Zirconocene-mediated cyclization

Scheme 1.3 Zirconocene-mediated cyclization of enyne, diyne, or diene...

These substrates could be also applied in the zirconocene-mediated cyclization reaction halogen-substituted dienes or enynes, dienes with aryloxy or alkoxy substituents at allylic position, m-alkenyl imine, to-alkynyl imine, or m-alkenyl carbamate. The presence of heteroatoms allows further yff-X elimination and thus leads to various useful transformations (Scheme 1.4) [20-24]. 

Tilley et al. reported zirconocene-mediated cyclization and polymerization of structurally rigid diynes to afford polymers, which could be further transformed into cyclic trimer 1-3 in high yield. The macrocyclic structure of 1-3 has been confirmed by X-ray crystal structure (Scheme 1.5) [25]. 

Scheme 1.4 Zirconocene-mediated cyclization of diene, enyne, < -alkenyl imine, or

Zirconacyclopentene 1-5 could also be applied in synthetic reaction (Scheme 1.8). For example, in the presence of CuCl and iodine, oxidative demetallation of 1-5 gives cyclobutene derivatives [34]. Reaction of 1-5 with acid chloride gives tri-subslimted cyclopentadiene derivatives [35]. This research group also reported zirconocene-mediated cyclization of alkyne, ethylene, and two molecules of aldehyde toward synthesis of 2-alkenyl tetrahydrofuran [36]. 

Scheme 1.8 Reaction chemistry of zirconacyclopentene and zirconocene-mediated cyclization of alkyne with aldehyde, ketone, nitrile, isocyanate,

Suzuki et al. reported in 2002 on zirconocene-mediated cyclization of 1,2,3-butatriene to afford highly strained zirconacyclopentyne 1-11 in high yield. This is the first reported example of metallacyclopentyne (Scheme 1.9) [40]. 

Based on the zirconocene-mediated cyclization of 1,3-butadiyne to form zirconacyclopentatriene, Yuanhong Liu et al. developed zirconocene-mediated cyclization of 1,3-butadiyne with two molecules of acyl nitrile to form azazirconacycle 1-15. 

Scheme 1.9 Zirconocene-mediated cyclization of 1,2,3-butatriene to form zirconacyclopentyne...

Scheme 1.10 Zirconocene-mediated cyclization of 1,3-butadiyne to form zirconacyclopentatriene...

Scheme 1.12 Zirconocene-mediated cyclization of imine with alkyne, isocyanate, or aldehyde and reaction chemistry of zirconaaziridines...

In 2000, Rosenthal and coworkers reported the zirconocene-mediated cyclization of tetraalkynylsilane (Scheme 1.15). A spirocompound containing silacyclobutene 1-27 was obtained when tetraalkynylsilane (RC=C)4Si was treated with Cp2Zr(thf)(Me3SiCCSiMe3) (l-12a) [52],... 

In 2007, Auner et al. successfully synthesized a series of new organosilicon-based spirocompounds 1-28 and 1-29 featuring silacyclobutene moiety, based on zirconocene-mediated cyclization of bis(alkynyl)silanes (Scheme 1.16). The optoelectronic... 

Scheme 1.18 Zirconocene-mediated cyclization of bis(alkynyl)silanes with benzyne...

Zirconacyclobutene-silacyclobutene complex 1-21 features two fused 4-membered metallacycles as well as two Zr-C bonds and two Si-C bonds. Moreover, 1-21 could be generated in situ via zirconocene-mediated cyclization of bis(alkynyl) silane, or isolated in pure form as a metallacyclic reagent. 1-21 is an isolable and stable compound under inert atmosphere however, it is highly reactive and is... 

Millward DB, Waymouth RM (1997) Zirconocene-mediated cyclization of 2-bromo a,[Pg.30]

Zirconocene-Mediated Cyclization of Bis (alkynyl)silanes and Nitriles Synthesis of N-Heterocycles and Isolation, Characterization, and Synthetic Application of Zr/Si-Containing Reactive Intermediates... 

Zirconocene-Mediated Cyclization of Bis(alkynyl)silanes and Nitriles. . 

Based on the mechanistic investigation and chemistry of reactive intermediates in zirconocene-mediated reactions, the author subjected organic azide to the reaction and developed a one-pot synthesis of pyrrolo[3,2-if]pyridazine derivatives via zirconocene-mediated cyclization of one bis(alkynyl)silane, two nitriles, and one azide. When TMSN3 was used as a special azide, pyrrole-2,3-diones were isolated in high yields. These functionalized pyrrole-2,3-diones could be eflhciently further transformed into pyrrole-fused heterocycles (Scheme 2.13). 

One-Pot Synthesis of Pyrrolo[3,2-d]pyridazlne Derivatives via Zirconocene-Mediated Cyclization of One Bis(alkynyl) silane, Two Nitriles, and One Azide... 

Scheme 2.13 One-pot S3mthesis of pyrrolo[3,2-rf]p5rridazine or pyirole-2,3-dione derivatives via zirconocene-mediated cyclization of one bis(alkynyl)silane, two nitriles, and one azide...

Scheme 2.15 One-pot synthesis of pyrrole-2,3-diones 2-24 via zirconocene-mediated cyclization of bis(aLkynyl)silane, nitriles, and TMSN3...

In Chap. 2, the author disclosed zirconocene-mediated cyclization of bis(alky-nyl)silanes, nitriles, and unsaturated compounds. The reactive intermediates involving two or three molecules of nitriles were isolated and characterized. Thus, the author expects to further isolate the one molecule of nitrile involved intermediate and demonstrates the reaction mechanism toward the formation of Zr-/Si-containing three-ring fused intermediates (Scheme 3.1). The author tried to use only one equivalents of nitrile, lower the reaction temperature, and quench the reaction mixture generated in situ or trap with electrophiles. However, all these attempts failed, and the isolation and characterization of one-nitrile-involved intermediates... 

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