Efficient kinetic resolution in the asymmetric hydrosilylation of imines of 3-substituted indanones and 4-substituted tetralones

Intermolecular Asymmetric Arylative Dearomatization of 1-Naphthols

Arylative dearomatization forms quaternary stereocenters in cyclic systems with the concomitant introduction of an aromatic ring. Pd-catalyzed arylative dearomatization, which uses conditions analogous to cross-coupling, has emerged as a powerful method in an intramolecular context. But translating this from intramolecular cyclizations to an intermolecular process has proven extremely challenging: examples are scarce, and those that exist have not been rendered enantioselective, despite the potential for broad application in medicinal chemistry and natural product synthesis. We describe a strategy that utilizes attractive interactions between the ligand and substrate to overcome this challenge and promote intermolecular, highly enantioselective arylative dearomatization of naphthols using a broad range of aryl bromide electrophiles. Crucial to success is the use of the readily accessed sulfonated chiral phosphine sSPhos, which we believe engages in attractive electrostatic interactions with the substrate. Not only does sSPhos control enantioselectivity but it also drastically accelerates the reaction, most likely by facilitating the challenging palladation step that initiates dearomatization.

Synthesis of tetralone and indanone derivatives via cascade reductive Friedel-Crafts alkylation/cyclization of keto acids/esters

We disclose herein a metal-free cascade reductive Friedel-Crafts alkylation/cyclization of keto acids/esters for the synthesis of tetralones and indanones. Owing to the simple reaction conditions and setup, this protocol features broad substrate generality, facile scalability, and remarkable functional group tolerance, including the synthesis of bioactive molecule sertraline.

Double asymmetric synthesis: faster reactions are more selective and a model to estimate relative rate

The catalysed reaction of an enantiopure substrate with formation of a new chirality element may result in higher diastereoselectivity with one enantiomer of a catalyst (matched pair) than with the other (mismatched pair). The hypothesis that the matched reaction is faster was investigated using literature examples of kinetic resolution procedures that result in the formation of a new stereogenic centre. With one exception from fifteen examples, the selectivity factor (s = kfast/kslow) = kmatched/kmismatched. A model to estimate the relative rate of a fast-matched reaction vs. the corresponding slow-mismatched reaction is proposed. This model also provides insight into the basis of the selectivity displayed in the kinetic resolution procedures studied.

Anti-HIV-1 activities of constituents from the rhizomes of Boesenbergia thorelii

A new lignan, thoreliin A (1), and a new bisnorlignan, thoreliin B (2), were isolated from a MeOH extract of the rhizomes of Boesenbergia thorelii. In addition, the known bisnorlignans 3 and 4, neolignan 5, phenylpropanoids 6-15, as well as benzenoids 18-21 were also obtained from the same source. The structures were elucidated based on their spectroscopic data. By single crystal X-ray analysis, the relative stereochemistry of 1 was confirmed. All isolated compounds were evaluated for anti-HIV-1 activities. Among them, thoreliin A (1) exhibited anti-HIV-1 activities on both HIV-1 reverse transcriptase (41.43% inhibition at 200 μg/mL) and syncytium reduction assays (EC₅₀ 20.6 μM, SI 3.7), while compounds 3-6, 9 and 11-21 showed anti-HIV-1 activity only in the anti-syncytium assay (EC₅₀ 6.6-454.1 μM, SI >1.32-7.75).

One-Pot Synthesis of 3,4-Dihydropyrimidin-2(1H)-Ones Using Cadmium Sulfate as Catalyst

A simple effective synthesis of 3,4-dihydropyrimidin-2(1 H)-one derivatives from aromatic aldehydes, 1,3-dicarbonyl compounds and urea in glacical acetic acid using cadmium sulfate as catalyst is described and compared with the classical Biginelli reaction conditions, this new method has the advantage of excellent yields (83–94%) and short reaction time (2-4 h).

