Alkenes cyclohexene

Photolysis of 21d (see earlier 21) in alkenes (cyclohexene, 1,1-diphenylethylene) always gave the cyclopropane derivatives 75 by a cis addition of the singlet carbene (64JOC3577) (Scheme 21). 

A Ni(salen) complex [salen = bis(salicylidene)ethylenediamine] encapsulated in zeolite is highly efficient in the hydrogenation of simple alkenes (cyclohexene, cyclooctene, 1-hexene).451 This method, which is the encapsulation of metal complexes into the cavities of zeolites, offers the unique possibility of shape-selective... 

SAMPLE SOLUTION (a) Allylic hydrogens are bonded to an allylic carbon. An allylic carbon is an sp3-hybridized carbon that is attached directly to an sp2-hybridized carbon of an alkene. Cyclohexene has four allylic hydrogens. 

Keywords benzylidenemethylamine, acetylacetone, montmorillonite K10, enam-ino ketone, /1-oxo alkene, cyclohexene... 

Alkene hydrogenation was also suggested to test for mass transfer effects during liquid-phase hydrogenations236,237. The method is based on the linear poisoning of hydrogen addition to alkenes (cyclohexene and apopinene) by CS2. When the active sites of Pd or Pt catalysts are titrated with CS2 the decrease in rate is linear unless mass transfer limitations occur. 

A clean, solvent-free method has been developed for the bis-hydroxylation of alkenes by the use of Nafion-based acidic catalysts and 30% H202.655 Nafion NR50 and SAC-13 exhibited high activity in the oxidation of isomeric C alkenes, cyclohexene [Eq. (5.228)], 1,4-cyclohexadiene, and allylic alcohols in the temperature... 

The range of alkenes which can be used in the intermolecular PK reaction is limited and there is a large variation in reaction rate between alkenes. It is found that strained alkenes (cyclohexene < cyclopentenecnorbornene) are the best substrates for the reaction and there has been extensive investigation into the reasons behind this. 

The overall course of reaction depends on the relative rate constants tor the various secondary radical processes. Aliphatic ketones are often photoreduced to secondary alcohols (4.32), but although there are interesting features in the stereochemistry of the reduction, the method is not a worthwhile alternative to thermal reduction using hydride reagents, except in cases where the substrate is sensitive to basic conditions. Photoaddition of methanol is promoted in the presence of titanium(iv) chloride, both for acyclic and cyclic (4.33) ketones the titanium involvement probahly starts in the early steps of the reaction, but the detailed mechanism is not known. Addition may also be a major pathway when cyclohexene is used as hydrogen source (4.34) unlike many other simple alkenes, cyclohexene does not readily give oxetanes by photocycloaddition (see p. 126). 

Little related work on the technetium analog has been completed. Much of the synthetic work with high-valent Tc has centered on imido complexes,54 or on complexes for use in radiopharmaceuticals.55 Methyl technetium trioxide has been prepared.8 This species is thermodynamically a powerful enough oxidant to cycloadd to alkenes cyclohexene gave (after hydrolysis) c/s-l,2-cyclohexanediol. No chemistry with H202 has been reported it is expected to behave in a similar manner to MTO, unless the change in the metal-oxo bond strength perturbs the overall thermodynamics. 

Most cyclic alkenes (cyclohexene being the notable exception because of its stability) undergo metathesis, but instead of dimerizing to form cyclodienes (equation 11.19), they usually polymerize instead to form polyalkenamers (path c, Scheme 11.1). Because this kind of metathesis involves rupturing the C=C and opening up the ring, the process is called ROMP. 

Selenenylation is a stereospecific anti addition with acyclic alkenes.Cyclohexenes undergo preferential diaxial addition. 

Epoxidation. Italian chemists have found that the epoxidation method of Cornforth and Green (3, 159) when applied to A -cholestene (1) leads to the tram, diaxial diol (2). They reasoned that the epoxide is formed but hydrolyzes ill the acidic medium. They then carried out the reaction in the presence of silver oxide to remove hydrogen iodide and obtained the oxides (3) and (4) in high yield. The reaction was then shown to be applicable to other alkenes (cyclohexene oxiile. 80%). 

---