Cyclopentadiene acrolein

Acrolein a.s Dienophile. The participation of acrolein as the dienophile in Diels-Alder reactions is, in general, an exothermic process. Dienes such as cyclopentadiene and l-dieth5laniino-l,3-butadiene react rapidly with acrolein at room temperature. 

Polyfluoro-2-acylimmopropanes exhibit an interesting dichotomy of reactivity they react as dienophiles with cyclopentadiene but as heterodienes with acrolein [112] (equation 93)... 

By using unactivated K-10 montmorillonite in the absence of solvent, the endo-exo selectivity of the cycloadditions of acrolein and methyl vinyl ketone with cyclopentadiene and cyclohexadiene is low [8] (Table 4.2, entry 3), while highly reactive dienophiles such as 1,4-benzoquinone and N-phenyl... 

The chiral catalyst 142 achieves selectivities through a double effect of intramolecular hydrogen binding interaction and attractive tt-tt donor-acceptor interactions in the transition state by a hydroxy aromatic group [88]. The exceptional results of some Diels-Alder reactions of cyclopentadiene with substituted acroleins catalyzed by (R)-142 are reported in Table 4.21. High enantio- and exo selectivity were always obtained. The coordination of a proton to the 2-hydroxyphenyl group with an oxygen of the adjacent B-0 bond in the nonhelical transition state should play an important role both in the exo-endo approach and in the si-re face differentiation of dienophile. 

Secondary orbital interactions (SOI) (Fig. 2) [5] between the non-reacting centers have been proposed to determine selectivities. For example, cyclopentadiene undergoes a cycloaddition reaction with acrolein 1 at 25 °C to give a norbomene derivative (Fig. 2a) [6]. The endo adduct (74.4%) was preferred over the exo adduct (25.6%). This endo selectivity has been interpreted in terms of the in-phase relation between the HOMO of the diene at the 2-position and the LUMO at the carbonyl carbon in the case of the endo approach (Fig. 2c). An unfavorable SOI (Fig. 2d) has also been reported for the cycloaddition of cyclopentadiene and acetylenic aldehyde 2 and its derivatives (Fig. 2b) [7-9]. The exo-TS has been proposed to be favored over the endo- IS. 

Hersh et al. found that the cationic complex [CpFe(CO)2(THF)]BF4 (23) can accelerate the [4 + 2] cycloaddition of acrolein and cyclopentadiene [32]. However, the catalytic activity was higher than expected from rate constants determined in stoichiometric experiments, indicating that a Brpnsted or Lewis acid impurity might accelerate this process and generating doubts about the role of 23. 

Acrolein 1951 (52), 1957 (77) l-Chlor(oder Jod)propin 1952 MW Furan 1939, 1951, auch MW Cyclopentadien (eine Lange) 1939 Methylacetylencyanid 1954 MW Cyclopropylcyanid (aufien) 1958 MW (2 8)... 

The results suggest that BLA 77 is the best catalyst. For example, the reaction of ( )-methyl acrolein with cyclopentadiene catalyzed by 77 (5 mol%) gives the adduct at 96% yield with 99% ee [(S configuration]. 

Recently, Diels-Alder reactions between cyclopentadiene and menthoxyaluminum dichloride-acrolein complexes were investigated by means of combined AM1/AM3 calculations and the results were compared to full AMI results211. 

Density functional theory has been used to investigate the Diels-Alder reactions of triazolinedione with s-cis- and. y-fran -butadiene. " Combined quantum mechanics-molecular mechanics calculations have been used to investigate the asymmetric Diels-Alder reaction of cyclopentadiene with the complex dienophiles AICI3-methyl acrylate and methoxyaluminium dichloride-acrolein.Equilibrium constants have been determined for the molecular complexes formed from 1-alkyl-1-(2-naphthyl)ethenes and 1-vinylnaphthalene with TCNE in C1(CH2)2C1 at 27.1 °C ... 

An unexpected and potentially useful mode of reactivity was observed in the reaction of cinnamaldehyde and cyclopentadiene catalysed by diarylprolinol silyl ether 39 [73]. Rather than observing a Diels-Alder adduct, the products resulting from an ene reaction were isolated in excellent yield. The transformation was found to be general for a series of P-aryl acroleins (40) with routinely excellent levels of... 

The potential activation of different Lewis acid catalysts and their load effect when used in combination with this solvent were explored, in order to determine the improvement of rates and selectivity to the endo and exo isomers. The list of Lewis acid catalysts included Li(OTf), Li(NTf2), Znl2, AICI3, BF3, HOTf, HNTf2, Ce(0Tf)4 5H20, Y(OTf)3, Sc(OTf)3, Sc(NTf2) and a blank without any Lewis acid. The reaction conditions were as follows 2.2 mmol of cyclopentadiene + 2.0 mmol of dienophile + 0.2 mol% of catalyst in 2 mL [hmim][BF4]. When no catalyst was added, the two ketones (R =Me-C=0 R2 = R3 = H and Ri=Et-C=0 R2 = R3 = H) showed modest activity ( 50% in 1 h) with endojexo selectivity = 85/15. Whereas acrolein showed modest activity (59% conversion in 2 h), methacrolein and crotonaldehyde were inert without a Lewis acid catalyst. Acrylonitrile and methyl acrylate underwent low conversions in 1 h (16-17%) whereas, N-phenylmaleimide, maleic anhydride and 2-methyl-1,4-benzoquinone showed complete reaction in 5 min with high endo isomer yields. 