Highly selective Friede–Crafts monoacylation of ferrocene catalysed by ytterbium(III) triflate

In the presence of a catalytic amount of ytterbium(III) triflate[Yb(OTf)3], ferrocene reacted with anhydrides or acyl chlorides to afford monoacylferrocenes in high yields under moderate conditions. An efficient, simple and environmentlly friendly procedure was provided. The catalyst was easily recovered and reused without any loss of activity.

Tandem Oxidative Ring-Opening/Cyclization Reaction in Seconds in Open Atmosphere for the Synthesis of 1-Tetralones in Water-Acetonitrile

A mild and practical tandem oxidative ring-opening/cyclization reaction mediated by Ce⁴⁺ for the synthesis of 1-tetralones is presented. This rapid transformation was completed within 30 s and conducted in an open reactor at 0 °C in a water-acetonitrile mixture. Various cyclobutanol derivatives are transformed into desired products in good to high yields, and this reaction can be easily scaled up to the gram scale.

Palladium-Catalyzed Reductive Coupling Reaction of Terminal Alkynes with Aryl Iodides Utilizing Hafnocene Difluoride as a Hafnium Hydride Precursor Leading to trans-Alkenes

Herein, we describe a reductive cross-coupling of alkynes and aryl iodides by using a novel catalytic system composed of a catalytic amount of palladium dichloride and a promoter precursor, hafnocene difluoride (Cp₂ HfF₂ , Cp=cyclopentadienyl anion), in the presence of a mild reducing reagent, a hydrosilane, leading to a one-pot preparation of trans-alkenes. In this process, a series of coupling reactions efficiently proceeds through the following three steps: (i) an initial formation of hafnocene hydride from hafnocene difluoride and the hydrosilane, (ii) a subsequent hydrohafnation toward alkynes, and (iii) a final transmetalation of the alkenyl hafnium species to a palladium complex. This reductive coupling could be chemoselectively applied to the preparation of trans-alkenes with various functional groups, such as an alkyl group, a halogen, an ester, a nitro group, a heterocycle, a boronic ester, and an internal alkyne.

Effect of methoxyl groups on the NMR spectra: configuration and conformation of natural and synthetic indanic and tetralinic structures

Here, we studied the influence of the methoxyl groups attached at C-7 and C-2' of natural and synthetic 1-arylindanes on the chemical shift of the signal of bibenzylic hydrogen and carbon atoms and J_1,2 coupling constants. This influence was also analysed in natural 1-aryltetralins and related compounds that possess methoxyl and/or hydroxyl groups bound at C-8 and C-2'. The methoxyl groups attached at C-7 in indanes or at C-8 in tetralins produce a deshielding signal at H-1 and shield at C-1 and a strong decrease in the value of J_1,2 due to the pseudoequatorial location adopted by the aryl group bound at C-1, avoiding an 'A^1,3 strain'. Furthermore, compounds with hydroxyl or methoxyl groups in C-2', in the absence of substituents of C-7 or C-8, present a strong deshielding signal at H-1, strong shield of the C-1 signal and a decrease in the value of J_1,2 . This is attributed to the stereoelectronic effects of the methoxyl or hydroxyl groups, which we have called 'Asarone effect'. NOESY experiments were conducted to confirm the configuration and conformation of some of the compounds included in this work. This study shows that both effects, A^1,3 strain and Asarone effect, must be taken into account when the structure of natural indanes and tetralins is analysed by using ¹ H-NMR and ¹³ C-NMR spectra. Copyright © 2016 John Wiley & Sons, Ltd.

Highly Enantioselective Synthesis of Indolines: Asymmetric Hydrogenation at Ambient Temperature and Pressure with Cationic Ruthenium Diamine Catalysts

A highly enantioselective synthesis of indolines by asymmetric hydrogenation of 1H-indoles and 3H-indoles at ambient temperature and pressure, catalyzed by chiral phosphine-free cationic ruthenium complexes, has been developed. Excellent enantio- and diastereoselectivities (up to >99 % ee, >20:1 d.r.) were obtained for a wide range of indole derivatives, including unprotected 2-substituted and 2,3-disubstituted 1H-indoles, as well as 2-alkyl- and 2-aryl-substituted 3H-indoles.

