Intermolecular [3 + 3]-Cycloadditions of Azides with the Nazarov Intermediate
作者:Owen Scadeng、Michael J. Ferguson、F. G. West
DOI:10.1021/ol102651k
日期:2011.1.7
Tetrasubstituted 1,4-dien-3-ones undergo Nazarov cyclization at low temperature, followed by reaction with organic azides via an apparent [3 + 3]-cycloaddition to give bridged bicyclic triazenes. These products do not appear to be intermediates in the previously described Schmidt-type process to furnish dihydropyridones. The reaction typically occurs with high diastereoselectivity.
Domino Electrocyclization/Azide-Capture/Schmidt Rearrangement of Dienones: One-Step Synthesis of Dihydropyridones from Simple Building Blocks
作者:Dong Song、Ali Rostami、F. G. West
DOI:10.1021/ja071041z
日期:2007.10.1
proceed via nucleophilic trapping of the 2-oxidocyclopentenyl intermediate, followed by Schmidt-type rearrangement to give a transient 1,4-dipole. In unsymmetrical examples, complete regioselectivity in favor of attack on the less substituted side was observed. The 1,4-dipole intermediate then rearranges to the observed dihydropyridone, via either proton transfer or 1,5-hydride shift.
A novel catalyst system—a combination of the readily available 2,2′-biphenol with the inexpensive, nontoxic, and eco-friendly B(OH)3—promoted the Nazarov cyclization of activated and inactivated divinyl ketones to afford the corresponding cyclopentenones up to 96% yield under, in a cis-selective manner. Compared with the conventional harsh conditions with hazardous reagents, user-friendly method was established with bench-stable and easy-to-handle reagents.