Gregory H. P. Roos

Bio: Gregory H. P. Roos is an academic researcher from University of Natal. The author has contributed to research in topics: Methyl acrylate & Reaction rate. The author has an hindex of 12, co-authored 21 publications receiving 972 citations. Previous affiliations of Gregory H. P. Roos include University of KwaZulu-Natal.

Synthesis and Structures of (2,2-cis)-Dirhodium(II) Tetrakis[methyl l-acyl-2-oxoimidazolidine-4(S)-carboxylates]. Chiral Catalysts for Highly Stereoselective Metal Carbene Transformations

Abstract: Dirhodium(II) tetracarboxamidates derived from chiral methyl 1-acyl-2-oxoimidazolidine-4(S)-carboxylates are highly enantioselective and diastereoselective catalysts for metal carbene transformations of diazoacetates. Four of these catalysts have been prepared by ligand substitution with dirhodium(II) acetate and characterized spectroscopically and by X-ray structural analysis. The simplest member of the series, (2,2-cis)-dirhodium(II) tetrakis[methyl 1-acetyl-2-oxoimidazolidine-4(S)-carboxylate], (2,2-cis)-Rh2(4S-MACIM)4, forms monoclinic crystals in space group P21 with cell constants of a = 9.959(1) A, b = 20.100(1) A, c = 11.678(1) A, β = 107.61(1)°, V = 2228.1(3) A3, and Z = 2. (2,2-cis)-Rh2(4S-MBOIM)4, whose 1-acyl group is phenyl, forms tetragonal crystals in space group P41212 with cell constants of a = 18.352(1) A, c = 17.067(1) A, V = 5748.1(6) A3, and Z = 4. The most enantioselective catalyst in many metal carbene transformations is the one with 3-phenylpropanoyl at the 1-position, (2,2-cis)-Rh...

Stereoselective Cyclopropanation Reactions

Abstract: Organic chemists have always been fascinated by the cyclopropane subunit.1 The smallest cycloalkane is found as a basic structural element in a wide range of naturally occurring compounds.2 Moreover, many cyclopropane-containing unnatural products have been prepared to test the bonding features of this class of highly strained cycloalkanes3 and to study enzyme mechanism or inhibition.4 Cyclopropanes have also been used as versatile synthetic intermediates in the synthesis of more functionalized cycloalkanes5,6 and acyclic compounds.7 In recent years, most of the synthetic efforts have focused on the enantioselective synthesis of cyclopropanes.8 This has remained a challenge ever since it was found that the members of the pyrethroid class of compounds were effective insecticides.9 New and more efficient methods for the preparation of these entities in enantiomerically pure form are still evolving, and this review will focus mainly on the new methods that have appeared in the literature since 1989. It will elaborate on only three types of stereoselective cyclopropanation reactions from olefins: the halomethylmetal-mediated cyclopropanation reactions (eq 1), the transition metal-catalyzed decomposition of diazo compounds (eq 2), and the nucleophilic addition-ring closure sequence (eqs 3 and 4). These three processes will be examined in the context of diastereoand enantiocontrol. In the last section of the review, other methods commonly used to make chiral, nonracemic cyclopropanes will be briefly outlined.