E. Bunuel

Z -2-Phenyl-4-[(S)- 2,2-dimethyl-1,3-dioxolan-4-ylmethylen]-5(4H)-oxazolone as the Dienophile in Asymmetric Diels-Alder Reactions

Abstract Diels-Alder reactions of Z-2-phenyl-4-[( S )-2,2-dimethyl-1,3-dioxolan-4-ylmethylen]-5(4H)-oxazolone and several cyclic and open chain dienes are studied. Less-reactive dienes required longer reaction times and led to isomerization of the Z-oxazolone and isolation of products derived from the E -isomer; Lewis acid catalysts were used to shorten the reaction times. In all cases high diastereofacial selectivity is observed and Diels-Alder adducts can be obtained in high optical purity. The stereochemistry of adducts has been elucidated by single crystal X-ray structure determinations, 1 H-NMR analysis and mechanistic considerations.

Study of the asymmetric Diels-Alder reaction of a chiral azlactone

Abstract The chiral Z-azlactone derived from 1,2-O-isopropylidene-D-glyceraldehyde underwent diastereoselective Diels-Alder reaction with cyclopentadiene. Catalyst temperature and solvent dependence of the product ratio is described.

Asymmetric Diels-Alder reaction of a chiral azlactone

Abstract The chiral Z-azlactone derived from 1,2-O-isopropylidene-D-glyceraldehyde underwent facial diastereoselective Diels-Alder reaction with cyclopentadiene. Catalyst and temperature dependence of the product ratio is described. The absolute configuration of the major compound was established by an X-ray crystallogrophic analysis.

Z-2-phenyl-4-[(S)-2,2-dimethyl-1,3-dioxolan-4-ylmethylen]-5(4H)-oxazolone as the dienophile in asymmetric diels-alder reactions. II

Abstract Diels-Alder reaction of Z-2-phenyl-4-[( S )-2,2-dimethyl-1,3-dioxolan-4-ylmethylen]-5(4H)-oxazolone and Danishefskys diene is studied. Thermally induced reaction took place at room temperature with a high diastereofacial selectivity and Diels-Alder adducts, obtained in very high diastereomeric purity, were easily transformed into valuable compounds. The stereochemistry of the adducts has been elucidated by single crystal X-ray structure determinations, 1 H-NMR analysis and mechanistic considerations.

Diastereoselective synthesis of (1S,2S,3R,4R) and (1R,2S,3R,4S)-bicyclo[2.2.1]hept-2-amino-2,3-dicarboxylic acids: New conformationally-constrained (S)-aspartic acid analogues

Abstract The title compounds were prepared from key intermediates readily obtained by the stereoselective Diels-Alder reaction of ( Z )-2-phenyl-4-[( S )-2,2-dimethyl-1,3-dioxolan-4-ylmethylene]-5(4H)-oxazolone, a chiral az-lactone derived from ( R )-glyceraldehyde and cyclopentadiene.

A New Conformationally Restricted Aspartic Acid Analogue with a Bicyclo[2.2.2]octane Skeleton

The bicyclo[2.2.2]octane cage in (2R,3S-3-benzamido-3- methoxycarbonylbicyclo[2.2.2]octane-2-carboxylic acid, C 18 H 21 NO 5 , has approximate D3 symmetry and the three six-membered rings of this fragment all deviate slightly from ideal boat conformations. The values determined for the torsion angles about the N-Cα (φ) and Cα-CO (φ) bonds correspond to a semi-extended conformation for the amino acid residue. The crystal structure is stabilized by two intermolecular hydrogen bonds (O-H...O and N-H...O) involving the carboxylic acid, the benzamido and the methyl ester groups.

(1R,2R,3S,4S,5S,6S)-exo-2-Cyano-exo-3-[(S)-1,2-dibenzyloxyethyl]-exo-5-iodobicyclo[2.2.1]heptane-endo-2,6-carbolactone

In the title compound (C 25 H 24 INO 4 ), an enantiomerically pure iodolactone, the absolute configurations at the chiral C1, C2, C3, C4, C5 and C6 centres have been unambiguously assigned as 1R, 2R, 3S, 4S, 5S and 6S, respectively. In the bicyclo[2.2.1]]heptane (norbornane) unit, the six-membered ring presents a boat conformation, and is fused with a five-membered lactone ring which adopts an envelope conformation.

A Lactone Derived from an Amino Acid with a Cyclohexyl Skeleton: (1S,6R,9S)-6-Benzamido-9-hydroxymethyl-8-oxabicyclo[4.3.0]non-3-en-7-one

In the title compound, C16H17NO4, the five-membered lactone ring is trans-fused to the cyclohexene ring. The cyclohexene ring exhibits a half-chair conformation with the benzamido group in an axial position. The γ-butyrolactone adopts an envelope conformation with the hydroxymethyl substituent in a pseudo-equatorial position. The crystal structure is stabilized by two intermolecular hydrogen bonds (O—H⋯O and N—H⋯O) involving the benzamido and hydroxy groups.

N-[Bis(methylthio)methylene]-didehydroalanine methyl ester a new and excellent dienophile for the synthesis of 2-aminonorbornene-2-carboxylic acid

Abstract N-[Bis(methylthio)methylene]-didehydroalanine methyl ester behaves as an excellent dienophile with cyclopentadiene to afford methyl N-[Bis(methylthio)methylene]-2-aminonorbornene-2-carboxylate in excellent yield and with high selectivity.

A Conformationally Restricted Aspartic Acid Analogue with a Norbornane Skeleton. II

In (1S,2R,3S,4R)-3-benzamido-3-methoxycarbonylbicyclo[2.2.1]heptane-2-carboxylic acid, C 17 H 19 NO 5 , the values determined for the torsion angles about the N-C α (φ) and C α -CO(ψfi) bonds correspond to a semi-extended conformation of the amino acid residue. The crystal structure is stabilized by two intermolecular hydrogen bonds (O-H...O and N-H...O) involving the benzamido, carboxylic acid and methyl ester groups.