Recent Advances in Minisci‐Type Reactions

Reactions that involve the addition of carbon‐centered radicals to basic heteroarenes, followed by formal hydrogen atom loss, have become widely known as Minisci‐type reactions. First developed into a useful synthetic tool in the late 1960s by Minisci, this reaction type has been in constant use over the last half century by chemists seeking to functionalize heterocycles in a rapid and direct manner, avoiding the need for de novo heterocycle synthesis. Whilst the originally developed protocols for radical generation remain in active use today, they have been joined in recent years by a new array of radical generation strategies that allow use of a wider variety of radical precursors that often operate under milder and more benign conditions. The recent surge of interest in new transformations based on free radical reactivity has meant that numerous choices are now available to a synthetic chemist looking to utilize a Minisci‐type reaction. Radical‐generation methods based on photoredox catalysis and electrochemistry have joined approaches which utilize thermal cleavage or the in situ generation of reactive radical precursors. This review will cover the remarkably large body of literature that has appeared on this topic over the last decade in an attempt to provide guidance to the synthetic chemist, as well as a perspective on both the challenges that have been overcome and those that still remain. As well as the logical classification of advances based on the nature of the radical precursor, with which most advances have been concerned, recent advances in control of various selectivity aspects associated with Minisci‐type reactions will also be discussed.     

Hierarchical Schur complement preconditioner for the stochastic Galerkin finite element methods

Use of the stochastic Galerkin finite element methods leads to large systems of linear equations obtained by the discretization of tensor product solution spaces along their spatial and stochastic dimensions. These systems are typically solved iteratively by a Krylov subspace method. We propose a preconditioner, which takes an advantage of the recursive hierarchy in the structure of the global matrices. In particular, the matrices posses a recursive hierarchical two‐by‐two structure, with one of the submatrices block diagonal. Each of the diagonal blocks in this submatrix is closely related to the deterministic mean‐value problem, and the action of its inverse is in the implementation approximated by inner loops of Krylov iterations. Thus, our hierarchical Schur complement preconditioner combines, on each level in the approximation of the hierarchical structure of the global matrix, the idea of Schur complement with loops for a number of mutually independent inner Krylov iterations, and several matrix–vector multiplications for the off‐diagonal blocks. Neither the global matrix nor the matrix of the preconditioner need to be formed explicitly. The ingredients include only the number of stiffness matrices from the truncated Karhunen–Loève expansion and a good preconditioned for the mean‐value deterministic problem. We provide a condition number bound for a model elliptic problem, and the performance of the method is illustrated by numerical experiments. Copyright © 2013 John Wiley & Sons, Ltd.     

Assessment of intake of a complex radionuclide bearing dust formed at a nuclear power plant

The aim of this work was to provide an experimental basis for assessing intakes of an industrial actinide-bearing dust from measurements of⁶⁰Co and¹³⁷Cs in the body or urine. Whilst these radionuclides comprised 72% and 19% of the radioactivity present, greater than 90% of the committed effective dose will result from the low concentrations of the actinides present, 0.4%. To assess the dose coefficient for the dust and predict the biokinetics of⁶⁰Co and¹³⁷Cs in workers, absorption parameters for transfer from lungs to blood obtained from an animal study were combined with information on particle deposition and clearance from the ICRP human respiratory tract model and with tissue distribution and excretion data from the most recent systemic models. All other radionuclides were assumed to have Type M absorption characteristics. The dose coefficient for the dust, 1.29·10^–7 Sv·Bq^–1 was estimated to contain 113 kBq⁶⁰Co, 29 kBq¹³⁷Cs and 0.64 kBq of the actinides. The predicted retention and excretion characteristics of⁶⁰Co and¹³⁷Cs in workers after acute or chronic exposure to the dust suggested that measurements of these radionuclides in the body or urine could detect intakes equivalent to a few percent of an annual dose limit of 20 mSv·y^–1.     

Syntheses using isoxazoles—V: The rearrangement of phenylhydrazones of 4,5,6,7-tetrahydro-4-oxo-isoxazolo[2,3-a]-pyridinium bromides

Rearrangement of the phenylhydrazone (6) and the 2,4-dinitrophenylhydrazone (7) from 4,5,6,7-tetrahydro-4-oxo-isoxazolo [2,3-a]pyridinium bromide (1), by boiling acetic anhydride, gave the 1-(N-anilino)pyrrolo[3,2-b] pyridinones, (9,12 and 13). and the pyrazolo[4,3-b]pyridine-3-carboxaldehyde (8) or its diacetate (11).     

Copper-catalyzed alkene arylation with diaryliodonium salts

Alkenes and arenes represent two classes of feedstock compounds whose union has fundamental importance to synthetic organic chemistry. We report a new approach to alkene arylation using diaryliodonium salts and Cu catalysis. Using a range of simple alkenes, we have shown that the product outcomes differ significantly from those commonly obtained by the Heck reaction. We have used these insights to develop a number of new tandem and cascade reactions that transform readily available alkenes into complex arylated products that may have broad applications in chemical synthesis.