One-pot Sequential Process Research Articles

Organocatalytic Deoxyhalogenation of Alcohols with Inorganic Halides

Direct substitution of alcohols has been a popular topic in organic chemistry. Deoxyhalogenation of alcohols represents one of the most important transformations for accessing organic halides. However, a practical catalytic protocol with readily available, inexpensive, and stable inorganic halides is still unknown. Herein, we report an organocatalytic deoxyhalogenation of alcohols with inorganic halides, which avoids the employment of stoichiometric activators and organic halogenating reagents. Various alcohols are transformed to the corresponding organic bromides and iodides in good yield. Through the one-pot sequential process, C–N, C–O, C–F, C–Cl, and C–S bond formation can also be achieved with good yield.

Synthesis of Oligosaccharides of Glucosamine by Automated Electrochemical Assembly

The automated electrochemical assembly is one of our arrial points for development of electrochemical methods for oligosaccharide synthesis. The one-pot sequential process of activation of thioglycoside building block by electrochemical oxidation and coupling with thioglycoside building block can be carried out in automated manner, and muliple cycles of the process enables us to synthesis oligosaccharides with desired chain length. We have synthesized oligoglucosamines with β-1,6- and β-1,4-glycosidic linkages. Total synthesis of TMG-chitotriomycin and Myc-IV (C16 : 0, S), which are biologically active oligoglucosamines derivatives, has also achieved. Ionic liquid tags were introduced to glucosamine building blocks to facilitate separation of products; however, they worked not only separation tag but also electrolyte and stereo-controlling group in electrochemical glycosylation. We also found that electrochemical glycosylation was also useful to convert linear oligosaccharides of glucosamines into the corresponding cyclic oligosaccharides.

Diastereoselective pot-and atom-economical synthesis of densely-substituted polycyclic 1,2- and 1,2,3-fused indole scaffolds

A simple, efficient, one-pot sequential process for the preparation of a family of 8,9-dihydropyrido[1,2–a]indol-6(7H)-one scaffolds in acceptable yields has been established under mild conditions. The Michael-hemiaminalization-oxidation reaction proceeds between methyl 2-(3-formyl-1H-indol-2-yl) acetate and trans-β-aryl/alkyl-substituted acroleins using pyrrolidine-BzOH as an efficient organocatalyst, followed by oxidation of in situ generated of C,N-fused hemiaminal adducts in the presence of PDC at room temperature. Excitingly, organobase-catalyzed highly diastereoselective (up to ≤9:1 dr) construction of a series of pharmacologically attractive 1,2,3-fused tetracyclic indole scaffolds with five contiguous chiral centers including an all-carbon stereogenic center has been realized through our developed method. Moreover, pyrrolidine-BzOH and PTSA as combined catalytic systems promote the uninterrupted sequential Michael-cyclization reaction, followed by N-alkylation reaction with carbazole to produce interesting class of 6-(9H-carbazol-9-yl)-6,7,8,9-tetrahydropyrido[1,2–a]indole derivatives in a diastereoselective manner.

An Organocatalytic Asymmetric Friedel-Crafts Addition/Fluorination Sequence: Construction of Oxindole-Pyrazolone Conjugates Bearing Vicinal Tetrasubstituted Stereocenters.

A highly efficient and practical one-pot sequential process, consisting of an organocatalytic enantioselective Friedel-Crafts-type addition of 4-nonsubstituted pyrazolones to isatin-derived N-Boc ketimines and a subsequent diastereoselective fluorination of the pyrazolone moiety, is developed. This reaction sequence delivers novel oxindole-pyrazolone adducts featuring vicinal tetrasubstituted stereocenters with a 0.5 mol % catalyst loading in high yield with excellent enantio- and diastereocontrol. Notably, chloro, bromo, and thioether functionalities can be readily incorporated, rendering a broad diversity of the product.

Organocatalytic asymmetric one-pot sequential reaction: synthesis of highly substituted spirocyclohexanepyrazolones with six contiguous stereogenic carbons

An atom-economical synthesis of chiral polyfunctionalized spiropyrazolone derivatives based on the development of a new organocatalytic enantioselective one-pot sequential Michael/Michael/Aldol reaction of 1,3-dicarbonyl compounds with unsaturated pyrazolones and α,β-unsaturated aldehydes has been developed. The notable features of this one-pot sequential process include the generation of up to six consecutive stereogenic carbon centers including one quaternary stereocenter and five tertiary stereocenters with high enantioselectivities (up to 95% ee) and excellent diastereoselectivities (>99:1 d.r.).

Synthesis of 3-tetrazolylmethyl-azepino[4,5-b]indol-4-ones in two reaction steps: (Ugi-azide/N-acylation/SN2)/free radical cyclization and docking studies to a 5-Ht6 model

A series of nine novel 3-tetrazolylmethyl-azepino[4,5-b]indol-4-ones were prepared in moderate to good overall yields in only two reaction steps. The first step consisted of a one-pot sequential process of an Ugi-azide multicomponent reaction, N-acylation and SN2 to give the xanthates. The second step was an intramolecular cyclization under free radical conditions. Also, their binding modes have been modelled using docking techniques.

