By combining an organocatalyzed Michael addition of 1,3‐diketones to hydroxy‐nitroolefins with a subsequent, innovative iron(0)‐catalyzed fragmentation, key enantioenriched ketones possessing additional nitro and protected alcohol functions could efficiently be prepared under excellent enantiocontrol (typically 95% ee). The reaction was made possible by the discovery that photochemical activation of iron pentacarbonyl [Fe(CO)5], a cheap widely available complex, efficiently catalyzed a Claisen‐type fragmentation under mild conditions, avoiding decomposition of the intermediates and products.
4H‐Pyran units are frequently present in molecules with significant biological and pharmaceutical activities. Herein, we present the first enantioselective formal [3+3] cycloaddition between 2‐(1‐alkynyl)‐2‐alken‐1‐ones and β‐keto esters catalyzed by a cyclohexyldiamine‐based thiourea‐tertiary amine bifunctional catalyst. Under the mild and eco‐friendly conditions, a wide range of polysubstituted 4H‐pyrans were obtained in moderate yields with good enantioselectivities.
A mild, metal‐free synthesis of polyfunctionalized N‐acyl‐N,O‐hemiacetals was developed via the nucleophilic addition of unactivated amides to ketones. The protocol demonstrated a wide substrate scope, with good isolated yields. Additionally, their O‐acetylated products serve as a precursor of α,α‐difunctionalized N‐acylimines. An addition reaction of broad scope of nucleophiles to generate N‐acylimines is also reported.
An iron(III)‐catalyzed C‐3 functionalization of flavones has been achieved using tert‐butyl peroxybenzoate (TBPB)/potassium persulphate (K2S2O8) oxidant combinations with a suitable solvent. In the presence of iron(III)/tert‐butyl peroxybenzoate/potassium persulphate, the reaction of flavones in cycloalkanes afforded exclusive C‐3 cycloalkylation via C –C coupling, whereas the solvent N,N‐dialkylformamide provided C‐3 amidation via C –C coupling. Under identical reaction conditions just by switching the solvent to chlorobenzene, C‐3 methylated flavones were obtained where tert‐butyl peroxybenzoate (TBPB) served as the source of the methyl group.
A Mitsunobu approach for the synthesis of sulfinate esters by direct nucleophilic substitution of alcohols is described. The salient features of this strategy include neutral and metal‐free conditions for the rapid synthesis of sulfinates in high yields. The present protocol using p‐toluenesulfonylmethyl isocyanide (TosMIC) and the triphenylphosphine (TPP)/diisopropyl azodicarboxylate (DIAD) reagent system represents the general synthetic route to this important class of compounds.
N‐Alkenylated triazolinone ylides were generated through copper‐catalyzed oxy‐N‐alkenylation of triazolopyridines. The mechanistic course of this aerobic tandem reaction has been experimentally elucidated and primary photophysical data of the ylide products are also given.
A catalyst‐controlled regiodivergent dehydrogenative Heck reaction of 4‐arylthiophene/furan‐3‐carboxylates has been realized. Use of a palladium catalyst led to the C‐5 alkenylation through electronic palladation, while a ruthenium catalyst favored the C‐2 alkenylation with the assistance of a directing group. This reaction exhibited good to excellent regioselectivities.
With the use of a bifunctional chiral phosphine as the catalyst, the asymmetric [3+2] annulation of Morita–Baylis–Hillman carbonates with cyclic 1‐azadienes proceeded smoothly under mild conditions to give various enantiomerically enriched cyclopentene derivatives bearing three consecutive tertiary stereocenters and a sulfamate moiety in moderate to excellent yields with moderate to excellent enantioselectivities and excellent diastereoselectivities.
Cobalt‐catalyzed C−H amination of arenes with alkylamines by the assistance of 8‐aminoquinoline as auxiliary through sp2 C−H bond functionalization has been achieved. Attractive features of this protocol include the low loading of the cobalt catalyst and the readily available reagents.
