The synthesis of a series of enantiomerically pure, C,-symmetric 4,4,5,5'-tetrahydro-2,2'-methylenebis[oxazoles] and 4,4',5,5'-tetrahydro-2,2'-bi(oxazoles) is reported. Copper complexes with anionic tetrahydromethylenebis[oxazole] ligands are efficient catalysts for the enantioselective cyclopropane formation from olefins and diazo compounds (up to 96% ee in the reaction of styrene with menthyl diazoacetate). Tetrahydrobi(oxazole)iridium(I) complexes were found to catalyze transfer hydrogenations of aryl alkyl ketones with i-PrOH (up to 91 % ee). Tetrahydrobi(oxazo1e)palladium complexes can be used as enantioselective catalysts for allylic nucleophilic substitution (up to 77% ee in the reaction of PhCH=CHCH(OAc)Ph with NaHC(COOMe),).Introduction. -In our previous papers in this series [l-31, we have reported on the synthesis and application of chiral semicorrins 1, a class of bidentate ligands specifically designed for enantioselective control of metal-catalyzed reactions. Essential structural features of the semicomns 1 are the conformationally rigid ligand framework and the C,-symmetric arrangement of the stereogenic centers in close proximity to the coordination site. In a metal complex, the substituents at the stereogenic centers effectively shield the metal ion from two opposite directions and, therefore, should have a distinct effect on the stereochemical course of a reaction taking place in the coordination sphere. So far, we have found two promising areas of application for semicorrin ligands: [Cu(semicorrinato)]-catalyzed cyclopropane formation from olefins and diazo compounds (up to 97% ee [ 1][3]) and [Co(semicorrinato)]-catalyzed conjugate reduction of a$-unsaturated carboxylic esters and amides (up to 99% ee [21[31).Symmetric 4,4',5,5'-tetrahydro-2,2'-methylenebis[oxazoles] 2 are structurally closely related to the semicorrins 1. Removal of a proton at the methylene bridge leads to anionic ligands which provide essentially the same steric environment for a coordinated metal ion as the corresponding semicorrinates (cf. 3). Chiral tetrahydrobis[oxazoles] of this type can be easily synthesized from amino alcohols and malonic acid. Starting from other dicarboxylic
SUMMARYA series of p-carboxyalkylphenylglyoxal and p-carboxyalkyl-1,2-diketo-bis-(N'-methylthiosemicarbazone) bifunctional ligands (TSC) have been prepared and evaluated for use in binding radioisotopes of copper to antibodies. We have developed an improved synthesis of the requisite a-ketoaldehyde and 1,2-diketone substrates used for derivatization to the bis-TSC bifunctional chelates. This approach utilizes a modified Kornblum method and provides a simple alternative to the usual method for fabrication of the 1,2-bis-TSC ligands, which avoids the use of highly toxic selenium dioxide for oxidation of substituted acetophenones to 1,2 dicarbonyl compounds. The overall yields of the bis-TSC chelates using this procedure were 840%. The effects of the alkyl chain length and substitution on the C-2 position on p-carboxyalkylphenyl-1,2-diketo bis-TSC bifunctional chelate for attaching radioisotopes of copper to proteins were studied. Following complexing copper-64 or copper-67 to the bis-TSC chelate, the acid moiety of the TSC chelate was activated as the tetrafluorophenyl ester.The copper-labeled activated TSC chelate was attached to bovine serum albumin under mild conditions in 3% to 40% yield.These studies have demonstrated that the shorter chain analogues of the TSC chelates from the 1,2-diketones give the highest radiolabeling yields.
Photolysis of cyclobutanones in the presence of acetic acid produced 2-acetoxy-5-alkoxytetrahydrofurans regiospecifically and with retention of configuration at the migrating α-position. The acetoxy
group was replaced by nucleophiles such as allylsilane, trimethylsilyl azide, diethylaluminum
cyanide, and silylated thymine in the presence of Lewis acids.
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