Amine-directed intramolecular hydroacylation of alkenes and alkynes

Medium-ring heterocycles are prepared via an amine-directed, rhodium(I)-catalyzed intramolecular hydroacylation. The presence of an allyl substituent on the amine accelerates the reaction and increases product yields.     

Catalytic hydroacylation as an approach to homoaldol products

A method has been developed for the intermolecular hydroacylation of homoallyl alcohols with salicylaldehydes to furnish homoaldol products in 50-98% yields. The method also applies to the hydroacylation of 2-hydroxystyrenes. This work highlights the use of hydroacylation as a unified approach to both aldol and homoaldol products.     

Calcium-mediated intramolecular hydroamination catalysis

The calcium-catalyzed intramolecular hydroamination of alkenes and alkynes is reported. The beta-diketiminato complex [{HC(C(Me)2N-2,6-iPr2C6H3)2}-Ca{N(SiMe3)2}(THF)] affects catalytic cyclization of a range of aminoalkenes and aminoalkynes with activities that are broadly commensurate to those of established rare earth catalysts.     

Rh(I)-catalyzed intramolecular hydroacylation in ionic liquids

Rh(I)-catalyzed hydroacylation of 4-alkenal or 4,6-dienal using ionic liquids (ILs) as reaction media proceeded smoothly, giving cyclopentanone or cycloheptenone derivatives in good yields. It was found that the IL recovered after the reaction, which should contain the Rh(I) catalyst, could be recycled 5-10 times without the loss of catalytic activity and enantioselectivity (in the case of asymmetric hydroacylation).     

Inter- and intramolecular hydroacylation of alkenes employing a bifunctional catalyst system

Based on a conceptually innovative bifunctional P,N ligand, an efficient protocol for the rhodium-catalyzed inter- and intramolecular hydroacylation of alkenes has been developed.     

Synthesis of 2,3-dihydro-1H-inden-1-one derivatives via Ni-catalyzed intramolecular hydroacylation

An efficient synthetic method for the formation of 2,3-dihydro-1H-inden-1-one derivatives through a Ni-catalyzed intramolecular hydroacylation of 2-(prop-2-ynyl)benzaldehydes has been developed. Examination of various nickel and other transition metal catalysts and phosphine ligands showed that the use of Ni(COD)₂ catalyst combined with P(i-Pr)₃ ligand was the best choice to the success of the present intramolecular hydroacylation. A wide range of functional groups were tolerated, affording the corresponding substituted α-lidene-2,3-dihydro-1H-inden-1-ones in good to high yields with a sole E-selectivity under present reaction conditions.     

The intramolecular carboxyarylation approach to podophyllotoxin

Since 1960, only seven plant-derived anticancer drugs have received FDA approval for commercial production. Two are semisynthetic derivatives of podophyllotoxin. This paper describes concise, highly convergent, and conceptually novel approaches to (-)-podophyllotoxin and its enantiomer. These highly convergent syntheses feature a late-stage domino radical reaction to install the lactone ring and the pendant trimethoxyphenyl group.     

Rhodium-catalyzed intramolecular hydroacylation of 1,2-disubstituted alkenes for the synthesis of 2-substituted indanones

The intramolecular hydroacylation of 1,2-disubstituted alkenes was considered to be a challenging task due to the side reactions resulted from the lack of additional substituent at 1-position and the low activity caused by the steric hindrance of substituent at 2-position, and an asymmetric version has not been considered possible due to problems associated with the racemization of the products. We have partially solved these problems. Catalyzed by an activated diphosphine-Rh complex and reacted in a selected dihalogenated solvent, the intramolecular hydroacylation of o-(2-arylvinyl)benzaldehydes provided the corresponding 2-aryl-1-indanones in high yields, and its asymmetric variant using o-(2-alkylvinyl)benzaldehydes afforded chiral 2-alkyl-1-indanones in high yields and with moderate enantioselectivities.     

Cooperative hydrogen-bonding effects in silanediol catalysis

The importance of cooperative hydrogen-bonding effects and SiOH-acidification is described for silanediol catalysis. NMR binding, X-ray, and computational studies provide support for a unique dimer resulting from silanediol self-recognition. The significance of this cooperative hydrogen-bonding is demonstrated using novel fluorinated silanediol catalysts for the addition of indoles and N,N-dimethyl-m-anisidine to trans-β-nitrostyrene.     

