Phosphine- and water-promoted pentannulative aldol reaction

Abstract

An intramolecular aldol reaction promoted by tributylphosphine and water is described. Thereby, metal-free access to highly functionalised cyclopenta-fused arenes and heteroarenes is achieved.

Phosphine-Catalyzed Intramolecular Vinylogous Aldol Reaction of α-Substituted Enones

“…The role of the solvent was subsequently investigated (entries 6–11). The polar aprotic solvents such as DMSO and acetonitrile delivered 2a in good yields (entries 8 and 9). This observation is in line with the success of the MBH or MBH-type reactions in polar media. , …”

“…With our experience in synthesizing multifunctional cyclopentanoids via organophosphine catalysis, we envisioned that the tethered α-substituted enone-aldehydes G undergo a cascade phospha-Michael/aldol reaction, akin to Morita–Baylis–Hillman (MBH) reaction, and generate the kinetically favored five-membered ring systems I (Scheme ). A subsequent 1,4-proton shift generates J , which undergoes phosphine elimination through γ-deprotonation assisted by the adventitious hydroxide, providing (hetero)­arene-fused 3-hydroxycyclopentanones K .…”

Synthesis, characterization and stability of phosphonium phenolate zwitterions derived from a (diphenylphosphino)phenol derivative and oxiranes

“…This redox reaction may be facilitated by water, as it has long been known that tertiary phosphines and water form the corresponding phosphine oxides and hydrogen under alkaline conditions [41]. Furthermore, it has been shown that the attack of water on phosphonium centers leads to the elimination of the corresponding newly formed phosphine oxide [42]. In a recent publication, this reactivity is exploited in a photocatalytic phosphine-mediated water activation for hydrogenation of alkenes [43].…”

Conceptual advances in nucleophilic organophosphine-promoted transformations

“…As part of our explorations leading to the development of the phosphine- and water-promoted reductive aldol method with α-substituted dienone-aldehydes 16 , we utilized dienone-ketones 19 , possessing enolisable protons, Scheme 10. 34 The RAR of 19 was expected to provide 20 under the prototypical conditions. But we isolated 21 , which is an intramolecular aldol product.…”