Me2AlCl, intramolecular

Another photochemically induced domino process consisting of three steps was employed for the formation of 1,2-disubstituted cyclopentanes 5-39, as described by Tietze and coworkers. Irradiation of a mixture of 5-36, dimethyl malonate and catalytic amounts of the Lewis acid Me2AlCl in a Pyrex flask caused a Norish Type I cleavage of 5-36, followed by an intramolecular hydrogen shift to give the acyclic... 

TABLE 5-7. Me2AlCl-Promoted Intramolecular Diels-Alder Reactions of Trienimides 138 and 141... 

The non-selective thermal Diels-Alder reaction of hexa-2,4-dienol with methyl acrylate is made enantioselective by using the Lewis acid template (86) to assemble the reagents for cycloaddition.91 The Me2AlCl-catalysed intramolecular Diels-Alder... 

The prochiral triene 16 (Figure 5) is a suitable precursor for the bicyclic core structure 17, and can be obtained in ten steps starting from dimethyl malonate. The intramolecular Diels-Alder cyclization to 17 proceeds with Me2AlCl catalysis in very good yield under mild conditions [12, 18],... 

The product distribution in these intramolecular reactions using LPDE-CSA seems to depend not only on the substitution pattern of both the dienoic and dienophilic moieties in the starting materials but also on the relative capability of cyclization (Sch. 27). For example, the formation of 58 undoubtedly arises via competitive protonation of the terminal diene and subsequent loss of a proton leading to the migrated diene 57 which undergoes very facile cyclization compared with 56 (Sch. 28) [75]. Taking into consideration the use of Me2AlCl, which necessitates slow addition of the substrate, the LPDE-CSA medium seems more convenient. 

They also reported the intramolecular version of this asymmetric Diels-Alder reaction [53]. ( , )-Trienecarboximides of type 45 derived from chiral oxazolidones undergo Me2AlCl-catalyzed intramolecular Diels-Alder reactions affording bicyclic compounds 46 with high endo and diastereoselectivity (endolexo = -100 1). The stereochemistry is controlled by the stereogenic center at C4 of the chiral auxiliary (Xc) (Sch. 29). 

Alkylaluminum halide catalyzed intramolecular ene reactions of p-ketoesters proceed in high yield to give cyclohexanols via either a type I or type II process (See Figure 14). 22 Treatment of 58a with 1.0-1.2 equivalents of Me2AlCl in nitromethane for 60 h at 25 C gives a 67% yield of the cw-fused ene adduct 59a by a type II intramolecular ene reaction. Similar cyclization of 58b gives a 90% yield of 59b. Treatment of 60 with the milder Lewis acid MesAl in nitromethane... 

The first total asymmetric synthesis of solanoeclepin A has been presented in 2011 by Tanino et al. [200]. It also features a Me2AlCl-catalyzed intramolecular Diels-Alder reaction as outlined in Scheme 26. Solanoeclepin A stimulates the hatching of potato cyst nematode, a parasite with destructive effect on several crops. One possible fight against this pest would be to induce early hatching of... 

As with the intermolecular reactions of allenes and furans (cf. Scheme 13.11), intramolecular reactions of allenic dien-ophUes provide access to important chiral architectures upon cycloaddition. For example, exposing 121 to catalytic amounts of Me2AlCl at —20°C produced 122 as a single... 

Tanino et al. s route to solanoeclepin A (448) involved an intramolecular [4-1-2] cycloaddition to fashion both the seven-membered ring and the oxabicycle moiety (Scheme 13.92) [151]. In the sequence, exposing methoxyfuran 446 to Me2AlCl followed by hydrolysis of the resulting enol ether produced 447 in 62% yield. Adjustment of oxidation states and protecting groups furnished 448. 

Although a-siloxyacroleins 84, 87a, and 87b had been separately prepared via a retro-hetero-Diels-Alder reaction of dioxin derivatives such as 83, Aungst and Funk also showed that tandem Me2AlCl-mediated decomposition of the dioxin derivative 97 to the a-siloxyenal intermediate 98 and intramolecular cycloaddition could occur in one pot to give good yields of fused bicyclic adducts (Scheme 18.21) [23]. 

Catalysis of Diels-Alder Reactions. Me2AlCl has been used as a Lewis acid caUilyst for inter- and intramolecular Diels-Alder reactions with a wide variety of dienophiles. High diastereoselectivity is obtained from chiral a,p-unsaturated N-ticyloxazolidinones with more than 1 equiv of Me2AlCl. Use of MezAlCl as a catalyst affords high yields in inter- and intramolecular Diels-Alder reactions of a,p-unsaturated ketones (eq 1), and intramolecular Diels-Alder reactions of a, 3-unsaturated aldehydes. Me2AlCl-catalyzed Diels-Alder reac-... 

Type-II intramolecular ene reactions of aldehydes and ketones proceed readily with Me2AICl as the Lewis acid. " Unsaturated aldehydes and ketones can be generated in situ by Mc2 AlCl-catalyzed reaction of Acrolein and Methyl Vinyl Ketone with alkylidenecycloalkanes at low temperatures (eq 12). The mono-cyclic aldehyde reacts further under these conditions. The mono-cyclic ketone can be isolated at low temperature but undergoes a second ene reaction at rt to give the bicyclic alcohol. p-Keto esters form tertiary alcohols in intramolecular ene reactions. The products are stable because they are converted to the aluminum alkoxide (eq 13). Intramolecular Me2AlCl-catalyzed ene reactions have been used for the preparation of the bicyclic mevinolin ring system (eq 14). ... 

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