Yoji Omata

Stereoselective formation of optically active 2-oxy-1,3-oxazolidin-4-ones from chiral O-acylmandelamides or lactamides

Abstract (−)- O -Acyllactamides or mandelamides in the presence of TBSOTf underwent cyclization reaction to give optically active 2-oxy-1,3-oxazolidin-4-ones, a novel nitrogen analog of orthoesters, in good yields. An X-ray analysis and NOE studies indicated that the absolute configuration at the newly formed chiral carbon was S . For their synthetic application, the 1,3-dipolar cycloaddition of nitrile oxide was examined. The cycloadducts were obtained in a stereoselective manner. Subsequent treatment of the adduct with TBAF resulted in the one-step removal of mandelamide, giving optically active 4,5-dihydroisoxazole and mandelamide in good yields.

Simple preparation of β-hydroxy-α-thiomethyl carbonyl compounds via stereoselective conjugate addition of thiol to Baylis–Hillman adducts

Abstract Nucleophilic addition of thiols to Baylis–Hillman adducts smoothly proceeded in the presence of catalytic amounts of lithium thiolate to give syn -β-hydroxy-α-thiomethyl carbonyl compounds stereoselectively.

Magnesium cation-induced anti-aldol selective tandem Michael/aldol reaction

A mixture of magnesium thiolate or selenolate, β-substituted-α,β-unsaturated ester and aldehyde affords a Michael/aldol tandem adduct, α-phenylthio- or α-phenylselenoalkyl-β-hydroxyester, in a good yield. The reaction proceeded in anti-aldol selective manner, which is contrast to the products from a similar reaction in the presence of lithium cation. An NMR study and an experiment for trapping the reaction intermediates suggest that magnesium thiolate, which forms precipitate in the reaction mixture, first attacks the aldehyde, not the unsaturated ester, to give α-alkoxysulfide.

Oxyoxazolidinone as an auxiliary for heterocyclic synthesis. Enantioselective formation of N-unprotected 2-pyrrolidones from selenocarboxylate and allylamines via radical cyclization

Abstract Optically active N-unprotected 2-pyrrolidones were prepared in a highly stereoselective manner through radical cyclization reaction of oxyoxazolidinone. Asymmetric induction from the oxyoxazolidinone ring system was generally high and oxazabicyclo[3.3.0]octanones were obtained in good yields. Treatment of the bicyclic compounds with TBAF resulted in the one-step cleavage of C–O and C–N bond, directly giving secondary 2-pyrrolidones in good yields along with recovery of chiral mandelic acid without loss of optical purity. The use of the present procedure gave optically active 4,5-disubstituted N-unprotected 2-pyrrolidone derivatives trans selectively.

Regioselective conjugate addition of thiols to unsymmetric fumaric esters in the presence of a lithium cation

Abstract Unsymmetrically substituted fumaric esters underwent highly regioselective conjugate addition of thiols in the presence of a lithium cation in non-coordinative media.

Stereoselective construction of multi-substituted tetrahydrofurans via three components-condensation reaction

Abstract Stereoselective construction of multi-substituted tetrahydrofurans is described. The procedure is consisted in three steps: stereoselective Michael/aldol tandem reaction, alkenylation, and radical cyclization. A chiral or racemic adduct of the tandem Michael/aldol reaction, β-hydroxyl-α-(phenylseleno)alkyl carbonyl compound, was alkenylated by treatment with propiolic ester to give a precursor of radical cyclization in good yields. Exposure of the precursor to Bu 3 SnH in hot toluene gave tri- or tetrasubstituted tetrahydrofurans in a good yield. The good control of relative configuration between C2 and C3 during the tandem reaction stage and the excellent 2,5- cis -induction in the radical cyclization brought the stereoselective formation of trisubstituted tetrahydrofurans. A prochiral radical carbon generated from a secondary selenide attacked the double bond in a stereoselective manner and one of four possible diastereomers of tetrahydrofuran was formed stereoselectively.

Stereoselective formation of optically active 2-oxy-1,3-oxazolidin-4-ones and an efficient synthesis of optically active secondary 2-pyrrolidones

Abstract Treatment of (−)-O-acyllactamides or mandelamides with TBSOTf in the presence of base gives optically active 2-oxy-1,3-oxazolidin-4-ones stereoselectively, which serve as useful precursors for the preparation of optically active secondary 2-pyrrolidones via radical cyclization and subsequent one-step removal of mandelic acid.

A simple preparation of syn-NH-amide aldols and amide-Baylis–Hillman adducts via a Michael–aldol tandem process

The thiolate- or selenolate-induced Michael–aldol tandem process using secondary α,β-unsaturated amides gave α-phenylthio- or α-phenylseleno-methyl-β-hydroxy amides syn-selectively, which were readily converted into NH-amide aldols or Baylis–Hillman adducts.