1-Alkenes isopropoxide

Epoxy alcohols. A few years ago Mihelich1 was granted a patent for preparation of epoxy alcohols by photooxygenation of alkenes in the presence of titanium or vanadium catalysts. Adam et al.2 have investigated this reaction in detail and find that Ti(IV) isopropoxide is the catalyst of choice for epoxidation of di-, tri-, and tetrasubstituted alkenes, acyclic and cyclic, to provide epoxy alcohols. When applied to allylic alcohols, the reaction can be diastereo- and enantioselective. The reaction actually proceeds in two steps an ene reaction to provide an allylic hydroperoxide followed by intramolecular transfer of oxygen catalyzed by Ti(0-i-Pr)4. The latter step is a form of Sharpless epoxidation and can be highly stereoselective. 

Now, for this oxidizing complex to react with an allylic alcohol, the alcohol must become coordinated to the titanium too, displacing a further isopropoxide ligand. Because of the shape of the complex the reactive oxygen atom of the bound hydroperoxide has to be delivered to the lower face of the alkene (as drawn), and the epoxide is formed in high enantiomeric excess. 

Bornane[10,2]sultams have been exploited as chiral auxiliaries for stereoselective aziridination of attached 7V-enoyl substituents28. The alkene substitution pattern markedly affected the diastereoselectivity, which was excellent when the C — C double bond was unsubstituted in this case the configuration of the prevalent diastereomer 5 was established by X-ray crystallographic analysis. Thus, the addition occurred to the Re-face at the a-carbon. In the other cases the stereochemistry of the major diastereomers was tentatively assigned by analogy. Furthermore, the yield dropped drastically when an a-substituent was present. Removal of the auxiliary was achieved by titanium isopropoxide alcoholysis, but was not optimized. No epimerization occurred during the cleavage process. 

It has an NiAs-type structure (Fig. 15-5), and the isolated methyl groups are presumably in the lattice as the pyramidal CHJ ion.35 Sofiium amd potasstuirralkyl5 can be used for metallation reactions- for example, in eq. 6-2. They can also be prepared from Na or K dispersed on an inert support material, and such solids act as carbanionic catalysts for the cyclization, isomerization or polymerization of alkenes. The so-called alfin catalysts for copolymerization of butadiene with styrene or isoprene to give rubbers consist of sodium alkyl (usually allyl) and alkoxide (usually isopropoxide) and NaCl, which are made simultaneously in hydrocarbons.33... 

The turn of the millenium will see the 20th anniversary of the seminal discovery of the asymmetric epoxidation [1, 2] of ally lie alcohols catalysed by titanium(IV) isopropoxide and tartrate esters. The utility of this transformation largely results from the regio- and stereocontrol possible in subsequent nucleophilic ring opening reactions of the derived epoxy alcohols. Thus, a sequence of asymmetric epoxidation, epoxide opening and further functionalisation leads to a diverse array of molecules in enantiomerically pure form. In comparision, asymmetric epoxidation of unfunctionalised alkenes [3] has yet to match the enantioselectivities which the Ti-tartrate system can deliver with allylic alcohols. The recent discovery of other asymmetric epoxidation reactions [4] suggests that a number of practical options may eventually become available. 

Balan and Adolfsson have reported that a-methylene-p-amino acid derivatives 267 are readily formed in a three-component one-pot MBH reaction of aryl aldehydes, sulfonamides and activated alkenes. The reaction is catalyzed efficiently by titanium isopropoxide [Ti-(OPr%] and 3-hydroxyquinuclidine (3-HQD) in the presence of molecular sieves, to afford the corresponding adducts in high yields with good to excellent chemoselectivities (Scheme 2.151). ... 

But, Yukawa et al. used lanthanum isopropoxide/BINOL system, 128, for the catalysis of asymmetric aza-Morita-Baylis-Hillman reaction (reaction 7.28), in which the electron-deficient alkenes, 129, reacted with... 

The formation of multiple metal-oxo bonds by penta or hexa valent transition metals (d°) is not surprising but the more recent discovery that scandium, yttrium, and the tervalent lanthanides form oxo-isopropoxides rather than triisopropoxides was unexpected. Considerable efforts have been devoted to ensuring that the formation of these pentanuclear oxo-alkoxides [M5(/r5-0)(/r,3-0Pr )4(/r-0Pr )4(0Pr )5] was not due to hydrolysis, and there is evidence that elimination of ether is involved. An alternative mode of decomposition would be alkene elimination with concomitant formation of alcohol (Eq. 5.5). 

An extensive series of alkene cations 1 (R = Me to //-G14H29) has been prepared and fully characterized by analytical and spectroscopic methods.Some analogous Cp complex cations have also been prepared. Some of the Gp-iron cations have been reacted with the isopropoxide ion to give new ether derivatives GpFe(GO)2 GH2GH[OGH(GH3)2]R (R = Me, Ft, > -Bu, or -Gi3H27). 

---