Designing an Apparently Orbital-Symmetry-Forbidden [3s,5s]-Sigmatropic Shift through Transition-State Complexation and Stereoelectronic Effects.

The [3s,5s]-sigmatropic shift is an example of an orbital-symmetry forbidden pericyclic reaction that is outcompeted by the allowed [3s,3s]-sigmatropic shift. Density functional theory calculations are used to show that Pd -complexed systems with strategically placed substituents engaging in key stereoelectronic effects can select for the [3s,5s] process, thereby outcompeting both orbital-symmetry-allowed [3s,3s]- and [3s,5a]-shifts.

Synthesis of 7-Aminocoumarins from 7-Hydroxycoumarins via Amide Smiles Rearrangement.

N-Substituted 7-aminocoumarins can be synthesized from readily available 7-hydroxycoumarins via alkylation with α-bromoacetamides and subsequent tandem O → N Smiles rearrangement-amide hydrolysis. The key rearrangement sequence proceeds under mild conditions to provide convenient access to various -alkyl and -aryl products in moderate to high yields. The process is operationally simple, inexpensive, transition-metal-free, and can be telescoped into a one-pot process.