Tadao Ishizuka

Mild and selective ring-cleavage of cyclic carbamates to amino alcohols

Abstract N-tert-Butoxycarbonylated 2-oxazolidinones and tetrahydro-2-oxazinones are smoothly cleaved to acyclic N-Boc-amino alcohols on treatment with catalytic amounts of cesium carbonate at room temperature. The versatility of the procedure is demonstrated in a facile cleavage of highly functionalized heterocycles without epimerization and β-elimination.

Highly efficient chiral 2-oxazolidinone auxiliaries derived from methylcyclopentadienes and 2-oxazolone

Abstract Sterically congested [4+2]cycloadduct-based 2-oxazolidinones, (1 R , 2 R , 6 S , 7 S )-1, 7, 8, 9, 10, 10-hexamethyl- and (1 S , 2 R , 6 S , 7 S , 10 R )-1, 7, 8, 9, 10, 10-pentamethyl-3-oxa-5-azatricyclo[5.2.1.0 2,6 ]dec-8-en-4-ones and their enantiomers, derived from hexamethyl- and pentamethylcyclopentadienes and 2-oxazolone, serve as extremely powerful chiral auxiliaries in the asymmetric alkylations and Diels-Alder reaction.

Chiral synthons for 2-amino alcohols. Facile preparation of optically active amino hydroxy acids of biological interest

Abstract A promising method for the versatile synthesis of chiral 2-amino alcohols is provided by the enantioselective functionalization of the olefinic moiety of the simple heterocycle, 2-oxazolone, involving a stereodefined introduction of easily replaceable groups followed by stepwise substitution. Versatility of this method is shown in chiral synthesis of unusual hydroxy amino acids such as statine and hydroxyglutamic acid, which are the key components of bioactive peptides.

Versatile chiral synthons for 1,2-diamines: (4S,5S)- and (4R,5R)-4,5-dimethoxy-2-imidazolidinones

Abstract (4 S ,5 S )- and (4 R ,5 R )-1-Acyl-4,5-dimethoxy-2-imidazolidinone derivatives, which are readily accessible from simple 1,3-dihydro-2-imidazolone heterocycles, represent good candidates for a new class of chiral synthons for use in the preparation of optically active threo -diamines such as 2 S ,3 R - and 3 S ,4 S -diamino carboxylic acids.

Lewis acid-promoted direct substitution of 4-methoxy- and 4-phenylthio-2-oxazolidinones by alkyl cuprates. Facile preparation of (3S,4S)-statine and (3S-4S)-cyclohexylstatine

Abstract Treatment of 4-methoxy- and 4-phenylthio-2-oxazolidinones with a combination of cuprates and BF 3 results in smooth formation of 4-alkyl and 4-aryl derivatives in high yield. By this method, the titled compounds of biological interest are readily synthesized from ( 4S , 5S )-5-allyl-4-methoxy (or 4-phenylthio)-2-oxazolidinones stereoselectively.

Chiral electrophilic 'glycinal' equivalents. New synthons for optically active α-amino acids and 4-substituted 2-oxazolidinones

Abstract The thermal reaction of 3-[(1 S )-2-alkoxy-1-apocamphanecarbonyl]-2-oxazolones ( 21a-c ) with dialkyl azodicarboxylates ( 9 ) results in exclusive formation of [4 + 2] type cycloadducts ( 22 and 23 ) with moderate levels of diastereofacial selection (up to 72% d.e.). The diastereomers thus obtained were readily purified and subsequent treatment with acidic methanol followed by removal of the auxiliary with LiBH 4 MeOH (1:2) gave optically pure 4-methoxy-5-hydrazino-2-oxazolidinones ( 26 and 27 ), which serve as α-aminoaldehyde templates useful for the synthesis of a wide variety of optically active α-amino acids as well as 4-alkyl and 4-aryl-2-oxazolidinones.

An unusual enhancement of chiral induction by chiral 2-imidazolidinone auxiliaries

Diastereoselectivity which is induced by the use of 2-imidazolidinone auxiliaries is greatly dependent on the N-substituents of the heterocycles, among which the bulky arenesulfonyl group is the moiety of choice. Reactions of this type afford an excellent level of diastereoselection in the methylation of N%-butyryl-2-imidazolidinones via the metal enolates.

FACILE ENANTIODIVERGENCE OF MESO-1,3-DIACYL-2-IMIDAZOLIDINONES TO CHIRAL 2-IMIDAZOLIDINONE AUXILIARIES

Abstract The enantioselective monodeacylation of meso -1,3-diacetyl-2-imidazolidinones, by treatmenmt with the lithium salts of sterically constrained N , N -dimethylaminoalcohol gives 1-acetyl-2-imidazolidinones in 89% ee. The latter compounds serve as good precursors for efficient chiral auxiliaries.

Sterically constrained tricyclic 2-oxazolidinone as excellent chiral auxiliary

Abstract A new class of conformationally rigid 2-oxazolidinones with effectively bulky substituents, derived from the [4+2] cycloadduct of cyclopentadiene and 2-oxazolone, serve as extremely powerful chiral auxiliaries for asymmetric alkylations, Diels-Alder reactions and conjugate addition reactions.

New camphor-derived auxiliaries in methoxyselenylation and methoxybromination with opposite diastereofacial selectivity. Preparation of β-amino alcohol chiral synthons

Abstract Methoxyselenylation and methoxybromination of chiral 3-acyl-2-oxazolones with PhSeCl/MeOH and Br2/MeC(OMe)3 smoothly proceed to result in highly stereoselective formation of chiral synthons for β-amino alcohols, but with opposite π-facial selectivity.