MeOTf-catalyzed formal[4+2]annulations of styrene oxides with alkynes leading to polysubstituted naphthalenes through sequential electrophilic cyclization/ring expansion

Me OTf-catalyzed formal[4+2]annulation of styrene oxides with alkynes to afford polysubstituted naphthalenes has been realized,which undergoes sequential electrophilic cyclization/ring expansion.A range of substrates were tolerated in the formation of naphthalene derivatives with high regioselectivity in satisfactory yields.The reaction could also be carried out on gram scale.

Electrochemical Ring Expansion to Synthesize Medium-Sized Lactams Through C–C Bond Cleavage

Medium-sized nitrogen heterocycles are prevalent motifs in many kinds of bioactive molecules and natural products.Owing to the unfavorable enthalpic and entropic barriers during the transition states,access to medium-sized rings is challenging.Herein,a general and practical electrochemical ringexpansion protocol has been developed from commercially available benzocyclic ketones and amides.In this regard,a series of highly functionalized eightto eleven-membered lactams could be successfully accessed in high yields and efficiencies.

A convenient synthesis of 2-aryl substituted benzo[f][1,2,4]triazolo[1,5-a]azepine derivatives

A convenient synthetic pathway to 2-aryl-5,6-dihydro-4H-benzo[f][1,2,4]triazolo[1,5-a]azepine derivatives 7 was developed.The synthesis was based on the cycloaddition of the 1,2,3,4-tetrahydronaphthalene α-acetoxy azo compounds 3 with Ar-CN in the presence of AlCl3 and the consecutive ring enlargement.

Metallacycle Expansion and Annulation:Access to Tetrazolo-Fused Osmacycles by Reaction of Cyclic Osmium Carbyne with Sodium Azide

The reaction of a cyclic osmacarbyne complex with sodium azide led to the formation of a ring expansion-annulation product,a unique tetrazole annulated polycyclic metallacycle.The reaction proceeds by insertion of a nitrogen atom into the metal carbon triple bond and the second azide participating in the[2+3]cycloaddition.The successful isolation and characterization of metalla-azirine complex and metallapyridinium derivative strongly validated the mechanism for the formation of the title complex.The work demonstrates a new strategy to enrich the varieties of aza-metallacyclic species.

C—F Bond Insertion into Indoles with CHBr_(2)F:An Efficient Method to Synthesize Fluorinated Quinolines and Quinolones

A mild and practical method for synthesizing fluorinated quinoline derivatives,which have a wide range of applications in pharmaceuticals,materials,and organic synthesis,was described through C—F bond insertion into indoles using CHBr_(2)F.The simple conditions,readily availability of CHBr_(2)F,as well as the versatility of the transformations make this strategy very powerful in synthesizing 3-fluoroquinoline and 3-fluoroquinolone.The mechanistic studies reveal that bromofluorocarbene generated in-situ under basic condition was the key intermediate.

[3+2]Cycloaddition of Vinyl Cyclopropane and Hydroxylamines via Isocynate Intermediate toγ-Lactams

Comprehensive Summary A general and efficient strategy for the synthesis ofγ-lactams has been reported.The hydroxylamines form Lossen rearrangement products of electron-deficient group migration with base and then undergo[3+2]cycloaddition reaction with vinyl cyclopropane,which could be performed with broad substrate scope,excellent functional group tolerance and high efficiency to produce the desired products.It also allowed further modification to other derivatives of theseγ-lactams.

Palladium-Catalyzed Skeletal Reorganization of Cyclobutanones Invoving Successive C—C Bond/C—H Bond Cleavage

The utilization of cyclobutanones as the synthon in transition metal catalysis has been made great success.Because C(carbonyl)−C bond of cyclobutanones can be cleaved through strain release.Despite those advancements,the main catalysts in literature are Rh catalysts or Ni catalysts and the reaction with C—H bond is still underdeveloped.Herein,we realized the first palladium-catalyzed skeletal reorganization of cyclobutanones involving successive cleavage of C(carbonyl)−C bonds and C—H bond cleavage,which constitutes an rapid access to diverse indanones.In contrast to the previous Rh-catalytic system,the Pd-catalytic system herein involves different mechanism and features several advantages:1)no need of directing group to facilitate the C(carbonyl)−C bond cleavage;2)much milder reaction condition and 3)simplified work-up.

Cycloadditions of 1-iminylphosphirane complexes with allenes

A cascade carbonylative ring expansion and [2+2]/[4+2] cycloaddition of strained 1-iminylphosphirane complexes with aryl allenes were reported.The carbonylative ring expansion of 1-iminylphosphirane complexes provides an azaphosphacyclohexone complex intermediate with a C=P double bond.The following [2+2] or dearomatic [4+2] cycloaddition of this intermediate with allenes is modulated by the aryl substituents on the imino carbon.The regioselective [2+2] cycloaddition with 1,1-diarylallene provides an entry to bicyclo[4.2.0]octan-4-one skeletons featuring a four-membered phosphacyclobutane moiety.While dearomatic [4+2] cycloaddition was preferred with less aromatic naphthalene and yielded octahydrochrysene skeleton containing heteroatoms.

Reversing Site-Selectivity in Formal Cross-Dimerization of Benzocyclobutenones and Silacyclobutanes

Formal cross-dimerization of two different strained rings represents an innovative strategy toward specific ring systems that are otherwise inaccessible.Yet,formidable challenges remain in controlling the reactivity and site-selectivity.Herein,we realized the reversal of site-selectivity in formal crossdimerization of benzocyclobutenones(BCBs)and silacyclobutanes(SCBs)by development of a nickel/magnesium synergistic catalytic system,in which the C(sp3)−C(carbonyl)bond of BCBs was exclusively cleaved,providing previously inaccessible eight-membered benzosilacycles.The catalytic cycle,the origin of this unconventional site-selectivity,and the role of MgCl2 have explicitly been elucidated by density functional theory calculations.Combined experimental and computational studies have clearly illustrated that the C1-C8 cleavage selectivity of BCBs in our reaction are mainly attributed to both the steric hindrance by introduction of substituents at the C3-and the proper choice of the Ni/Mg synergistic catalytic system.