Trivalent Phosphine-Catalyzed [4+1] Spiro-annulation Reaction Using Allenyl Imide and Methylene Cyclocompounds.

The trivalent phosphine-catalyzed [4+1] spiro-annulation reaction of allenyl imide and activated methylene cyclocompounds has been developed for the construction of various spiro-2-cyclopenten-1-ones. Oxindoles, 3-isochromanones, and 2-indanones are selected as 1C synthons to capture the in situ-generated bis-electrophilic α,ß-unsaturated ketenyl phosphonium intermediate, affording the corresponding monospiro- and bispiro-cyclopentenones in good to excellent yields (≤91%) under mild conditions. The primary attempt at asymmetric catalysis using monophosphine (R)-SITCP provides promising enantioselectivity (45% ee). A plausible reaction mechanism is also proposed.

Phosphine-Catalyzed Annulations Based on [3+3] and [3+2] Trapping of Ketene Intermediates with Thioamides.

With the aim of developing novel annulations via ketene intermediates, allenyl imide and alkynoates bearing good leaving groups are used for their function in a tandem conjugate addition-elimination reaction (SN2' type) promoted by nucleophilic phosphine catalysts. By utilizing thioamides as 1S,3N-bis-nucleophiles, [3+3] and [3+2] annulations have been established to allow rapid access to 1,3-thiazin-4-ones and 5-alkenyl thiazolones in high yields, respectively. Furthermore, the possible reaction mechanisms are proposed on the basis of deuterium labeling experiments and density functional theory calculations.

Diastereodivergent Synthesis of Chiral 4-Fluoropyrrolidines (exo and exo') Based on the Cu(II)-Catalyzed Asymmetric 1,3-Dipolar Cycloaddition.

1,3-Dipolar cycloaddition of azomethine ylides and electron deficient alkenes is widely studied for rapid installation of pyrrolidine frameworks. Despite significant advances, the major limitations of this process are creating chiral pyrrolidines bearing a quaternary stereogenic center and controlling the diastereoselectivity. Herein, we present an exo-selective asymmetric 1,3-dipolar cycloaddition to access chiral pyrrolidines with four contiguous stereogenic centers, including a fluorinated quaternary stereogenic center at C4, wherein a Cu(OAc)2/(S)-tol-BINAP catalyst and α-fluoro-α,ß-unsaturated arylketone dipolarophiles are used. Epimerization promoted by 5.0 equiv of DBU at 90 °C results in the formation of chiral 4-fluoropyrrolidines (exo') while maintaining the optical purity.

[Therapeutic effect of long-snake moxibustion combined with western medication on diarrhea type irritable bowel syndrome of spleen and kidney yang deficiency].

OBJECTIVE: To compare the therapeutic effect between long-snake moxibustion combined with western medication and simple medication on diarrhea type irritable bowel syndrome (IBS-D) of spleen and kidney yang deficiency. METHODS: A total of 60 patients with IBS-D of spleen and kidney yang deficiency were randomized into an observation group and a control group, 30 cases in each one. In the control group, loperamide hydrochloride capsule (2.0 mg each time, 3 times a day) and bacillus licheniformis live capsule (0.5 mg each time, 3 times a day) were given orally. In the observation group, long-snake moxibustion was added on the basis of the treatment in the control group, ginger-partitioned moxibustion was applied from Dazhui (GV 14) to Yaoshu (GV 2) of governor vessel, once a week. The treatment was given for 8 weeks in both groups. The scores of main symptom and IBS quality of life questionnaire (IBS-QOL) were observed before and after treatment, and the therapeutic effect was evaluated in both groups. RESULTS: Compared before treatment, the symptom scores of abdominal pain, defecation frequency, mucous stool and appetite reduction were decreased (P<0.05), the scores of daily social intercourse, daily activity, diet, work, emotion, sleep quality, mental state and energy change were increased in both groups (P<0.05). After treatment, each sub-item score of main symptom in the observation group was lower than the control group (P<0.05), each sub-item score of IBS-QOL was higher than the control group (P<0.05). The total effective rate was 96.7% (29/30) in the observation group, which was superior to 73.3% (22/30) in the control group (P<0.05). CONCLUSION: Long-snake moxibustion combined with western medication can effectively treat the IBS-D of spleen and kidney yang deficiency, relieve the clinical symptoms and improve the quality of life, the effect is superior to the simple treatment of oral western medication.

Asymmetric Petasis reaction for the synthesis of chiral α- and ß-butadienyl amines.

The Petasis reaction using (1S,2R)-1-amino-2-indanol as the substrate and an activator to construct α- and ß-butadienyl amines in optically pure forms was realized, which are otherwise difficult to prepare. The reactions feature a metal-free nature, broad substrate scope, complete regioselectivities (γ-selectivity of pinacol homoallenyl- and isoprenylboronates), and high to excellent chirality induction (up to >20 : 1 dr). The favored nucleophilic addition across the Si-face of the imine intermediate was explained using DFT calculations of the six-membered chair-like transition state.

