Convenient Structural Diversity‐Guided Synthesis of Functionalized Sulfur‐Containing Heterocycles via α‐Substituted Cyanoacetamides

A convenient molecular diversity‐oriented synthesis of various functional sulfur‐containing heterocyclic scaffolds mainly including isothiazole, 2H‐1,3‐thiazine, and thiazolidine via different methods from α‐substituted cyanoacetamides is described. The target molecules have been identified on the basis of analytical spectral data, which may serve as useful structural subunits in the fields of drug discovery.     

Synthesis of Fluoroalkylated Heterocycles via the Reaction of 3-（1-Hydropolyfluoroalkenyl）-l-oxo-2,4,1-benzoxazines with Dinucleophilic Reagents

The reaction of 3-（1-hydropolyfluoroalkenyl）-1-oxo-2,4,1-benzoxazines 1 with some dinucleophiles was investigated. 7-Fluoroalkyl-2,3-dihydro- 1,4-diazepine[ 1,2-d]quinazolin- 11-ones 2, 2-fluoroalkylisoxazolo[3,2-b]quinazolin-9-ones 3 and 2-fluoroalkylbenzoimidazoles 4 were obtained from the reaction of 1 with 1,2-diaminoethane, hydroxylamine hydrochloride and 1,2-diaminobenzene respectively.     

Facile Synthesis of Monofluoro γ-Lactones and Pyrrolidine Derivatives via Electrophilic Fluorination of Allenoic Acids and Amides

A convenient method to synthesize a series of monofluoro γ-lactones and pyrrolidine derivatives in moderate to good yields via the electrophilic fluorination of γ-allenoic acids and tosylamides using Selectfluor was developed.     

Heterocycles from α‐Aminonitriles

Owing to their various modes of reactivity, α‐aminonitriles represent versatile building blocks for the construction of a wide range of nitrogen heterocycles. The present Concept article focuses on synthetic methodologies using their bifunctional nature which is the basis of their reactivity as α‐amino carbanions and as iminium ions. Reactions exclusively taking place on either the amine or on the nitrile moiety will not be considered.     

Catalytic Asymmetric Synthesis of α‐Arylpyrrolidines and Benzo‐fused Nitrogen Heterocycles

Herein, we report a practical two‐step synthetic route to α‐arylpyrrolidines through Suzuki–Miyaura cross‐coupling and enantioselective copper‐catalyzed intramolecular hydroamination reactions. The excellent stereoselectivity and broad scope for the transformation of substrates with pharmaceutically relevant heteroarenes render this method a practical and versatile approach for pyrrolidine synthesis. Additionally, this intramolecular hydroamination strategy facilitates the asymmetric synthesis of tetrahydroisoquinolines and medium‐ring dibenzo‐fused nitrogen heterocycles.     

NHC‐Catalyzed Electrophilic Trifluoromethylation: Efficient Synthesis of γ‐Trifluoromethyl α,β‐Unsaturated Esters

Described herein is a highly regioselective and efficient N‐heterocyclic‐carbene‐catalyzed γ‐trifluoromethylation of vinylogous enolates. Control experiments and DFT calculations provided important insight into the reaction mechanism.     

β‐Functionalization of Carboxylic Anhydrides with β‐Alkyl Substituents through Carbene Organocatalysis

The first NHC‐catalyzed functionalization of carboxylic anhydrides is described. In this reaction, the β carbon behaves as a nucleophilic carbon and undergoes asymmetric reactions with electrophiles. Anhydrides with challenging β‐alkyl substituents work effectively.     

Stereoselective Synthesis of Tropanes via a 6π‐Electrocyclic Ring‐Opening/ Huisgen [3+2]‐Cycloaddition Cascade of Monocyclopropanated Heterocycles

The synthesis of tropanes via a microwave‐assisted, stereoselective 6π‐electrocyclic ring‐opening/ Huisgen [3+2]‐cycloaddition cascade of cyclopropanated pyrrole and furan derivatives with electron‐deficient dipolarophiles is demonstrated. Starting from furans or pyrroles, 8‐aza‐ and 8‐oxabicyclo[3.2.1]octanes are accessible in two steps in dia‐ and enantioselective pure form, being versatile building blocks for the synthesis of pharmaceutically relevant targets, especially for new cocaine analogues bearing various substituents at the C‐6/C‐7 positions of the tropane ring system. Moreover, the 2‐azabicyclo[2.2.2]octane core (isoquinuclidines), being prominently represented in many natural and pharmaceutical products, is accessible via this approach.     

