Diels-Alder reaction perchlorate

In 1990 Grieco introduced a 5 molar solution of lithium perchlorate as a new medium for the Diels-Alder reaction that is capable of inducing not only an improvement of the rate but also of the endo-... 

The cationic aqua complexes prepared from traws-chelating tridentate ligand, R,R-DBFOX/Ph, and various transition metal(II) perchlorates induce absolute enantio-selectivity in the Diels-Alder reactions of cyclopentadiene with 3-alkenoyl-2-oxazoli-dinone dienophiles. Unlike other bisoxazoline type complex catalysts [38, 43-54], the J ,J -DBFOX/Ph complex of Ni(C104)2-6H20, which has an octahedral structure with three aqua ligands, is isolable and can be stored in air for months without loss of catalytic activity. Iron(II), cobalt(II), copper(II), and zinc(II) complexes are similarly active. 

A study of the Diels-Alder reaction was carried out by Earle et al. [42]. The rates and selectivities of reactions between ethyl acrylate (EA) and cyclopentadiene (CP) in water, 5 m lithium perchlorate in diethyl ether (5 m EPDE), and [BMIM][PE(3] were compared. The reactions in the ionic liquid [BMIM][PE(3] were marginally faster than in water, but both were slower than in 5 m EPDE [42, 43] (see Table 5.1-1 and Scheme 5.1-18). It should be noted that these three reactions give up to 98 % yields if left for 24 hours. The endo. exo selectivity in [BMIM][PE(3] was similar to that in 5 M EPDE, and considerably greater than that in water (Table 5.1-1). 

Lithium perchlorate in nitromethane (LP-NM) is sometimes a more effective reaction medium than LP-DE for certain Diels-Alder reactions. The cycloaddition of 2,3-dimethylbutadiene with nitrostyrenes (Scheme 6.24) occurs with low... 

Acid catalyzed intramolecular Diels-Alder reactions in lithium perchlorate-diethyl ether acid promoted migration of terminal dienes prior to [4 + 2] cycioaddition in conformationally restricted substrates [101]... 

Acid catalyzed ionic Diels-Alder reactions in concentrated solutions of lithium perchlorate in diethyl ether [43]... 

Lithium catalyzed hetero-Diels-Alder reactions. Cyclocondensation of N-protected ot-amino aldehydes with 1-methoxy-3-fert-butyldimethylsilyloxybutadiene in the presence of lithium perchlorate [104]... 

Diels-Alder reactions of quinones generated in situ by electrochemical oxidation in lithium perchlorate-nitromethane [105]... 

Catalysis by lithium perchlorate in dichloromethane Diels-Alder reactions and 1,3-Claisen rearrangements [100]... 

Can a chiral catalyst containing the same ligand/metal components promote the formation of both enantiomers enantioselectively The bis(oxazoline)magnesium perchlorate-catalyzed asymmetric Diels-Alder reaction [103]... 

Lithium trifluoromethanesulfonimide in acetone or diethyl ether as a safe alternative to lithium perchlorate in diethyl ether for effecting Diels-Alder reactions. Unexpected influence of the counterion on exo/endo selectivity [47]... 

Keywords imines derived from formylphosphonate undergo Diels-Alder reactions only in those cases which carry a strongly electron-withdrawing N-substituent. Lewis acidity, solvent effect, lithium perchlorate in diethyl ether... 

In the presence of copper perchlorate, the heterogenized catalyst was successfully used for the test Diels-Alder reaction and proved to be similarly active and enantioselective than its homogeneous counterpart. It was further-... 

Grieco investigated the intramolecular Diels-Alder reaction of imi-nium ions in polar media such as 5.0 M lithium perchlorate-diethyl ether and in water129 to form carbocyclic arrays. They showed that water as the solvent provided good-to-excellent yields of tricyclic amines with excellent stereocontrol (Eq. 12.58). 

A warning was given that the 5 molar solution in ether used as a solvent for Diels-Alder reactions would lead to explosions [1], Such a reaction of dimethyl acetylenedicarboxylate and cyclooctatetraene in this solvent exploded very violently on heating. The cyclooctatetraene was blamed, with no supporting evidence [2], It would appear desirable to find the detonability limits of the mixture with ether before any attempt is made to scale up. A safe alternative to lithium perchlorate/ether as a solvent for Diels-Alder reactions is proposed [3],... 

