Phenyl trimethyl ammonium tribromide mediated robust one-pot synthesis of spiro-oxacycles – an economic route – stereoselective synthesis of oxaspirohexacyclodieneones

Abstract

This paper entails the first recognition of Phenyl Trimethyl Ammonium Tribromide (PTAB) as an effective reagent for spiro-cyclizations proceeding via oxidative dearomatization. The experiment exhibits economical, metal and ligand free one-pot accomplishment of these significant transformations. The described protocol presents the first generalised methodology of spiro-oxacycle synthesis which can be applied towards various directions. A stereoselective synthesis of oxa-spirocyclooxadieneones has been accomplished.

Controlling Stereoselectivity in Tribromide Mediated Oxidative Dearomatisations – Synthesis of Selective Spirofurano‐naphthalones

“…effective steric crowding is the determining factor) was to be hand‐picked to get the best stereoselectivity. The relative stereochemistry has been denoted on the basis of nOe experiments (Figure ).…”

“…Our group has been focusing on oxidative dearomatisation reactions. Recently, we have developed an ammonium tribromide mediated spiro‐cyclisation of phenols and naphthols (Scheme a). Hitherto, the achieved diastereoselectivity in substituted spirofurans was unsatisfactory.…”

“…Hitherto, the achieved diastereoselectivity in substituted spirofurans was unsatisfactory. The presence of ammonium counterpart in the reactive intermediate, mentioned in our previous report, insisted us to study the possible aspects of tuning the ammonium counterpart and see the desired effect on the aforesaid diastereoselectivity. Interestingly, it was found that not only changing the ammonium counterpart of tribromides but also altering the solvents had an impact on diastereoselectivity.…”

Ruthenium(VIII)-Catalyzed ipso-Dearomative Spiro-Etherification and Spiro-Amidation of Phenols

“…Some important reports included the catalytic intramolecular spirolactonization by Ishihara and Kita . A quite generalized, tribromide-mediated spiro-oxacyclization was reported by our group . Reterosynthetically, it is envisaged that a preferred ipso -attack of a tethered chain in a phenol can deliver spirocyclization that proceeds via oxidative dearomatization.…”

“…11 A quite generalized, tribromide-mediated spiro-oxacyclization was reported by our group. 12 Reterosynthetically, it is envisaged that a preferred ipso-attack of a tethered chain in a phenol can deliver spirocyclization that proceeds via oxidative dearomatization. It would be inspiring if the desired catalysis were an open air transformation.…”