Synthesis of Some New 1,4‐Dihydropyridine Derivatives through a Facile One‐pot Hantzsch Condensation Catalyzed by Triethylamine

A facile and efficient synthesis of new 1,4‐dihydropyridine derivatives was reported via Hantzsch three‐component condensation reaction of aldehydes or formylphenylboronic acids, ethyl acetoacetate, and ammonium acetate in the presence of a catalytic amount of triethylamine under solvent‐free conditions. The method described here offers several advantages including high yields, short reaction times, and simple work‐up procedure.     

Ruthenium‐Catalyzed Transfer‐Hydrogenative Cyclization of 1,6‐Diynes with Hantzsch 1,4‐Dihydropyridine as a H2 Surrogate

The transfer‐hydrogenative cyclization of 1,6‐diynes with Hantzsch 1,4‐dihydropyridine as a H₂ surrogate was performed in the presence of a cationic ruthenium catalyst of the type [Cp′Ru(MeCN)₃PF₆]. Exocyclic 1,3‐dienes or their 1,4‐hydrogenation products, cycloalkenes, were selectively obtained, depending on the substrate structure and the reaction conditions.     

Hydrogallierungsreaktionen mit den Monoalkinen H5C6‐C≡C‐SiMe3 und H5C6‐C≡C‐CMe3 – cis/trans‐Isomerie und Substituentenaustausch

Hydrogallation Reactions Involving the Monoalkynes H₅C₆‐C≡C‐SiMe₃ and H₅C₆‐C≡C‐CMe₃ – cis/trans Isomerisation and Substituent Exchange Phenyl‐trimethylsilylethyne, H₅C₆‐C≡C‐SiMe₃, reacted with different dialkylgallium hydrides, R₂Ga‐H (R = Me, Et, nPr, iPr, tBu), by the addition of one Ga‐H bond to its C≡C triple bond (hydrogallation). The gallium atoms attacked selectively those carbon atoms, which were also attached to trimethylsilyl groups. The cis arrangement of Ga and H across the resulting C=C double bonds resulted only for the sterically most shielded di(tert‐butyl)gallium derivative, while in all other cases spontaneous cis/trans rearrangement occurred with the quantitative formation of the trans addition products. The diethyl compound Et₂Ga‐C(SiMe₃)=C(H)‐C₆H₅ ( 2 ) gave by substituent exchange the secondary products EtGa[C(SiMe₃)=C(H)‐C₆H₅]₂ ( 7 , Z,Z) and Ga[C(SiMe₃)=C(H)‐C₆H₅]₃ ( 8 ). Interestingly, compound 8 has two alkenyl groups with a Z configuration, while the third C=C double bond has the cis arrangement of Ga and H (E configuration). The reversibility of the cis/trans isomerisation of hydrogallation products was observed for the first time. tert‐Butyl‐phenylethyne gave the simple addition product, R₂Ga(C₆H₅)=C(H)‐CMe₃ ( 9 ), only with di(n‐propyl)gallium hydride.     

Cd(NO3)2.4H2O Catalyzed One‐Pot Synthesis of 1,4‐Dihydropyridine and Polyhydroquinoline Derivatives through the Hantzsch Multicomponent Condensation

The synthesis of various 1,4‐dihydropyridine and polyhydroquinoline derivatives was achieved in good to excellent yields using cadmium (II) nitrate as catalyst to promote the classical and modified Hantzsch conditions in good yields under mild conditions.     