A formal [3 + 3] cycloaddition of allenyl imide and activated ketones for the synthesis of tetrasubstituted 2-pyrones.

CsOH·H2O-catalyzed formal [3 + 3] cycloadditions of allenyl imide with ß-ketoesters, 1,3-diketones or ß-ketonitriles for the synthesis of tetrasubstituted 2-pyrone derivatives have been demonstrated. The allenyl imide was utilized as a C3-synthon, and a ketenyl intermediate was proposed via the process of 1,4-addition of carbon anion to allene followed by elimination of the 2-oxazolidinyl group.

Catalytic asymmetric aldehyde prenylation and application in the total synthesis of (-)-rosiridol and (-)-bifurcadiol.

Chiral phosphoric acid-catalyzed asymmetric aldehyde prenylation has been established using an α,α-dimethyl allyl boronic ester. The transformation provides expedient access to a wide array of aryl, heteroaryl, aryl-substituted alkenyl and primary and secondary aliphatic homoprenyl alcohols with excellent asymmetric induction. The utility of this asymmetric catalysis strategy has been demonstrated through a short and efficient total synthesis of the two natural products (-)-rosiridol and (-)-bifurcadiol.

Brønsted Acid-Catalyzed General Petasis Allylation and Isoprenylation of Unactivated Ketones.

Brønsted acid-catalyzed general Petasis allylation and isoprenylation of unactivated ketones were developed by using o-hydroxyaniline and the corresponding pinacolyl boronic esters. This robust methodology provided access to a broad variety of quaternary homoallylic amines and dienyl amines in high yields, proved to be applicable to a gram-scale synthesis, and allowed the synthesis of a potentially bioactive quaternary homoallylic aminodiol.

Phosphine-Catalyzed [4+1] Cycloadditions of Allenes with Methyl Ketimines, Enamines, and a Primary Amine.

Unprecedented phosphine-catalyzed [4+1] cycloadditions of allenyl imides have been discovered using various N-based substrates including methyl ketimines, enamines, and a primary amine. These transformations provide a one-pot access to cyclopentenoyl enamines and imines, or (chiral) γ-lactams through two geminal C-C bond or two C-N bond formations, respectively. Several P-based key intermediates including a 1,4-(bis)electrophilic α,ß-unsaturated ketenyl phosphonium species have been detected by 31 P NMR and HRMS analyses, which shed light on the postulated catalytic cycle. The synthetic utility of this new chemistry has been demonstrated through a gram-scaling up of the catalytic reaction as well as regioselective hydrogenation and double condensation to form cyclopentanoyl enamines and fused pyrazole building blocks, respectively.

Diastereodivergent Asymmetric 1,3-Dipolar Cycloaddition of Azomethine Ylides and ß-Fluoroalkyl Vinylsulfones: Low Copper(II) Catalyst Loading and Theoretical Studies.

A CuII -catalyzed asymmetric 1,3-dipolar cycloaddition using ß-fluoroalkyl alkenyl arylsulfones as dipolarophiles and glycine/alanine iminoesters as azomethine ylide precursors has been developed. Remarkably, a catalyst loading as low as 0.5 mol % is highly efficient. Accordingly, a wide range of enantioenriched 3-fluoroalkyl pyrrolidines, as well as Δ2 -pyrroline and pyrrole derivatives, are generated in good to excellent yields with high asymmetric induction. This synthetic approach is diastereodivergent in that exo-adducts could be converted into the corresponding exo'-adducts by 1,8-diazabicyclo[5.4.0]undec-7-ene mediated epimerization at C2 of the pyrrolidine core. The free-energy profiles from DFT calculations suggest the Michael addition of the 1,3-dipole to be the rate- and enantiodetermining step, and the origin of stereoselectivity is studied by means of the noncovalent interaction (NCI) analysis.

Palladium-Catalyzed Direct Ortho-C-H Selenylation of Benzaldehydes Using Benzidine as a Transient Directing Group.

Benzidine was found to be a novel transient directing group to enable Pd-catalyzed direct selenylation of inert C(sp2)-H bonds of benzaldehydes. Diverse diarylselenides were readily constructed in high efficiency and satisfactory yields with good functional group tolerance. The practical usage of the method was further demonstrated by enlarged reaction to gram scale and application in the facile access to two selenoxanthenes and one fluorescent probe.

Air- and Light-Stable S-(Difluoromethyl)sulfonium Salts: C-Selective Electrophilic Difluoromethylation of ß-Ketoesters and Malonates.

