Enantioselective lanthanide-catalyzed Mukaiyama aldol, carbonyl-ene, Sakurai-Hosomi, and quinone Diels-Alder reactions

I. Asymmetric catalysis with chiral Sc complexes. Asymmetric transformations catalyzed by chiral scandium complexes have gained significant prominence in the last decade. This review encompasses enantioselective Sc(III)-catalyzed processes of general synthetic utility.;II. Sc-catalyzed Mukaiyama aldol reactions. Cationic scandium-based Lewis acid complexes have been found to catalyze the Mukaiyama aldol reaction between aryl enolsilanes and ethyl glyoxylate with high enantiomeric excesses (eq 1). The aldol adducts were converted to cis and trans beta,beta-dialkyl-gamma-substituted pantolactone derivatives using either a hydroxyl-directed syn or anti reduction, followed by acid-catalyzed lactonization (eq 2). Unsubstituted pantolactone derivatives were prepared by the hydrogenation of the corresponding thioester aldol adducts followed by cyclization. The required aldol products were also prepared using cationic scandium-based Lewis acid complexes.*;III. Sc-catalyzed carbonyl-ene reactions. An enantio- and diastereoselective carbonyl-ene reaction catalyzed by chiral scandium pyridyl-bis(oxazolinyl) (pybox) complexes has been developed (eq 3). 1,1-Disubstituted and trisubstituted olefins were efficient coupling partners with N-phenyl glyoxamide. The use of trisubstituted olefins generated the syn product while maintaining high levels of enantio- and diastereoselectivity. The scope of the copper bis(oxazolinyl) (box) mediated carbonyl-ene reaction has also been extended to include trisubstituted olefins. All products were highly crystalline solids.*;IV. Sc-catalyzed Sakurai-Hosomi reactions. An enantio- and diastereoselective Sakurai-Hosomi reaction catalyzed by chiral scandium pyridyl-bis(oxazoline) (pybox) complexes has been developed (eq 4). Both alkyl- and aryl-substituted allylic silanes were effective coupling partners with N-phenyl glyoxamide. Products were highly crystalline solids. In addition, an efficient one-step route for the preparation of (E)-cinnamyltrimethylsilane derivatives via an olefin-cross metathesis reaction is described.*;V. Sm- and Gd-catalyzed quinone Diels-Alder reactions. An enantioselective quinone Diels-Alder reaction catalyzed by chiral samarium and gadolinium pyridyl-bis(oxazolinyl) (pybox) complexes has been developed (eq 5). The permutations of reactions involving three quinones and five dienes were carried out with excellent enantio- and regioselectivities. These catalyst systems are able to distinguish very small steric differences between substituents found on the diene. In all cases, only the endo product is observed.*;*Please refer to dissertation for diagrams.