Pyridines from azabicyclo[3.2.0]hept-2-en-4-ones through a proposed azacyclopentadienone

Pyridines have been formed by heating azabicyclo[3.2.0]hept-2-en-4-ones in toluene. The generation of a 3-azacyclopentadienone intermediate via a [2+2]-cycloreversion is proposed as the key step. A Diels-Alder reaction of a styrene, extrusion of carbon monoxide and loss of hydrogen then gives the pyridine. The process parallels the well-known synthesis of benzenes from cyclopentadienones. The azabicyclo[3.2.0]hept-2-en-4-ones were synthesized from the reaction between readily available cyclopropenones and 1-azetines, in which the cyclopropenones behave as all-carbon 1,3-dipolar equivalents

Skeletal Editing Approach to Bridge-Functionalized Bicyclo[1.1.1]pentanes from Azabicyclo[2.1.1]hexanes

Azabicyclo[2.1.1]hexanes (aza-BCHs) and bicyclo[1.1.1]pentanes (BCPs) have emerged as attractive classes of sp3-rich cores for replacing flat, aromatic groups with metabolically resistant, three-dimensional frameworks in drug scaffolds. Strategies to directly convert, or "scaffold hop", between these bioisosteric subclasses through single-atom skeletal editing would enable efficient interpolation within this valuable chemical space. Herein, we describe a strategy to "scaffold hop" between aza-BCH and BCP cores through a nitrogen-deleting skeletal edit. Photochemical [2+2] cycloadditions, used to prepare multifunctionalized aza-BCH frameworks, are coupled with a subsequent deamination step to afford bridge-functionalized BCPs, for which few synthetic solutions currently exist. The modular sequence provides access to various privileged bridged bicycles of pharmaceutical relevance

Skeletal Editing Approach to Bridge-Functionalized Bicyclo[1.1.1]pentanes from Aza-Bicyclo[2.1.1]hexanes

The ability to rapidly navigate a wide diversity of chemical space from simple building blocks is a cornerstone of medicinal chemistry campaigns. Aza-bicyclo[2.1.1]hexane (aza-BCH) and bicyclo[1.1.1]pentane (BCP) scaffolds have recently emerged as attractive classes of sp3-rich cores for replacing flat, aromatic scaffolds with metabolically resistant, three-dimensional frameworks. Over the last decade, these pharmaceutically desirable properties and increased synthetic accessibility have led to a marked increase in the adoption of aza-BCHs and BCPs into drug scaffolds. While multiple, independent methods have been developed for the preparation of these structural motifs, strategies to directly convert, or scaffold hop, between these bioisosteric subclasses through single-atom skeletal editing would enable efficient interpolation within this valuable chemical space. Herein, we describe a strategy to scaffold hop between aza-BCH and BCP cores through a nitrogen-deleting skeletal edit. Photochemical [2+2] cycloadditions, used to prepare multifunctionalized aza-BCH frameworks, are coupled with a subsequent deamination step to afford bridge-functionalized BCPs, for which few synthetic solutions currently exist. The modular sequence provides access to various privileged bridged bicycles of pharmaceutical relevance bearing substituents that can be further derivatized