无金属和未催化的Hantzsch酯还原 a, b-不饱和酮反应

Hantzsch酯和 a, b-不饱和酮在氩气保护下,直接在二甲苯中回流可以得到相应的饱和酮,整个过程不需要加入任何金属或有机催化剂。     

Synthesis of 1,2,4‐Triazolo[4,3‐a]pyrimidine Derivatives by Cyclocondensation of a 2‐Thioxopyrimidin‐4(3H)‐one with Hydrazonoyl Halides

The reaction of 1,2‐dihydro‐6‐(phenylamino)‐2‐thioxopyrimidin‐4(3H)one ( 16 ) with N‐arylhydrazonoyl halides 15 in CHCl₃ in the presence of Et₃N under reflux afforded the corresponding 1,2,4‐triazolo[4,3‐a]pyrimidin‐5‐ones of type 20 in good yields (Scheme 3). The structure of one of the derivatives, 20d , has been established by X‐ray crystallography. Conceivable reaction mechanisms are discussed in Schemes 3 and 4. The products of type 20 easily undergo reactions with electrophiles such as benzenediazonium chloride, chloroacetyl chloride, and NaNO₂ in AcOH to give 6‐phenylazo, 6‐chloroacetyl, and 6‐nitroso derivatives 21, 23 , and 25 , respectively (Scheme 5).     

Methylenecyclopropane Annulation by Manganese(I)‐Catalyzed Stereoselective C−H/C−C Activation

C−H/C−C functionalizations with methylenecyclopropanes (MCPs) were accomplished with a versatile base‐metal catalyst. A robust manganese(I) complex enabled the expedient annulation of MCPs by synthetically meaningful ketimines to deliver, upon one‐pot hydroarylation, densely substituted polycylic anilines in a step‐economical fashion. Mechanistic studies provided strong support for a facile organometallic C−H manganation, while typical cobalt, ruthenium, rhodium, and palladium catalysts were found completely ineffective.     

Practical Synthesis of (20S)‐10‐(3‐Aminopropyloxy)‐7‐ethylcamptothecin,a Water‐Soluble Analogue of Camptothecin

A robust, practical synthesis of (20S)‐10‐(3‐aminopropyloxy)‐7‐ethylcamptothecin (T‐2513, 5 ), which is a water‐soluble analogue of camptothecin, has been developed. The key step in this synthesis is a highly diastereoselective ethylation at the C20 position by using N‐arylsulfonyl‐(R)‐1,2,3,4‐tetrahydroisoquinoline‐3‐carboxylic acid ester as a chiral auxiliary, which affords the key intermediate ethyl‐(S)‐2‐acyloxy‐2‐(6‐cyano‐5‐oxo‐1,2,3,5‐tetrahydroindolizin‐7‐yl)butanoate ( 8 k ) in 93 % yield and 87 % de. Optically pure compound 8 k was obtained by a single recrystallization from acetone and its further elaboration through Friedlander condensation afforded compound 5 . This synthesis does not require any chromatographic purification steps and can provide compound 5 on a multi‐gram scale in 6.3 % overall yield (16 steps).     

Ruthenium(II)‐Catalyzed C−C Arylations and Alkylations: Decarbamoylative C−C Functionalizations

Ruthenium(II)biscarboxylate catalysis enabled selective C−C functionalizations by means of decarbamoylative C−C arylations. The versatility of the ruthenium(II) catalysis was reflected by widely applicable C−C arylations and C−C alkylations of aryl amides, as well as acids with modifiable pyrazoles, through facile organometallic C−C activation.     

Click Inspired Synthesis of 1,2,3‐Triazole‐linked 1,3,4‐Oxadiazole Glycoconjugates

The glycoconjugation of biologically privileged 1,3,4‐oxadiazole scaffold is described via Cu(I)‐catalyzed azide–alkyne cycloaddition. A series of glycosyl alkynes 1b – i , obtained from various commercial sugars, were treated with azide functionalized 1,3,4‐oxadiazole using click chemistry to access triazole‐linked glycosylated 1,3,4‐oxadiazoles 10b – i in good yields. The structure of the developed glycoconjugates has been ascertained by extensive spectroscopic analysis (¹H &¹³C NMR, IR, and MS).     

Synthesis of Mesoionic Isoquinolines by Rhodium(III)‐Catalyzed C−H Activation

Hydroxyl‐substituted benzaldimines underwent a Rh^III‐catalyzed C?H activation and annulation with alkynes to provide novel mesoionic isoquinoline derivatives in moderate to excellent yields using oxygen as an internal anion source. This simple and efficient approach has a broad substrate scope.