According to both the NFPA Guide and Bretherick (Refs 5 13), sulfuric acid causes explosions and/or fires when in intimate contact with a large number (over 70) of materials including acetic anhydride, acet and nitric acid, acrolein, alcohols, alcohols and hydrogen peroxide, anun hydroxide, aniline, bromine and metals, carbides, chlorates, cyclopentadiene, ethylene glycol, various hydrocarbons, hydrochloric acid, iron, mercuric nitride, powdered metals, perchlorates, picrates, pyridine, Na carbonate, steel, sucrose, vinyl acetate, and w. Illustrative... 

Reactions with dienes and carbonyl compounds did either not occur below 150°C (e.g. 2,3-dimethylbutadiene, cyclopentadiene, tetrachloro-a-pyron acetaldehyde), or were accompanied by decomposition (2,3-dicarbomethoxybutadiene, hexachlorocyclopentadiene, 1,3-diphenylisobenzofuran acrolein ). However, 1,3-dipoles reacted readily to give well-defined addition products ... 

Diels-Alder catalyst. The Diels-Alder reaction of cyclopentadiene with acrolein (equation I) catalyzed by BF3 etherate gives a mixture of endo- and exoadducts in the ratio 9 1. The endo-selectivity is improved by use of trimethylalu-minum. Introduction of a more bulky group on aluminum by use of DAD results... 

DFT has also proved useful for the calculation of substituent effects on rates. For example, studies of reactions of butadiene and cyclopentadiene with acrolein predict a large s-trans preference of the acrolein, and a 1 kcal/mol lower activation energy than with the ethylene reaction, but very similar energies of exo- and endo- transition states [38]. Jursic has also studied several heterocyclic cases [39]. 

With the complex [(indenyl)Ru(acetone)(Me4BIPHOP-F)]SbF6 as catalyst [22], the reaction afforded the exo cycloadduct as the major product for the reaction of acrolein with cyclopentadiene, whereas this noncatalyzed reaction is known to give the endo derivative as the major product. Analogously the catalyst 41 performed the asymmetric 1,3-dipolar addition of nitrones with enals [24]. 

Work has been reported on the conversion of aldehyde 81, the Diels-Alder cycloadduct of acrolein and cyclopentadiene, to its fully saturated primary alcohol and thereafter to bicyclo[3.3.0]octyl hydrocarbons.133 A silica/alumina catalyst system provides cu-bicyclo[3.3.0]octane, while phosphoric acid and Kieselguhr gives the A2-olefin. Since this cyclic alkene reacts under Koch-Haaf conditions to produce the... 

Nevertheless, there are some examples known with larger, although still moderate, solvent effects [124, 125, 129, 538-540]. Over a range of solvents from o-xylene to trichloromethane, the reaction rates for the addition of tetracyanoethene to anthracene have been found to increase by a factor of 70 [125]. In the case of the reaction between cyclopentadiene and acrolein, changing the solvent from ethyl acetate to acetic acid causes a 35-fold acceleration in rate [129]. A strongly dipolar activated complex is unlikely, as reflected by this small sensitivity to solvent. These data are more consistent with the following mechanism first the diene and dienophile form an EPD/EPA com-... 

Cationic ansa metallocenes can be utilized as chiral catalysts in Diels-Alder reactions. For example, in the presence of the cationic zirconocene complex [(ebthi)Zr(Ot-Bu) thf]+, the [4 + 2] cycloaddition of acrolein and cyclopentadiene proceeds efficiently to afford endo and exo cycloadducts (equation 71). In reactions in which methyl acrylate is used as the dienophile, cycloadditions occur with lower levels of enan-tioselection (23% ee), but with significantly higher degrees of diastereoselectivity (17 1 endo, exo). In these processes, recent studies demonstrated the great influence of chiral metallocene structure and the dramatic solvent effect. ... 

The complexes are isolated, characterized and used as chiral Lewis acids. Dissociation of the labile ligand liberates a single coordination site at the metal center. These Lewis acids catalyze enantioselective Diels-Alder reactions. For instance, reaction of methacrolein with cyclopentadiene in the presence of the cationic iron complex (L = acrolein) occurs with exo selectivity and an enantiomeric excess of the same order of magnitude as those obtained with the successful boron and copper catalysts (eq 3). ... 

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