Electrophilic Bromination of N‐Acylated Cyclohex‐3‐en‐1‐amines: Synthesis of 7‐Azanorbornanes

The intramolecular bromo‐amidation and the dibromination‐cyclisation of the N‐acylcyclohex‐3‐en‐1‐amines 4, 8, 9, 11, 13, 14 , and 16 was studied in view of the synthesis of bicyclic amines that are of interest as building blocks and potential glycosidase inhibitors. The trifluoroacetamides 4, 9 , and 14 reacted with N‐bromosuccinimide (NBS) in AcOH to give dihydro‐1,3‐oxazines in good yields. The stereoselectivity of the dibromination of the alkenes 8 and 9 depends on the nature of the protecting group, the reagent, and the reaction conditions. Br₂ in CH₂Cl₂ transformed the alkenes 8 and 9 predominantly into diaxial trans,trans‐dibromides. Bromination of 9 with PhMe₃NBr₃ or with Br₂ in the presence of Et₄NBr gave predominantly the diequatorial trans,cis‐ 27 besides some trans,trans‐ 28 . A similar bromination of the C(5)‐substituted N‐acyl‐4‐aminocyclohexenes 11, 13, 14 , and 16 with PhMe₃NBr₃ was accompanied by intramolecular side reactions that were suppressed by the addition of excess Et₄NBr. Under these conditions, 11 gave diastereoselectively trans‐dibromides, while its reaction with Br₂ gave trans‐dibromides along with the dihydrooxazinone 31 . Also the carbamate 13 reacted with PhMe₃NBr₃/Et₄NBr selectively to the trans‐dibromide 32 and with Br₂ to the trans‐dibromides 32 and 33 , the dihydrooxazinone 34 , and the bicyclic ether 35 . Similarly, the trifluoroacetamide 14 provided the dibromide 36 (89%), while its reaction with Br₂ led to the dihydrooxazine 22 , and the dibromides 36 and 37 . The N‐benzyl‐N‐Boc derivative 16 did not yield any dibromide; it reacted with PhMe₃NBr₃/Et₄NBr to the dihydrooxazinone 38 , and with Br₂ to the oxazinone 38 and the bicyclic ether 39 . The high stereoselectivity of the bromination with PhMe₃NBr₃/Et₄NBr suggests an anchimeric assistance of the NHR substituent. Deprotection, cyclisation, and carbamoylation transformed the dibromides 27, 29 , and 32 into the 7‐azanorbornanes 42, 49 , and 53 . The diols 45 and 57 were obtained from 42 and 53 via HBr elimination and stereoselective dihydroxylation; they proved weak inhibitors of several glycosidases. In no case could the formation of a bicyclic azetidine (6‐azabicyclo[3.1.1]heptane) from the dibromides 26 and 30 be observed.     

Vanadium‐Catalyzed Solvent‐Free Synthesis of Quaternary α‐Trifluoromethyl Nitriles by Electrophilic Trifluoromethylation

The direct electrophilic trifluoromethylation of silyl ketene imines (SKIs) with hypervalent iodine reagents leads to the formation of quaternary α‐trifluoromethyl nitriles in good yields. This new reaction has been carried out with a variety of substituted SKIs under solvent‐free conditions using a vanadium(IV) catalyst (5 mol %). The corresponding products may be transformed into useful organofluorine building blocks.     

