A palladium-catalyzed direct arylation of isoxazoles with aryl iodides has been achieved. The C-H bond at the 5-position is activated selectively to give coupling products in moderate to good yields. This direct arylation was applied to the synthesis of a spiro-type chiral ligand, which proved to be most effective to the palladium-catalyzed tandem cyclization of a dialkenyl alcohol.

An enantioselective intermolecular Rauhut-Currier (RC) reaction of nitroalkenes with ethyl allenoate has been established with quinidine-derived β-isocupreidine. The present RC reaction afforded α-functionalized allenoates 3 in up to 94% yield with 59% enantiomeric excess (ee). Key words Rauhut-Currier reaction; chiral organocatalysis; nitroalkene; α-functionalized allenoateThe Rauhut-Currier (RC) reaction 1,2) is a Lewis base-catalyzed carbon-carbon bond-forming reaction between two different α,β-unsaturated carbonyl compounds, wherein one compound acts as a latent enolate, providing α-substituted enones. In contrast to the related Morita-Baylis-Hillman (MBH) and aza-MBH reactions, [2][3][4][5] wherein the latent enolate reacts with another aldehyde or imine, the RC reaction lacks reactivity and selectivity; using two distinct α,β-unsaturated carbonyl compounds leads to a mixture of homo-and heterocouplings.Nitroalkenes are widely used as electron-deficient alkenes; they are employed in diverse organic reactions and act as Michael acceptors, dienophiles, and 1,3-dipoles.6) Despite the fact that nitroalkenes are excellent Michael acceptors, nitroalkenes mostly work as nucleophiles in the RC reaction because the Lewis base catalyst initially reacts at the β-position of the nitroalkene, resulting in the corresponding α-nucleophilic carbanion.7) In 2007, Henry and Kwon presented an achiral phosphine-catalyzed intramolecular RC reaction of a nitroalkene (Michael acceptor) and an allenoate (nucleophile) as a solitary example; in their system, sequential bond-formation took place after the intramolecular RC reaction, leading to a formation of the tricyclic product 8) (Chart 1a). Controlling chemoselectivity and imparting asymmetric induction to the product in the RC reaction of nitroalkenes and allenoates remain a challenging task.Herein we report the first chemo-, regio-, and enantioselective intermolecular RC reaction of allenoates 2 with nitroalkenes 1. Quinidine-derived β-isocupreidine (β-ICD) 9) was the optimal tested catalyst for the RC reaction, affording α-functionalized allenoates 3 10) with excellent yields under mild reaction conditions in a single operation (Chart 1b).As part of our efforts to explore enantioselective bifunctional catalysis, 11) we were interested in facile accesses to chiral α-substituted allenoates, which are useful platforms for the rapid asymmetric construction of complex molecules. 14) and β-ICD afforded the desired RC product 3a in moderate-to-good yields (entries 4 and 5). The RC reaction rate ordinarily increases in Brϕnsted acid.2) Although 2-naphthol (20 mol %) was added to the reaction mixture, the reaction rate decreased and the racemic form of 3a was obtained in less than 10% yield (entry 6). We also examined the catalytic effects of other cinchona alkaloid derivatives, however, no reaction was observed in any of the cases (entries 7 and 8).Encouraged by these results, we went on to study the effects of solvent on the reaction of 1a with 2a (Table 2). Ethereal solvents such a...

Apalladium-catalyzed direct arylation of isoxazoles with aryl iodides has been achieved. The C À Hb ond at the 5-position is activated selectively to give coupling products in moderate to good yields.T his direct arylation was applied to the synthesis of aspiro-type chiral ligand, whichp roved to be most effective to the palladium-catalyzed tandem cyclization of adialkenyl alcohol.

A stereoselective [4 + 2] annulation of acyclic all-carbon tetrasubstituted alkenes with allenoates was described. The reaction with DABCO proceeded smoothly leading to the formation of highly functionalized 4H-pyran derivatives in good yields. We have also reported first b-ICD-catalyzed [4 + 2] annulation affording functionalized enantioenriched 2H-pyran derivatives bearing a chiral all-carbon quaternary center.[a] T.Scheme 1. Lewis base (LB)-catalyzed reactions of allenoates with electrophiles (E).Scheme 2. Tertiary amine-catalyzed annulation of allenoates with electrophiles.