A multifunctional chiral phosphine‐catalyzed enantioselective [3+2] annulation of Morita–Baylis–Hillman carbonates with barbiturate‐derived alkenes has been achieved under mild conditions, providing a variety of chiral spirobarbiturate‐cyclopentenes in moderate to excellent yields with moderate to excellent diastereo‐ and enantioselectivities.
The first highly enantioselective intramolecular N−H bond insertion was realized by using copper catalysts modified with chiral spirobisoxazoline ligands, which provides a novel strategy for the synthesis of chiral 2‐carboxytetrahydroquinolines. This reaction features fast reaction rate, high yield, high enantioselectivity, and mild reaction conditions.
An efficient and easy method for C −C homocoupling was developed using cobalt bromide as catalyst. A series of functionalized alkyl bromides and alkyl chlorides were coupled in high yields under mild conditions. This reaction seems to involve a radical intermediate.
A pair of epimeric l ‐proline derived chiral auxiliaries have been developed for the diastereoselective lithiation–substitution of η6‐arene chromium tricarbonyl complexes. Lithiation of the anti epimer affords planar chiral imidazolones in >95:5 dr upon electrophile quench. Application of the same reaction sequence to the syn epimer provides products with opposite planar chirality in equally high levels of diastereomeric purity. The ortho‐substituted epimeric imidazolones give rise to planar chiral enantiomers upon acid‐induced elimination, thus precluding the need to prepare a d ‐proline‐derived starting material.
An asymmetric total synthesis of ent‐ancistrocladinium A was developed via chiral phosphoric acid‐catalyzed asymmetric reductive amination of 1‐aryl‐2‐propanone and naphthylamine followed by a Bischler–Napieralski reaction. Direct use of the naphthyl moiety in the amine as a key building block in the natural product allowed us to achieve the total synthesis of ancistrocladinium A in only three steps from the known starting materials.
A chiral aluminum catalyst system has been developed for the enantioselective vinylation of aldehydes. β,β‐Disubstituted (E)‐vinylaluminum reagents, generated regio‐ and stereoselectively by the carboalumination of terminal alkynes with trimethylalumunim (Me3Al), were used straightforwardly without transmetalation to vinyltitanium reagents in the subsequent enantioselective addition to aldehydes with a DPP‐H8‐BINOL‐derived chiral aluminum catalyst at low catalyst loading (5 mol%). The reaction afforded the corresponding enantiomerically enriched secondary allylic alcohols with a reversal of the selectivity observed in closely related reactions catalyzed by a chiral titanium complex derived from the same ligand.
An efficient copper‐catalyzed regioselective C—H bond carbonylation of benzamides has been developed using 2,2′‐azobisisobutyronitrile (AIBN) as traceless cyanating agent. The non‐toxic and readily available AIBN was used for the carbonylative cyclization of benzamides via copper catalysis. The method is also applicable for the regioselective cyanation of furan, benzofuran, thiophene, benzothiophene, and pyrrole carboxamide derivatives.
A copper(I)‐catalyzed addition of alkylborane reagents to α‐iminoacetates has been developed to assemble both acyclic and cyclic α‐branched α‐amino carboxylic acid derivatives in good yields. A wide variety of unactivated alkenes are well tolerated in this transformation.
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.
2,3‐Dihydroindenes and isoindolines are important skeletons present in medicinal and synthetic chemistry. In this paper, an acetyl bromide promoted metal‐free construction of 2,3‐dihydroindenes and isoindolines with high synthetic efficiency is developed.
This review describes the recent developments in the field of Suzuki–Miyaura cross‐coupling reaction, in particular with regard to ligand‐free catalysis. The catalysts outlined here allow convenient and green synthetic pathways specifically for the construction of C–C bonds. They enable the synthesis of biaryls by the coupling arylboronic acids with aryl halides. The literature reporting ligand‐free synthesis of biaryls from 2010 to May 2015 has been reviewed.
An operationally simple, and cost efficient conversion of carboxylic acids into hydroxamic acid derivatives via a high‐energy mechanochemical activation is presented. This ball milling methodology was applied to a wide variety of carboxylic acids dramatically improving purification issues associated with this class of molecules, which still remain one of the main bottlenecks of classical methodologies.
By the design of suitable starting materials, a silver(I)‐catalyzed epoxide ring‐opening/1,2‐acyl migration/cyclization cascade has been developed, which allowed us to systematically prepare unsymmetrical 3‐formylfurans. Various 3‐formylfurans were prepared in good to excellent yields. In addition, the distinct fluorescence properties of 3‐formylfurans in solution and the solid state are disclosed.
The formation of an amide bond via incorporation of two isocyanide units during a palladium‐catalyzed construction of the indoloquinoline ring afforded N‐substituted 6H‐indolo[2,3‐b]quinoline‐11‐carboxamides as new cytotoxic agents. The solvent and base play a key role in the selective and unprecedented synthesis of this class of amides.
A bifunctional squaramide‐catalyzed Michael/Michael cascade reaction for the construction of spirotetrahydrofuran bispirooxindoles was developed. The products were obtained in moderate to excellent yields with excellent diastereo‐ and enantioselectivities (up to >20:1 dr, >99% ee). This straightforward process serves as a powerful method for the enantioselective construction of potentially bioactive bispirooxindoles in which two of the four contiguous chiral centers are spiro all‐carbon quaternary centers on a single tetrahydrofuran ring. Meanwhile, the synthetic practicality of this methodology was illustrated by performing the reaction on a gram‐scale with the same efficiency and stereoselectivity.
A facile and efficient potassium hydroxide (KOH)‐catalyzed tandem reaction involving sequential Michael addition of electron‐deficient alkenes with malonic esters, ring opening of activated aziridines and lactamization has been described. A highly functionalized indane‐fused tricyclic scaffold containing three rings, three adjacent stereocenters and a quaternary center was constructed by the formation of two new C–C bonds and one new C–N bond in a diastereoselective manner.
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.
