Epoxy alkenes

The El mode can be used in IDA, provided that characteristic ions of high intensity are available for quantification. In some cases, however, it is necessary to improve the efficiency of IDA by changing and optimizing the ionization technique as recently demonstrated for epoxy-alkenals (Blank et al., 1999). 

Cyclization of epoxy alkenes.2 The reaction of 8,e-unsaturated epoxides with 2 equiv. of Cp2TiCl in THF results in cyclization to cyclopentanemethanols. The reaction is compatible with keto and nitrile groups but not aldehyde groups. 

MejSiOTf) greatly enhances the ields CycUzation of epoxy alkenes. ... 

The radical cyclization of epoxy-alkenes using cyclopentadienyltitanium chloride (CpjTiCl) in THF has been described for the conversion of 64 into 65. ... 

Intramolecular alkyne metathesis is now well-established as a robust and useful method for organic S5mthesis. It was also known that Ru-mediated metathesis of an alkyne with ethylene could lead to the diene. The question facing Angew. Chem. Int. Ed. 2007, 46, 5545) Alois Fiirstner of the Max-Planck-Institut, Mulheim was whether these transformations could be carried out on the very deUcate epoxy alkene 21. In fact, the transformations of 21 to 22 and of 22 to 23 proceeded weU, setting the stage for the total synthesis of Amphidinolide V 25. 

Alkylated and alkenated toluenediamines are used as antioxidants (qv) in oils and elastomers (10,53,63—65), as chemical intermediates for polyamides, polyimides, and polyesterimides (53,1) and as epoxy curatives (53,58,66) (see Epoxy resins). 

Irans alkenes are converted into their cis isomers and vice versa on epoxi-dation followed by treatment of the epoxide with tviphenylphosphine. Propose a mechanism for the epoxide — alkene reaction. 

Treatment of an or.jS-unsaturated ketone with basic aqueous hydrogen peroxide yields an epoxy ketone. The reaction is specific to unsatnrated ketones isolated alkene double bonds do not react. Propose a mechanism. 

In a formal synthesis of fasicularin, the critical spirocyclic ketone intermediate 183 was obtained by use of the rearrangement reaction of the silyloxy epoxide 182, derived from the unsaturated alcohol 180. Alkene 180 was epoxidized with DMDO to produce epoxy alcohol 181 as a single diastereoisomer, which was transformed into the trimethyl silyl ether derivative 182. Treatment of 182 with HCU resulted in smooth ring-expansion to produce spiro compound 183, which was subsequently elaborated to the desired natural product (Scheme 8.46) [88]. 

Enantioselective epoxidation of unfunctionalized alkenes was until recently limited to certain ds-alkenes, but most types of alkenes can now be successfully epoxi-dized with sugar-derived dioxiranes (see Section 9.1.1.1) [2]. Selective monoepox-idation of dienes has thus become a fast route to vinylepoxides. Functionalized dienes, such as dienones, can be epoxidized with excellent enantioselectivities (see Section 9.1.2). 

In a different type of reaction, alkenes are photooxygenated (with singlet O2, see 14-8) in the presence of a Ti, V, or Mo complex to give epoxy alcohols formally derived from allylic hydroxylation followed by epoxidation, for example, ... 

The overall transformation of alkenes to alcohols that is accomplished by epoxi-dation and reduction corresponds to alkene hydration. Assuming a nucleophilic ring opening by hydride addition at the less-substituted carbon, the reaction corresponds to the Markovnikov orientation. This reaction sequence is therefore an alternative to the hydration methods discussed in Chapter 4 for converting alkenes to alcohols. 

Hidalgo FJ, Zamera R (2004) Strecker-type degradation produced by the lipid oxidation products 4, 5 epoxy-2-alkenals. J Agri Food Chem 52 7126-7131... 

As a, (3-unsaturated ketones are electron-poor alkenes, they do not generally give epoxides when treated with peracids. They can be epoxidized with hydrogen peroxide which involves nucleophilic attack by HOO- to give the epoxy ketone (Figure 4.1). 

Trisphenol epoxy novolacs, 10 371-372 Tristimulus colorimeters, 7 325 Trisubstituted alkene synthesis, 13 653 Trisubstituted silyl group, in silylation, 22 691... 

---