Modulating Escape Channels of Cycloheptatrienyl Rhodium Carbenes To Form Semibullvalene

We describe the various escape channels available to dirhodium carbene intermediates from cycloheptatrienyl diazo compounds located with density functional theory. An intramolecular cyclopropanation would, in principle, provide a new route to semibullvalenes (SBVs). A detailed exploration of the potential energy surface reveals that methylating carbon-7 suppresses a competing β-hydride migration pathway to heptafulvene products, giving SBV formation a reasonable chance. During our explorations, we additionally discovered unusual spirononatriene, spironorcaradiene, and metal-stabilized 9-barbaralyl cation structures as local minima.

Selective reduction of 1,5-diazacyclooctatetraenes: synthesis and structures of aromatic diazacyclooctatetraenyl dianions and a 2,6-bipyrrolinyl dianionic Co(ii) complex

The first structurally well-defined aromatic 1,5-diazacyclooctatetraenyl dianion and a 2,6-bipyrrolinyl dianionic Co(ii) complex were obtained selectively via reduction of 1,5-diazacyclooctatetraenes.

Synthesis of dibromo- and tetrabromo-bipyrrolines and their corresponding 2,6-diazasemibullvalene derivatives

Treatment of Δ¹-dipyrrolines with NBS afforded α,α′-dibromo-Δ¹-bipyrrolines and α,α,α′,α′-tetrabromo-Δ¹-bipyrrolines, which were efficiently transformed into 2,6-diazasemibullvalene derivatives via reduction with lithium.

Semibullvalene and diazasemibullvalene: recent advances in the synthesis, reaction chemistry, and synthetic applications

Semibullvalene (SBV) and its aza analogue 2,6-diazasemibullvalene (NSBV) are theoretically interesting and experimentally challenging organic molecules because of four unique features: highly strained ring systems, intramolecular skeletal rearrangement, extremely rapid degenerate (aza-)Cope rearrangement, and the predicted existence of neutral homoaromatic delocalized structures. SBV has received much attention in the past 50 years. In contrast, after NSBV was predicted in 1971 and the first in situ synthesis was realized in 1982, no progress on NSBV chemistry was made until our results in 2012. We have been interested in the reaction chemistry of 1,4-dilithio-1,3-butadienes (dilithio reagents for short), especially for their applications in the synthesis of SBV and NSBV, because (i) the cyclodimerization of dilithio reagents could provide the potential eight-carbon skeleton of SBV from four-carbon butadiene units and (ii) the insertion reaction of dilithio reagents with C≡N bonds of two nitriles could provide a 6C + 2N skeleton that might be a good precursor for the synthesis of NSBV. Therefore, we initiated a journey into the synthesis and reaction chemistry of SBV and NSBV starting from dilithio reagents that has been ongoing since 2006. In this Account, we outline mainly our recent achievements in the synthesis, structural characterization, reaction chemistry, synthetic application, and theoretical/computational analysis of NSBV. Two efficient strategies for the synthesis of NSBV from dilithio reagents and nitriles via oxidant-induced C-N bond formation are described. Structural investigations of NSBV, including X-ray crystal structure analysis, determination of the activation barrier for the aza-Cope rearrangement, and theoretical analysis, show that the localized structure of NSBV is the predominant form and that the homoaromatic delocalized structure exists as a minor component in the equilibrium. We also discuss the reaction chemistry and synthetic applications of NSBV. Several novel reaction patterns have been explored, including thermolysis, C-N bond insertion, rearrangement-cycloaddition, oxidation, and nucleophilic ring-opening reactions. Diverse and interesting N-containing polycyclic skeletons can be constructed, such as nickelaazetidine, 1,5-diazatriquinacenes, and triazabrexadienes, which are not available by other means. Our results show that NSBV not only features a rapid aza-Cope rearrangement with a low activation barrier but also acts as unique synthetic reagent that is significantly different from aziridine. The strained rigid ring systems as a whole can be involved in the reactions. Our achievements highlight two significant advances: (i) the well-established efficient synthesis and isolation of NSBV has greatly accelerated the development of NSBV chemistry, and (ii) the previously unattainable molecules have become "normal" and routine starting materials for the synthesis of otherwise unavailable but interesting structures. We expect that our pursuits will inspire and help direct future chemical and physical research on NSBV.

Efficient synthesis of aza-triquinacene derivatives via cycloaddition of 2,6-diazasemibullvalenes with nitroso compounds

The reaction between 2,6-diazasemibullvalenes and nitroso compounds was investigated. Aza-triquinacene derivatives of interesting structural and synthetic chemistry were generated highly selectively in good to excellent isolated yields. This reaction, which was rarely found between common aziridine derivatives and nitroso compounds, could be attributed to the rigid polycyclic ring system and the substitution patterns of 2,6-diazasemibullvalenes. Δ(1) -Bipyrroline derivatives were formed in excellent yields when these aza-triquinacene derivatives were treated with SmI2 .

Organometallic intermediate-based organic synthesis: organo-di-lithio reagents and beyond

Metal-mediated organic reactions have become one of the great frontiers of organic synthesis.

Synthesis and applications of 1-iodo-4-MgCl-1,3-dienes and 1-iodovinyl phenylmagnesium chlorides

This work reports on selective generation and synthetic applications of functionalized Grignard reagents (1-iodo-4-MgCl-1,3-dienes and 1-iodovinyl phenylmagnesium chlorides).