Me2AlCl, catalysis

Both Ugi and Passerini reactions have been explored, using 3-substituted propy-noic acids as dienophiles. The multicomponent adducts 93 have been submitted to IMDA under different conditions, depending upon the heteroatom X in the tether Ugi adducts could be converted smoothly, usually under thermal conditions, to give 94 as the major stereoisomer (less than 10% of any other stereoisomer detected). On the contrary, Passerini adducts proved to be unreactive under thermal conditions, but reacted cleanly under Me2AlCl catalysis to give bicyclic lactones in a highly stereoselective way (Scheme 1.33) [83],... 

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],... 

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-... 

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