Keitaro Ishii

A novel dynamic kinetic resolution accompanied by intramolecular transesterification: asymmetric synthesis of a 4-hydroxymethyl-2-oxazolidinone from serinol derivatives

Reaction paths of the one-pot reaction of (R)-2-(α-methylbenzyl)amino-1,3-propanediol (1) and 2-chloroethyl chloroformate with DBU giving (4S,αR)-4-hydroxymethyl-3-(α-methylbenzyl)-2-oxazolidinone [(4S)-2] (94% de) were investigated. Intermediates of this reaction, 2-chloroethyl (2S)- and 2-chloroethyl (2R)-3-hydroxy-2-[(αR)-α-methylbenzyl]aminopropyl carbonates [(2S)-4 and (2R)-4], were synthesized individually. After the addition of DBU to the respective solution of the carbonate (2S)-4 and that of (2R)-4 in dichloromethane, the intramolecular transesterification between (2S)-4 and (2R)-4 and the diastereoselective intramolecular cyclization proceeded to afford (4S)-2 in high diastereomeric excess. Therefore, two monocarbonates (2S)-4 and (2R)-4 were kinetically resolved by this cyclization during the intramolecular transesterification between (2S)-4 and (2R)-4. We found that this process involved dynamic kinetic resolution accompanied by intramolecular transesterification.

ASYMMETRIC SYNTHESIS OF THE 4-HYDROXYMETHYL-2-OXAZOLIDINONE FROM THE SERINOL DERIVATIVE AND CHLOROFORMATES

Asymmetric desymmetrization of 2-[(αR)-α-methylbenzyl]amino-1,3-propanediol (1) with 2-chloroethyl chloroformate and DBU at room temperature gave optically active (4S)-4-hydroxymethyl-N-[(αR)-α-methylbenzyl]-2-oxazolidinone [(4S)-2] (up to 94% de). This reaction involves kinetic resolution and [1,3]-alkoxyacyl migration of 2-chloroethyl (2S)- and 2-chloroethyl (2R)-3-hydroxy-2-[(αR)-α-methylbenzyl]aminopropyl carbonates [(2S)-4 and (2R)-4].

Chemoselective Debezylation of the N-1-Phenylethyl Group in 2-Oxazolidinones by the Anisole-Methanesulfonic Acid System

The chemoselective removal of N-1-phenylethyl group in 2-oxazolidinones by the anisole-methanesulfonic acid system was investigated. Optically active 4,5-cis- and 4,5-trans-diphenyl-2-oxazolidinones (1a-d) were easily synthesized from dl-stilbene oxides (trans- and cis-7a) using this debenzylation.

Photochemical reactions of α,β-unsaturated γ,δ-epoxy ketones and nitriles in the presence of amine

Direct irradiation (λ 254 nm) of the α,β-unsaturated γ,δ-epoxy ketone (1) and nitrile (2) in acetonitrile in the presence of aliphatic amines gave the divinyl ethers (5) and (11), respectively, as the main products, whose formation was shown to depend on solvent polarity and ionization potential of amines. On the other hand, when compounds (1) and (2) were irradiated in various alcohols in the presence of an amine they afforded the corresponding ketals (14)–(19) and (21) in 85–21% yield. Photochemical reactions of ketone (3) and nitrile (4) in methanol, were also studied.

One-pot acylation and fractional crystallization: preparation of optically active serinol monobenzoates

Abstract Mono-O-acylation of (R)-2-(α-methylbenzyl)amino-1,3-propanediol 1 with 4-nitrobenzoyl chloride and DMAP in dichloromethane at room temperature gave crystals of optically active (2S,αR)-3-hydroxy-2-(α-methylbenzyl)aminopropyl 4-nitrobenzoate hydrochloride [(2S)-2a·HCl] in 33% yield by fractional crystallization. Optically active oxazolidinones, aziridines, and serinol derivatives were synthesized from the benzoate (2S)-2a.

1,3-Dipolar cycloadditions of photoinduced carbonyl ylides from α,β-unsaturated γ,δ-epoxy dinitriles

The photoinduced carbonyl ylides B and C from the α,β-unsaturated γ,δ-epoxy dinitriles 2 and 3 undergo 1,3-dipolar cycloaddition with enol ethers, leading regioselectively to the 8-oxabicyclo[3.2.1]octane system.

Photochemical reactions of nitrile compounds. Part 2. Photochemistry of an α,β-unsaturated γ,δ-epoxy nitrile and an γ,δ-cyclopropyl nitrile

Direct irradiation (λ 254 nm) of the α,β-unsaturated γ,δ-epoxy nitrile(1) led selectively to the products (13)–(19) arising from a carbonyl ylide or a carbene intermediate. However, products of an (E/Z)isomerization and a transformation via C(γ)–O bond cleavage of the oxirane, which are triplet processes, were not observed. On singlet excitation (λ 254 nm), the α,β-unsaturated γ,δ-cyclopropyl nitrile (4) afforded (38) as the main product along with (39) whereas, on triplet excitation of (4)(E/Z)-isomerization was the main process observed. Acid-catalysed rearrangements of compounds (1) and (8) were also studied.

Stereoselective Gram-Scale Synthesis of (S)-5,5-Dimethyl-4-phenyloxazolidin-2-one

A stereoselective gram-scale synthesis of (S)-5,5-dimethyl-4-phenyl-oxazolidin-2-one, SuperQuat [(S)-1], is described. The key step is the diastereoselective reduction of (E)-imine (2), which is synthesized from 2-hydroxy-2-methylpropiophenone (4) and (S)-α-methylbenzylamine using sodium borohydride and acetic acid to give (1S,αS)-2-methyl-1-(a-methyl-benzyl)amino-1-phenylpropan-2-ol (5).

Photochemistry of α,β-unsaturated γ,δ-epoxy nitrile: a new methodology for synthesis of spiroketals

Photoinduced intramolecular cyclization of δ-hydroxybutyl-α,β-unsaturated γ,δ-epoxy nitriles 5a, b provides rapid access to the spiro ketal skeleton.

Photoreactions of β-aziridinylacrylonitrile. 1,3-Dipolar cycloadditions of photoinduced azomethine ylide

The photoinduced azomethine ylide A from the 3-(1-benzylaziridin-2-yl)prop-2-enenitrile 1 undergoes 1,3-dipolar cycloaddition with electron-deficient olefins to give the head-to-head adducts selectively and efficiently.