Air- and light-stable electrophilic difluoromethylating reagents, S-(difluoromethyl)- S-phenyl- S-(2,4,6-trialkoxyphenyl) sulfonium salts were successfully developed, and the introduction of intramolecular hydrogen bonds plays a crucial role for the stabilities and reactivities of these reagents. C-selective difluoromethylation of a broad range of ß-ketoesters and malonates proceeded smoothly under mild reaction conditions to give good to excellent yields with excellent C/O regioselectivities.

Neighboring phenolic group-activated gem-difluoroallylboration of imines for the catalyst-free synthesis of gem-difluorohomoallylamines.

We herein report an unprecedented addition reaction of pinacol gem-difluoroallylborates and imines enabled by a neighboring phenolic group in an N-protecting group under catalyst-free conditions, thus facilitating the construction of a wide range of racemic gem-difluorohomoallylamine derivatives. Based on the control experiments, a plausible transition state via the Zimmerman-Traxler model was proposed to elucidate the significance of the neighboring phenolic group, as well as the γ-selectivity of the boronate reagents.

Petasis-Type gem-Difluoroallylation Reactions Assisted by the Neighboring Hydroxyl Group in Amines.

A three-component Petasis-type gem-difluoroallylation reaction of using pinacol gem-difluoroallylboronates, aldehydes or isatin, and ß-amino alcohols enabled by the neighboring hydroxyl group in amine is reported, affording various racemic and chiral gem-difluorohomoallylamine derivatives with good to excellent results. Based on the control experiment and stereochemistry of the product, a proposed reaction pathway is illustrated to clarify the origin of regio- and stereoselectivity under protic solvent conditions.

Enantioselective Synthesis of 1,3-Disubstituted 1,3-Dihydroisobenzofurans via a Cascade Allylboration/Oxo-Michael Reaction of o-Formyl Chalcones Catalyzed by a Chiral Phosphoric Acid.

The first chiral Brønsted acid-catalyzed asymmetric cascade allylboration/oxo-Michael reaction between o-formyl chalcones and allylboronate has been successfully discovered, which afforded chiral 1,3-disubstituted 1,3-dihydroisobenzofurans with a yield, diastereoselective ratio (dr) and enantioselective excess (ee) up to 94%, 2.5:1, and 98%, respectively. In addition, 2,3-dienylboronic pinacol ester was also applied into this cascade reaction with good catalytic results.

Catalytic Asymmetric 1,3-Dipolar Cycloaddition of ß-Fluoroalkylated α,ß-Unsaturated 2-Pyridylsulfones with Nitrones for Chiral Fluoroalkylated Isoxazolidines and γ-Amino Alcohols.

2-Pyridylsulfone- and fluoroalkylated group-activated olefins underwent highly efficient diastereo- and enantioselective 1,3-dipolar cycloadditions across various aromatic and aliphatic nitrones in the presence of a chiral NiII /bis(oxazoline) catalyst. The process was tuned by 4 Šmolecular sieves, chiral bis(oxazoline) ligands, reaction solvents, and temperature. A wide array of optically pure fluoroalkylated isoxazolidines were obtained, thus facilitating the asymmetric synthesis of an enantioenriched α-trifluoromethylated γ-amino alcohol in gram-scale and a trifluoromethylated derivative of 1,3-oxazinan-2-one with potential pharmaceutical interest. A stereochemical model, based on the absolute configuration of one adduct and some control experiments, was postulated to account for the observed endo- and enantioselectivity.

Catalytic asymmetric synthesis of enantioenriched heterocycles bearing a C-CF3 stereogenic center.

Given the important agricultural and medicinal application of optically pure heterocycles bearing a trifluoromethyl group at the stereogenic carbon center in the heterocyclic framework, the exploration of efficient and practical synthetic strategies to such types of molecules remains highly desirable. Catalytic enantioselective synthesis has one clear advantage that it is more cost-effective than other synthetic methods, but remains limited by challenges in achieving excellent yield and stereoselectivities with a low catalyst loading. Thus far, numerous models of organo- and organometal-catalyzed asymmetric reactions have been exploited to achieve this elusive goal over the past decade. This review article describes recent progress on this research topic, and focuses on an understanding of the catalytic asymmetric protocols exemplified in the catalytic enantioselective synthesis of a wide range of complex enantioenriched trifluoromethylated heterocycles.

Revised stereochemistry of ceramide-trafficking inhibitor HPA-12 by X-ray crystallography analysis.

In response to Berkes's report revising the stereochemistry of HPA-12, an important ceramide-trafficking inhibitor that was discovered and synthesized and its stereochemistry determined in 2001, the synthesis and the stereochemistry were reinvestigated. A large-scale synthetic method for HPA-12 based on a Zn-catalyzed asymmetric Mannich-type reaction in water was developed. Single crystals of HPA-12 for X-ray crystallographic analysis were obtained from ethyl propionate/n-hexane, and the stereochemistry was definitely determined to be 1R,3S, consistent with Berkes's revised structure.