Aluminum Chloride Diels-Alder reactions

DIELS-ALDER REACTION Aluminum chloride. Cupric fluoroborate. 1,3-Di-phenylnaphtho[2.3-c]furane. 4-Phenyl-l,2,4-triazoline-3,5-dione. 3-Sulfolene. 

DIELS-ALDER CATALYSTS Aluminum chloride. Boron trifluoiide etherate. DIELS-ALDER REACTIONS 2,3-Bis-(trimethylsilyloxy)-l,3-butadiene. 

Other methods for the preparation of cyclohexanecarboxaldehyde include the catalytic hydrogenation of 3-cyclohexene-1-carboxaldehyde, available from the Diels-Alder reaction of butadiene and acrolein, the reduction of cyclohexanecarbonyl chloride by lithium tri-tcrt-butoxy-aluminum hydride,the reduction of iV,A -dimethylcyclohexane-carboxamide with lithium diethoxyaluminum hydride, and the oxidation of the methane-sulfonate of cyclohexylmethanol with dimethyl sulfoxide. The hydrolysis, with simultaneous decarboxylation and rearrangement, of glycidic esters derived from cyclohexanone gives cyclohexanecarboxaldehyde. 

The Diels-Alder reaction was thought for many years to be only slightly influenced by catalysts. However, in 1960, Yates and Eaton (6) clearly demonstrated that with certain dienophiles, the presence of a molar equivalent of aluminum chloride can cause a remarkable acceleration of the reaction. Providing the diene is not polymerized (7) or otherwise destroyed by the catalyst, the modification can be fruitfully employed to carry out the reaction at lower temperature and for shorter times. 

The discovery that Lewis acids can promote Diels-Alder reactions has become a powerful tool in synthetic organic chemistry. Yates and Eaton [4] first reported the remarkable acceleration of the reactions of anthracene with maleic anhydride, 1,4-benzoquinone and dimethyl fumarate catalyzed by aluminum chloride. The presence of the Lewis-acid catalyst allows the cycloadditions to be carried out under mild conditions, reactions with low reactive dienes and dienophiles are made possible, and the stereoselectivity, regioselectivity and site selectivity of the cycloaddition reaction can be modified [5]. Consequently, increasing attention has been given to these catalysts in order to develop new regio- and stereoselective synthetic routes based on the Diels-Alder reaction. 

Chloroaluminate ionic liquids (typically a mixture of a quaternary ammonium salt with aluminum chloride see Table 6.9) exhibit at room temperature variable Lewis acidity and have been successfully used as solvent/catalyst for Diels-Alder reactions [57]. The composition of chloroaluminate ionic liquids can vary from basic ([FMIM]C1 or [BP]C1 in excess) to acidic (AICI3 in excess) and this fact can be used to affect the reactivity and selectivity of the reaction. The reaction of cyclopentadiene with methyl acrylate is an example (Scheme 6.31). 

Lewis acids such as zinc chloride, boron trifluoride, tin tetrachloride, aluminum chloride, methylaluminum dichloride, and diethylaluminum chloride catalyze Diels-Alder reactions.22 The catalytic effect is the result of coordination of the Lewis acid with the dienophile. The complexed dienophile is more electrophilic and more reactive toward electron-rich dienes. The mechanism of the addition is believed to be concerted and enhanced regio- and stereoselectivity is often observed.23... 

Inukai and Kojima (9) have studied the aluminum chloride catalyzed diene condensation of butadiene and methyl acrylate in benzene solution. The stoichiometry for this Diels-Alder reaction is... 

Chiral a,/ -unsaturated A-acyloxazolidinones have been regarded as a complement for type I dienophile reagents. Evans et al.4 reported a Diels-Alder reaction promoted by dialkyl aluminum chloride. In this reaction, chiral a,/ -unsaturated A-acyloxazolidinones were used as highly reactive and diaster-eoselective dienophiles. The stereogenic outcome of the Diels-Alder adducts... 

The first report of an asymmetric Diels-Alder reaction with chiral Lewis acids (252) was made by Russian chemists in 1976 (253). Koga was probably the first to report a meaningful enantioselective Diels-Alder reaction (Scheme 105) in which the cyclopentadiene-methacro-lein exo adduct was obtained in 72% ee with the aid of 15 mol % of a menthol-modified aluminum chloride (254). The ee is highly dependent on the structures of the substrates, and asymmetric induction has not been observed with methyl acrylate as dienophile. Disproportionation... 

In the presence of aluminum chloride, which presumably lowers the energy of the LUMO of the heterodiene by Lewis acid complexation, electron-rich alkenes give dihydropyrans on reaction with acyl cyanides at room temperature (82AG(E)859). Unsaturated esters further extend the range of diene components of value in these Diels-Alder reactions with inverse electron demand (82TL603). 

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... 

Within the last few years, it has conclusively been demonstrated that the Diels-Alder reaction is susceptible to catalysis with Lewis acids or Friedel-Crafts catalysts such as aluminum chloride (15, 18, 36, 37, 38, 39, 40, 57, 67, 68, 69, 70, 71, 82, 86). As a result of catalysis, it was possible to change the following ... 

Diek-AUer reactions (10, 432-433). The para regioselectivity of Diels-Alder reactions of 1 is improved dramatically by catalytic amounts of aluminum chloride. Examples ... 