Desimoni and coworkers84 probed the catalytic effect of metal perchlorate salts on the rate of the Diels-Alder reactions between malonates 88 and cyclopentadiene (equation 27). They found that especially magnesium perchlorate was able to catalyze the reaction by binding two malonates in a bidentate fashion. Reaction times were shortened up to 1000 times. The endo/exo selectivity was inverted from 89/90 = 40/60 (n =4) and 17/83 (n = 5) for the thermal uncatalyzed reactions to 89/90 = 60/40 (n = 4) and 80/20 (n = 5) for the magnesium perchlorate catalyzed reactions. 

The electrochemical oxidation of phenols produces quinones that can be used as dienophiles for the Diels-Alder reaction. A typical example is shown in Scheme 14, where a lithium perchlorate/nitromethane system and an electrode coated with a PTFE [poly-(tetrafluoroethylene)] fiber, to create a hydrophobic reaction layer. 

Earle, M. J., McCormac, P. B. Seddon, K. R. Diels-Alder reactions in ionic liquids a safe recyclable green alternative to lithium perchlorate-diethyl ether mixtures. Green Chem., 1999, 1(1), 23-25 Doherty, S. Goodrich, P. Hardacre, C. et al. Marked enantioselectivity enhancements for Diels-Alder reactions in ionic liquids catalysed by platinum diphosphine complexes. Green Chem., 2004, 6(1), 63-67. 

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. 

On the other hand, lithium perchlorate catalyzed Diels-Alder reaction between 4-[(ethoxycarbonyloxy)methylene]-2-phenyl-5(47/)-oxazolone 829 and cyclopenta-diene is more efficient and affords a mixture of the corresponding exo-830 and endo-831 cycloadducts. These cycloadducts have been converted to 2-amino-3-hydroxynorbornenecarboxylic acid derivatives 832 and 833 or to 2-amino-3-hydroxynorbornanecarboxylic acids 834 and 835 after a series of careful transformations.In addition, 830 and 831 have been further elaborated to new conformationally constrained serine analogues, the polyhydroxy 2-aminonorbor-nanecarboxylic acids 836-839 as shown in Scheme 7.257. ° ... 

Kanemasa, Curran, and co-workers did an extensive study on the metal and counterion effects in the Diels-Alder reaction using the DBF-box ligand Their results are summarized in Table 9.12 (Fig. 9.27). It has been shown that, for this ligand, the optimal conditions were use of nickel(II) perchlorate at 40 °C for 14 h leading to 96% yield of cycloadduct in a ratio of 97 3 (endo/exo) with >99% endo ee. 

The Diels-Alder reaction is an important and widely used reaction in organic synthesis (Sauer and Sustmann, 1980), and in the chemical industry (Griffiths and Previdoli, 1993). Rate enhancement of this reaction has been achieved by the use of solvents such as water, surfactants, very high pressure, lithium amides, alkylammonium nitrate salts, and macrocyclic hosts (Sherman et ak, 1998). Diels-Alder reactions can be ran in neutral ionic liquids (such as 1-butyl-3-methylimidazolium trifluoromethanesulfo-nate, l-butyl-3-methylimidazolium hexafluorophophate, l-butyl-3-methylimidazolium tetrafluoroborate, and l-butyl-3-methylimidazolium lactate). Rate enhancements and selectivities are similar to those of reactions performed in lithium perchlorate-diethyl ether mixtures. 

The indolone 160 in a Diels-Alder reaction with cyclopentadiene at 20°C in the presence of aluminum chloride or perchloric acid gave 161.98... 

The Diels-Alder reaction between cyclopentadiene and acryloyloxazolidinone is enantioselectively catalysed by the bis(oxazoline)-magnesium perchlorate complex.214... 

The kinetics of high-pressure cycloaddition reactions of tropone with dienophiles and enophiles have been reviewed.254 The Diels-Alder reaction of 9,10-dimethylanthracene with acrylonitrile has been investigated at high pressure in acetonitrile and in ethereal solutions of lithium perchlorate.255 The combination of high pressure and a solution of lithium perchlorate in diethyl ether is an excellent reaction rate accelerator in 4 + 2-cycloaddition reactions.256... 

Attempts to develop enantioselective protocols for the aza-Diels-Alder reaction were reported simultaneously with those described above. A first contribution in this area was the report by the. Mrgensen group,85 who studied the influence of salts of copper, silver, palladium, and zinc. Copper(I) perchlorate provides optimal yields and enantioselectivity, but complexes of BINAP (87) and Tol-BINAP (203) with AgSbF6, AgOTf, and AgC104 were able to catalyze the reaction, albeit with low enantioselectivity (Scheme 2.52). 

Catalytic Diels-Alder reactions between 1,3-dienes and a,/3-unsaturated ketones are promoted by the combined use of diphenyltin sulfide (Ph2Sn=S) and silver perchlorate (Equation (97))-... 

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