Titanocene-Catalyzed Reductive Epoxide Opening: The Quest for Novel Hydrogen Atom Donors

Gansäuer, Andreas; Barchuk, Andriy; Fielenbach, Doris

doi:10.1055/s-2004-831207

Cited by 31 publications

(18 citation statements)

References 9 publications

(9 reference statements)

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“…15 No formation of 6 was observed without Cp 2 TiCl 2 (entry 2), and 3 was reisolated in >85% yield. This rules out alernative pathways, such as epoxide isomerization to an allylic alcohol and hydrogenation or radical reduction by adventitious water.…”

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confidence: 98%

Sustainable Radical Reduction through Catalytic Hydrogen Atom Transfer

2008

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confidence: 98%

Sustainable Radical Reduction through Catalytic Hydrogen Atom Transfer

2008

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“…Gansäuer et al [7] extended the catalyst group for epoxides reduction by the titanium derivatives 127-130. Beside titanocenes complexes of other elements (strontium, niobium) were also used in the reactions [116] (Scheme 63).…”

Section: Epoxides Reduction Through Formation Of Radical and Ion Radimentioning

confidence: 99%

“…In [7] new opportunities were considered for hydrogen donors in epoxy compounds reduction, and into the series of donors compounds 131-133 etc. were included.…”

Section: Epoxides Reduction Through Formation Of Radical and Ion Radimentioning

confidence: 99%

“…The existing reviews on the reactivity of epoxides [4][5][6][7][8][9][10] either describe their reactions with reducers only to a limited degree or are out of date to a great extent. The existing reviews on the reactivity of epoxides [4][5][6][7][8][9][10] either describe their reactions with reducers only to a limited degree or are out of date to a great extent.…”

Section: Introduction Reducers and Reaction Mechanismsmentioning

confidence: 99%

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10.1007/s11178-008-2001-z

2010

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Analysis was performed of reduction processes of epoxy derivatives obtained from unsaturated compounds belonging to various groups: alkenes, cycloalkenes, spiroalkanes, and substituted norbornenes. The regio-and stereochemistry was discussed of reactions between epoxides and complex metal hydrides, of catalytic hydrogenation, and some other processes. The mechanisms were considered of the reduction reactions, in particular, those involving radical and ion radical intermediates.

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“…Gansäuer [6,7] later showed that the epoxide openings can be performed using catalytic [8] amounts of titanocene(III) chloride.…”

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A New Method for the Generation of Titanium(III) Complexes and its Application in Pinacol Coupling Reactions

Knoop

Studer

2005

Adv Synth Catal

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A new method for the in situ generation of various Ti(III) complexes is presented. Cyclohexadienyl-Ti(IV) derivatives, which are readily prepared from the corresponding lithiated cyclohexadienes, afford the corresponding Ti(III) complexes upon thermal C À Ti-bond homolysis. The Ti(III) compounds generated using this novel method have successfully been used in the reductive dimerization of benzaldehyde. In particular, TiBr 3 , TiCp 2 Cl and Ti(O-i-Pr) 3 have been generated via this approach. Moreover, the method also offers an entry to new chiral Ti(III) complexes as documented by the preparation of Ti(III)CpTADDOLate.Keywords: radical chemistry; reductive cyclization; stereoselective reductions; synthetic methods; titanium Radical chemistry has gained increasing importance during the last 30 years.[1] In contrast to ionic chemistry, many functional groups are tolerated under radical conditions. Several methods for the clean generation of radicals have been reported to date. However, most of the radical reactions are conducted using toxic trialkyltin hydrides. To circumvent the use of toxic tin compounds, many research groups are currently looking at environmentally benign radical processes.[2] Electron-transfer reagents have successfully been used in this context. In particular, samarium diiodide (SmI 2 ) has been found to be a highly efficient electron-transfer reagent for conducting various radical processes.[3] However, SmI 2 is rather expensive and is readily oxidized on air.As an alternative to SmI 2 , Ti(III) complexes have been studied by various groups. [4 -11] Nugent and RajanBabu showed that titanocene(III) chloride can be applied to reductively open epoxides.[5] The b-titanoxy radicals thus generated can be used in radical cyclizations and intermolecular addition reactions. Gansäuer [6,7] later showed that the epoxide openings can be performed using catalytic [8] amounts of titanocene(III) chloride.Reduction of activated alkyl halides have been achieved using Ti(III).[9] Moreover, Ti(III) complexes have successfully been used in pinacol reactions. [10,11] Even enantioselective couplings have recently been reported. [12] Most of the Ti(III) complexes studied have been generated from the corresponding Ti(IV) compounds and a coreducing reagent. [13] Recently, we published our results on the use of cyclohexadienyl-Ti compounds in ionic allylations (Scheme 1). [14] We assumed that these compounds may also offer a clean entry to Ti(III) complexes upon simple thermal Ti-carbon bond homolysis. In contrast to established methods for the generation of Ti(III) derivatives, a coreducing reagent is not necessary in our approach. [15] Since the starting cyclohexadienyl-Ti(IV) compounds are readily prepared by transmetalation using the appropriate Ti(IV) complex, new unexplored Ti(III) reagents should be available via this route. In this communication we report first results on the use of cyclohexadienyl-Ti(IV) derivatives as precursors for Ti(III) complexes. Moreover, these reducing reagents will be appli...

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Titanocene-Catalyzed Reductive Epoxide Opening: The Quest for Novel Hydrogen Atom Donors

Cited by 31 publications

References 9 publications

Sustainable Radical Reduction through Catalytic Hydrogen Atom Transfer

Sustainable Radical Reduction through Catalytic Hydrogen Atom Transfer

10.1007/s11178-008-2001-z

A New Method for the Generation of Titanium(III) Complexes and its Application in Pinacol Coupling Reactions

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