Microwave‐Assisted Synthesis of Heterocycles by Rhodium(III)‐Catalyzed Annulation of N‐Methoxyamides with α‐Chloroaldehydes

α‐Chloroaldehydes have been used as alkyne equivalents in rhodium‐catalyzed syntheses of isoquinolones and 3,4‐dihydroisoquinolins starting from N ‐methoxyamides. Compared to the existing technology, a complementary regioselectivity is achieved. Mechanistic investigations have been performed, and it was found that steric effects of both substrate and additive determine the product selectivity. Various other heterocycles, such as isoquinolines and lactones, can be prepared by transformation of the obtained products.     

Selenium‐Containing Heterocycles from Isoselenocyanates: Synthesis of 5‐Amino‐2,4‐dihydro‐3H‐1,2,4‐triazole‐3‐selones

The reaction of S‐methylisothiosemicarbazide hydroiodide (=S‐methyl hydrazinecarboximidothioate hydroiodide; 1 ), prepared from thiosemicarbazide by treatment with MeI in EtOH, and aryl isoselenocyanates 5 in CH₂Cl₂ affords 3H‐1,2,4‐triazole‐3‐selone derivatives 7 in good yield (Scheme 2, Table 1). During attempted crystallization, these products undergo an oxidative dimerization to give the corresponding bis(4H‐1,2,4‐triazol‐3‐yl) diselenides 11 (Scheme 3). The structure of 11a was established by X‐ray crystallography.     

New Synthesis of Pyrrolidines via Reaction of γ‐Halocarbanions with Imines

γ‐Chlorocarbanions of proper nucleophilicity, generated from 3‐chloropropyl pentachlorophenyl sulfone (=pentachloro[(3‐chloropropyl)sulfonyl]benzene; 1 ; Ar=C₆Cl₅), add to electron‐deficient formal imines 3a – l to produce anionic adducts that enter intramolecular substitution leading to substituted pyrrolidines. This new and simple synthesis of pyrrolidines mimics a 1,3‐dipolar cycloaddition, although it proceeds in two distinct steps.     

A Direct Synthesis of Highly Substituted π‐Rich Aromatic Heterocycles from Oxetanes

The ubiquitous use of π‐rich five‐membered heterocycles has driven the development of new methods for their synthesis for more than a century. Here, we disclose a general and reliable reaction manifold for the construction of highly substituted heterocycles through a facile Lewis‐acid‐catalyzed oxetane rearrangement. Notably, this methodology employs a keto‐oxetane motif as a 1,4‐dicarbonyl surrogate, which can be synthesized using robust alkylation or alkenylation reactions, and thus obviates the need to access 1,4‐dicarbonyl compounds via umpoled starting materials. We harnessed this reactivity to generate a broad range of substituted furans and pyrroles, and extended this methodology to produce benzo‐fused versions thereof.     

2‐Pyrazolin‐5‐One‐Based Heterocycles: Synthesis and Characterization

A novel series of pyrazoline and thiazole derivatives incorporating 2‐pyrazolin‐5‐one moiety were synthesized starting from α,β‐unsaturated ketones under the effect of hydrazine derivatives and thiosemicarbazide. The obtained pyrazolines 4a , 4b were treated with different reagents to afford N‐substituted pyrazolines 5a , 5b , 6a , 6b , 7a , 7b , 8a , 8b . N‐Thiocarbamoyl pyrazolines 12a , 12b were cyclized using phenacyl bromide, 2,3‐dichloroquinoxaline, and monochloroacetic acid afforded the novel pyrazolinyl thiazoles 13a , 13b , 14a , 14b , 15a , 15b , 16a , 16b , 16c , 16d , 16e , 16f . The newly synthesized compounds were characterized by analytical and spectral data.     

Copper‐Catalyzed Electrophilic Cyclization of N‐Propargylamines with Sodium Sulfinate for the Synthesis of 3‐Sulfonated Quinolines

A convenient and effective protocol for the synthesis of 3‐sulfonated quinolines via copper‐catalyzed electrophilic cyclization of N‐propargylamines has been developed, in which cheap and stable sodium sulfinates were utilized as green sulfonylation reagents. This cascade transformation involves radical addition, cyclization and dehydrogenative aromatization processes in a one‐pot reaction under mild conditions.