Studies on the acid-catalyzed opening of non-rigid: acylcyclopropanes: a dramatic solvent effect. A route to the bicyclo[2.2.1]heptane ring system

Arylcyclopropane yet in its infancy: the challenges and recent advances in its functionalization

Electronically unbiased arylcyclopropane functionalization has always been a challenge to organic chemists, and the emergence of donor-acceptor cyclopropanes (DACs) has not only vehemently overshadowed them but still dominates the cyclopropane chemistry. Unlike DACs, the absence of pre-installed functional groups makes it harder for them to activate and participate in a reaction. The field has witnessed considerably slow progress since its inception due to the inherent challenges. There are only a few strategies available to open arylcyclopropanes. Therefore, this work is still in its infancy stage in spite of these materials being one of the earliest known type of cyclopropanes. This review manifests the history, endeavors, and achievements alongside the associated challenges, opportunities, and the need for concerted efforts to accomplish the long-awaited golden age of arylcyclopropanes.

Carbocycles from donor–acceptor cyclopropanes

Donor–acceptor cyclopropane annulations – not just for heterocycles.

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.

Domino carbocationic cyclization of functionalized cyclopropyl ketones: facile one-pot access to peri- and angularly fused polycyclic aromatic and heteroaromatic frameworks

Conjugate adducts obtained by base-induced 1,4-addition-elimination of various aryl/heteroaryl acetonitriles with 1-(2-arylcyclopropyl)-3,3-(bismethylthio)-2-propen-1-ones have been shown to undergo facile acid-induced domino carbocationic rearrangement yielding a variety of substituted tricyclic aromatic and heteroaromatic frameworks in high yields in a one-pot operation. The methodology provides efficient, high-yield routes for synthesis of novel substituted dihydrophenalenes, dihydrobenzo[d,e]anthracene, cyclopenta[a]naphthalene, and fused heteroaromatics such as substituted 4,5-dihydrobenzo[c,d]indole, dihydronaphtho[1,8-b,c]thiophene, dihydroindeno[5,4-b]- and -[4,5-b]-thiophenes, cyclopenta[a]carbazole, and dihydrocyclopenta[e]indazol-3-one derivatives. The probable mechanism of this interesting domino process appears to involve stepwise or concomitant acid-induced ring opening and intramolecular cyclocondensation of cyclopropyl ketones to give benzo-fused arene (or heteroarene) intermediates bearing a reactive benzylic carbocation that is captured intramolecularly either by a preexisting aromatic (or heteroaromatic) ring or by a newly formed benzene ring to give either peri-fused or angularly fused products, respectively. Thus, the overall domino process entails formation of two C-C bonds, a substituted benzene ring along with a peri-fused cyclohexane or angularly fused cyclopentane ring in a single operation.