Acid catalyzed ring opening of α-bis(methylthio)methylenealkyl cyclopropyl ketones: An intramolecular alkylation approach to substituted cyclopentanones

Stereoconvergent Direct Ring Expansion of Cyclopropyl Ketones to Cyclopentanones

Recyclization of the ring-opening species of alkyl cyclopropyl ketones to cyclopentanones, which proceeds through an unfavored 5-endo-trig cyclization predicted by Baldwin's rules, is elusive. Herein, as assisted by a strong aryl donor and the Thorpe-Ingold strain on a quaternary cyclopropyl center, stereoconvergent direct ring expansion of cyclopropyl ketones to cyclopentanones promoted by TfOH or BF₃·Et₂O is described, providing a modular construction of polysubstituted cyclopentanones from aldehydes, alkyl methyl ketones, and α-keto esters within three steps.

Domino Carbocationic Rearrangement of α-[Bis(methylthio)methylene]alkyl-2-(3/2-indolyl) Cyclopropyl Ketones

Domino carbocationic rearrangement of a number of substituted 3- and 2-indolylcyclopropyl ketones with an alpha-bis(methylthio)methylene group in the presence of various protic/Lewis acids yields a variety of products, mainly the pentaleno fused indoles and the carbazole derivatives.

Domino carbocationic rearrangement of aryl-2-(1-N-methyl/benzyl-3-indolyl)cyclopropyl ketones: a serendipitous route to 1H-cyclopenta[c]carbazole framework

Aryl-2-(N-methyl/benzyl-3-indolyl)cyclopropyl ketones 2a-m are shown to undergo a novel unexpected domino carbocationic rearrangement in the presence of SnCl(4)/CH(3)NO(2) yielding 2-aroyl-3-aryl-1H-cyclopenta[c]carbazoles 3a-m in good yields. The possible mechanistic pathway for this interesting transformation involves a series of cascade events, (a) electrophilic ring opening of cyclopropyl ketone, (b) intermolecular enol capture of the resulting zwitterionic intermediate, (c) electrophilic dimerization of indole moieties to give tetrahydrocarbazole intermediate and its subsequent aromatization by elimination of an indole moiety and dehydrogenation, and (d) intramolecular aldol condensation of the side chain to give a cyclopentene ring. The overall transformation involves formation of three carbon-carbon bonds along with a fused benzene and a substituted cyclopentene ring in one-pot operation from simple indole precursors.

A Facile Synthesis of 3-Cyclopropyl- and 5-Cyclopropyl-isoxazoles

The regioselective synthesis of isomeric isoxazoles 3-(2-arylcyclopropyl)-5-methylthio- and 5-(2-arylcyclopropyl)-3-methylthio-isoxazoles is described.