Ene reaction mechanism

Type I The 5- and (less) 6-e.w-cyclization product is usually a 2-vinylcyclopentanol or 2-vinylcyclohexanol. The carbonyl ene reaction mechanism is also found for 5-exo and 6-exo reactions. It is worth noting that ene reactions forming cyclopentanols are reversible due to ring strain10. 

Type II The tw/o-cyclization product is a 2- or a 3-cyclopentenol. however, the carbonyl ene reaction mechanism predominates for 6- and 1-endo reactions. 

Type III An exo or endo cyclization where the alkene-bearing side chain is attached to the carbonyl oxygen gives cyclic ethers as products. The carbonyl ene reaction mechanism is disfavored because the reaction is thought to proceed via a stepwise process. 

Our previous study showed that the reaction zone in the interior of the catalyst was not the w hole resin during the course of reaction because two liquid phases were undisturbed and unmixed in the center of the catalyst (42J. The phospha/ene reaction mechanism is shown in Figure 5. How ever, the reaction zone varied according to the solvent properties of two liquid phases. The plot of consumption of reactant and productions of pr(xiucts with space time is shown in Figure 9. The unsteady period of this reaction was larger than 2 h. The turnover number for the first substitution reaction was around 1,2x10 s at 30"X and lOOOrpm. Assuming the efl ectiveness factor q, to be constant at the steady state condition, the relative reaction-rate constant was calculated and listed in Table 1. The apparent reaction-rate constants k opi, (- calculated varied proportionately with the amount of the... 

This mechanism is distinct from a Diels-Alder mechanism, which may also occur though, if so, in low yield. A chromanone mechanism has also been proposed and leaves no unsaturation upon crosslink formation. Though this has now become the most likely mechanism, the six-membered ene reaction mechanism may still play a role in crosslink formation but, again, at a low yield. 

In the Michael reaction of HC=C-COMe with primary amines having an a-substituent containing impaired electrons (methoxylamine, ethyl glycinate, hydrazine, etc.), an unexpectedly small influence of this substituent (the a-effect) was observed. The reaction of heterocyclic enamines with HC C-COaEt and Et02C-C=C-C02Et has been systematically studied. In contrast to their heterocyclic ketene aminai analogues, heterocyclic enamines (178) reacted with electrophilic alkynes via the Michael addition pathway (178) -> (179) rather than via the aza-ene reaction mechanism (181). In the presence of a strong base, such as EtONa and NaH,... 

Nuclear magnetic resonance spectroscopy CTC detection tool, 208-211 Diels-Alder structure proof, 117 ene reaction mechanism study, 168 MA copolymer studies, 281, 290 MA-ene adduct structure proof, 153 MA grafted polyisoprene, 466 for maleate isomerization analysis, 484 MA monomer spectrum, 8, 10 MA polymer analyses, 241, 245, 249, 256, 259 MA protonation study, 211 polyester structural analysis, 484 Nylons, MA grafted, 477... 

A mechanistically significant feature of this reaction is the kinetic preference for formation of )8,y-unsaturated ketones. It has been suggested that this regiochemistry results from an intramolecular deprotonation, as shown in the mechanism above." A related reaction occurs between alkenes and acylium ions, as exemplified by the reaction between 2-methylpropene and the acetylium ion. The reaction leads regio-specifically to j8,y-enones. A concerted ene reaction mechanism has been suggested. 

Vougioukalakis GC, Rouhelakis MM, Alherti MN, Orfanopoulos M. Solvent-dependent changes in the triazolinedione-alkene Ene reaction mechanism. Chem. Eur. J. 2008 14 (31) 9697-9705. 

The reaction of 4,4-bis(tnfluoromethyl)-I,3-diaza-1,3-butadienes with certain a,P-unsaturated ketones yields pyrimidine derivatives A two-step mechanism, metathesis-electrocyclic ring closure and metathesis-intramolecular ene reaction, is a plausible explanation for the experimental results (pathway 4, equa-bon 25) [259]... 

The mechanism of the reaction of ethyl glyoxylate 4 with 2,3-dimethyl-l,3-hutadiene 5 leading to the ene product 7 is shown in Scheme 4.5. This brief introduction to the reaction mechanism for cycloaddition reactions of carhonyl compounds activated hy Lewis acids indicates that many factors influence the course of the reaction. 

Treating diene-yne derivatives 50 with ferrate 40 does not lead to the expected ene-allenes, instead the [4 + 2]-cycloaddition products 51 are obtained in moderate yields (eq. 1 in Scheme 11). As metal-catalyzed Diels-Alder-reactions of unactivated aUcynes and dienophiles are assumed to proceed via metaUacyclic intermediates, this supports the mechanism for the Alder-ene-reaction discussed before. 

Selenium dioxide is a useful reagent for allylic oxidation of alkenes. The products can include enones, allylic alcohols, or allylic esters, depending on the reaction conditions. The mechanism consists of three essential steps (a) an electrophilic ene reaction with Se02, (b) a [2,3]-sigmatropic rearrangement that restores the original location of the double bond, and (c) solvolysis of the resulting selenium ester.183... 

Ene reactions offer an excellent means of commencing a domino process, and typical carbon-ene reactions are described in this section (for details of the reaction mechanisms, see Chapter 1). 

Several relevant papers and review articles have appeared recently. These contain reports on the mechanism and kinetics of the ene reaction of ADC compounds,243-245 examples of four-membered ring formation,246-247 other cycloadditions of ADC compounds,248-252 the synthesis of azoalkanes,253 the use of chiral l,2,4-triazole-3,5-diones,254 and the use of the DEAZD/PI13P reagent in organic synthesis.255... 

Song and Beak161 have used intramolecular and intermolecular hydrogen-deuterium kinetic isotope effects to investigate the mechanism of the tin tetrachloride catalysed ene-carbonyl enophile addition reaction between diethyloxomalonate and methylenecy-clohexane (equation 105). These ene reactions with carbonyl enophiles can occur by a concerted (equation 106) or a stepwise mechanism (equation 107), where the formation of the intermediate is either fast and reversible and the second step is slow k- > k-i), or where the formation of the intermediate (the k step) is rate-determining. 

An enantioselective imino-ene reaction was developed by Lectka to provide ct-amino acid derivatives.27 Aryl alkenes (cr-methyl styrene, tetralene), aliphatic alkenes (methylene cyclohexane), and heteroatom-containing enes, all gave high yields and high ee s of the homoallylic amides (Equation (17)). The mechanism of this reaction has been proposed to proceed through a concerted pathway. This mechanism is evidenced by a large kinetic isotope effect observed in the transfer of H(D). 

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