Nobuyuki Komine

Enantioselective [2,3]-Wittig rearrangement induced by asymmetric lithiation with a t-butyllithium/chiral bis(oxazoline) system

Abstract The [2,3]-Wittig rearrangement of (E)-crotyl propargylic ethers, when induced with a t-BuLi/chiral bis(oxazoline) complex, is shown to provide high enantioselectivity (up to 89% ee) along with high diastereoselectivity.

Enantioselective carboxylation of α-methoxybenzyllithium generated via asymmetric lithiation with a t-BuLi/chiral bis(oxazoline) complex

Abstract Treatment of benzyl methyl ether with a t -BuLi/chiral bis(oxazoline) complex followed by carboxylation is shown to afford α-methoxy phenylacetic acid in high % ee (up to 95%). The asymmetric induction was proved to occur at the post-lithiation step.

Cyclization of enantio-enriched α-(homoallyloxy)alkyllithiums: Evidence for retention of configuration at the carbanion center

Abstract The titled cyclization induced by SnLi transmetallation of the enantio-defined stannanes is shown to proceed with complete retention of configuration at the Li-bearing sp 3 -carbon to afford the enantio-enriched α,β-disubstituted tetrahydrofurans.

Probing the Steric and Electronic Characteristics of a New Bis-Pyrrolide Pincer Ligand

A new pincer ligand is synthesized to be dianionic, with the potential to be redox active. It has pyrrrole rings attached to both ortho sites of a pyridine, as the linking element. This H2L can be doubly deprotonated and then used to replace two chloride ligands in MCl2(NCPh)2, to form LM(NCPh) for M = Pd, Pt. The acid form H2L reacts with ZnEt2 with elimination of only 1 mol of ethane to yield (HL)ZnEt, a three-coordinate species with one pendant pyrrole NH functionality. This molecule binds the Lewis base p-dimethylaminopyridine (DMAP) to give first a simple 1:1 adduct that eliminates ethane on heating to form four-coordinate LZn(DMAP), which has an unusual structure due to the strong preference of the pincer ligand to bind in a mer (planar) geometry. A molecule with two HL(-) ligands each bonded in a bidentate manner to FeCl2 is synthesized and shown to contain four-coordinate iron with a flattened-tetrahedral structure. The electrochemistry of LM(NCPh) and (L)Zn(DMAP) shows three oxidation processes, which is interpreted to involve at least two oxidations of the pyrrolide arms.

Enantioselective reactions of α-methoxybenzyllithium generated by t-BuLi/chiral bis(oxazoline) complex with aldehydes

Abstract The title reaction is shown to afford the corresponding 1,2-diol monomethyl ethers in moderate-to-high levels of % ee (up to 98%) and % de (up to 90% anti ), depending markedly on the aldehyde reactivity. The origin of the enantioselectivity is discussed in terms of a dynamic thermodynamic resolution mechanism.

Enantioselective carbanion cyclization of 5-alkenyl carbamates induced by asymmetric lithiation with s-butyllithium/(−)-sparteine system

Abstract Treatment of ( E )-6-phenyl-5-hexenyl carbamates with s -BuLi/(−)-sparteine is shown to afford the trans -1,2-disubstituted cyclopentane derivatives in high % ee, along with the bicyclo[3.1.0]hexanes (bicyclization products).

Catalytic synthesis of thiobutyrolactones via CO insertion into the C–S bond of thietanes in the presence of a heterodinuclear organoplatinum–cobalt complex

Heterodinuclear organoplatinum-cobalt complex having a 1,2-bis(diphenylphosphino)ethane ligand (dppe)MePt-Co(CO)4 catalyzes CO insertion into the C-S bond of thietanes in THF at 100 degrees C under 1.0 MPa of CO for 2 h to give gamma-thiobutyrolactone in quantitative yield.

Asymmetric Cross-Dimerization between Methyl Methacrylate and Substituted Alkene by Ru(0)–Bicyclononadiene Complex

New Ru(0)-naphthalene complexes containing a bicyclononadiene ligand catalyze the linear cross-dimerization between methyl methacrylate and substituted alkenes by an oxidative coupling mechanism. The chiral (S,S)-2-methylbicyclo[3.3.1]nona-2,6-diene complex (S,S)-1b catalyzes asymmetric linear cross-dimerization between methyl methacrylate and 2,5-dihydrofuran to give the cross-dimer in 74% yield in 80% ee.

Stoichiometric CH Bond Cleavage Reaction in a Bis(carboxylato)ruthenium(II) Complex and Its Application to the Catalytic H–D Exchange Reaction of Carboxylic Acids

A cationic complex [Ru{OC(O)CMeCH2‐κ2O,O′}(PMe3)4]+CH2CMeCO2− (5 a) and its related carboxylato complexes are newly prepared by the reaction of [cis‐RuH2(PMe3)4] (4) with carboxylic acids in methanol in 76–100 % yield. Complex 5 a reversibly transforms to the neutral form [cis‐Ru{OC(O)CMeCH2‐κ1O}2(PMe3)4] (2 a) in nonpolar solvents. Complex 2 a reversibly liberates a PMe3 group to give [Ru{OC(O)CMeCH2‐κ1O}{OC(O)CMeCH2‐κ2O,O′}(PMe3)3] (12 a) from which a stereoselective CH bond cleavage reaction occurs to give a ruthenalactone [Ru{OC(O)CMeCH‐κ2O,C}(PMe3)4] (1 a) from the release of methacrylic acid. Complexes 2 a and 5 a also give 1 a but the prior dissociation of a PMe3 is indispensable for the CH bond cleavage reaction. Complex 1 a establishes an equilibrium with 2 a (or 5 a) in solution. In this reaction, one coordinated carboxylato ligand is engaged in the CH bond cleavage reaction as a proton acceptor, but neither the added carboxylato anion nor typical proton acceptors such as proton sponge assist the reaction. In [D4]MeOH, a catalytic stereospecific deuteration of carboxylic acids has been achieved by 4, in which the equilibrium between 5 a and 1 a plays a key role.

Synthesis and Reactions of Water-soluble Diorganoplatinum(II) Complexes

Ligand displacement reactions of PtR 2 (cod) with water soluble tertiary phosphines such as 1,2-bis{di(hydroxymethyl)-phosphino}ethane (DHMPE) or tris(hydroxymethyl)phosphine (THMP) gave new water-soluble diorganoplatinum(II) complexes PtR 2 L 2 [L 2 = (HOCH) 2 ) 2 PCH 2 CH 2 P(CH 2 OH) 2 : R = Me (1a); Et (1b); Ph (1c), L = P(CH 2 OH) 3 : R = Me (2a); Et (2b); Ph (2c)] at room temperature. They were considerably stable in water and the thermolyses of 1b and 2b at 80 C liberate ethylene and ethane via β-hydrogen elimination and hydrolysis.