Amine synthesis via transition metal homogeneous catalysed hydrosilylation

This review summarizes the preparation of amines involving homogeneous transition metal catalysed hydrosilylation including reductions of imines, amides, nitro and nitriles, reductive aminations and N-methylation of amines with CO₂.

Asymmetric decarboxylative 1,4-addition of malonic acid half thioesters to vinyl sulfones: highly enantioselective synthesis of 3-monofluoromethyl-3-arylpropanoic esters

An asymmetric decarboxylative 1,4-addition of malonic acid half thioesters (MAHTs) to 2-aryl-substituted vinyl sulfones has been developed, yielding adducts with excellent enantioselectivity (up to 97 % ee). In view of tuning pKa values, a quinine-based benzyl-substituted thiourea was designed and demonstrated as the most efficient catalyst. The enantioselective synthesis of 3-monofluorinated analogues of 3-methyl indanone and (+)-turmerone has been accomplished from decarboxylative 1,4-addition adducts with satisfactory results.

Kinetic resolution of unsaturated amides in a chlorocyclization reaction: concomitant enantiomer differentiation and face selective alkene chlorination by a single catalyst

The first example of a kinetic resolution via chlorofunctionalization of olefins is reported. The enantiomers of racemic unsaturated amides were found to have different hydrogen-bonding affinities for chiral Lewis bases in numerous solvents. This interaction was exploited in developing a kinetic resolution of racemic unsaturated amides via halocyclization. The same catalyst serves to both "sense chirality" in the substrate as well as mediate a highly face-selective chlorine delivery onto the olefin functionality, resulting in stereotriad products in up to 99:1 dr and up to 98.5:1.5 er. The selectivity factors were typically greater than 50 to allow for the simultaneous synthesis of both the products and unreacted substrates in highly enantioenriched form at yields approaching 50%. The reaction employs catalytic amounts (≤0.50 mol %) of a commercially available and recyclable organocatalyst.

Stereoselective amination of chiral benzylic ethers using chlorosulfonyl isocyanate: total synthesis of (+)-sertraline

The stereoselective amination of various chiral benzylic ethers using chlorosulfonyl isocyanate is developed, and the application of this method to the total synthesis of a potent antidepressant, (+)-sertraline, from readily available 1-naphthol is also described.

Chemical constituents of Aristolochia constricta: antispasmodic effects of its constituents in guinea-pig ileum and isolation of a diterpeno-lignan hybrid

Twenty constituents were isolated from the n-hexane and chloroform extracts of Aristolochia constricta, a plant whose aerial parts have been used empirically in folk medicine for various purposes. The inhibitory effects of these constituents on smooth muscle contraction in isolated guinea-pig ileum were studied in order to observe their antispasmodic effects. 3,4-Dibenzyldihydrofuran-type lignans [(-)-cubebin, (-)-hinokinin, and (-)-pluviatolide] and a kaurene-type diterpene [(-)-kaur-16-en-19-oic acid] were isolated as active principals. They inhibited electrically induced and acetylcholine-induced contraction in the isolated guinea-pig ileum. In addition, 9- O-[(-)-kaur-15-en-17-oxyl]cubebin was isolated as a new diterpeno-lignan hybrid, although this constituent did not exhibit antispasmodic activity.

Synthesis of chiral 3-substituted indanones via an enantioselective reductive-Heck reaction

An efficient intramolecular palladium-catalyzed, asymmetric reductive-Heck reaction has been developed, which allowed for the synthesis of either enantiomerically enriched 3-substituted indanones or alpha-exo-methylene indanones depending on the base used.