New methods for the elaboration of zirconacycles : application to organic synthesis
New methods for the elaboration of zirconacycles : application to organic synthesis
Zirconacyclopentenes, which contain two different Zr-C bonds, react with allyl carbenoids, via migratory insertion at the sp3 C-Zr bond, to form cyclic zirconocene η3-allyl complexes. Subsequent reaction with BF3-activated aldehydes provides a short, high yielding route to homoallylic alcohols, which are found with modest levels of 1,6 diastereoselectivity. Application of this protocol to monocyclic zirconacyclopentenes, containing regiospecific vinyl stannane substituents, has led to the stereoselective synthesis of precursors to naturally occurring terpenes such as crinitol, tadshferin and moritoside. The regioselective migratory insertion of allenyl carbenoids into the sp3 C-Zr bond of zirconacyclopentenes, allows access to a range of cyclic zirconocene complexes containing an η3-allenyl/propargyl unit. Whilst protonolysis gives mixtures of alkyne and allene products, BF3-activated aldehyde addition yields allenyl alcohols or, via an unexpected rearrangement and ring closure, cyclic dienols. The product structure is determined by the substitution pattern of the carbenoid added to zirconacyclopentene and the type of aldehyde used to quench the subsequently formed η1, η3 zirconacycle. Zirconacyclopentanes undergo the tandem insertion of propargyl carbenoids and BF3-activated aldehydes to yield mixtures of cyclic enols and homopropargylic alcohols.
Lithium chloropropargylides insert into the sp3 C-Zr bond of zirconacyclopentenes to yield η3-propargyl/allenyl bond zirconacycles. These species undergo methanolysis to yield preferentially allene products, whilst acetic acid protonolysis almost exclusively gives alkynes. The subsequent slow reaction with Lewis acid-activated aldehydes gives homopropargylic alcohols. Higher levels of 1,2 diastereoselectivity are noted for TiCl4-activation than those observed with BF3.
University of Southampton
1997
Gordon, George Johnston
(1997)
New methods for the elaboration of zirconacycles : application to organic synthesis.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Zirconacyclopentenes, which contain two different Zr-C bonds, react with allyl carbenoids, via migratory insertion at the sp3 C-Zr bond, to form cyclic zirconocene η3-allyl complexes. Subsequent reaction with BF3-activated aldehydes provides a short, high yielding route to homoallylic alcohols, which are found with modest levels of 1,6 diastereoselectivity. Application of this protocol to monocyclic zirconacyclopentenes, containing regiospecific vinyl stannane substituents, has led to the stereoselective synthesis of precursors to naturally occurring terpenes such as crinitol, tadshferin and moritoside. The regioselective migratory insertion of allenyl carbenoids into the sp3 C-Zr bond of zirconacyclopentenes, allows access to a range of cyclic zirconocene complexes containing an η3-allenyl/propargyl unit. Whilst protonolysis gives mixtures of alkyne and allene products, BF3-activated aldehyde addition yields allenyl alcohols or, via an unexpected rearrangement and ring closure, cyclic dienols. The product structure is determined by the substitution pattern of the carbenoid added to zirconacyclopentene and the type of aldehyde used to quench the subsequently formed η1, η3 zirconacycle. Zirconacyclopentanes undergo the tandem insertion of propargyl carbenoids and BF3-activated aldehydes to yield mixtures of cyclic enols and homopropargylic alcohols.
Lithium chloropropargylides insert into the sp3 C-Zr bond of zirconacyclopentenes to yield η3-propargyl/allenyl bond zirconacycles. These species undergo methanolysis to yield preferentially allene products, whilst acetic acid protonolysis almost exclusively gives alkynes. The subsequent slow reaction with Lewis acid-activated aldehydes gives homopropargylic alcohols. Higher levels of 1,2 diastereoselectivity are noted for TiCl4-activation than those observed with BF3.
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Published date: 1997
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Local EPrints ID: 460245
URI: http://eprints.soton.ac.uk/id/eprint/460245
PURE UUID: 69520e0a-975b-4ff6-a722-ebf12d1c4c00
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Date deposited: 04 Jul 2022 18:16
Last modified: 04 Jul 2022 18:16
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Author:
George Johnston Gordon
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