Michiko Miyazaki

Catalytic asymmetric allylation of 3,4-dihydroisoquinolines and its application to the synthesis of isoquinoline alkaloids.

A catalytic asymmetric allylation of 3,4-dihydroisoquinoline was carried out with allyltrimethoxylsilane-Cu as the nucleophile in the presence of DTBM-SEGPHOS as the chiral ligand to afford corresponding chiral 1-allyltetrahydroisoquinoline derivatives in good yield and stereoselectivity. The allyl adduct thus obtained was applied to the synthesis of several isoquinoline alkaloids such as crispine A and homolaudanosine. The reaction was further used for the synthesis of the isoquinoline moiety of schulzeine A.

Reductive amination of aldehydes and ketones by a Hantzsch dihydropyridine using scandium triflate as a catalyst

Direct reductive amination of aldehydes and ketones was carried out using a Hantzsch dihydropyridine as a reducing agent in the presence of a catalytic amount of a Lewis acid.

Asymmetric addition of nucleophiles to C-1 position of isoquinolines using (S)-alanine derivatives as chiral auxiliaries

Abstract 5,8-Dibromoisoquinoline derivatives were allowed to react with a nucleophile (silyl enol ether or allyltributyltin) in the presence of an acyl chloride derived from (S)-alanine to afford the 1,2-addition products in good chemical yields and high stereoselectivity. The bromo groups were readily removed by a reduction process in which the double bond at C3–C4 was also reduced. Thus the reaction system provided a general method to synthesize asymmetric 1-substituted tetrahydroisoquinolines. In order to determine the absolute configuration of the reaction product, (−)-homolaudanosine was synthesized in an enantiopure form. The stereoselectivity was rationally understood from the conformation of intermediary N-acylated isoquinolinium salts.

Reaction of amides with nitric oxide (NO)

Amides were allowed to react with nitric oxide in aprotic and non-ethereal solvents to give the corresponding N-nitroso derivatives. The reaction was accelerated by addition of oxygen. The solvent effect revealed that the reaction did not proceed in the presence of protic media.

Radical scavenging by N-aminoazaaromatics

N-Aminoazaaromatics were found to react with nitric oxide in the presence of oxygen to afford deaminated products in high yields. The reaction proceeded almost instantaneously in various solvents including water, and one to two equivalent of NO was consumed depending upon the amount of oxygen coexisted, and 1 equivalent of N2O was released in the reaction. In addition, N-aminoazoles were deaminated by potassium superoxide to give parent azoles in good yields. Two equivalents of superoxide was consumed, and about half equivalents of both nitrite and nitrate ion were released. The results demonstrated that N-aminoazoles have ability to protect the biological system against the oxidation promoted by radicals such as nitrogen oxides and superoxide.

Asymmetric Synthesis and Catalytic Activity of 3-Methyl-β-proline in Enantioselective anti-Mannich-type Reactions

Enantiomerically pure 3-methyl-β-proline was synthesized using an asymmetric phase-transfer-catalyzed alkylation of a cyanopropanoate to establish the all-carbon stereogenic center. The catalytic activity of 3-methyl-β-proline in the Mannich-type reaction between a glyoxylate imine and ketones/aldehydes was subsequently investigated. The catalyst was designed and found to be more soluble in nonpolar organic solvents relative to the unsubstituted β-proline catalyst, and as a result allowed for added flexibility during optimization efforts. This work culminated in the development of a highly anti-diastereo- and enantioselective process employing low catalyst loading.

FORMAL SYNTHESES OF DIHYDROCORYNANTHEINE AND ISORHYNCHOPHYLLINE VIA PROLINE CATALYZED MANNICH-MICHAEL REACTION

Proline catalyzed Mannich-Michael reaction of 3-ethyl-3-buten-2-one with 9-tosyl-3,4-dihydro-β-carboline proceeded in a highly stereoselective manner. The reaction was applied to formal syntheses of dihydrocorynantheine and isorhynchophylline.

A general method for the asymmetric synthesis of both enantiomers of 1-substituted 1,2,3,4-tetrahydro-β-carbolines employing pyroglutamic acid derivatives as chiral auxiliaries

9-(S)-Pyroglutaminyl-β-carbolines were allowed to react with a nucleophile (allyltributyltin or a silyl enol ether) in the presence of 2,2,2-trichloroethyl chloroformate to give 1,2-addition products in good yields and high diastereoselectivity. The chiral auxiliary at N-9 was readily removed by a mild hydrolysis. The same chiral source afforded both enantiomers by simply altering a protecting group of the amide nitrogen. That is, (S)-pyroglutaminyl groups which had an N-alkyl group afforded the (S) isomer, whereas the ones having an N-acyl group produced the (R) isomer of the addition products.

Addition Reaction of Imidazoles and Thiazoles with Silyl Enol Ethers in the Presence of Alkyl Chloroformate

Abstract Silyl enol ethers and ketene silyl acetals reacted with imidazole, thiazole, and their benzo derivatives in the presence of an alkyl chloroformate to give 2-substituted imidazolines and thiazolines in good yields via the intermediacy of unstable N-acylated quaternary salts of azoles. In addition, it was found that silyl enol ethers formed in situ were also useful for the reaction to afford the adducts only by simple sequential addition of five commercially available reagents.

Asymmetric Acyl-Strecker Reaction Promoted by Novel Thiourea Organocatalyst

Asymmetric acyl-Strecker reaction using novel thiourea organocatalyst is described. Screening experiments of the catalysts revealed that a bifunctional organocatalyst afforded an enantio-enriched product via an unique mechanism. That is, dihydroisoquinoline derivatives were converted to a corresponding 1-cyano-1,2,3,4-tetrahydroisoquinolines using the bifunctional thiourea catalyst derived from Betti base in moderate yield and enantioselectivity. .