A new means to activate diazoalkanes has been discovered and applied broadly over the past few years. Brønsted acids, both achiral and chiral, have been used to promote the formation of carbon-carbon and carbon-heteroatom bonds with a growing number of diazoalkane derivatives. Aside from their straightforward ability to build structural and stereochemical complexity in innovative new ways, these transformations are remarkable owing to their ability to skirt competitive diazo protonation--a reaction that has long been used to prepare esters efficiently and cleanly from carboxylic acids. In cases where achiral Brønsted acids are used, high diastereoselection can be achieved. Meanwhile, chiral Brønsted acids can deliver products with both high diastereo- and enantioselectivity. More recently, systems have emerged that combine Brønsted acids and either Lewis acids or transition metals to promote carbon-carbon bond formation from diazoalkanes.

The mechanism of the Brønsted acid-catalyzed aza-Darzens reaction is explored by charting the stereochemical outcome of the triflic acid-promoted conversion of trans-triazolines to cis-aziridines. These experiments are consistent with the intermediacy of an α-diazonium-β-amino ester intermediate.

A novel series of HIV-1 integrase inhibitors were identified from a 100 member (4R(1) x 5R(2) x 5R(3)) library of pyrrolidinedione amides. A solid-phase route was developed which facilitates the simultaneous variation at R(1), R(2), and R(3) of the pyrrolidinedione scaffold. The resulting library samples were assayed for HIV-1 integrase activity and analyzed to determine the R(1), R(2), and R(3) reagent contributions towards the activity.

A novel alpha-diazo imide reagent and its activation by strong Brønsted acid is shown to produce the product of a syn-glycolate Mannich transform with high diastereoselection.

In den letzten Jahren wurden neue Aktivierungsmöglichkeiten für Diazoalkane entdeckt und bereits umfangreich angewendet. Mit chiralen und achiralen Brønsted‐Säuren als Katalysatoren gelangen Kohlenstoff‐Kohlenstoff‐ und Kohlenstoff‐Heteroatom‐Verknüpfungen mit einer zunehmenden Zahl von Diazoalkan‐Derivaten. Auf diesem Weg lassen sich sehr einfach in struktureller und stereochemischer Hinsicht komplizierte Verbindungen erhalten. Außerdem wird auch die konkurrierende Protonierung der Diazoverbindung umgangen – eine Reaktion, die seit langem zur effizienten Veresterung von Carbonsäuren genutzt wird. Achirale Brønsted‐Säuren als Katalysatoren erreichen hohe Diastereoselektivitäten, und chirale Brønsted‐Säuren führen zu den gewünschten Produkten mit sowohl hoher Diastereo‐ als auch Enantioselektivität. Seit einiger Zeit gibt es auch Systeme zur Kohlenstoff‐Kohlenstoff‐Verknüpfung, die eine Brønsted‐Säure mit einer Lewis‐Säure oder einer Übergangsmetallverbindung kombinieren.

Isopropyl chloroformate Aniline Triethylamine n‐ Butyllithium Acetic anhydride 1,1,1,3,3,3‐Hexamethyldisilazane Isopropyl acetyl(phenyl)carbamate 2,2,2‐Trifluoroethyl trifluoroacetate 4‐Acetamidobenzenesulfonyl azide Carbamic acid N ‐(2‐diazoacetyl)‐ N ‐phenyl‐ 1‐methylethyl ester

Developing simpler, more accessible, and more affordable methods for the determination of the boiling point of microscale amounts of liquid may lead to increased utilization in research and teaching laboratories as an analytical technique. Our efforts toward that goal have revealed that digital hot plates can be used as the heat source. One option is to simply use a test tube and a digital thermometer, requiring 300 μL of liquid that accurately determines boiling points that range from 35 to 150 °C. An alternative method, requiring as little as 30 μL of liquid, utilizes a modified aluminum block and a temperature control probe coupled to the digital hot plate that results in the accurate determination of boiling points that range from 35 to 205 °C. Both modifications to the Siwoloboff–Wiegand method provide consistent, reliable, and accurate boiling points for a variety of liquids with a wide range of boiling points.

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