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

Abstract

A series of ammonium tribromides were screened for exploring the role of ammonium counterpart attached to tribromides on generation of stereoselective spiro‐furans via oxidative dearomatisation of naphthols. The proposition enlightens a suitable combination of the ammonium tribromide and solvent employed, deliver the best achieved diastereoselectivities. This in turn, has also envisioned the mechanistic aspects related to this category of reactions. The mentioned dearomative spiro‐furano naphthalones has also been successfully achieved on a large‐scale.

Visible‐light Catalysed Trifluoromethylthiolation and Related Dearomative Spirocyclizations

“…[2] It may be noted that amongst, all globally registered pharmaceutical drugs, 22% contain one or more fluorine atoms and 34% of agrochemicals are organo-fluorine compounds. [3] Predominance of fluorodexoyglucose in Positron Emission Tomography (PET) analysis in the form of 18 F (halflife 110 min) over 11 C (half-life 20 min), 13 N (half-life 10 min) and 15 O (half-life 2 min) makes the fluorine addition to the organic molecules more important to medicinal chemist. [4] Of late, spirocycles are important molecules of interest with promising structural architecture, [5] and also primarily used as chiral ligands owing to its helical properties as well as conformational transmission and photochromism.…”

“…Thus, in a nutshell, we look forward towards a one-pot visible-light transformation of the biaryl ynones to structurally complex spirocyles involving a dearomatization of the arene and trifluoromethylthio group insertion along with varied CÀ S bond generations (Figure 1). In this context, with our continued interest in dearomative spirocyclizations, [15] our group has recently achieved an efficient CÀ Br bond forming photo-redox cascade cyclisation of biaryl ynones. [16] The unexpected discovery of 3'-bromo-2'-aryl-4'H-spiro[cyclohexa [2,5]diene-1,1'-naphthlene]-4,4'-dione in 38% yield without any photocatalyst has drawn our attention to explore the fact in mechanistic point of view.…”

Photo-redox Catalyzed C-S and C-C Bond Forming Cascade Cy-clization/Dearomatization of Biaryls: Sustainable Route to Func-tionalized Spirocyclohexa[5.5] and [4.5]trienones

“…Therefore, the development of more efficient and green process for trifluoromethylthiolation and sulfonylation reactions of C-C unsaturated bond via radical cascade cyclisation is still in demand. With our continued interest in dearomative spirocyclisations 14 and photochemical reactions 15 we explored the present visiblelight mediated approach for the generation of spiro [4.5] and [5.5]trienones featuring -SCF3, -SO2Ar, -SAr, -COAr. This methodology represents significant advances in photochemical C-S and C-C bond formation of biaryl ynones that overcomes existing challenge associated with the uncontrolled photodecomposition processes occurring due to the high-energy photons.…”

Empowering Visible Light Catalysis: Brominative Dearomatizationof Biaryl Ynones

“…Over the past decade, visible light driven photoredox catalysis has gained colossal interest in the exploration of novel transformations employing photocatalyst to promote the reactions under external oxidant-free or reductant-free conditions. 18 Driven by our prolonged interest in dearomatisation chemistry 19 and newly gained interest in visible light promoted reaction, we explored the possibility of brominative carbannulation of biaryl ynones to form spiro[5.5]-trienones and bromo-dibenzocycloheptenones. Herein, we would like to introduce the application of Riboflavin tetraacetate (RFTA) as a metal-free photocatalyst 20 to facilitate the primary photoinduced events.…”