molecules.
2018
With the goal to produce molecules with high electron accepting capacity and low reorganization energy upon gaining one or more electrons, a synthesis procedure leading to the formation of a B–N(aromatic) bond in a cluster has been developed. The research was focused on the development of a molecular structure able to accept and release a specific number of electrons without decomposing or change in its structural arrangement. The synthetic procedure consists of a parallel decomposition reaction to generate a reactive electrophile and a synthesis reaction to generate the B–N(aromatic) bond. This procedure has paved the way to produce the metallacarboranylviologen [M(C2B9H11)(C2B9H10)-NC5H4-…
Strecker reactions with hexacyanoferrates as non-toxic cyanide sources
2019
The Strecker reaction is the most widely applied three-component reaction. Although highly useful for the preparation of α-amino nitriles, α-amino acids, hydantoins and numerous related compounds, the need for the application of toxic sources of HCN limits its application in both academic and industrial settings. Here, we present a facile protocol for Strecker reactions using a mixture of potassium ferri- and ferrocyanides as a non-toxic substitute.
Regio-, Diastereo-, and Enantioselective Organocatalytic Addition of 4-Substituted Pyrazolones to Isatin-Derived Nitroalkenes
2019
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A P-chirogenic β-aminophosphine synthesis by diastereoselective reaction of the α-metallated PAMP–borane complex with benzaldimine
2004
International audience; The diastereoselective synthesis of a P-chirogenic β-aminophosphine ligand with carbon–carbon bond formation of the ethano bridge in a 3:1 ratio via reaction of an α-metallated P-chirogenic phosphine borane with a benzaldimine is described. The diastereoselectivity is attributed to a transition state where the lithium cation chelates the phosphine borane carbanion and the nitrogen of the imine and the attack of the C@N occurs on the face opposite to the P–B bond, due to its interaction with the antibonding P–B bond. The major diastereoisomeric β-aminophosphine borane was then separated and decomplexed into the corresponding β-aminophosphine under neutral conditions a…