Stereochemistry of the Asymmetric Carbopalladation of Allenes Followed by Nucleophilic Substitution Reactions with Carbo- and Aminonucleophiles

Asymmetric bifunctionalization of allenes with aryl iodides and amino acids enabled by chiral aldehyde/palladium combined catalysis

Even though catalytic asymmetric bifunctionalization of allenes has been extensively studied, almost all of the reported examples have been achieved in a two-component manner. In this study, we report a highly efficient asymmetric bifunctionalization of allenes with iodohydrocarbons and NH2-unprotected amino acid esters. The adopted chiral aldehyde/palladium combined catalytic system precisely governs the chemoselectivity, regioselectivity, and stereoselectivity of this three-component reaction. A wide range of substituted aryl iodides, allenes and amino acid esters can well participate in this reaction and deliver structurally diverse α,α-disubstituted α-amino acid esters with excellent experimental outcomes. One of the resulting products is utilized for the total synthesis of the molecule (S,R)-VPC01091.

Efficient Synthesis of the N-(buta-2,3-dienyl)carboxamide of Isopimaric Acid and the Potential of This Compound towards Heterocyclic Derivatives of Diterpenoids

The N‐(2,3‐butadienyl)carboxamide of isopimaric acid, that is, compound 3, was prepared through a two‐step synthetic procedure starting from the natural diterpene isopimaric acid. The Pd‐catalyzed cross‐coupling and subsequent cyclization of terpenoid allene 3 with several aryl iodides and aryl bromides gave access to optically active diterpenoid–oxazoline derivatives in good to excellent yields. The functional group tolerance in the aryl iodides was demonstrated by several examples, including substrates with additional N‐tert‐butoxycarbonyl‐protected amino, hydroxy, and carboxy substituents in the ortho position. The cross‐coupling–cyclization reaction of those compounds with allene 3 proceeded selectively with the formation of cyclization products on the substituent in the aromatic ring. This transformation opens a potential route to the synthesis of hybrid compounds containing a tricyclic diterpenoid and several heterocycles.

Rhodium-catalyzed annulation of arenes with alkynes through weak chelation-assisted C–H activation

This feature article reviews the recent achievements of rhodium-catalyzed annulation of arenes with alkynes through weak chelation-assisted C–H activation, which sets a stage for the synthesis of diverse appealing polycyclic compounds.

Chirality transfer in metal-catalysed intermolecular addition reactions involving allenes

This review covers chirality transfer in metal-catalysed intermolecular addition reactions involving allenes, including axial-to-central chirality transfer, asymmetric catalysis and racemization.

Recent Applications of Chiral Ferrocene Ligands in Asymmetric Catalysis

Despite the impressive progress achieved in asymmetric catalysis during the last decade, an increasing number of new catalysts, ligands, and applications are reported every year to satisfy the need to embrace a wider range of reactions and to improve the efficiency of existing processes. Because of their availability, unique stereochemical aspects, and wide variety of coordination modes and possibilities for the fine-tuning of the steric and electronic properties, ferrocene-based ligands constitute one of the most versatile ligand architectures in the current scenario of asymmetric catalysis. Over the last few years ferrocene catalysts have been successfully applied in an amazing variety of enantioselective processes. This Review documents these recent advances, with special emphasis on the most innovative asymmetric processes and the development of novel, efficient types of ferrocene ligands.

Palladium-Catalyzed Coupling of Allenylphosphonates, Phenylallenes, and Allenyl Esters: Remarkable Salt Effect and Routes to Novel Benzofurans and Isocoumarins

Coupling reactions of allenylphosphonates (OCH(2)CMe(2)CH(2)O)P(O)CH=C=CRR' [R, R' = H (1a), R = H, R' = Me (1b), R = R' = Me (1c)] with aryl iodides, iodophenol, and iodobenzoic acid in the presence of palladium(II) acetate are investigated and compared with those of phenylallenes PhCH=C=CR2 [R = H (2a), Me (2b)] and allenyl esters EtO(2)CCH=C=CR(2) [R = H (2c), Me (2d)]. While 1b and 1c couple with different stereochemical outcomes using PhI in the presence of Pd(OAc)(2)/PPh(3)/K(2)CO(3) to give phenyl-substituted 1,3-butadienes, 1a does not undergo coupling but isomerizes to the acetylene (OCH(2)CMe(2)CH(2)O)P(O)CCMe (7). In the reaction of 1c with PhI, use of K(2)CO(3) affords the butadiene (Z)-(OCH(2)CMe(2)CH(2)O)P(O)CH=C(Ph)-C(Me)=CH(2) (12); in contrast, the use of Ag(2)CO(3) leads to the allene (OCH(2)CMe(2)CH(2)O)P(O)C(Ph)=C=CMe(2) (20), showing that these bases differ very significantly in their roles. The reaction of 1a with PhI or PhB(OH)2 in (t)he presence of Pd(OAc)2/CsF/DMF leads mainly to (E)-(OCH(2)CMe(2)CH(2)O)P(O)CH=C(Me)Ph (21) and (OCH(2)CMe(2)CH(2)O)P(O)CH2-C(Ph)=CH(2) (22) and is thus a net 1,2-addition of Ph-H. Compound 1b reacts with iodophenol in the presence of Pd(OAc)(2)/PPh(3)/K(2)CO(3) to give a benzofuran that has a structure different from that obtained by using 1c under similar conditions. Treatment of 1a with iodophenol/Pd(OAc)(2)/CsF/DMF also gives a benzofuran whose structure is different from that obtained by using 2a under similar conditions. In the reaction with 2-iodobenzoic acid, 1a and 2c afford one type of isocoumarin, while 1b,c and 2a,b give a second type of isocoumarin. The structures of key compounds are established by X-ray crystallography. Utility of the phosphonate products in the Horner-Wadsworth-Emmons reaction is demonstrated.

Studies on Pd0-Catalyzed Cyclization ofN-3,4-Alkadienyl Toluenesulfonamides with Organic Halides: Selective Synthesis of 2,3-Dihydropyrroles, 1,2,3,6-Tetrahydropyrridines, and Azetidines

The palladium-catalyzed coupling-cyclization of beta-amino allenes with organic halides ranging from aryl halide to 1-alkenyl halide was studied. 2,3-Dihydro-1H-pyrroles were obtained by reaction of 3-substituted-5-unsubstituted-3,4-allenyl amides under conditions A, while the reaction of 5-substituted-3,4-allenyl amides afforded 1,2,5,6-tetrahydropyridines and/or azetidines with high de under conditions B or C. The skeleton and relative configuration of the six-membered products were established by the X-ray diffraction studies of 10 ka. Allenyl amide 4 q reacted with 1,4-diiodobenzene 6 r to afford double cyclization product 15. The structure of its major stereoisomer was also determined by the X-ray diffraction study.