Aromatic alkenes

This synthesis method can be utilised by any alkene or alkyne, but steric hindrance on internal double bonds can cause these reactions to be quite slow. Conjugated dienes and aromatic alkenes are not suited for the ultraviolet light-initiated process. The use of other free-radical initiators is required in free-radical-initiated reactions involving these species. 

A breakthrough in iron-catalyzed asymmetric epoxidation of aromatic alkenes using hydrogen peroxide has been reported by our group in 2008. Good to excellent isolated yields of aromatic epoxides are obtained with ee-values up to 97% for stilbene derivatives using diphenylethylenediamines 9 as ligands (Scheme 5) [45, 46]. 

The first example of anti-Markovnikoff hydroamination of aromatic alkenes has been demonstrated with cationic rhodium complexes.170 A combination of [Rh(COD)2]+/2PPh3 in THF under reflux yields the N-H addition product as the minor species alongside that resulting from oxidative amination (Scheme 37). Hydrogenation products are also detected. 

CH2 and CH3 groups. It should be noted that no bands are observed above 3000 cm indicating the absence of an aromatic, alkene or alkyne structure. 

Kojima, M., Nakajoh, M., Matsubara, C. and Hashimoto, S. (2002). Photooxygenation of aromatic alkenes in zeolite nanocavities. J. Chem, Soc. Perkin Trans. 2, 1894-1901... 

Table 9.2 Selective reduction of conjugated aromatic alkenes catalyzed by Pd-PMHS nanocomposites. (Reprinted with the permission of the American Chemical Society [52])...

Table 6.3 Epoxidation of some aromatic alkenes by [RuVI(L1)02] (la).

Table 6.3 depicts the results of the asymmetric epoxidation of some aromatic alkenes. 

Electron transfer sensitization allows either the radical cation or the radical anion of an aromatic alkene to form as desired, which finally results in nucleophile addition with Markovnikov and anti-Markovnikov regiochemistry. In an apolar solvent, the tight radical ion pair undergoes a stereoselective reaction when the electron-accepting sensitizer is chiral (Figure 3.10). ... 

Summary of octane number aromatics, alkenes, and alkynes > cyclic alkanes and branched alkanes > straight-chain alkanes. 

For several alkene substrates, the yield of the epoxide product was lower when the reactions were carried out in pure CH2CI2 than in a mixed solvent system consisting of [BMIM]PFg/CH2Cl2 (3 1, v/v). The catalyst was also highly active for the epoxidation of aromatic alkenes. Although PhIO is an oxidant commonly used in organic solvents, it was found that the use of PhI(OAc)2 under the same conditions in the mixed solvent led to higher yields of the epoxides. 

As stoich. [Ru(0)(bpy)(tmtacn)]VCH3CN it functioned as a competent (sic) epoxidant for alkenes, though the products were often contaminated with by-products (e.g. fran -stilbene gave fran -stilbene oxide and benzaldehyde cw-stilbene gave cis- and trans- epoxides). Kinetics of the epoxidation of norbomene and styrene were reported, with activation parameters measured and discussed [682]. Kinetics of its non-stereospecific, stoicheiometric epoxidation of aromatic alkenes in CH3CN were studied, and the rates compared with those of oxidations effected by other Ru(IV) 0x0 complexes with N-donors, e. g. [Ru(0)(tmeda)(tpy)] ", trans-[Ru(0)(Cl3bpy)(tpy)] " and [Ru(0)Cl(bpy)(ppz )] + [676]. 

The Paterno-Biichi reaction has been employed in the synthesis, often in high yield, of a large variety of substituted oxetanes. In addition to simple aliphatic and aromatic alkenes, cycloaddition of ketones to, for example, fumaronitrile,284 l,3-diacetylimidazolin-2-one288 [Eq. (73)], and allenes286 has been reported. Allenes yield both 1,5- and l,6-dioxaspiro[3.3]heptanes as well as the 2-alkylidene-oxetane this is illustrated for benzophenone and tetramethylallene in Eq. (74). Cycloaddition of ketones to ketenimines to form 2- and... 

Perrin s group220 concluded that, for aromatic alkenes (R = aryl), the transition state, schematically represented as 89, may be imbalanced in that the delocalization of the positive... 

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