Synthesis of Fused Bromofurans via Mg-Mediated Dibromocyclopropanation of Cycloalkanone-Derived Chalcones and Cloke–Wilson Rearrangement

Abstract

A convenient two-step sequence for the conversion of alkylidenecycloalkanones to bromofurans is reported. The steps involve Mg-mediated diastereoselective dibromocyclopropanation of alkylidenecycloalkanone followed by acidic alumina-mediated regioselective ring expansion of the cyclopropyl ketone. The scope of the reaction was investigated using alkylidenecycloalkanones derived from tetralone, indanone, and benzosuberone to afford 2-aryl-3-bromofurans fused to various benzocycloalkanes. Representative examples of stereoconvergent dibromocyclopropanation and total aromatization of the furobenzocycloalkane are also reported.

Synthesis of Novel Spiro[Cyclopropane-Indazole] Derivatives Via Magnesium-Mediated Conjugate Addition of Bromoform

“…This stereochemistry of the products 3a-i is similar to the result reported previously. 12 A plausible mechanism for the conversion of 2 to 3 is outlined in Scheme 2. Firstly, magnesium reacts with excess bromoform to form initially tribromomethylmagnesium-bromide which undergoes conjugate addition to the enone moiety of the indazolone 2.…”

Recent Advances in the Cycloaddition Reactions of 2‐Benzylidene‐1‐benzofuran‐3‐ones, and Their Sulfur, Nitrogen and Methylene Analogues

“…In 2013, Namboothiri's group reported a convenient two-step synthesis of indene-fused bromofurans (Scheme 9a). [38] The first step is Mg-mediated diastereoselective dibromocyclopropanations 51 of alkylidenecycloalkanones 5, and the second step is acidic alumina-mediated regioselective ring expansion of the cyclopropyl ketones.…”

Synthesis of Heteroarene‐Fused Cyclopentadienes and Related Compounds Suitable for Metallocene Preparation

“…[143,[145][146][147] Gopi and Namboothiri proposed an efficient method for the synthesis of 2-aryl-3-bromo-4H-indeno[1,2-b] furans 193-198 from easily accessible products of the Knoevenagel condensation of 1-indanone with aromatic aldehydes via cyclopropanation followed by acid-catalyzed rearrangement (Scheme 29D). [147] 2,3-Diphenyl-4H-indeno[1,2-b]furan 199 was prepared by the oxidative coupling of deoxybenzoin and indene promoted by CuCl 2 ; the proposed reaction mechanism included the formation of an α-keto radical followed by the addition of this radical to indene (Scheme 30). [148]…”