A New Synthesis of 1,5-Di-<i>tert</i>-butyl-1,3-cyclopentadiene by Dehydration of an Epoxide and Characterization of its Diels−Alder Dimer

Hughes, Russell P.; Kowalski, and Angela S.; Lomprey, Jeffrey R.; Neithamer, David R.

doi:10.1021/jo9515586

Cited by 14 publications

(7 citation statements)

References 26 publications

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“…This reduces the steric bulk in the narrow portion of the wedge, thereby expediting formation of the ansa -zirconocene. Since the direct synthesis of 1,2-dialkyl-substituted cyclopentadienes is often tedious, we opted for the preparation of silylated cyclopentadienes to exploit facile silyl and hydrogen migrations, which may provide the desired regiochemistry . Linking bis-trimethylsilyl cyclopentadienes with a standard dimethylsilylene bridge yields metallocenes as a mixture of regio- and stereochemical isomers .…”

Section: Resultsmentioning

confidence: 99%

A Convenient Method for the Synthesis of Zirconocene Hydrido Chloride, Isobutyl Hydride, and Dihydride Complexes Using tert-Butyl Lithium

2002

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Preparation of zirconocene hydrido chloride complexes has been accomplished via addition of 1 equiv of tert-butyllithium to the corresponding zirconocene dichlorides. In this manner, both Cp*Cp′′Zr(H)Cl and Cp′′ 2 Zr(H)Cl (Cp* ) C 5 Me 5 , Cp′′ ) 1,3-(SiMe 3 ) 2 C 5 H 3 ) were prepared in high yield. Further addition of t BuLi to Cp*Cp′′Zr(H)Cl affords the isobutyl hydride complex Cp*Cp′′Zr(CH 2 CHMe 2 )(H), which upon addition of 1 atm of dihydrogen undergoes rapid hydrogenolysis yielding the monomeric dihydride Cp*Cp′′ZrH 2 . In the absence of dihydrogen, the zirconocene dihydride undergoes reversible C-H activation of a cyclopentadienyl trimethylsilyl group, affording the "tuck-in" derivative Cp*(η 5 -1-SiMe 3 C 5 H 3 -3-(η 1 -SiMe 2 -CH 2 ))ZrH. Addition of 2 equiv of t BuLi to the ansa-zirconocene i Pr 2 Si(η 5 -3-SiMe 3 C 5 H 3 )(η 5 -3,4-(SiMe 3 ) 2 C 5 H 2 )ZrCl 2 results in the corresponding zirconocene isobutyl hydride complex, which upon exposure to H 2 affords the dimeric dihydride [ i Pr 2 Si(η 5 -3-SiMe 3 C 5 H 3 )(η 5 -3,4-(SiMe 3 ) 2 C 5 H 2 )ZrH 2 ] 2 . In a similar procedure the substituted indenyl complexes rac-(1-CMe 3 -C 9 H 6 )Zr(H)Cl and rac-(1-CMe 3 -C 9 H 6 )Zr(CH 2 CHMe 2 )(H) have been prepared. This synthetic methodology allows for the preparation of metallocene alkyl hydrides and dihydrides inaccessible by more traditional routes.Supporting Information Available: Crystallographic data for 2, 8, and 12 including complete atom labeling schemes, tables of atomic coordinates, and complete bond distances and angles. Representative 1 H NMR spectra of zirconocene isobutyl hydride complexes and NOESY data for 8. This material is available free of charge via the Internet at http://pubs.acs.org.

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Section: Resultsmentioning

confidence: 99%

A Convenient Method for the Synthesis of Zirconocene Hydrido Chloride, Isobutyl Hydride, and Dihydride Complexes Using tert-Butyl Lithium

2002

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“…This indicates that, with only a small energetic cost, these larger substituents can adopt conformations that are little different from a methyl group in terms of steric hindrance toward the incoming dienophile during syn addition. (In contrast, a tertiary butyl group at C-5 would not be able to avoid hindering an incoming dienophile, so it is not surprising that dimerization of such a diene would proceed exclusively by anti addition …”

Section: Resultsmentioning

confidence: 99%

Diels−Alder Reactions of 5-Alkyl-1,3-cyclopentadienes

Burnell

1997

J. Org. Chem.

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Facial selectivity in the Diels-Alder reactions of 1,3-cyclopentadienes substituted at C-5 by a variety of simple alkyl groups has been assessed with a number of dienophiles. The results are consistent with an explanation based on steric hindrance. Syn addition is more favored with sterically less demanding dienophiles. Diene 6, which is substituted at C-5 with methoxymethyl, shows a remarkable preference for syn addition with less encumbered dienophiles. This may indicate a conformational difference in its syn transition state relative to the transition states for addition syn to methyl, ethyl, or n-butyl substituents (dienes 1, 4, and 5). Dienophiles are more reluctant to add syn to the larger C-5 group with 1,2,3,4,5-pentamethyl-1,3-cyclopentadiene (2) and derivatives (3, and 7) and conformational effects become very important when C-5 bears two alkyl groups, as in dienes 3 and 7.

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“…38 Silica gel chromatography was performed using a Biotage SP1 purification system in open air with HPLC-grade solvents. Literature procedures were used for the preparation of 1,2-di-tert-butylcyclopentadiene, 39 4-methoxybenzene diazonium tetrafluoroborate, 40 and KC 8 . 41 Re 2 (CO) 10 was purchased from Strem and used as received.…”

Section: Experimental Materialsmentioning

confidence: 99%

Photoinduced N2 loss as a route to long-lived organometallic alkane complexes: A time-resolved IR and NMR study

et al. 2010

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A New Synthesis of 1,5-Di-tert-butyl-1,3-cyclopentadiene by Dehydration of an Epoxide and Characterization of its Diels−Alder Dimer

Cited by 14 publications

References 26 publications

A Convenient Method for the Synthesis of Zirconocene Hydrido Chloride, Isobutyl Hydride, and Dihydride Complexes Using tert-Butyl Lithium

A Convenient Method for the Synthesis of Zirconocene Hydrido Chloride, Isobutyl Hydride, and Dihydride Complexes Using tert-Butyl Lithium

Diels−Alder Reactions of 5-Alkyl-1,3-cyclopentadienes

Photoinduced N2 loss as a route to long-lived organometallic alkane complexes: A time-resolved IR and NMR study

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