Diels-Alder reactions of methyl vinyl ketone

Tire results of a study of the effect of these catalysts on the model Diels-Alder reaction of methyl vinyl ketone (4.8) with cyclopentadiene (4.6) are summarised in Table 4.1... 

Rare-earth-metal triflates are efficient catalysts in Diels-Alder reactions, and Sc(OTf)3 is clearly more effective than Ln(OTf)3 as a catalyst.45,53-55 In the presence of 10mol.% Y(OTf)3 or Yb(OTf)3, only a trace amount of the adduct was obtained in the Diels-Alder reaction of methyl vinyl ketone (MVK) with isoprene. In contrast, the reaction proceeded smoothly to give the adduct in 91% yield in the presence of 10mol.% Sc(OTf)3 (Scheme 13).45 Sc(OTf)3 has also proved to be an efficient catalyst for the Diels-Alder reaction of imines (aza Diels-Alder reactions).56,57... 

Entries 6-10 deal with the Diels-Alder reactions of methyl vinyl ketone with furan and also include the use of AICI3 (entry 6), high pressure (entry 7) and Cu ion-exchanged Y-zeolite (entry 9). This series, however, displayed only modest exo selectivities. The highest product ratio (258 Y = 0)/(259 Y = O) = 20 80 was found on adsorption of the educts on dry Si02 MgO (entry 10). 

Scheme 61 and Table 10 illustrate the influence of SnCU or solid supports on the Diels-Alder reactions of methyl vinyl ketone or acrolein with isoprene. Apart from the reaction rate, the regiochemical control was substantially increased, e.g. from 59 41 to 99.5 0.5 (entries 5/7) in favor of the para products (260). 

Kelly et al. [12] applied these hydrogen bonding systems to control not only endo exo selectivity but also reaction rate in the Diels-Alder reaction of methyl vinyl ketone (MVK) and cyclopentadiene (Scheme 9.3). The presence of dibenzocyclobutane-1,8-diol leads to a 90% yield of the endo adduct, whereas the same adduct is given only in 3 % yield without the... 

Table 9.8 Catalytic activity of thioureas for the Diels-Alder reaction of methyl vinyl ketone and cyclopentadiene...

Diels-Alder reaction of methyl vinyl ketone (MVK) with iso-prene, the adduct is obtained in 91% yield in the presence of 10 mol % Sc(OTf)3, while 10 mol % Y(OTf)3 or Yb(OTf)3 gives only a trace amount of the adduct.Sc(OXf)3-catalyzed Diels-Alder reactions generally provide high yields with high endo selectivities. The present Diels-Alder reaction even proceeds in aqueous media. Thus, naphthoquinone reacts with cyclopenta-diene in H2O-THF (9 1) at room temperature to give the corresponding adduct in high yield (100% endo) (eq 16). Sc(OTf)3 also serves as an effective catalyst for Diels-Alder reactions in supercritical carbon dioxide (sc C02). ... 

The catalytic effect of thiourea derivative 26 (a bidentate hydrogen-bond donor) was investigated in the Diels-Alder reaction of methyl vinyl ketone (27) with cyclopentadi-ene (5) in cyclohexane (that has negligible interactions with the solutes), chloroform (a weak hydrogen-bond donor), and in water (a high polar solvent) to give 5-norbornene-2-methylketone (28) (Table 5.2). 

Table 5.2 Diels-Alder reactions of methyl vinyl ketone (27) with cyclopentadiene (5) catalyzed by thiourea derivative 26 in water and organic solvents...

To overcome poor Lewis acidity of Li" ", interesting bimetallic dual activation system has been developed (Scheme 3.7) [25]. Two Li" ", oriented at an appropriate distance, coordinate to two oxygen lone pair of carbonyl group and induce greater activation. Bidentate lithium Lewis acid (3) promotes Diels-Alder reaction of methyl vinyl ketone with cyclopentadiene to provide the cycloadduct in 71% yield. 

Figure 1.5. Chemical potential of the initial state, the transition state and the product of the Diels-Alder reaction between methyl vinyl ketone and cyclopentadiene in water as compared to 1-propanol The data are taken from r. 56.

In the Mukaiyama aldol additions of trimethyl-(l-phenyl-propenyloxy)-silane to give benzaldehyde and cinnamaldehyde catalyzed by 7 mol% supported scandium catalyst, a 1 1 mixture of diastereomers was obtained. Again, the dendritic catalyst could be recycled easily without any loss in performance. The scandium cross-linked dendritic material appeared to be an efficient catalyst for the Diels-Alder reaction between methyl vinyl ketone and cyclopentadiene. The Diels-Alder adduct was formed in dichloromethane at 0°C in 79% yield with an endo/exo ratio of 85 15. The material was also used as a Friedel-Crafts acylation catalyst (contain-ing7mol% scandium) for the formation of / -methoxyacetophenone (in a 73% yield) from anisole, acetic acid anhydride, and lithium perchlorate at 50°C in nitromethane. 

