A swift citrusy path to chiral phosphorus: The phosphates in the backbones of DNA and RNA are often drawn like crosses but are in fact tetrahedral. Sulfur is sometimes substituted for one of the phosphate oxygens during development of nucleotide-based drugs. Because of the geometry, this swap can lead to two different isomers. Knouse et al. report a pair of phosphorus reagents that conveniently produce either isomer selectively. This ability depended on the configuration of appended limonene substituents that are subsequently jettisoned. In addition to simplifying the route to sulfur-substituted oligonucleotides, these reagents will enable more precise studies of each isomer's distinct bioactivity. Science , this issue p. 1234

Historically accessed through two-electron, anionic chemistry, ketones, alcohols, and amines are of foundational importance to the practice of organic synthesis. After placing this work in proper historical context, this Article reports the development, full scope, and a mechanistic picture for a strikingly different way of forging such functional groups. Thus, carboxylic acids, once converted to redox-active esters (RAEs), can be utilized as formally nucleophilic coupling partners with other carboxylic derivatives (to produce ketones), imines (to produce benzylic amines), or aldehydes (to produce alcohols). The reactions are uniformly mild, operationally simple, and, in the case of ketone synthesis, broad in scope (including several applications to the simplification of synthetic problems and to parallel synthesis). Finally, an extensive mechanistic study of the ketone synthesis is performed to trace the elementary steps of the catalytic cycle and provide the end-user with a clear and understandable rationale for the selectivity, role of additives, and underlying driving forces involved.