Nobuyoshi Nomura

Random Copolymerization of ε-Caprolactone with Lactide Using a Homosalen−Al Complex

The bulky substituents of homosalen complexes decelerate the ring-opening polymerization of racemic lactide (LA). The substituent effects provide the first catalysis for the random copolymerization of epsilon-caprolactone (CL) with LA (CL/LA = 1:1). The copolymerization of CL with LA (CL/LA = 1:1) by the iPr(3)Si-substituted homosalen-Al complex 2 affords the practically random copolymer in a controlled manner. The reactivity ratios, average sequence lengths of CL and LA during the copolymerization, abundance ratios of the triad caproyl sequences, and T(g) value of the obtained copolymer indicate that the copolymer was random with a somewhat alternative tendency (r(CL)r(LA) = 0.80).

Transition metal-catalyzed substitution reaction of allylic phosphates with Grignard reagents

Abstract SN2-selective Grignard coupling with primary allylic diphenylphosphates was successfully achieved using Ni or Fe catalyst. In sharp contrast, a catalytic amount of CuCN·2LiCl promoted a SN2′-selective coupling reaction. In the presence of the copper catalyst, stereochemically homogeneous γ- disubstituted allyl Grignard reagents reacted at the less substituted allylic terminus (α-position) with an allylic diphenylphosphate selectively without losing the double bond geometry.

Hydrovinylation and Related Reactions: New Protocols and Control Elements in Search of Greater Synthetic Efficiency and Selectivity

New reaction conditions and stereochemical control elements for heterodimerization between ethylene (or propylene) and functionalized vinyl arenes are highlighted (see equation). For example, an enantioselective version of the hydrovinylation reaction uses [{(allyl)NiBr}2], a noncoordinating counter anion, (bis-CF3−C6H3)4B−, and a hemilabile ligand such as MOP. Other applications include intramolecular cyclization of 1,6-dienes and heterodimerization of norbornene and ethylene.

Nickel-catalyzed asymmetric allylation of alkyl Grignard reagents. Effect of ligands, leaving groups and a kinetic resolution with a hard nucleophile

Abstract Enantioselective addition of Grignard reagents to methyl 1,3-diphenylallyl ether in the presence of Ni(0)-phosphine catalysts is reported. Kinetic resolution (79 %ee) observed in the addition of MeMgBr has important implications for the mechanism and further development of this reaction as a valuable synthetic reaction.

Ligand Tuning as a Tool for the Discovery of New Catalytic Asymmetric Processes

In this era of heightened environmental awareness and ever-increasing demand for higher efficiency from chemical processes, one of the major challenges facing organic synthesis is the utilization of abundantly available carbon sources as precursors for more advanced intermediates. The dual problems of activation of thermodynamically stable precursors and their stereoselective incorporation pose new challenges, solutions of which may have broader implications in asymmetric catalysis. This review summarizes our recent efforts to discover broadly applicable control elements in key enantioselective carbon-carbon and carbon-hydrogen bondforming reactions. Transition metal complexes of 1,2-diol phosphinites derived from readily available monosaccharides catalyze a variety of asymmetric reactions of prochiral olefins including Markovnikov addition of HCN to vinyl arenes and hydrogenation of dehydroamino acids. Enantioselectivities of these reactions can be optimized through steric and electronic tuning of the bis-phosphinite ligand system. Both R and S enantiomers of the precursors of protoptypical 2-arylpropionic acids and of various α-amino acids can be prepared by these routes. We have also discovered new protocols for a nearly quantitative and highly selective codimerization of ethylene or propylene, and various functionalized vinylarenes and strained olefins. Various strategies for stereochemical control in an enantioselective version of this reaction will be discussed. These include design and synthesis of new ligands and applications of the ‘hemi-labile ligand concept’. During these investigations important synergistic relationships between such ligands and coordinating properties of various counter ions were also uncovered. These discoveries may contribute to the discovery of more selective homogeneous catalysts. Dedicated to Professor Henri B. Kagan in recognition of his seminal contributions to catalytic asymmetric synthesis *Address correspondence to this author at the Department of Chemistry, The Ohio State University, 100 W. 18 Avenue, Columbus, Ohio 43210, USA; Tel: 614-688-3543; Fax: 614-292-1685; E mail:rajanbabu.1@osu.edu *Current Address: 1. The DuPont Company; 2. Aventis Pharmaceuticals; 3. Nagoya University; Japan; 4. Smith-Kline-Beckmann Pharmaceuticals; 5. Pharmacopeia

An Efficient Protocol of Iridium-Catalyzed Allylic Substitution Reaction and Its Application to Polymer Synthesis : Complementary Regio-and Stereoselective Allylation Polycondensation via Ir and Pd Catalyses

An efficient protocol of the Ir-catalyzed allylic substitution reaction is reported using N,O-bis(trimethylsilyl)acetamide as a base in the presence of nBu4NF as a cocatalyst. The reaction completely proceeded under very mild conditions, and a branched allylated compound that is not easy to access via the Tsuji-Trost reaction can be synthesized. The reaction system is practical enough to be applicable for polymer syntheses. The Ir- and Pd-catalyzed allylation polycondensations generally show complementary regio- and stereoselectivities. The Ir-catalyzed reaction is versatile, and a mixed dual regioselectivity such as a branched-linear selectivity on each electrophile can also be achieved.

Palladium-catalyzed allylic substitution reaction: oxidative addition versus dissociation in an olefin–palladium(0) complex

Abstract The reaction behavior of a transient olefin–palladium(0) complex after the first allylation was studied. Highly efficient palladium-catalyzed cascade double alkylation of a diallylic substrate is achieved by tuning the ligands. As a result, bidentate ligands which could form cyclic catalysts with a four-methylene bridge between two phosphorus atoms were effective for high selectivity and catalytic activity.

Nickel-catalyzed regioselective allylation of allylic alcohols

Abstract Regioselective allylmetallation of allylic alcohol has been accomplished by treatment with allylzinc in the presence of a nickel catalyst. Benzylic protective group of allyl alcohol facilitates the allylmetallation.