Lewis ethylaluminum dichloride

As Lewis acid, titanium tetrachloride, boron trifluoride or ethylaluminum dichloride is often used. The stereochemical outcome of the reaction strongly depends on the Lewis acid used. The Sakurai reaction is a relatively new carbon-carbon forming reaction, that has been developed into a useful tool for organic synthesis. ... 

The Lewis acid of choice for most of the cyclization reactions is ethylaluminum dichloride, because of its exceptional properties it is a mild Lewis acid, and, as an organometallic compound, can serve as a proton sponge , and thereby inhibit competitive protodesilyla-tion37. The desired precursors reacted smoothly with 1.1 equivalents of ethylaluminum dichloride in toluene or dichloromethane at low temperature to generate diastereoselectively the desired spiro[4.5]decanones38. 

Ring closure of functionalized dienones occurs again in 1,4-fashion to give an annulated six-membered ring. Both Lewis acid (ethylaluminum dichloride) and fluoride ion can be employed, but the chemical yield of this particular cyclization is low and no stereoselection regarding the position of the vinyl side chain was achieved35. 

Dienones, such as 4-[4-(trimethylsilyl)-2-butenyl]-3-vinyl-2-cyclohexenone, are useful precursors for these particular transformations the allylsilane side chain is too short for effective 1,4-addition, but just right for 1,6-addition, resulting in six-ring annulation. Three different Lewis acids can be used titanium(IV) chloride, boron trifluoride diethyl ether complex, and ethylaluminum dichloride. The best chemical yields and complete asymmetric inductions were obtained with ethylaluminum dichloride. 

Table 2. Stereoselective Annulation with 1,3-Asymmetric Induction Using Ethylaluminum Dichloride as Lewis Acid...

Tricyclic compounds can be obtained directly by annulation on to cyclic allylsilanes, using either ethylaluminum dichloride or titanium(IV) chloride as Lewis acids57. The stereochemical outcome of this particular cyclization is controlled by the relative configuration of the cyclic allylsilane. The reaction follows the usual anti" SE2 process for reactions of allylsilanes with electrophiles. Thus, the reaction was stereospecific, which makes it very useful for stereocon-trolled syntheses of complex ring systems57. 

In the course of dolastane synthesis (the dolastanes are a group of marine diterpenes) interesting rearrangements catalyzed by Lewis acids were found. Treatment of the trienone 293 with excess (1.5 eq) ethylaluminum dichloride at low temperatures (—5°C, 48 h) gave the tetracyclic enone 295 in 53% yield while the tricyclic dienone 296 (50%) was formed at room temperature (equation 102)156. It was assumed that both products can be derived from the common zwitterion 294 which undergoes intramolecular alkylation at low temperatures (path a) whereas an alkyl shift takes place at elevated temperatures (path b), followed by a 1,2-hydride shift (equation 102). 

Catalyst systems with improved heat transfer capability for the production of PIB polymers in continuous slurry polymerization processes have been described. The catalyst consists of a Lewis acid, including Friedel-Crafts catalysts such as AICI3, and a tertiary halide containing compound, e.g., 2-chloro-2,4,4-trimethylpentane or ethylaluminum dichloride (12,13). 

Majetich reports a general intramolecular Lewis acid allylation protocol for the synthesis of bicy-clo[5.4.0]undecen-3-ones (168) and bicyclo[4.4.0]decen-3-ones (170), which are 1,6-addition products (Scheme 27). The same precursors, (167) and (169), when submitted to the fluoride ion cyclization protocol, also afford 1,2- and 1,4-addition products.73 Typically, ethylaluminum dichloride, a proton sponge Lewis acid, is used in order to minimize adventitious protonic desilylation. Other 0,y-unsatu-rated silanes also undergo similar intramolecular Lewis acid catalyzed additions for example, the si-lylpropargylic enones (171) undergo intramolecular cyclization to the allenylspiro system (172).74... 

Allylic suffoxides. Alkenes can be converted directly into allylic sulfoxides by an ene reaction withp-toluenesulfinyl chloride catalyzed by ethylaluminum dichloride in ether at 25°. In this reaction C2H5A1C12 serves as a Lewis acid and as a proton scavenger by reaction with the HC1 liberated to form A1C13 and ethane.4... 

Aluminumtriethyl Diethylaluminum chloride Ethylaluminum dichloride Lewis base + Cyclic di- and triolefins Aliphatic ethers Carboxylic acid esters... 

