Enantioselective synthesis of rigid 2-aminotetralins. Utility of silicon as an oxygen and nitrogen surrogate in the tandem addition reaction

Total Synthesis of Polysubstituted γ-Butyrolactone Lignans (-)-Hinokinin, (-)-Bicubebin B, and (-)-Isodeoxypodophyllotoxin via Oxime Carbonate Formation

The diverse structures and profound biological activities of lignan natural products have enticed significant effort in the exploration of new methodologies for their total synthesis. We have prepared γ-butyrolactone oximes from readily available δ-nitro alcohols via Boc2O mediated cyclization. The mild conditions are compatible with a wide range of functional groups, and this methodology has been applied to the total synthesis of five lignan natural products.

Naphthalenones from a Perenniporia sp. inhabiting the larva of a phytophagous weevil, Euops chinesis

The new naphthalenone derivatives perenniporides A-D (1-4) were isolated from solid cultures of a fungus Perenniporia sp. inhabiting the larva of Euops chinesis, a phytophagous weevil with high host specificity to the medicinal plant Fallopia japonica. The structures of 1-4 were elucidated primarily by NMR experiments, and 1 was confirmed by X-ray crystallography. The absolute configuration of 1 and 2 was assigned by electronic circular dichroism (ECD) calculations, whereas that of the C-10 tertiary alcohol in 3 was deduced via the CD data of the in situ formed [Rh(2)(OCOCF(3))(4)] complex and supported by the ECD data. Compound 1 showed antifungal activity against five plant pathogens.

Stereoselective synthesis of an active metabolite of the potent PI3 kinase inhibitor PKI-179

The synthesis and stereochemical determination of 1-(4-(4-((1R,5R,6R)-6-hydroxy-3-oxa-8-azabicyclo[3.2.1]octan-8-yl)-6-morpholino-1,3,5-triazin-2-yl)phenyl)-3-(pyridin-4-yl)urea (2), an active metabolite of the potent PI3 kinase inhibitor PKI-179 (1), is described. Stereospecific hydroboration of the double bond of 2,5-dihydro-1H-pyrrole 8 gave the 2,3-trans alcohol 9 exclusively. The configuration of the 3-hydroxyl group in 9 was inverted by an oxidation and stereoselective reduction sequence to give the corresponding 2,3-cis isomer 23. Both exo (21) and endo (27) isomers of the metabolite 2 were prepared via a practical synthetic route from 9 and 23, respectively, and the stereochemistry of 2 was determined to be endo. The endo isomer (27) was separated into two enantiomers 28 and 29 by chiral HPLC. Compound 2 was found to be enantiomerically pure and identical to the enantiomer 28. The absolute stereochemistry of the enantiomer 28 was determined by Mosher's method, thus establishing the stereochemistry of the active metabolite 2.

Stereoselective synthesis of 3-aryloctahydroindoles and application in a formal synthesis of (-)-pancracine

A stereoselective synthesis of 3-aryloctahydroindoles from enantiomerically enriched gamma-nitroketones has been developed. Reduction of imines derived form the nitroketones provides the trans-fused octhaydroindole motif selectively. The cis-octahydroindole skeleton is accessible by an invertive cyclization strategy involving a diastereomerically pure nitromesylate intermediate. This approach was employed in the synthesis of an advanced intermediate to (-)-pancracine. The gamma-nitroketone starting materials are readily available via an organocatalytic Michael reaction.

Iridium-catalyzed asymmetric ring-opening reactions of N-Boc-azabenzonorbornadiene with secondary amine nucleophiles

Iridium-catalyzed asymmetric ring-opening reactions of N-Boc-azabenzonorbornadiene with a number of secondary amines has been developed for the first time. The reaction gave 1,2-trans-diamine derivatives in moderate to good yields with high enantioselectivity in the presence of 2.5 mol % of [Ir(COD)Cl]2 and 5 mol % of (S)-BINAP. The trans-configuration of the 1,2-diamino products was confirmed by X-ray crystallography.

Deuterium-Labeling and NMR Study of the Dearomatization of N-Alkyl-N-benzyldiphenylphosphinamides through Anionic Cyclization: Ortho and Benzylic Lithiation Directed by Complex-Induced Proximity Effects

The mechanism of the anionic cyclization dearomatizing reaction of N-benzyl-N-methyldiphenylphosphinamide (1) upon treatment with s-BuLi in tetrahydrofuran (THF) at -90 degrees C has been analyzed by deuterium-labeling and natural abundance multinuclear magnetic resonance ((1)H, (2)H, (7)Li, (13)C, (31)P) studies. In the absence of coordinating cosolvents such as hexamethylphosphoramide (HMPA), eight major anionic species were identified, which allowed us to unravel the pathway of the metalation reaction. In agreement with the complex-induced proximity effect (CIPE) mechanism, the sequence of transformations emerging from this study involves the coordination of the lithium base to the P=O group of 1 to give four dimeric precomplexes whose NMR data are consistent with structures Va/Vb and VIIIa/VIIIb. The diastereomers Va/Vb are the precursors of the monomeric benzylic anion II, whereas the VIIIa/VIIIb diastereomers are assumed to undergo ortho deprotonation leading to anions I. Translocation from the ortho anion to the benzylic one is not observed. Intramolecular conjugate addition of anion II to the P-phenyl rings happens in a reversible way, affording the monomeric dearomatized anions III, IV, VI, and VII. The reaction progresses to yield a mixture containing only the species I, III, and IV. HMPA acts as a catalyst for the ortho-to-benzylic translocation and anionic cyclization reactions. Two-dimensional (2D) (7)Li,(31)P[(1)H] shift correlations and (7)Li[(31)P] NMR spectra proved to be crucial for the structural assignment of the anionic species. These techniques also demonstrated the diastereotopicity of the two achiral ligands involved in a dimer with s-BuLi (Vb) owing to the slow configuration inversion of the carbanion center.

The Intramolecular Carboxyarylation Approach to Podophyllotoxin

Since 1960, only seven plant-derived anticancer drugs have received FDA approval for commercial production. Two are semisynthetic derivatives of podophyllotoxin. This paper describes concise, highly convergent, and conceptually novel approaches to (-)-podophyllotoxin and its enantiomer. These highly convergent syntheses feature a late-stage domino radical reaction to install the lactone ring and the pendant trimethoxyphenyl group.