A highly diastereoselective synthesis of anti-α-allyl-β-fluoroamines has been developed involving enantioselective α-fluorination of aldehydes followed by a diastereoselective Petasis allyl borono-Mannich reaction. The products are obtained generally in good overall yields for the two steps and with drs of 97 : 3-99 : 1 and ees of 86-92%. Selected products were converted to 3-, 5- and 6-membered ring heterocycles, the latter two types incorporating an exo-cyclic fluorine.
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http://dx.doi.org/10.1039/c9cc02765c | DOI Listing |
J Org Chem
January 2025
Department of Chemistry, New York University, 100 Washington Square East, New York, New York 10003, United States.
Nucleophilic substitution reactions of C-2-acyloxy furanosyl acetals can be highly diastereoselective. We here show that the presence of a less electron-donating -nitrobenzoyloxy group at C-2 of a furanosyl acetal can be of use to control the 1,2- stereoselectivity of acetal substitution reactions with higher stereoselectivity than the analogue with the more electron-donating benzoyloxy group, just as what was observed in the pyranosyl system. Computational results support a reaction manifold involving both open oxocarbenium ions and -dioxolenium ions to provide the 1,2- and 1,2- products.
View Article and Find Full Text PDFAngew Chem Int Ed Engl
January 2025
Shanghai Institute of Materia Medica Chinese Academy of Sciences, Chemical Biology Research Center, 201203, Shanghai, CHINA.
Aldolases are powerful C-C bond-forming enzymes for asymmetric organic synthesis because of their supreme stereoselectivity, diverse electrophiles and nucleophiles, and promising scalability. Stereodivergent engineering of aldolases to tune the selectivity for the synthesis of stereoisomers of chiral molecules is highly desirable but has rarely been reported. This study documented the semirational engineering of the decarboxylative aldolase UstD with the focused rational iterative site-specific mutagenesis (FRISM) strategy to perform a C-C bond-forming reaction with dione electrophiles.
View Article and Find Full Text PDFJ Am Chem Soc
January 2025
Institute of Organic Chemistry, University of Leipzig, 04103 Leipzig, Germany.
The enantioselective synthesis of 1,4-dicarbonyl compounds continues to pose a significant challenge in organic synthesis, and a catalytic process which generates two adjacent stereogenic centers with full stereochemical control is lacking until now. The 1,4-relationship of the functional groups requires an Umpolung strategy as one of the α-carbonyl positions has to be inverted into an electrophilic center to react with a normal enolate. We report herein the highly enantio- and diastereoselective addition of silyl ketene acetals toward electrophilic 1-azaallyl cations to furnish chiral 4-hydrazonoesters, which are masked 1,4-dicarbonyl compounds.
View Article and Find Full Text PDFJ Am Chem Soc
January 2025
Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.
A concise and convergent synthesis of the isosteroidal alkaloids veratramine and 20--veratramine has been accomplished. A Horner-Wadsworth-Emmons olefination joins two chiral building blocks of approximately equal complexity and a transition-metal catalyzed intramolecular Diels-Alder cycloaddition-aromatization cascade constructs the tetrasubstituted arene. Other key steps include a highly diastereoselective crotylation of an -sulfonyl iminium ion and an Eschenmoser fragmentation.
View Article and Find Full Text PDFSynthesis of complex, multiring, spirocyclic, 1,3-dicarbonyl fused, and highly functionalized 5-phenyl-1-azabicyclo[3.1.0]hexanes (ABCH) has been achieved by an intermolecular reaction of 2-(2'-ketoalkyl)-1,3-indandiones or α,γ-diketo esters with (1-azidovinyl)benzenes under transition metal-free conditions.
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