1,6-Conjugate Additions of Carbon Nucleophiles to 2-[(1E,3E)-4-Arylbuta-1,3-dien-1-yl]-4H-chromen-4-ones

KGaA, Weinheim The 1,6-conjugate addition of nitromethane to 2-[(1E,3E)-4-arylbuta-1,3-dien-1-yl]-4H-chromen-4-ones was accomplished and led mainly to the corresponding β-(nitromethyl)chromones. (E)-5′-(Nitromethyl)-3′-styryl-[1,1′-biphenyl] -2-ol and 3′-aryl-2′-nitro-5′-(nitromethyl)spiro[chromane-2,1′-cyclohexan]-4-one derivatives were also isolated as minor products from tandem processes, which result from the addition of a second molecule of nitromethane. The nucleophile scope was investigated with malononitrile, acetylacetone, ethyl cyanoacetate, and diethyl malonate, which gave the expected 1,6-addition products; in the last case, it was also possible to isolate a minor product formed through a 1,8-/1,6-addition sequence. Computational calculations provided a rationale for the experimental reactivity of carbon nucleophiles with 2-[(1E,3E)-4-arylbuta-1,3-dien-1-yl] -4H-chromen-4-ones. The further functionalization of some adducts allowed the preparation of new nitrogen-containing heterocyclic compounds, such as new styrylpyrrolidines and new pyrazole and bis(pyrazole) derivatives.Thanks are due to the University of Aveiro and Fundação para a Ciência e a Tecnologia (FCT)/Ministerio de Educación y Ciencia (MEC) for the financial support of the QOPNA research unit (FCT UID/QUI/00062/2013) through national funds and, where applicable, cofinanced by Fundo Europeu de Desenvolvimento Regional (FEDER) within the PT2020 Partnership Agreement, and to the Portuguese NMR Network as well as the Instituto Politécnico de Bragança. H. M. T. A. is grateful to Fundação para a Ciência e a Tecnologia (FCT) for his PhD grant (SFRH/BD/86277/ 2012).info:eu-repo/semantics/publishedVersio

1,2-stereochemical induction in the Pd^II-catalyzed conjugate addition of boronic acids

Palladium(II) catalysis has been used in the substrate-controlled 1,2-chiral induction of the conjugate addition of boronic acids to enantiopure α,β-unsaturated ketones and esters without competition from the Mirozoki-Heck reaction. Bedford's palladacycle was found to control the stereoselectivity without the need for additional chiral ligands. We report that the PdII-catalyzed conjugate addition reaction between boronic acids and acyclic ketones or esters that bear a hydroxyl substituent at their γ-position (glyceraldehyde derivatives) can afford high levels of anti stereoselection, comparable to those reported previously using more expensive RhI catalysts. On the other hand, high levels of syn stereoselectivity were observed with acyclic esters that bear an amino substituent at their γ-position (serine derivatives). In this case, the levels of stereoselection could be enhanced by using cyclic derivatives derived from Garner's aldehyde.Peer Reviewe

(Ph3P)AuCl-catalyzed homocoupling of arylboronic acids under benchtop conditions: Synthesis of biphenyls

(Ph3P)AuCl was discovered to be a powerful catalyst in the homocoupling of arylboronic acids and potassium aryltrifluoroborates for the synthesis of symmetrical biaryls. The reactions take place under benchtop reaction conditions in 96% EtOH at temperatures between rt and 50 °C with no exclusion of air or humidity, in the presence of F-TEDA (Selectfluor™) as an oxidant. The procedure is very functional group tolerant, and affords the corresponding biaryls in high yields with large substrate scope (26 examples).Ministry of Science and Education, Spain (PID2021–124419NB-I00)4.6 Q2 JCR 20220.761 Q2 SJR 2022No data IDR 2021UE

Arylation of Benzo-Fused 1,4-Quinones by the Addition of Boronic Acids under Dicationic Pd(II)-Catalysis

The first examples of the direct arylation of benzo-fused 1,4-quinones by the dicationic Pd(II)-catalyzed addition of arylboronic acids are reported. The addition reaction is carried out under very mild conditions (dioxane-H2O, rt, open air atmosphere) and is tolerant of free OH groups. In addition, the reaction shows high regioselectivity when using nonsymmetrical quinones as starting materials.Projects UCM-BSCH GR58/08-910815 and CTQ2006-15279-C03-01 (both to A.G.C.), and SAF2006- 04698 (to M.T.M.), are gratefully acknowledged for financial support.Peer reviewe

N-Heterocyclic Carbene-Catalyzed Monoacylation of 1,4-Naphthoquinones with Aldehydes

The NHC-catalyzed conjugate hydroacylation of 1,4-naphthoquinones allows for the synthesis of monoacylated 1,4-dihydroxynaphthalene derivatives. These targets, difficult to prepare selectively by standard protocols, represent important intermediates in the elaboration of highly substituted 1,4-naphthoquinone derivatives, which constitute relevant pharmaceutical scaffolds. High regioselectivity has been observed in the hydroacylation reaction when starting from nonsymmetrical quinones.Projects UCM-BSCH GR58/08-910815 and CTQ2006-15279-C03-01 (both to A.G.C), and SAF2006-04698 (to M.T.M.), are gratefully acknowledged for financial support.Peer reviewe