Chemoenzymatic dynamic kinetic resolution of α-trifluoromethylated amines: influence of substitutions on the reversed stereoselectivity

Enzymatic resolution of α-trifluoromethylated amines via kinetic resolution (KR), dynamic kinetic resolution (DKR) employing CALB-Pd/Al2O3, and a one-pot sequential process of KR/DKR/KR was investigated comparatively for the first time. Although CALB-catalyzed KR of α-trifluoromethylated amines with substituents of methyl (1a), isopropyl (1c), phenyl (1d) and benzyl group (1e) can provide good stereoselectivity factors E from 31 to >200 respectively, DKR and sequential process of KR/DKR/KR possess better practical application potential because of the higher conversion (62%–84%) and the similar enantiomeric excesses (90%–99%). The enantiopreference and inversion for the α-trifluoromethylated amines displayed by CALB were observed and explained by docking modes. Namely, for 1,1,1-trifluoro-2-propylamine (1a), the product amide with R-configuration was obtained, and the enantiopreference was converted to S for the amines (1b–1e) with substituents larger than methyl group. The catalysts recycle, and scale-up experiments were demonstrated successfully. All these results indicated the high efficiency and green feature of this enzymatic process, and its application significance.

En Route to (S)-Selective Chemoenzymatic Dynamic Kinetic Resolution of Aliphatic Amines. One-Pot KR/Racemization/KR Sequence Leading to (S)-Amides

A one-pot sequential process, involving a radical racemization and an enzymatic resolution, provides access to (S)-amides, from racemic amines, with ee and yields ranging from 78 to 94% and 58 to 80%, respectively.

Multicomponent, One-Pot Sequential Synthesis of 1,3,5- and 1,3,5,5-Substituted Barbiturates

Carbodiimides and malonic acid monoethylesters readily react to afford N-acylurea derivatives that could be cyclized in situ by addition of a suitable base. This process represents a general and straightforward one-pot sequential synthesis of 1,3,5-trisubstituted barbiturates in very mild conditions (organic solvent/2 N NaOH aqueous solution, 20 degrees C). Performing the reaction in the presence of an electrophile resulted in the formation of fully substituted (namely, 1,3,5,5-tetrasubstituted) barbiturates through a three-component one-pot sequential process. The latter, however, occurred only with highly reactive electrophiles, such as benzyl and, in some instances, allyl halides. In order to expand the scope of the process, we sought to develop a general method for the C-alkylation of 1,3,5-trisubstituted barbiturates. We found that C-alkylation occurred upon treatment of 1,3,5-trisubstituted barbiturates with an alkyl halide in CH3CN at 120 degrees C in the presence of anhydrous K2CO3 affording the target 1,3,5,5-tetrasubstituted barbiturates in good yields. The multicomponent process was accomplished by combining the three steps in a one-pot sequential fashion, i.e., the condensation of carbodiimides with malonic acid monoethylesters, the cyclization of the resulting N-acylureas, and the C-alkylation of the resulting 1,3,5-substituted barbiturates. A detailed study of the influence of the structure of the reactants on the reaction outcome and mechanism is presented. By selective N'-deprotection of 1,3,5,5-tetrasubstituted barbiturates, the corresponding 1,5,5-trisubstituted barbiturates were also prepared.

Synthetic study toward 17-thiasteroids: synthesis of the 1-thiahydrinden-5-one subunit using a new annulation procedure and investigation of its reduction

The enantioselective syntheses of ketones 6 and 7 featuring the CD subunit of 17-thiasteroid are described. The key bicyclic 1-thiahydrindenone ( S)- 5 was assembled in three steps from Michael adduct ( S)- 12 via β-keto ester 15 using a one-pot sequential process involving cleavage of both the ketal group and the tert-butyl ester group, decarboxylation, and finally intramolecular aldol condensation. Hydridoalkyl cuprate-induced conjugate reduction of 1-thiahydrindenone ( S)- 5 and its corresponding sulfone ( S)- 23 gave 1-thiahydrindanones 6 and 7, respectively, which display unexpectedly the unnatural cis-ring junctions.

A facile one-pot synthesis of acyclic β-enamino ketones, an important class of versatile synthetic intermediates

A one-pot sequential process consisting of nucleophilic substitution of the lithiated acetylides with Weinreb amides followed by a Michael reaction of the extruded N-methoxy- N-methylamine after quenching with saturated NH 4Cl, provided β-enamino ketones in high yield and in a single geometrical isomeric form. It has been demonstrated that this method is applicable to a wide variety of such amides and to different acetylides.