Assisted Tandem Pd Catalysis Enables Regiodivergent Heck Arylation of Transiently Generated Substituted Enol Ethers.

Two complementary regiodivergent Pd-catalyzed assisted tandem [isomerization/Heck arylation] reactions are reported. They provide access to a broad array of acyclic trisubstituted vinyl ethers starting from readily available alkenyl ethers. In both cases, the isomerization is conducted with a [Pd-H] precatalyst supported by tris-tert-butyl phosphine ligands. When the catalyst is modified by the addition of a chelating bisphosphine ligand (dppp), an organic base (Cy2NMe), sodium acetate, and aryl triflates are used as electrophiles, the α-arylation pathway is promoted preferentially. The ß-arylation pathway is favored for electron-deficient and electron-neutral aryl halides when the catalyst is simply modified by the addition of an excess of an organic base (Et3N) after completion of the isomerization reaction. Electron-rich aryl halides lead to reduced levels of regiocontrol. The moderate stereoselectivity obtained are proposed to reflect the absence of stereocontrol in the isomerization step. Computational analyses suggest that migratory insertion is selectivity-determining for both the arylations. For the ß-selective arylation, an energy decomposition analysis underscored that electronic factors favor α-regioselectivity and steric effects favor ß-regioselectivity. Preliminary investigations show that high levels of stereoselectivity can be achieved for the α-selective arylation by ligand control. Complementarily, reaction conditions for postcatalytic stereo-correction have also been identified for each catalytic system.

Cooperative iodine and photoredox catalysis for direct oxidative lactonization of carboxylic acids.

A new method for the formation of γ- and δ-lactones from carboxylic acids through direct conversion of benzylic C-H to C-O bonds is described. The reaction is conveniently induced by visible light and relies on a mild cooperative catalysis by the combination of molecular iodine and an organic dye.

Multiple Halogenation of Aliphatic C-H Bonds within the Hofmann-Löffler Manifold.

An innovative approach to position-selective polyhalogenation of aliphatic hydrocarbon bonds is presented. The reaction proceeded within the Hofmann-Löffler manifold with amidyl radicals as the sole mediators to induce selective 1,5- and 1,6-hydrogen-atom transfer followed by halogenation. Multiple halogenation events of up to four innate C-H bond functionalizations were accomplished. The broad applicability of this new entry into polyhalogenation and the resulting synthetic possibilities were demonstrated for a total of 27 different examples including mixed halogenations.

Designing Homogeneous Bromine Redox Catalysis for Selective Aliphatic C-H Bond Functionalization.

The potential of homogeneous oxidation catalysis employing bromine has remained largely unexplored. We herein show that the combination of a tetraalkylammonium bromide and meta-chloroperbenzoic acid offers a unique catalyst system for the convenient and selective oxidation of saturated C(sp3 )-H bonds upon photochemical initiation with day light. This approach enables remote, intramolecular, position-selective C-H amination as demonstrated for 20 different examples. For the first time, an N-halogenated intermediate was isolated as the active catalyst state in a catalytic Hofmann-Löffler reaction. In addition, an expeditious one-pot synthesis of N-sulfonyl oxaziridines from N-sulfonamides was developed and exemplified for 15 transformations. These pioneering examples provide a change in paradigm for molecular catalysis with bromine.

Cooperative Light-Activated Iodine and Photoredox Catalysis for the Amination of Csp3 -H Bonds.

An unprecedented method that makes use of the cooperative interplay between molecular iodine and photoredox catalysis has been developed for dual light-activated intramolecular benzylic C-H amination. Iodine serves as the catalyst for the formation of a new C-N bond by activating a remote Csp3 -H bond (1,5-HAT process) under visible-light irradiation while the organic photoredox catalyst TPT effects the reoxidation of the molecular iodine catalyst. To explain the compatibility of the two involved photochemical steps, the key N-I bond activation was elucidated by computational methods. The new cooperative catalysis has important implications for the combination of non-metallic main-group catalysis with photocatalysis.

Factors influencing parent reports on quality of life for children with asthma.

Children and parents often differ in their perceptions of a complex disease such as asthma. This ancillary study of children with mild to moderate asthma that was conducted at four of the eight clinics in the Childhood Asthma Management Program had two aims: (1) to relate quality of life to asthma symptoms, sociodemographic characteristics, child psychosocial adjustment and family social support and (2) to relate agreement between child- and parent-reported quality of life to child age. For this study participants completed the Caregiver's Pediatric Asthma Quality of Life Questionnaire (C-PAQLQ), Pediatric Asthma Quality of Life Questionnaire, and a battery of psychosocial health outcomes questionnaires at the 12-month follow-up. The average asthma symptom score from diary cards for the 2 weeks before the visit was also collected. Parent-reported family burden was the strongest correlate of C-PAQLQ scores. Although the average asthma symptom score was not associated with parent-reported quality of life, the study had low power to detect a relationship because of the few episodes of asthma reported during the assessment period. The correlation between child and parent reported quality of life improved with increasing age of the child, suggesting increased child-parent agreement about quality of life outcomes was associated with increasing age of the child. Family characteristics, such as degree of cohesion among family members, are not associated with quality of life ratings.