Ti-catalyzed ring-opening oxidative amination of methylenecyclopropanes with diazenes.

The ring-opening oxidative amination of methylenecyclopropanes (MCPs) with diazenes catalyzed by pyTiCl(NR) complexes is reported. This reaction selectively generates branched α-methylene imines as opposed to linear α,β-unsaturated imines, which are difficult to access other methods. Products can be isolated as the imine or hydrolyzed to the corresponding ketone in good yields.

Divergent Mechanisms of the Banert Cascade with Propargyl Azides.

Triazoles are privileged heterocycles for a variety of applications. The synthesis of 1-triazoles can be accomplished by the Banert cascade from propargylic azides. Depending on the substrate and conditions, the Banert cascade can proceed by either a sigmatropic or prototropic mechanism.

On the Winstein rearrangement: equilibrium and mechanism.

Allylic azides are underutilized in organic synthesis when compared to other organic azides or other allylic functionality. This is likely because allylic azides rearrange at room temperature, resulting in a potentially complex mixture of azides. This rearrangement has been termed the Winstein rearrangement.

Kinetic Resolution of Cyclic Secondary Azides, Using an Enantioselective Copper-Catalyzed Azide-Alkyne Cycloaddition.

An enantioselective copper-catalyzed azide-alkyne cycloaddition (E-CuAAC) is reported by kinetic resolution. Chiral triazoles were isolated in high yield with limiting alkyne (up to 97:3 enantiomeric ratio (er)). A range of substrates were tolerated (>30 examples), and the reaction was scaled to >1 g.

Catalytic Racemization of Activated Organic Azides.

The first detailed description of the catalytic racemization of activated benzylic and allylic azides under mild conditions is reported. A kinetic analysis of the observed racemization indicates a first-order dependence on azide, a first-order dependence on catalyst, and that the rate of racemization correlates to σ. A variety of azides with varying substitution patterns undergo facile racemization, and catalyst selection can tune this process.

Evidence for a Sigmatropic and an Ionic Pathway in the Winstein Rearrangement.

The spontaneous rearrangement of allylic azides is thought to be a sigmatropic reaction. Presented herein is a detailed investigation into the rearrangement of several allylic azides. A combination of experiments including equilibrium studies, kinetic analysis, density functional theory calculations, and selective N-isotopic labeling are included.

Dynamic Kinetic Resolution of Allylic Azides via Asymmetric Dihydroxylation.

The catalytic enantioselective preparation of densely functionalized amines is a fundamental synthetic challenge. To address this challenge, we report for the first time that the Winstein rearrangement can be enlisted as the racemization pathway in a dynamic kinetic resolution of allylic azides. Alkene functionalization by Sharpless dihydroxylation affords tertiary azides in excellent enantioselectivity (up to 99:1 er).