Rhodium-catalyzed intramolecular alkyne-carbodiimide Pauson-Khand-type reaction

[structure: see text]. An efficient, Rh-catalyzed intramolecular Pauson-Khand-type carbonylation of alkyne-carbodiimides leading to 4,5-dihydro-1H-pyrrolo[2,3-b]pyrrolin-2-ones and 1H-pyrrolo[2,3-b]indol-2-ones is described.     

Rhodium-catalyzed isomerization of alpha-arylpropargyl alcohols to indanones: involvement of an unexpected reaction cascade

A rhodium-catalyzed isomerization of alpha-arylpropargyl alcohols to indanones has been developed under mild conditions. Considering the ease of preparation of these propargyl alcohols (terminal alkynes + aromatic aldehydes), this method provides a new way of constructing indanones with high efficiency. By the mechanistic investigations using deuterium-labeled substrates, it has also been demonstrated that the reaction goes through an unexpected cascade, with a 1,4-hydrogen shift being the turnover-limiting step of the catalytic cycle.     

Copper-catalyzed enantioselective intramolecular alkene amination/intermolecular Heck-type coupling cascade

Enantioselective copper-catalyzed cyclization of γ-alkenylsulfonamides and a δ-alkenylsulfonamide in the presence of a range of vinyl arenes results in variously functionalized 2-substituted chiral nitrogen heterocycles via a formal alkene C-H functionalization process. Application of this reaction to the concise synthesis of a 5-HT(7) receptor antagonist is demonstrated.     

Diastero- and enantioselective intramolecular carbometalation reaction

The zinc-catalyzed addition of various alkynes to acylsilanes followed by a Zn-Brook rearrangement and either the Zn-ene-allene or Zn-yne-allene cyclization led to the enantio- and diastereoselective formation of carbocycles in a single-pot operation.     

Research on Liebeskind-Srogl coupling/intramolecular Diels-Alder reaction cascade

The Liebeskind-Srogl coupling/intramolecular Diels-Alder (IMDA) reaction cascade that stereoselectively affords a tricarbocyclic compound with a trans–trans-cis fused ring system including an all-carbon quaternary stereogenic center at the ring junction is described. The cascade reactions proceed quickly and stereoselectively afford the products within 2?h at room temperature in the presence of a suitable thioester. The developed protocol as well as the prepared chiral compounds are useful for the enantioselective total synthesis of terpenoids with the trans–trans-cis fused ring system.     

A highly enantioselective catalytic intramolecular Stetter reaction

A family of chiral triazolium salts has been developed for inducing the asymmetric intramolecular Stetter reaction. The use of an aminoindanol-derived catalyst affords optimal results, with the product keto esters formed in 82-97% ee and very good chemical yield. Aromatic and aliphatic aldehydes are equally competent substrates for this reaction. The reaction conditions are reasonably mild and allow the isolation of the newly formed stereocenter without epimerization, although the presumed carbenic intermediates are strong bases.     

Dual catalyst control in the enantioselective intramolecular Morita-Baylis-Hillman reaction

The intramolecular Morita-Baylis-Hillman (MBH) reaction has been achieved with unprecedented levels of enantioselectivity. Using a co-catalyst system involving pipecolinic acid and N-methylimidazole, cyclic MBH products have been obtained with enantiomer ratios of 92:8 (84% ee). In addition, reactions may be carried out with a "kinetic resolution quench" involving acetic anhydride and an asymmetric acylation catalyst such that ee enhancement occurs to deliver products with >98% ee with an isolated yield of 50%. [reaction: see text]     

Desymmetrization of malonamides via an enantioselective intramolecular Buchwald-Hartwig reaction

A new form of enantioselective nitrogen arylation reaction is described. Beginning with symmetrical α-(2-bromobenzyl)malonamides, intramolecular palladium-catalyzed cross-coupling using a catalyst system including 3.3 mol % Pd(OAc)₂ and 6.6 mol % of the chiral biaryl monophosphine (R)-MOP, desymmetrized quinolinone products are obtained in nearly quantitative yields in enantiomeric ratios up to 88:12. This Letter represents a rare example of enantioselective Buchwald-Hartwig reaction.     

