Lewis or Brønsted acid-catalysed reaction of propargylic alcohol-tethered alkylidenecyclopropanes with indoles and pyrroles for the preparation of polycyclic compounds tethered with indole or pyrrole motif.

We developed a facile synthetic method to access cyclopenta[b]naphthalene derivatives via the Lewis or Brønsted acid catalysed cascade nucleophilic addition, electronic cyclization, ring-opening rearrangement of propargylic alcohol-tethered alkylidenecyclopropanes with indole and pyrrole derivatives. The reaction exhibited a broad substrate scope and good functional group tolerance under metal-free conditions, affording the desired products in moderate to good yields.

The Construction of Molecular Complexity from Functionalized Alkylidenecyclopropanes (FACPs).

As a special family of cyclopropanes, alkylidenecyclopropanes (ACPs), exhibit outstanding physical and chemical activities, which provide opportunities to participate in fascinating chemical transformations to access cyclopropane-containing units without ring-opening processes and other unavailable compounds through conventional routes with ring-opening processes owing to their strain-driven reactivity and synthetic accessibility. Nowadays, intramolecular reactions of methylenecyclopropanes (MCPs) or ACPs with adjacent functionalities have emerged as a powerful synthetic protocol for the construction of a variety of polycyclic and heterocyclic compounds with different sized skeletons through catalytic methods. Recently, we put forward the concept of functional alkylidenecyclopropanes (FACPs) and in this Minireview, we will summarize the reactions of FACPs after 2016 including several important early works from three aspects: 1) reactions with distal C-C bond cleavage, 2) reactions with proximal C-C bond cleavage (including ring-expansion reactions), and 3) reactions without C-C bond cleavage.

Cu(I)-Catalyzed Coupling and Cycloisomerization of Diazo Compounds with Terminal Yne-Alkylidenecyclopropanes: Synthesis of Functionalized Cyclopenta[ b]naphthalene Derivatives.

A Cu(I)-catalyzed coupling and cycloisomerization of diazo compounds with terminal yne-alkylidenecyclopropanes (ACPs) has been presented. This reaction starts from the formation of an allenic intermediate in the Cu(I)-catalyzed cross-coupling reaction of a diazo compound with terminal alkyne in yne-tethered ACP and then undergoes a domino cycloisomerization of a 6π-electrocyclization and cyclopropane ring-opening rearrangement to give functionalized cyclopenta[ b]naphthalene derivatives in moderate to excellent yields under mild conditions.

Cascade Amination/Cyclization/Aromatization Process for the Rapid Construction of [2,3-c]Dihydrocarbazoles and [2,3-c]Carbazoles.

An intramolecular cascade amination/cyclization/aromatization reaction of functionalized alkylidenecyclopropanes has been developed in the presence of silver acetate, affording a variety of [2,3-c]dihydrocarbazoles and [2,3-c]carbazoles in moderate to excellent yields. The mechanistic investigations revealed that this cascade reaction proceeds through a radical initiated process. Moreover, further transformations for the synthesis of eustifoline-D and an OLED exhibit a potential synthetic utility of this method.

Copper-catalyzed trifluoromethylazidation and rearrangement of aniline-linked 1,7-enynes: access to CF3-substituted azaspirocyclic dihydroquinolin-2-ones and furoindolines.

A set of reactions involving copper-catalyzed trifluoromethylazidation and then rearrangement of aniline-linked 1,7-enynes with the relatively poorly reactive Togni reagent I and TMSN3 was developed, and provided facile access to structurally diverse and useful CF3-substituted azaspirocyclic dihydroquinolin-2-ones bearing two adjacent quaternary carbon centers. We were also able to obtain these products on a large scale. Moreover, the obtained products were further transformed into a range of synthetically valuable furoindolines bearing three consecutive quaternary carbon centers after reduction by NaBH4. Also, the delivery of multi-functionalized aziridines as a result of alcoholysis and LiAlH4-reduction of corresponding dihydroquinolin-2-ones 2ba demonstrated the synthetic value of this newly developed protocol.

Recent advances in the chemical transformations of functionalized alkylidenecyclopropanes (FACPs).

During the past several years, functionalized alkylidenecyclopropanes (FACPs) have attracted intensive attention in synthetic chemistry. Many interesting transformations of FACPs have been developed to synthesize a lot of structurally diverse and valuable polycyclic and heterocyclic compounds. This review will classify FACPs into aryl-FACPs, alkyl-FACPs and ring-FACPs for the first time, and recent interesting chemical transformations in these research fields will be included, respectively, from 2011. Moreover, we will pay more attention to the clarification of the reaction mechanism, in which the C-C bond cleavage of alkylidenecyclopropanes (ACPs) will be emphasized.

Electronic halocyclization and radical haloazidation of benzene-linked 1,7-dienes for the synthesis of functionalized 3,1-benzoxazines.

A novel electronic halocyclization and radical haloazidation of benzene-linked 1,7-dienes for the formation of functionalized 3,1-benzoxazines has been achieved by using TMSN3 as an azido source and NBS as a halogen source. This methodology is highlighted by its mild conditions and wide substrate scope, which concomitantly introduces one C-N and two C-halogen bonds into one molecule.

Copper-catalyzed cascade cyclization of 1,5-enynes via consecutive trifluoromethylazidation/diazidation and click reaction: self-assembly of triazole fused isoindolines.

Copper-catalyzed cascade cyclization of 1,5-enynes with two types of hypervalent reagents was developed via consecutive trifluoromethylazidation/diazidation and intramolecular click reaction (CUAAC), providing one-pot self-assembly of triazole fused isoindolines bearing a trifluoromethyl or an azide moiety. Moreover, the construction of a trifluoromethylcyclopropyl unit, which has been considered as a metabolically stable replacement for a tert-butyl moiety and was difficult to access, was also achieved under trifluoromethylazidation conditions. All these reactions exhibited excellent chemoselectivity, good to excellent yields and broad functional group tolerance.

Palladium-catalyzed cascade cyclization of allylamine-tethered alkylidenecyclopropanes: facile access to iodine/difluoromethylene- and perfluoroalkyl-containing 1-benzazepine scaffolds.

The unprecedented palladium-catalyzed cascade cyclization of allylamine-tethered alkylidenecyclopropanes with an ethyl difluoroiodoacetate or perfluoroalkylated reagent is developed, providing facile access to a variety of synthetically and medicinally valuable iodine/difluoromethylene- and perfluoroalkyl-containing 1-benzazepine frameworks. These reactions exhibited good yields and functional group tolerance via a radical mechanism.

Thermally induced formal [3+2] cyclization of ortho-aminoaryl-tethered alkylidenecyclopropanes: facile synthesis of furoquinoline and thienoquinoline derivatives.

We have developed a facile synthetic method to access furoquinoline and thienoquinoline derivatives via a thermally induced ring-opening and cyclization reaction from ortho-aminoaryl-tethered alkylidenecyclopropanes with the in situ generation of isocyanates or isothiocyanates. These reactions exhibited excellent yields and functional group tolerance under metal-free conditions.

Copper(I)-Catalyzed Intramolecular Trifluoromethylation of Methylenecyclopropanes.

Copper(I)-catalyzed intramolecular trifluoromethylation of methylenecyclopropanes has been developed to produce a variety of CF3-substituted dihydronaphthalenes in moderate to good yields, relying on the construction of C(sp(2))-CF3 bonds under mild conditions. The reactions proceed through a radical process under copper(I) catalysis with a good compatibility for the functional group.