Enantioselective PCCP Brønsted acid-catalyzed aza-Piancatelli rearrangement.

An enantioselective aza-Piancatelli rearrangement has been developed using a chiral Brønsted acid based on pentacarboxycyclopentadiene (PCCP). This reaction provides rapid access to valuable chiral 4-amino-2-cyclopentenone building blocks from readily available starting material and is operationally simple.

Developing a Gel-Based Sensor Using Crystal Morphology Prediction.

The stimuli-responsive nature of molecular gels makes them appealing platforms for sensing. The biggest challenge is in identifying an appropriate gelator for each specific chemical or biological target. Due to the similarities between crystallization and gel formation, we hypothesized that the tools used to predict crystal morphologies could be useful for identifying gelators. Herein, we demonstrate that new gelators can be discovered by focusing on scaffolds with predicted high aspect ratio crystals. Using this morphology prediction method, we identified two promising molecular scaffolds containing lead atoms. Because solvent is largely ignored in morphology prediction but can play a major role in gelation, each scaffold needed to be structurally modified before six new Pb-containing gelators were discovered. One of these new gelators was developed into a robust sensor capable of detecting lead at the U.S. Environmental Protection Agency limit for paint (5000 ppm).

Cascade rearrangement of furylcarbinols with hydroxylamines: practical access to densely functionalized cyclopentane derivatives.

This article describes the aza-Piancatelli rearrangement with hydroxylamines to 4-aminocyclopentenones and subsequent transformations that highlight the versatility of the cyclopentene scaffold and the value of the hydroxylamine nucleophile in this transformation.

Importance of off-cycle species in the acid-catalyzed aza-Piancatelli rearrangement.

The observed rate of reaction in the dysprosium triflate catalyzed aza-Piancatelli rearrangement is controlled by a key off-cycle binding between aniline and catalyst. Deconvoluting the role of these ancillary species greatly broadens our understanding of factors affecting the productive catalytic pathway. We demonstrate that the rate of reaction is controlled by initial competitive binding between the furylcarbinol and nitrogen nucleophile using either a Brønsted or Lewis acid catalyst and that the resulting rearrangement proceeds without involving the Brønsted and Lewis acid catalyst. This shows conclusively that the rate-controlling step and selectivity of reaction are decoupled.