Triethylborane as an efficient promoter for palladium-catalyzed allylation of active methylene compounds with allyl alcohols

Without prior activation of allyl alcohols, allylation of a variety of active methylene compounds with allyl alcohols proceeds smoothly at rt-50°C in the presence of catalytic amounts of Pd(OAc)₂ (1-10 mol%), Et₃B (30-240 mol%), a phosphine ligand (1-20 mol%), and a base (0 to 50-60 mol%).     

Use of allyl, 2-tetrahydrofuryl, and 2-tetrahydropyranyl ethers as useful C3-, C4-, and C5-carbon sources: palladium-catalyzed allylation of aldehydes

Palladium-diethylzinc or palladium-triethylborane catalytically promotes self-allylation of 2-(allyloxy)tetrahydrofurans, 2-(allyloxy)tetrahydropyrans, and their hydroxy derivatives on the rings (ribose, glucose, mannose, deoxyribose, deoxyglucose). All the reactions proceed at room temperature and provide polyhydroxyl products, sharing a structural motif of a homoallyl alcohol, in good to excellent yields with high levels of stereoselectivity. Useful C3-unit elongation, which makes the best use of an allyl ether as a protecting group and a nucleophilic allylation agent, is demonstrated. Mechanisms for the umpolung reaction (of an allyl ether into an allylic anion) and stereoselectivity associated with allylation of aldehydes are discussed.     

Recent topics in the syntheses of β-keto carboxylic acids and the derivatives

β-Keto carboxylic acids are key intermediates in organic syntheses, used for the development of fine chemicals, natural products, and various biologically relevant molecules. Their utilities stem from the structural features and facile bond formations, e.g., asymmetric reduction of carbonyl groups for the synthesis of β-hydroxy carboxylic acids and conjugated addition reactions through decarboxylative enolate nucleophiles, which utilize the amphiphilic reactivity of β-keto carboxylic acids. Despite their versatility and utilities, development of efficient and straightforward synthetic methods for β-keto carboxylic acids has not attracted considerable attention owing to their instability. As efficient synthetic strategies for β-keto carboxylic acids and their derivatives, reactions of α-diazoesters, acylation of malonate anions, cross-coupling reactions, and CO₂ insertion reactions are summarized in this review.     

Enantioselective synthesis mediated by chiral crystal of achiral hippuric acid in conjunction with asymmetric autocatalysis

Enantiomorphous crystals composed of achiral hippuric acid, i.e., naturally occurring N-benzoylglycine, have been used successfully as chiral inducers in enantioselective synthesis in combination with asymmetric autocatalysis to afford the product with extremely high enantiomeric excess.     

Dienyl homoallyl alcohols via palladium catalyzed ene-type reaction of aldehydes with 1,3-dienes

The combination of Pd catalyst and Xantphos ligand in the presence of Et(3)B nicely promotes the allylation of aldehydes with conjugated dienes to provide dienyl homoallyl alcohols in excellent yields. The reaction occurs selectively at the C-C double bond bearing higher electron density.     

Super strong nuclear force caused by migrating K? mesons - Revival of the Heitler-London-Heisenberg scheme in kaonic nuclear clusters

We have studied the structure of K⁻pp comprehensively by solving this threebody system in a variational method, starting from the Ansatz that the Λ(1405) resonance (≡Λ^*) is a K⁻p bound state. The structure of K⁻pp reveals a molecular feature, namely, the K⁻ in Λ^* as an “atomic center” plays a key role in producing strong covalent bonding with the other proton. We point out that strongly bound $\bar{K}$ nuclear systems are formed by “super strong” nuclear force due to migrating real bosonic particles $\bar{K}$ a la Heitler-London-Heisenberg, whereas the normal nuclear force is caused by mediating virtual mesons. We have shown that the elementary process, p + p → K⁺ + Λ^* + p, which occurs in a short impact parameter and with a large momentum transfer, leads to unusually large self-trapping of Λ^* by the involved proton, since the Λ^*-p system exists as a compact doorway state propagating to K⁻pp.     

Ab initio approach to s-shell hypernuclei 3lambdaH, 4lambdaH, 4lambdaHe,and 5lambdaHe with a lambdaN-sigmaN interaction

Variational calculations for s-shell hypernuclei are performed by explicitly including Sigma degrees of freedom. Four sets of YN interactions [SC97d(S), SC97e(S), SC97f(S), and SC89(S)] are used. The bound-state solution of 5lambdaHe is obtained and a large energy expectation value of the tensor lambdaN-sigmaN transition part is found. The internal energy of the 4He subsystem is strongly affected by the presence of a Lambda particle with the strong tensor lambdaN-sigmaN transition potential.     

Fully coupled channel approach to doubly strange s-shell hypernuclei

We describe ab initio calculations of doubly strange, S = -2, s-shell hypernuclei (4(LambdaLambda)H, 5LambdaLambda)H, 5(LambdaLambda)He, and 6(LambdaLambda)He) as a first attempt to explore the few-body problem of the full-coupled channel scheme for these systems. The wave function includes LambdaLambda, LambdaSigma, NXi, and SigmaSigma channels. Minnesota NN, D2' YN, and simulated YY potentials based on the Nijmegen hard-core model are used. Bound-state solutions of these systems are obtained. We find that a set of phenomenological B8B8 interactions among the octet baryons in S = 0,-1, and -2 sectors, which is consistent with all of the available experimental binding energies of S = 0,-1, and -2 s-shell (hyper)nuclei, can predict a particle stable bound state of 4(LambdaLambda)H. For 5(LambdaLambda)H and 5(LambdaLambda)He, LambdaN-SigmaN and XiN-LambdaSigma potentials significantly affect the net LambdaLambda-NXi coupling, and a large Xi probability is obtained even for a weaker LambdaLambda-NXi potential.     

Nickel-catalyzed multi-component coupling reaction of aldimine, alkyne, and dimethylzinc via dimerization of butadiene

In the presence of a Ni/phosphine ligand catalyst, dimethylzinc, alkyne, butadiene, aldehyde, and primary amine were successively combined via dimerization of butadiene to provide (3E,7E,10Z)-dodecatrienylamine in good yields with excellent regio and stereoselectivities.