The palladium‐catalyzed tandem reactions of 2,7‐alkadiynylic carbonates with 2,3‐allenyl sulfamides for the syntheses of fused tricycles such as 1,3,6,7,8,9‐hexahydrofuro[3,4‐h]isoquinoline, 2,3,6,7,8,9‐hexahydro‐1H‐pyrrolo[3,4‐h]isoquinoline, and 2,3,4,7,8,9‐hexahydro‐1H‐cyclopenta[h]isoquinoline derivatives have been developed. A mechanism has been proposed based on the isolation of a by‐product.
A novel one‐pot reaction which combines halogenation, decarboxylation/desulfonamidation with oxidation has been developed. Diverse valuable 3,3‐dihalo‐2‐oxindole compounds can be produced rapidly and safely with isolated yields of up to 98% under mild conditions.
Branched allyl amines or linear amines can be obtained from E‐4‐hydroxybuten‐2‐yl methyl carbonate using the palladium/1,2‐diaminocyclohexane (DACH)‐catalysed allylic amination by just starting from the unprotected or the protected derivative, respectively. Unhindered primary amines can be used as nucleophiles, thus enlarging the scope of the Pd/DACH catalytic system. Hydrogen bonding involving the free hydroxy group in the unprotected allylic carbonate is proposed to be responsible for the control of the regioselectivity to afford branched isomers, obtained in high ee. A short and enantioselective formal synthesis of the glycosidase inhibitor fagomine is described using this method.
The acyloxy group of 2‐acyloxy‐2H‐azirines has been displaced by carboxylic acids to generate the corresponding 2‐acyloxy‐2H‐azirines by using potassium iodide as a promotor. This metal‐free method can be performed with a wide scope of substrates readily generating products in moderate to high yields. It also represents an example of nucleophilic substitution between esters and carboxylic acids under metal‐free reaction conditions for the first time.
An efficient regio‐ and stereoselective metal‐catalyzed addition of two Grignard reagents (homo‐coupling, 2 RMgX or hetero‐coupling, R1MgX+R2MgX) to methyl coumalate (methyl 2‐oxo‐2H‐pyran‐5‐carboxylate) is described. This synthetic approach opens the access to a wide variety of functionalized β,γ‐unsaturated carboxylic acids in a modular way. Control of the chemo‐ and stereoselectivity of this one‐pot procedure is discussed.
The introduction of a trifluoromethyl group into the 2′‐position of spiro‐pyrrolidine‐3,3′‐oxindoles is described. By using 1 mol% of a quinine‐derived squaramide as catalyst, the 2,2,2‐trfluoroethylamine (CF3CH2NH2)‐derived ketimine is transformed initially into a trifluoromethylimine through an umpolung reaction. The subsequent 1,3‐dipolar cycloaddition gives the pharmaceutical important target compounds in excellent yields, enantioselectivities and diastereoselectivies.
A domino reaction of palladium(II)‐catalyzed dual C–H functionalization with subsequent intramolecular annulation is presented. This method provides a convenient synthesis of a range of symmetrical and unsymmetrical biologically important (E)‐bisindole‐2‐ones under extremely mild reaction conditions – room temperature, green oxidant and no additive. The reaction mechanism is elucidated in light of the yield values as well as additional control experiment results.
The ruthenium(II)‐ or rhodium(III)‐catalyzed pyrimidinyl‐directed Grignard‐type C−H additions of N‐heterocycles with activated aldehydes and ketones are described. A cationic ruthenium catalyst and sodium acetate additive in dichloroethane as solvent were found to be optimal catalytic system for the construction of C‐7 alkylated indolines. In sharp contrast, a cationic rhodium complex allows the generation of C‐2 alkylated indoles and pyrroles as well as C‐1 alkylated carbazoles. The site‐selective C−H functionalization of these heterocyclic scaffolds could be an important asset towards the development of novel bioactive compounds.
An efficient ligand‐free copper‐manganese (Cu‐Mn) spinel oxide‐catalyzed direct tandem C−H oxygenation and N‐arylation of benzylamines has been developed. The method has been utilized for the synthesis of medicinally important 2‐arylquinazolin‐4(3H)‐ones. Salient features of this method include recyclable catalyst, no ligand, excellent product yields, shorter reaction times and a broad substrate scope.
