Mechanisms of ene reaction

D. Mechanism of ene reaction. In the ene reaction, the double bond is shifted to the allyl position with respect to the starting material according to the scheme proposed by Schenck. This involves (i) attachment-of the oxygen molecule to one of the carbon atoms of the double bond (e.g. CJ, (ii) shift of the double bond to allyl position (e.g. to C -> Cj) and (iii) migration of the allyl hydrogen atom to the terminus of the peroxy group. 

Meyer, M.P., Leach, A.G., Kuwata, K.T., Chen, J.S., Greer, A., Foote, C.S. and Houk, K.N. (2003) Mechanism of ene reactions of singlet oxygen. A Two-Step No-intermediate mechanism. Journal of the American Chemical Society, 125, 1319-1328. 

Song, Z. Beak, P. Investigation of the mechanisms of ene reactions of carbonyl enophiles by intermolecular and intramolecular hydrogen-deuterium isotope effects Partitioning of reaction intermediates, J. Am. Chem. Soc. 1990,112, 8126-8134. 

The mechanism of ene reaction is similar to that of Diels-Alder Reaction. 

Singleton DA et al (2003) Mechanism of ene reactions of singlet oxygen. A two-step nointermediate mechanism. J Am Chem Soc 125 1319-1328... 

Singleton DA, Hang C, Szymanski MJ, Meyer MP, Leach AG, Kuwata KT, Chen JS, Greer A, Foote CS, Houk KN. Mechanism of ene reactions of singlet oxygen. A two-step no-intermediate mechanism. J. Am. Chem. Soc. 2003 125 (5) 1319-1328. 

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. 

The mechanism of the reaction is not knotvii with certainty. It is known from studies utilising as tracer that no change in the carbon skeletcsi occurs during the reaction, and also that unsaturated hydrocarbons can undergo reactions very similar to those of ketones thus both styr ene and phenyl-acetylene can react with sulphur and morpholine to produce phenylaceto-thiomorpholide, hydrolysis of which yields phenylacetic acid ... 

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). 

Isopropyl diarylphosphinites (Ar2POPr ) catalyse the dimerization of acrylonitrile to a mixture of cis- and fra 5 -l,4-dicyanobut-l-ene (136), rrani-l,4-dicyanobut-2-ene (137), and 2,4-dicyanobut-l-ene (138). The kinetics and mechanism of the reaction. 

Similarly, activated olefins react with triphenylchromium. Bicyclo [2.2.1] hepta-2 5-diene reacts to produce 2,5-diphenylbicyclo [2.2.1] hept-2-ene. The mechanism of this reaction is not clear, but an initial addition of phenylchromium to the unsaturated system is probably involved (67),... 

The 1,4- and 1,5-benzothiazepines (421) and (423) have been prepared by the photochemical reactions of the benzoisothiazole (420) and the benzothiazole (422) respectively with ethyl vinyl ether (81TL529, 2081). The mechanisms of these reactions are not fully established but it is interesting to note that the reactions of (422) with cis- and trans-but-2-ene are stereospecific. 

Olefins can add to double bonds in a reaction different from those discussed in 5-15, which, however, is still formally the addition of RH to a double bond. This reaction is called the ene synthesis44,1 and bears a certain similarity to the Diels-Alder reaction (5-47). For the reaction to proceed without a catalyst, one of the components must be a reactive dienophile (see 5-47 for a definition of this word) such as maleic anhydride, but the other (which supplies the hydrogen) may be a simple alkene such as propene. There has been much discussion of the mechanism of this reaction, and both concerted pericyclic (as shown above) and stepwise mechanisms have been suggested. The reaction between maleic anhydride and optically active PhCHMeCH=CH2 gave an optically active product,441 which is strong evi-... 

During the reductive isomerization of 7/3-methyl- 14-isoestr-4-ene-3,17-dione 272 in HF SbF5/methylcyclopentane at 0°C, it was found879 that a 1,3-hydride shift occurs followed by kinetically controlled hydride transfer (Scheme 5.91). The mechanism of the reaction was confirmed by employing the deuteriated donor cyclohexane- as well as a specifically deuterium-labeled starting steroid. 

This reaction is discussed in Section 5.2.3, p. 496, where the broad mechanism of the reaction and its preparative value is considered. The example included here is the preparation of 2-oxoundec-3-ene from octanal and diethyl 2-oxopropane-phosphonate,249 (Expt 5.211). The interest of the procedure is that the reaction is carried out under heterogeneous liquid-liquid conditions using a high concentration of potassium carbonate, but in the absence of an organic solvent and a phase transfer catalyst. This may be contrasted with the conditions which employ an aprotic solvent and a base such as sodium hydride (cf. Expt 5.17). 

Recent developments in the stereoselective singlet oxygen allylic photo-oxygenations of alkenes have been reviewed. A number of factors, such as solvent, electronic effects, and non-bonded interactions that dictate the ene product selectivity, and also the various mechanisms of this reaction, have been highlighted.239... 

The selenium-dioxide mediated allylic oxidation of alkenes was explored by means of 2H and 13C KIEs to clarify the mechanism of ene step.85 Changes of isotopic composition were determined for unreacted 2-methyl-2-butene 33 in reaction with Se02 at 25°C in ferf-butyl alcohol (Equation (49)). 

As in other applications of 7V-acyl-l,3-oxazolidin-2-ones, 2-thiones, and sthiazolidine-2-thiones, chelation of the Lewis acid center for restricted rotation is considered decisive for the reactions occurring under the influence of the Ti-TADDOLates. Generally, the attack of the nucleophilic component (diene or ene) on the chelated electrophile occurs from the bottom face if the chelate ring is drawn as shown in structures (17) and (18), (19), and (lO). For the oxazolidinones, this means that the trigonal a-carbonyl center is approached from the (/ e)-face when an (/ ,/ )-Ti-TADDOLate is used (rel. topicity like) the mechanism of this reaction has been discussed. ... 

Magnesio-ene reaction, 46 47, 356 357 Mechanism of Barbier reaction, 406 407 Mechanism of Grignard reagents addition reactions. 219 248 concerted (polar), 221, 237 242 cyclic transition state see Mechanism of Grignard reagents, addition reactions, concerted [polar]) development of reactivity spectrum. 225-235, 246... 

Yamaguchi, K., Yabushita, S., Fueno, T., Houk, K. N. Mechanism of photooxygenation reactions. Computational evidence against the diradical mechanism of singlet oxygen ene reactions. J. Arrr. Chem. Soc. 1981, 103, 5043-5046. 

The mechanism of the reaction of vinylation in the ort/io-position to the stannyloxy group of different organotin phenoxides must still be regarded as an open question as to whether it is an ene reaction or a simple aromatic substitution. 

The other reaction is pyrolytic cleavage (via a retro-ene reaction) of a fatty acid containing a homoallylic alcohol in the chain. This is used to produce two important feedstocks, heptanal and undecylenic acid, from ricinoleic acid, the major fatty acid component of castor oil. The mechanism of this reaction is shown in Scheme 4.61. 

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