Rhodium-catalyzed intramolecular hydroacylation of 5- and 6-alkynals: convenient synthesis of alpha-alkylidenecycloalkanones and cycloalkenones

A novel intramolecular hydroacylation of 5- and 6-alkynals leading to alpha-alkylidenecycloalkanones was accomplished by using cationic a rhodium(I)/BINAP complex. For all cyclizations described, a single (E)-olefin isomer was obtained. At elevated temperature, hydroacylation and double bond migration of 5- and 6-alkynals proceeded in a one-pot reaction to give cycloalkenones. An intramolecular hydroacylation of a 7-alkynal was unsuccessful. This method represents an attractive new route to highly functionalized alpha-alkylidenecycloalkanones and cycloalkenones.     

A theoretical study on the trans-addition intramolecular hydroacylation of 4-alkynals catalyzed by cationic rhodium complexes

The mechanism of the intramolecular hydroacylation reaction of 4-alkynals is studied for a 4-pentynal-[Rh(PH2CH2CH2PH2)]+ model system using MP2 calculations. The endo-cyclization to form a rhodacyclohexenone intermediate is kinetically less favorable than the exo-cyclization to form a rhodacyclopentanone intermediate. The kinetic preference toward the endo-cyclization is found to be enhanced by complexation of donor ligands (H2CO, NCH, and HCCH). The formation of cyclopentenone product proceeds via reductive elimination from one of the two rhodacyclohexenone intermediates, whereas the formation of cyclobutanone product from the two rhodacyclopentanone intermediates requires high activation energy. Addition of an acetylene stabilizes the highly electron-poor rhodacyclopentanone intermediate generated from exo-cyclization and leads to an insertion to give [4 + 2] annulation product, cyclohexenone. The role of a coordinating acetone solvent in the formation of cyclopentenone product is also discussed.     

Asymmetric catalysis on the intramolecular cyclopropanation of alpha-diazo-beta-keto sulfones

This work describes the development of a highly enantioselective asymmetric catalysis on the intramolecular cyclopropanation of alpha-diazo-beta-keto sulfones. We have found that the catalytic asymmetric intramolecular reactions of alpha-diazo-beta-keto sulfones generally proceed with high enantioselectivity when the alpha-diazo-beta-keto mesityl sulfone is used with the newly prepared ligand 2e. The absolute configuration of products has been determined by X-ray crystallographic analysis, and the outcome of the enantioselectivities is explained well by our proposed models A and B. The products possess great potential for natural product synthesis because (1) many different chemistries of cyclopropane, ketone, and sulfone are available, and (2) the products are generally highly crystalline, facilitating the supplies of enantiomerically pure synthetic intermediates.     

Cooperative catalysis by silica-supported organic functional groups

Hybrid inorganic-organic materials comprising organic functional groups tethered from silica surfaces are versatile, heterogeneous catalysts. Recent advances have led to the preparation of silica materials containing multiple, different functional groups that can show cooperative catalysis; that is, these functional groups can act together to provide catalytic activity and selectivity superior to what can be obtained from either monofunctional materials or homogeneous catalysts. This tutorial review discusses cooperative catalysis of silica-based catalytic materials, focusing on the cooperative action of acid-base, acid-thiol, amine-urea, and imidazole-alcohol-carboxylate groups. Particular attention is given to the effect of the spatial arrangement of these organic groups and recent developments in the spatial organization of multiple groups on the silica surface.     

Neocuproine-KOtBu promoted intramolecular cross coupling to approach fused rings

Polycycles can be produced with different linkages (A, B = O, N, C, S) by constructing biaryl C-C bonds via neocuproine-KO(t)Bu promoted cross coupling between C-Xs and C-Hs.     

A readily prepared neutral heterobimetallic titanium(IV)-rhodium(I) catalyst for intramolecular hydroacylation

The combination of HOCMe2CH2PPh2, Ti(OiPr)4, and [Rh(cod)Cl]2 (3:1:1) in either benzene or dichloromethane produces a discrete species (tentatively formulated as complex) that is an active catalyst for intramolecular hydroacylation reactions of 3-substituted pentenals.     

An intramolecular diels-alder approach to the galanthan ring system

A novel “phenylbutadiene + Δ²-pyrroline” intramolecular cycloaddition has been used to construct a functionalized galanthan.     

On the intramolecular pyrone Diels-Alder approach to basiliolide B

A unified synthetic approach to the basiliolides/transtaganolides is outlined herein, along with studies illustrating the feasibility of the strategy with respect to the total synthesis of basiliolide B. This work lays the foundation for chemical synthesis of an emerging family of Thapsia metabolites.