Rhodium-catalyzed enantioselective diboration of simple alkenes

Enantioselective catalytic reactions that operate directly on inexpensive unactivated alkenes are extraordinarily useful for the preparation of chiral organic building blocks and new materials. While a number of such processes have been developed, our ability to meet the intensifying demand for inexpensive stereochemically complex materials will require a significant expansion of practical catalytic asymmetric reaction methodology. In this regard, the rhodium-catalyzed enantioselective diboration reaction has been developed in order to address a number of extant problems in catalytic alkene transformation simultaneously. This process provides an enantiomerically enriched reactive dimetalated intermediate which can be converted to a variety of difunctional reaction products.     

Alder-ene reaction of aryne with olefins

A novel intermolecular Alder-ene reaction based on aryne and olefins was developed. We performed this transformation under mild conditions such as at room temperature, and this reaction displayed high selectivity and good yields only in the presence of CsF. Hence, the intermolecular Alder-ene reaction of aryne with olefins provides an effective route to synthesize derivatives of olefins.     

Cysteine-derived organocatalyst in a highly enantioselective intramolecular Michael reaction

Asymmetric intramolecular Michael reaction catalyzed by an organocatalyst derived from cysteine has been developed for the synthesis of chiral bicyclo[4.3.0]nonene and cis-disubstituted cyclopentane skeletons with a creation of three or two contiguous chiral centers in good yield with high diastereo- and excellent enantioselectivities.     

The enantioselective intramolecular Morita-Baylis-Hillman reaction catalyzed by amino acid-derived phosphinothiourea

A series of chiral bifunctional phosphinothioureas derived from l-amino acids have been developed to promote the enantioselective intramolecular Morita-Baylis-Hillman reaction. The process afforded the cyclic hydroxyl enones with up to 84% ee and good yields under mild conditions.     

Rhodium-catalyzed reformatsky-type reaction

A novel Reformatsky-type reaction was developed using RhCl(PPh(3))(3) and diethylzinc. Inter- and intramolecular Reformatsky-type reactions were achieved efficiently under mild reaction conditions to give beta-hydroxy esters.     

Chiral phosphine-squaramides as enantioselective catalysts for the intramolecular Morita-Baylis-Hillman reaction

Novel squaramides containing tertiary phosphine were developed as chiral bifunctional organic catalysts to promote the asymmetric intramolecular Morita-Baylis-Hillman reaction of ω-formyl-enones. The adducts were obtained in high yields with good-to-excellent enantioselectivity (up to 93% ee).     

Alder-ene reaction: aromaticity and activation-strain analysis

We have computationally explored the trend in reactivity of the Alder-ene reactions between propene and a series of seven enophiles using density functional theory at M06-2X/def2-TZVPP. The reaction barrier decreases along the enophiles in the order H₂CCH₂ > HCCH > H₂CNH > H₂CCH(COOCH₃) > H₂CO > H₂CPH > H₂CS. Thus, barriers drop in particular, if third-period atoms become involved in the double bond of the enophile. Activation-strain analyses show that this trend in reactivity correlates with the activation strain associated with deforming reactants from their equilibrium structure to the geometry they adopt in the transition state. We discuss the origin of this trend and its relationship with the extent of synchronicity between H transfer from ene to enophile and the formation of the new C C bond. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011     

Construction of polycyclic spiro-indolines via an intramolecular oxidative coupling/cyclization cascade reaction process

An efficient protocol for assembling a polycyclic spiroindoline scaffold is developed, which involves an intramolecular oxidative coupling of dianions derived from indole-embodied β-ketoamides using iodine as the oxidant, and subsequent attack of oxygen anion to the resultant imine moiety. A number of tetracyclic spiroindolines are prepared with moderate to good yields.