Diphenyl-BINOL-derived chiral aluminum reagents are prepared in situ by addition of Ethylaluminum Dichloride or Diethylaluminum Chloride to 3,3 -diphenyl-BINOL. These chiral aluminum reagents promote the enantioselective Diels-Alder reaction of cyclopentadiene with the oxazolidone dienophile (eq 14). Endo products are obtained with a high level of asymmetric induction (>90% ee) however, a stoichiometric amount of the Lewis acid is required. The preparation and use of a C3 symmetric BINOL-derived boronate has been reported (eq 15). BINOL-B(OAr)3 complexes have recently been developed for the asymmetric Diels-Alder reaction with imines (eq 16). ... 

Cycloadditions. The asymmetric Diels-Alder reaction of phenylmenthyl acrylate with 5-benzyloxymethyl-cyclopentadiene in the presence of Aluminum Chloride produces an 89% yield of the endo cycloadduct (eq 1), accompanied by 7% of the exo adduct. This provides a useful intermediate for the preparation of various prostaglandins. The Tin(IV) Chloride and Titanium(IV) Chloride catalyzed reactions with Cyclopenta-diene deliver a mixture of endo and exo adducts in 89% de, and 90% de, respectively (eq 2). The TiCU reaction gives an 89 11 endo. exo ratio, while the SnCU reaction gives an 84 16 endoiexo ratio. From a practical point of view, the titanium and tin catalysts are the best of the various Lewis acids surveyed. The use of TiCl4 is also the most effective for the reaction of the acrylate... 

Aben and Scheeren discovered that bornyloxyaluminum dichloride, which can be easily prepared from bomeol, aluminum chloride, and lithium alanate, acts as an effective catalyst for the hetero Diels-Alder reaction of siloxy dienes and a variety of aldehydes, as illustrated in Sch. 18 [37]. 

The earliest report of a reaction mediated by a chiral three coordinate aluminum species describes an asymmetric Meerwein-Poimdorf-Verley reduction of ketones with chiral aluminum alkoxides which resulted in low induction in the alcohol products [1]. Subsequent developments in the area were sparse until over a decade later when chiral aluminum Lewis acids began to be explored in polymerization reactions, with the first report describing the polymerization of benzofuran with catalysts prepared from and ethylaluminum dichloride and a variety of chiral compounds including /5-phenylalanine [2]. Curiously, these reports did not precipitate further studies at the time because the next development in the field did not occur until nearly two decades later when Hashimoto, Komeshima and Koga reported that a catalyst derived from ethylaluminum dichloride and menthol catalyzed the asymmetric Diels-Alder reaction shown in Sch. 1 [3,4]. This is especially curious because the discovery that a Diels-Alder reaction could be accelerated by aluminum chloride was known at the time the polymerization work appeared [5], Perhaps it was because of this long delay, that the report of this asymmetric catalytic Diels-Alder reaction was to become the inspiration for the dramatic increase in activity in this field that we have witnessed in the twenty years since its appearance. It is the intent of this review to present the development of the field of asymmetric catalytic synthesis with chiral aluminum Lewis acids that includes those reports that have appeared in the literature up to the end of 1998. This review will not cover polymerization reactions or supported reactions. The latter will appear in a separate chapter in this handbook. 

Diels-AUer catalyst. Certain Diels-Alder reactions are markedly accelerated by aluminum chloride "- and by other Friedel-Crafts type catalysts " (SnC U. BFj. FeCIa, TiCU). Thus the reaction of equimolecular amounts of anthracene, dimethyl fumarute, and aluminum chloride in methylene chloride is complete at room temperature in less than 2 hrs. In refluxing dioxane in the absence of catalyst the reaction requires 2- days. Without catalyst, the reaction of butadiene with methyl vinyl... 

In a paper concerning the aluminum chloride-catalyzed Diels-Alder reaction between 4-methyl-1,3-pentadiene (piperylene) and the nitrile 930, rose oxide is mentioned, but the authors do not describe the synthesis. 

In 1960, Yates and Eaton reported that an approximate rate acceleration of 10 was observed for the Diels-Alder reaction of anthracene and maleic anhydride in the presence of aluminum chloride (Scheme 1) [8]. This finding had important practical ramifications since it demonstrated that the Diels-Alder reaction could be conducted under mild conditions when an electropositive metal was used to lower the energy of activation. 

Diels-Alder catalyst [1, 31-32, after line 8], Ciganek (Du Pont) found thal aluminum chloride strongly accelerates the Diels-Alder reaction of benzene with dicyanoacetylene.338 In the presence of this Lewis acid the reaction proceeded at room temperature to furnish the adduct (1) in 63% yield and smaller amounts of the Friedel-Crafts products phenylmaleonitrile (2) and phenylfumaronitrile (3). In the absence of aluminum chloride the adduct (1) was produced in yield of only 14% after a reaction period of 2 days at 180°. 

Diels-Alder catalyst, 1, 31-32 2, 21-22. The Diels-Alder reaction of 1-carbo-methoxypyrrole (1) with dimethyl acetylenedicarboxylate catalyzed by aluminum chloride gives 2,3,7-tricaibomethoxy-7-azanorbomadiene (2) in 90% yield. The uncatalyzed reaction gives yields of 35-40%. The improved yield is attributed to the milder reaction conditions and the fact that formation of a complex of (2) with AICI , renders the reaction irreversible. The reaction is the first step in an im-... 

C16H260, Mr 234.38, bp031 kpa 134-135 °C, reg° 1.498-1.500, is a synthetic amber fragrance. It is prepared by a Diels-Alder reaction of myrcene and 3-methyl-3-pen-ten-2-one in the presence of aluminum chloride and cyclization of the substituted... 

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