Synthesis of unusually strained spiroheterocyclic ring systems and their exploits in synthesis

Cyclopropenylidenephosphoranes: Rearrangement to Azetidinylidene-Methylphosphoniums

“…Finally, the involvement of a quite stable spiro-bicyclic intermediate 7 , 5.7 kcal/mol lower in energy than 3a , is suggested by an analogy of 5a with cyclobutanone (Scheme ): both exhibit an exocyclic double bond (C = X) to an electronegative group, X = CHP + and X = O, respectively, and cyclobutanone is formed by the rearrangement of oxaspiropentane, an analogue of 7 . A zwitterionic valence isomer of 7 , optimized as 8 and found to be iso-energetic to 3a , would be obviously prone to rearrange to 5 , overcoming a low energy barrier of 10.2 kcal/mol, but the formation of 8 would also require overcoming a prohibitive barrier of 64.8 kcal/mol from 3a .…”

Chemistry of the β-Thiolactones: Substituent and Solvent Effects on Thermal Decomposition and Comparison with the β-Lactones.

“…The β-lactones (2-oxetanones) have enjoyed considerable interest from the synthetic organic and medicinal chemistry communities over a period of many years because of their interesting and varied reactivity patterns. − Interest in the medicinal chemistry of the β-lactones continues apace with the recent discovery of potent proteasome inhibitors based upon them, − and their recent application as potent inhibitors for a number of bacterial virulence factors. − Indeed, it is this interest that is currently driving efforts toward more effective stereocontrolled syntheses of this class of molecule. ,− …”

Gold(I)-Catalyzed Formation of Bicyclo[4.2.0]oct-1-enes

“…Transition-metal catalysts play a prominent role in promoting the kinetic viability of a variety of synthetic reactions. When used in combination with thermodynamically favorable transformations, like the consumption of C–C unsaturation , and the release of ring strain, − numerous useful methodologies have emerged. The construction of complex polycyclic structures from relatively simple starting materials has been the subject of a number of research efforts aimed at accessing biomimetic carbocycles. − …”