Akira Yanagisawa

Rigid P-Chiral Phosphine Ligands with tert-Butylmethylphosphino Groups for Rhodium-Catalyzed Asymmetric Hydrogenation of Functionalized Alkenes

Both enantiomers of 2,3-bis(tert-butylmethylphosphino)quinoxaline (QuinoxP*), 1,2-bis(tert-butylmethylphosphino)benzene (BenzP*), and 1,2-bis(tert-butylmethylphosphino)-4,5-(methylenedioxy)benzene (DioxyBenzP*) were prepared in short steps from enantiopure (S)- and (R)-tert-butylmethylphosphine-boranes as the key intermediates. All of these ligands were crystalline solids and were not readily oxidized on exposure to air. Their rhodium complexes exhibited excellent enantioselectivities and high catalytic activities in the asymmetric hydrogenation of functionalized alkenes, such as dehydroamino acid derivatives and enamides. The practical utility of these catalysts was demonstrated by the efficient preparation of several chiral pharmaceutical ingredients having an amino acid or a secondary amine component. A rhodium complex of the structurally simple ligand BenzP* was used for the mechanistic study of asymmetric hydrogenation. Low-temperature NMR studies together with DFT calculations using methyl α-acetamidocinnamate as the standard model substrate revealed new aspects of the reaction pathways and the enantioselection mechanism.

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.

A short way to prostacyclin

Abstract A facile, stereospecific preparation of prostacyclin has been accomplished starting from a 5,6-dehydroprostaglandin F 2α derivative.

Regioselective allylation and propargylation using acylsilanes: facile synthesis of PGE3 and F3α methyl ester

Abstract Regioselective allylation and propargylation were achieved using acylsilanes as electrophiles and this methodology was applied to the synthesis of PGE3 and F3α methyl ester.

Regiospecific α-dialkoxymethylation of preformed enolates

Abstract Reaction of a preformed lithium enolate and trimethyl orthoformate with added boron trifluoride leads to the corresponding α-dimethoxymethyl ketone.

Enantioselektive Addition von Allyltrimethoxysilanen an Aldehyde mitp-Tol-BINAP⋅AgF als Katalysator

Die katalytische asymmetrische Allylierung von Aldehyden mit Allyltrimethoxysilanen wurde mit dem p-Tol-BINAP⋅AgF-Komplex als Katalysator erreicht [Gl. (a); p-Tol-BINAP=2,2′-Bis(di-p-tolylphosphanyl)-1,1′-binaphthyl)]. Bei der Reaktion mit Crotyltrimethoxysilan wurde unabhangig von der Konfiguration der Doppelbindung eine hohe anti- und Enantioselektivitat erhalten.

Asymmetric aldol reaction of enol trichloroacetate catalyzed by (S, S)-(EBTHI)TiCl(OMe).

(S,S)-Ethylenebis(tetrahydroindenyl)titanium chloride methoxide, (S, S)-(EBTHI)TiCl(OMe) (3) was synthesized from the corresponding titanium dichloride. The asymmetric aldol reaction of enol trichloroacetate of cyclohexanone 1 with aromatic aldehydes was studied in the presence of a catalytic amount of the chiral titanium complex 3, with the result that the optically active syn aldol adduct 2 was preferentially obtained with up to 91% ee.

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.

Selective isomerization of 1,2-epoxyalkanes to aldehydes with lithium dialkylamides

Reaction of a variety of 1,2-epoxyalkanes with 2.5 equiv. of bulky metal amide—lithium 2,2,6,6-tetramethylpiperidide—affords the corresponding aldehydes exclusively in high yields; this is the first example of base-promoted isomerization of monosubstituted epoxides to aldehydes.

Highly regioselective allylation of imines with allylic barium reagents

Aldimines are transformed into homoallylic amines by treatment with allylic barium reagents in which both the α- and γ-adducts are selectively obtained by simply changing the reaction temperature.