Rhodium-Catalyzed Addition of Aryl Boronic Acids to 2,2-Disubstituted Malononitriles

β-Ketonitriles bearing a quaternary carbon at the 2-position were prepared through Rh-catalyzed addition of aryl boronic acids to 2,2-disubstituted malononitriles. In contrast to the previously described transnitrilative cyanation of aryl boronic acids with dialkylmalononitriles, the present reaction avoids retro-Thorpe collapse of the intermediate addition product through the use of a milder base. The reaction was amenable to a variety of aryl boronic acids and disubstituted malononitriles, providing a diverse array of β-ketonitriles. The products could be further derivatized to valuable chiral α,α-disubstituted-β-aminonitriles through addition reactions to the corresponding N-tert-butanesulfinyl imines.     

Phosphinine-Based Ligands in Gold-Catalyzed Reactions

A series of substituted phosphinines, 1-phosphabarrelenes and 5-phosphasemibullvalenes were synthesized and evaluated for their potential application as ligands in homogeneous catalytic reactions. While their buried volume (%V_bur) was calculated to get insight into the steric properties, [LNi(CO)₃] complexes were prepared in order to determine the corresponding Tolman electronic parameter. ETS-NOCV (extended-transition-state natural orbital for chemical valence) calculations on [LAuCl] complexes further allowed an estimation of the σ- and π-contributions to the L− M interaction. Au^I coordination compounds of selected examples were prepared and characterized by single crystal X-ray diffraction. Finally, the three classes of P^III compounds were successfully used in the Au^I-catalyzed cycloisomerization of N-2-propyn-1-ylbenzamide, showing very good activities and selectivities, which are comparable with the reported data of cationic phosphorus-based gold catalysts.     

Inverse electron demand hetero-Diels–Alder reaction in preparing 1,4-benzodioxin from o-quinone and enamine

A process for synthesizing 1,4-benzodioxin, through oxidation of a phenol to an o-quinone followed by treatment with an enamine, has been developed. Adduct stereochemistry is found to be retained via this one-pot reaction. The method uses hypervalent iodine reagent under mild conditions and is compatible with a wide scope of phenols and enamines.     

Carbon K‐edge spectra of carbonate minerals

Carbon K‐edge X‐ray spectroscopy has been applied to the study of a wide range of organic samples, from polymers and coals to interstellar dust particles. Identification of carbonaceous materials within these samples is accomplished by the pattern of resonances in the 280–320 eV energy region. Carbonate minerals are often encountered in the study of natural samples, and have been identified by a distinctive resonance at 290.3 eV. Here C K‐edge and Ca L‐edge spectra from a range of carbonate minerals are presented. Although all carbonates exhibit a sharp 290 eV resonance, both the precise position of this resonance and the positions of other resonances vary among minerals. The relative strengths of the different carbonate resonances also vary with crystal orientation to the linearly polarized X‐ray beam. Intriguingly, several carbonate minerals also exhibit a strong 288.6 eV resonance, consistent with the position of a carbonyl resonance rather than carbonate. Calcite and aragonite, although indistinguishable spectrally at the C K‐edge, exhibited significantly different spectra at the Ca L‐edge. The distinctive spectral fingerprints of carbonates provide an identification tool, allowing for the examination of such processes as carbon sequestration in minerals, Mn substitution in marine calcium carbonates (dolomitization) and serpentinization of basalts.