Using 2-chloro-2,4,4,-trimethylpentane as the initiator and ethylaluminum dichloride as the Lewis acid, McDonald [5] and Shaffer [6] prepared high molecular weight polyisobutylene with perfluorinated alkanes as polymerization solvents. 

Intramolecular cyclization of allylsilanes." An intramolecular version of the Sak-urai reaction (7, 371 11, 529-530) provides a route to functionalized spiro(4,5]decanones. For cyclization of 1 to 2, ethylaluminum dichloride is the preferred Lewis acid activator. The diastereoselectivity depends on the temperature and the solvent. 

Dodecatrienals undergo intramolecular Diels-Alder cyclization in the presence of ethylaluminum dichloride or the milder Lewis acid diethylaluminum chloride at — 78 to -23°. -Example ... 

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). ... 

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. 

This general procedure has also been extended to allow for the insertion of a methoxy-containing carbon. The uncatalyzed addition of the lithium anion of methoxymethyl enyl sulfone to ketones proceeds readily at low temperature in dimethoxyethane to form the intermediate adduct. Addition of a Lewis acid (ethylaluminum dichloride or diisobutylaluminum diisopropylamide) directly to the reaction mixture effects the rearrangement reaction to produce the ring-expanded a-methoxy ketone. This sequence, illustrated by the example in Scheme 28, is limited to the expansion of four- and five-membered ring ketones. ... 

Figure 8.6 illustrates, for example, the complicated equilibria [19] in initiation by alkyl halides which are widely used as initiators in combination with coinitiator such as aluminum alkyl halides or aluminum halide Lewis acids. Each carbocation can initiate polymerization or remove an alkyl (ethyl) group from the counterion to produce a saturated hydrocarbon, REt, and a more acidic Lewis acid. The propagating cation can also terminate by the same process to produce ethyl-capped polymers and new Lewis acids. Thus, even though the coinitiator used is diethylaluminum chloride there may be major contributions to the polymerization from ethylaluminum dichloride or aluminum chloride. 

Similarly, asymmetric metal-catalyzed hydrovinylation of various other olefins has been investigated, usually catalyzed by nickel systems prepared from Ni(IJ) salts or / -allylnickel halides, activated by Lewis acids such as ethylaluminum dichloride or diethylaluminum chloride, and modified by chiral phosphanes. Surveys of these results are found in more general reviews11-12 and reviews dealing preferentially with this subject -5-7-13 - A... 

Acryloyl- and 3-crotonoyl-4,4-dimethyl-l,3-oxazolidin-2-ones can form a rigid complex with the Lewis acid. They react with cyclopentadiene in the presence of chiral Lewis acids, prepared in situ from ethylaluminum dichloride and chiral diols with moderate enantioselectiv-ity (36% cc)9. 

Three arm amphiphilic star-block copolymers of isobutyl vinyl ether (IBVE) and 2-hydroxyethyl vinyl ethers were also prepared by Higashimura et al. [23]. The synthetic strategy involved the sequential living cationic polymerization of IBVE and 2-acetoxyethyl vinyl ether, initiated by the trifunctional initiator system composed of tris(trifluoroacetate) and ethylaluminum dichloride, with excess of 1,4-dioxane as a carbocation-stabilizing Lewis base (Scheme 8). 

Several fluorinated monomers have been polymerized via homogeneous cationic polymerization in compressed carbon dioxide. For example, vinyl ethers with fluorinated side chains were polymerized in SCCO2 at 40 °C using adventitious water initiation with ethylaluminum dichloride as the Lewis acid coin-... 

Piersanti and coworkers explored the effectiveness of a range of Lewis acids in promoting alkylation of indole by methyl a-acetamidoacrylate. This led not only to successful p-addition but also to a-addition (amidoalkylation, see Sect. 7). Ethylaluminum dichloride (two equiv.) and ZrCLt were the most effective in giving the p-adduct, while several soft Lewis acids, of which Bi(OTf)3 was most practical, gave the a-adducts. 1-Methylindole and several C-5 analogs showed the same selectivity [292]. 

The ene reaction of olefins was employed to hydroxymethylate jojoba wax using Lewis acids as catalyst (15). Ethylaluminum dichloride and formaldehyde gave both... 

Electrophilic (Methylthio)methylation. Lewis acids such as aluminum chloride or ethylaluminum dichloride assist the het-erolytic cleavage of the C-SO2 bond of the dithioacetal 5,5-dioxide to produce a MeS-stabilized carbocation, which reacts with allylsilanes and benzene rings (eq 12). 

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