Linders, J.T.M., Briel, P., Fog, E., Lie, T.S. and Maat, L., Chemistry of opium alkaloids, Part XXVIII preparation of 6-demethoxy-N-formyl-N-northebaine and its Diels-Alder reactions with methyl vinyl ketone and nitroethene novel 8-nitro-substituted 6a,14a-ethenoisomorphinans and 6 3,14 3-ethenomorphinans, Rec. 

A new synthesis of racemic oleuropeic acid (216) starts with the known Diels-Alder reaction between methyl vinyl ketone and chloroprene, yielding the chloro-ketone (217). The acid function is introduced by exchanging the chlorine atom for lithium, followed by conversion into the aldehyde with dimethylformamide, and the additional methyl group is put in with a Grignard reaction (Scheme 16). ... 

Water has been shown to be the polar solvent of choice for the intramolecular Diels-Alder cycloaddition of immonium ions, e.g. (77), to produce the single tricyclic amine (78) (Scheme 28). The activation free energy and transmission coefficient for the Diels-Alder reaction between methyl vinyl ketone and cyclopentadiene in water have been calculated using molecular-dynamics and reaction-flux simulations. Water has been shown to enhance significantly the Ni +- and Co -catalysed Diels-Alder reaction between 3-phenyl-l-(2-pyridyl)prop-2-en-l-ones and... 

A total synthesis of adaline (550) has been performed (73BSB699). The vinyl ketone 547 was submitted to hetero Diels-Alder reaction with methyl vinyl ether to yield the dihydropyran derivative 548 in 60% yield. Acid hydrolysis of 548 produced the keto aldehyde 549. Finally, a Mannich reaction involving... 

A variation in this technique has recently been reported, although not necessarily using the high pressures described above. Diels-Alder reactions can be done under pressure in supercritical carbon dioxide., although the synthetic application may be limited by slow reaction rates. Addition of a Lewis acid appears to overcome this problem, as in Kobayashi s use of scandium triflate in the reaction of methyl vinyl ketone with 2-methyl-1,3-butadiene to give a 93 7 mixture of 137/138. " 7a Rayner and co-workers had previously reported the use of scandium triflate in supercritical and observed that the maximum selectivity was obtained... 

Amorphous fumed silica promotes several Diels-Alder reactions in gaseous CO2 and scC02. For the reaction of methyl vinyl ketone and penta-1,3-diene at 80 C, the yield decreases as the CO2 pressure increases because the concentration of the reactant adsorbed on the silica surface decreases. 

Figure 1.2. Endo and exo pathway for the Diels-Alder reaction of cyclopentadiene with methyl vinyl ketone. As was first noticed by Berson, the polarity of the endo activated complex exceeds that of the exo counterpart due to alignment of the dipole moments of the diene and the dienophile K The symmetry-allowed secondary orbital interaction that is only possible in the endo activated complex is usually invoked as an explanation for the preference for endo adduct exhibited by most Diels-Alder reactions.

For example, the Diels-Alder reaction of A-benzyl-3-carboxamido-1,6-dihydro-pyridine (14a) andlV-benzyl-3-cyano-l,6-dihydropyridine (14b) with methyl vinyl ketone yielded isoquinuclidines 15a and 15b, respectively, which can be converted into ibogamine alkaloid (16). 

It is believed that clay minerals promote organic reactions via an acid catalysis [2a]. They are often activated by doping with transition metals to enrich the number of Lewis-acid sites by cationic exchange [4]. Alternative radical pathways have also been proposed [5] in agreement with the observation that clay-catalyzed Diels-Alder reactions are accelerated in the presence of radical sources [6], Montmorillonite K-10 doped with Fe(III) efficiently catalyzes the Diels-Alder reaction of cyclopentadiene (1) with methyl vinyl ketone at room temperature [7] (Table 4.1). In water the diastereoselectivity is higher than in organic media in the absence of clay the cycloaddition proceeds at a much slower rate. 

Table 4.1 Diels-Alder reactions of cyclopentadiene (1) with methyl vinyl ketone catalyzed by Fe(II)-K-10 montmorillonite in various solvents...

The Diels-Alder reactions of cyclopentadiene with methyl vinyl ketone and acrylonitrile are accelerated when carried out in water in the presence of jS-CD but are slower with a-CD [65a] (Scheme 4.16). This is in agreement with the observation that the transition states of these cycloadditions fit into the hydro-phobic cavity of P-CD but not in the smaller a-CD cavity. 

Rideout and Breslow first reported [2a] the kinetic data for the accelerating effect of water, for the Diels Alder reactions of cyclopentadiene with methyl vinyl ketone and acrylonitrile and the cycloaddition of anthracene-9-carbinol with N-ethylmaleimide, giving impetus to research in this area (Table 6.1). The reaction in water is 28 to 740 times faster than in the apolar hydrocarbon isooctane. By adding lithium chloride (salting-out agent) the reaction rate increases 2.5 times further, while the presence of guanidinium chloride decreases it. The authors suggested that this exceptional effect of water is the result of a combination of two factors the polarity of the medium and the... 

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