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.     

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%).     

Palladium-catalyzed allylation of imines with allyl alcohols

A catalytic system, Pd(OAc)2 (10 mol %)-P(n-Bu)3 (20 mol %)-Et3B (360 mol %), promotes allylic alcohols to undergo the allylation of anisidine-imines of aromatic and aliphatic aldehydes and furnishes homoallylamines in good to moderate yields. The reaction shows unique stereoselectivity, giving anti-isomers selectively. [reaction: see text]     

An Ultrastable,Small {Ag7}5+ Nanocluster within a Triangular Hollow Polyoxometalate Framework

Small Ag_n nanoclusters (n<10) have been emerging as promising materials as sensing, biolabeling, and catalysis because of their unique electronic states and optical properties. However, studying synthesis, structure determination, and exploration of their properties remain major challenges as a result of the low stability of small Ag nanoclusters. Herein, we synthesized an atomically precise face‐centered‐cubic‐type small {Ag₇}⁵⁺ nanocluster supported by a novel triangular hollow polyoxometalate (POM) framework [Si₃W₂₇O₉₆]^18?. The cluster showed unique {Ag₇}⁵⁺‐to‐POM charge transfer bands in both visible and UV light regions. Furthermore, this small {Ag₇}⁵⁺ nanocluster exhibited an unprecedented ultrastability in solution, despite having exposed Ag sites that can be accessed by small molecules, such as O₂, water, and solvents.     

Rationality of Moduli Spaces of Parabolic Bundles

The moduli space of parabolic bundles with fixed determinantover a smooth curve of genus greater than one is proved to berational whenever one of the multiplicities of the quasi-parabolicstructure equals one. This gives a new proof that the modulispace of vector bundles of coprime rank and degree is stablyrational, a result originally due to Ballico, and the boundon the level is strong enough to deduce rationality in manycases, extending results of Newstead.     

Descent Kummer theory via Weil restriction of multiplicative groups

We prove a Kummer duality for certain fields without roots of unity by using the Weil restriction of the multiplicative groups. This is a natural generalization of the classical Kummer theory.     

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.     

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.