Alkene derivatives

In contrast, the ultrasonic irradiation of organic Hquids has been less studied. SusHck and co-workers estabHshed that virtually all organic Hquids wiU generate free radicals upon ultrasonic irradiation, as long as the total vapor pressure is low enough to allow effective bubble coUapse (49). The sonolysis of simple hydrocarbons (for example, alkanes) creates the same kinds of products associated with very high temperature pyrolysis (50). Most of these products (H2, CH4, and the smaller 1-alkenes) derive from a weU-understood radical chain mechanism. 

For historical reasons, there are a few alkenes whose names are firmly entrenched in common usage blit don t conform to the rules. For example, the alkene derived from ethane should be called etheite, but the name ethylene has... 

Alkene derived compatible with alkoxymercuration method... 

The Meerwein reaction is a valuable method for the arylation of alkenes because of the easy availability of cheap aromatic amines and compounds containing double bonds. A disadvantage is that the yield is often low (normally 20-50%, in exceptional cases reaching 80%, see Table 10-3). The reaction can be carried out in water if the alkene derivative is sufficiently soluble otherwise an organic co-solvent is necessary. Meerwein et al. (1939) used acetone, which is still the most popular solvent used today. The mechanistic function of acetone will be discussed later in this section. 

Cationic polymerization of alkenes and alkene derivatives has been carried out frequently in aqueous media.107 On the other hand, the reaction of simple olefins with aldehydes in the presence of an acid catalyst is referred to as the Prins reaction.108 The reaction can be carried out by using an aqueous solution of the aldehyde, often resulting in a mixture of carbon-carbon bond formation products.109 Recently, Li and co-workers reported a direct formation of tetrahydropyranol derivatives in water using a cerium-salt catalyzed cyclization in aqueous ionic liquids (Eq. 3.24).110... 

Saito and coworkers have used C2-symmetrical alkenes derived from a variety of tartaric acid derivatives, for controller in discriminating 71 faces of dipolarophile in nitrone cycloaddition. Excellent endolexo and diastereofacial selectivity (de) are obtained. Endo transition state assembly shown in Eq. 8.50 could be responsible for the formation of preferred distereoisom-... 

Previous derivatization of the extract is necessary to improve the stability of the compounds and the sensitivity and precision of subsequent GC-MS analysis. Silyl derivatives formed for example with MSTFA [43], halogenated alkene derivatives produced with heptafluorobutyric anhydride (HFBA) [36] or pentafluoropropionic acid [58] or anhydride (PFPA), as well as acetate derivatives formed using acetic anhydride [48] have been widely employed. 

There are at least six different routes for alkene elimination from C H2h+2N+ species. However, the two most important involve loss of an alkene derived from an intact N-alkyl substituent. 

Allenes with terminal double bonds are selectively reduced in the terminal position, whereas internal allenes afford a mixture of the corresponding olefins120. Some hydrogenations resulted in the cis alkene derivative (equation 46)121. 

CH3CN/H2O solution leads to various tertiary phosphines [33] examples include 1, 25, 27. In order to avoid the formation of phosphine oxides and/or the hydrolysis of some alkene derivatives (e.g. acryl esters) a small amount of Et4N Oir was used as base, and a small quantity of ditertbutylphenol was... 

The stabilizing effect of alkyl groups appears to involve overlap of a C-H (or C-C) orbitals with the n system of the alkene, rather as we have seen with car-bocations (see Section 6.2.1). The more alkyl groups attached, the more stabilization the alkene derives. 

We have seen a number of reactions in which alkene derivatives can be polymerized. Radical polymerization (see Section 9.4.2) is the usual process by which industrial polymers are produced, but we also saw the implications of cationic polymerization (see Section 8.3). Here we see how an anionic process can lead to polymerization, and that this is really an example of multiple conjugate additions. 

Catalyst IX (5 mol %) was also used for RCM or self-metathesis of different alkene derivatives. It allowed the preparation of macrocycles the nonylprodigiosin precursors and their analogs or the efficient self-metathesis of multifunctional alkene (Scheme 8.18) [62]. 

Chiral alkenes derived from ot,p-unsaturated aldehydes have also been applied in asymmetric 1,3-dipolar cycloadditions (142). Soucy et al. (142) used (—)-8-(benzylamino)menthol (94) and acrolein for the exclusive formation of 95 having an equatorial C(2) vinyl group (Scheme 12.31). The 1,3-dipolar cycloaddition of acetonitrile oxide with 95 gave 96 with a selectivity of > 90% de. 

The N-heterocyclic alkenes derived from ring-closing metathesis are useful substrates for further transformation. In a synthesis directed toward the insecticidal cripowellin 12, Dieter Enders of RWTH Aachen has shown (Angew. Chem. Int. Ed. 2005,44, 3766) that the tertiary amide 8 cyclizes efficiently to the nine-membered alkene 9. The vision was that an intramolecular Heck cyclization could then deliver the cripowellin skeleton. Indeed, the Heck did proceed, and, depending on conditions, could be directed toward either 10 or 11. Unfortunately, the conformation of 9 is such that the cyclization proceeded cleanly across the undesired face. Nevertheless, both 10 and 11 appear to be valuable intermediates for further transformation. 

The aldehyde precursor, with the co-alkene derived from lyxose (42.0 mg, 0.12 mmol) was drawn into a syringe with a solution of 1 mL of THF-methanol (3 1 v/v) and added dropwise to a cooled solution ( 78°C) of Sml2 (3.6 mL, 0.1 M in THF), over 5 min. The solution was kept at —78°C for 1 h. When the reaction was complete, as indicated by TLC analysis, it was quenched with aqueous saturated sodium bicarbonate solution (1 mL) and extracted with ether. Chromatography using 50 50 ether-hexane gave 31.0 mg (73%) of pure syn-cyclic alcohol. 

C3-hydroxy benzylation, through alkylation of the intermediate 2,3-0-dibutylstannylene of mannose acetal 24, gives 25 (Scheme 5). Hydroboration of the exocyclic 5-alkene derived from this material provides 26, in which the C5 stereochemistry is inverted. Benzylation and acetate methanolysis leads to the suitable glycosyl acceptor 27. 

Several excellent comprehensive reviews that include the hydroformylation reaction and related reactions of carbon monoxide have appeared in the past decade.1-2 Because of the industrial importance of these reactions, much of the literature is process oriented and has focused on the carbonylation of simple alkenes derived from petroleum feedstock. 

In the dihydroxylation of cyclohexene by Me3N+—O-, catalysed by OsC>4, aromatic amines and aliphatic chelating (TMEDA) or bridging (DABCO, hexamine) amines were found to retard the oxidation, owing to the formation of amine adducts of the dioxomonoglycolatoosmium(VI) ester intermediates, which are more resistant to the further oxidation required for product formation.98 Alkenes derived from Gamer s aldehyde, A-Boc-/V,0-acctonide of the aldehyde of L-serine, may be dihydroxylated by OsC>4 with excellent selectivities that may be explained by A1,3 strain.99... 

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