Selectivity in epoxidation: acyclic diastereo- and enantio-selection with peroxide mediated by titanium(iv) and with peracid

Isobe, Mitsuaki; Kitamura, Masato; Mio, Shigeru; Goto, Toshio

doi:10.1016/s0040-4039(00)86790-8

Cited by 44 publications

(15 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The stereochemical outcome for all the Ti(IV)-catalyzed reactions was similar, while Cp 2 TiCl 2 furnished systematically higher yields than Ti(i-PrO) 4 . The trans/cis ratios slightly decreased changing the R group from Ph to Me (1b), a result that can be ascribed to the less sterically demanding Me group.…”

Section: Methodsmentioning

confidence: 88%

“…The diastereomeric mixture may be obtained with high stereoselectivity but, then the Lewis acidic titanium might equilibrate the isomeric mixture. Cp 2 TiCl 2 /MS and Ti(i-PrO) 4 produced lower diastereomeric ratios (runs 7-9), when compared with the oxidation of dithianes 1a and 1b. Interestingly, Ti(i-PrO) 4 showed to be, in this instance, more diastereoselective in the absence of (+)-DET ligand (run 7 and literature data 15 ).…”

Section: Methodsmentioning

confidence: 99%

“…Cp 2 TiCl 2 /MS and Ti(i-PrO) 4 produced lower diastereomeric ratios (runs 7-9), when compared with the oxidation of dithianes 1a and 1b. Interestingly, Ti(i-PrO) 4 showed to be, in this instance, more diastereoselective in the absence of (+)-DET ligand (run 7 and literature data 15 ). In order to prevent the acid catalyzed equilibration of diastereomers a non-nucleophilic base, namely the 2,6-di-tert-butyl-4-methylpyridine, was added, but no significant improvement in the trans/cis ratio was observed (run 10).…”

Section: Methodsmentioning

confidence: 99%

“…The known 1:1 trans/cis mixture of monosulfoxide 2g 14,18 was obtained by Ti(i-PrO) 4 -catalyzed oxidation of commercially available 1,3-dithiane 1g. The reduction of 2g by DIBAL-H or NaBH 4 , afforded a 1:1 mixture of the same compounds isolated after the titanocene oxidation of 1f, as confirmed by 1 H NMR analysis.…”

Section: Methodsmentioning

confidence: 99%

“…In the present work, we compare some simple achiral titanocenes with the traditional Ti(IV) catalyst, namely Ti(i-PrO) 4 , as promoters in the TBHP oxidation of 2-substituted 1,3-dithianes and 1,3-dithiolanes 1a-f (Scheme 1). Diastereoselectivity, yield, catalyst loading as well as its cost and ease of handling, were taken into account for each titanium compound.…”

mentioning

confidence: 99%

See 4 more Smart Citations

Titanocene Dichloride as a Convenient Catalyst for the Diastereoselective Oxidation of 2-Substituted 1,3-Dithianes and 1,3-Dithiolanes

Sala¹,

Labano²,

Lattanzi³

et al. 2002

Synthesis

View full text Add to dashboard Cite

Cp 2 TiCl 2 is an efficient catalyst for the diastereoselective mono-oxidation of 2-substituted 1,3-dithianes and 1,3-dithiolanes by tert-butyl hydroperoxide; comparable stereoselectivities and better yields than Ti(i-PrO) 4 were obtained. Activities are similar, provided activated 4Å molecular sieves are present in the titanocenepromoted process. Furthermore, Cp 2 TiCl 2 is a more moisture stable compound than Ti(i-PrO) 4 and therefore can be used in catalytic amounts of 1 mol%.The d 0 transition metal/alkyl hydroperoxide system has been extensively used for the oxidation of a number of organic compounds, in particular alkenes and thioethers. 1 In several instances, fairly good diastereoselectivities can be obtained in the oxidation of allylic alcohols 2 and thioethers 3 containing a stereogenic center. The level of the stereoselectivity, however, is dependent on the metal catalyst and the substrate structure.Ti(IV) alkoxides are commonly employed as catalysts in the diastereo-2b,4 and enantioselective 5 epoxidation of allylic alcohols as well as in the enantioselective oxidation of thioethers. 6 Surprisingly, cyclopentadienyl Ti(IV) compounds, despite their great availability and wide employment as catalysts in many homogeneous processes, 7 have been scarcely used in these oxidation reactions. 8 We have recently shown the applicability of titanocenes such as Cp 2 TiCl 2 , CpTiCl 3 and bis(cyclopentadienyl)titanium (IV) bis(trifluoromethanesulfonate) [Cp 2 Ti(OTf) 2 ] in the diastereoselective epoxidation of allylic 9 and bishomoallylic 10 alcohols and in the enantioselective sulfoxidation 11 using tert-butyl hydroperoxide (TBHP) as oxidant; the catalytic activity is markedly enhanced in the presence of activated 4Å molecular sieves.As an extension of our work, we became interested in the diastereoselective oxidation of dithianes. A great deal of data is avalaible in the literature on the oxidation of racemic 2-substituted 1,3-dithianes and 1,3-dithiolanes as models of cyclic thioethers. Except for enzymatic reactions, 12 d 0 transition metal/alkyl hydroperoxides proved to be the most stereoselective oxidizing systems for this type of substrates. 13 However, the chiral Kagan and Modena catalyst, a Ti(i-PrO) 4 /(+)-diethyl tartrate [(+)-DET] modified system, 13a,b,14,15 has been mostly used in stoichiometric amount to achieve a diastereo-and enantioselective process. The diastereoselectivity is merely associated with facial discrimination, whereas the enantioselectivity is a result of both facial selectivity and selection between the two enantiotopic sulfur atoms. In order to perform a diastereoselective transformation, a simple achiral transition-metal catalyst can be employed.Very few systematic reports 16 have appeared concerning the use of an achiral reagent for the diastereoselective oxidation of thioethers. Indeed, a catalytic (using minimal amount of catalyst) process would be highly desiderable and the use of cheap, safe and stable catalysts should be highly preferable.In the present work, we compare s...

show abstract

Section: Methodsmentioning

confidence: 88%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

See 3 more Smart Citations

Titanocene Dichloride as a Convenient Catalyst for the Diastereoselective Oxidation of 2-Substituted 1,3-Dithianes and 1,3-Dithiolanes

Sala¹,

Labano²,

Lattanzi³

et al. 2002

Synthesis

View full text Add to dashboard Cite

show abstract

Titanium Compounds, Organic

Putzig

Pesco

2000

Kirk-Othmer Encyclopedia of Chemical Technology

View full text Add to dashboard Cite

Organic titanium compounds are materials having a covalent bond between titanium and another atom that is also bonded to a carbon‐based group. Titanium tetrachloride, the basic raw material from which organic titanate compounds are made, is readily converted to tetraisopropyl titanate, TYZOR TPT, by the Nelles process. This ester can be converted by alkoxy exchange (transesterification) to a wide variety of tetraalkyl titanates, which in turn react with other ligands and chelating agents to give complexes having properties significantly different from the starting materials. This article covers all aspects of the organic titanium compound, from properties, reactions, and synthesis, to uses and health and safety factors.

show abstract