Search results for "stereochemistry"

Addition reactions of heterocycles. VI. Reactions of 1,2-dimethylpyrrole and 1-methyl-2-carbomethoxypyrrole with nitrilimines

1978

Addition reactions of 1,2-dimethylpyrrole and 1-methyl-2-carbomethoxypyrrole with C-acetyl-N-phenylnitrilimine, have been investigated. 1,2-Dimethylpyrrole gives three different types of adducts: i.e. bis-cycloadducts (Vc) and (VIc), spirocycloadduct (IX), and non cyclic bis-adduct (XII). On the other hand, 1-methyl-2-carbomethoxypyrrole gives the bis-cycloadduct (VIb) only. Compound XII arises probably through a double 1,3-addition reaction, whereas the formation of cycloadducts Vc, VIc, and IX depends on the substituents present at C2 of the pyrrole ring and consequentially on the intermediary occurence of mono-cycloadduct (IIIc), its methylenic tautomer VII, VIc, and XL The behaviour of …

Addition reactions of heterocycles. VII. Pyrrole andC-Acetyl-N-phenylnitrilimine

1978

The addition reaction of C-acetyl-N-phenylnitrilimine to pyrrole has been investigated. The products obtained show that the reaction proceeds via two distinct pathways. The 1,3-addition reaction leads to the non-cyclic-adduct III, whereas the 1,3-cycloaddition reaction gives a mixture of regioisomeric Δ2-pyrroline IV and V, and Δ1 -pyrroline VI and VII mono-cycloadducts. These latter compounds cannot be isolated because they undergo a further 1,3-cycloaddition reaction leading to the N-substituted bis-adducts X and XI, and to the bis-adduets XII and XIII. The stereochemical assignment for X, XI, XII and XIII is provided by nmr data which suggest also that in X and XI the rotation around the…

The structure and stereochemistry of atractyligenin

1966

Abstract The structure of atractyligenin C19H28O4, the nor-diterpenoidic aglycone of atractyloside C30H44O16S2K2 has been substantiated as Ia. The absolute configuration shown in Ia proves it to be a derivative of (−)kaurene.

Biosynthesis of Monoterpenoid Indole Alkaloid Ajmaline Catalyzed by Novel Reductases1

2006

Synthesis of (+)-pechueloic acid and (+)-aciphyllene. Revision of the structure of (+)-aciphyllene

2007

Abstract 1α H ,7α H ,10α H -Guaia-4,11-dien-3-one and its 1β H ,10β H diastereomer, easily obtained from (+)-dihydrocarvone, are good starting materials for the synthesis of natural guaiane derivatives. Allylic oxidation of the 1α H ,10α H isomer gave as main product its 13-hydroxy derivative and a small amount of (+)-7β-hydroxy-1α H ,10α H -guaia-4,11-dien-3-one, whereas the 1β H ,10β H diastereomer afforded selectively the (−)-7α-hydroxy-1β H ,10β H enantiomer in excellent yield. From the 13-hydroxy derivative (+)-pechueloic acid and (+)-methyl pechueloate were synthesized. Deoxygenation at C 3 of the 1β H ,10β H guaiadienone afforded a guaiadiene with the reported structure for aciphylle…

Der einfluß benachbarter grundbausteine auf die ammonolyse von essigsäureestern phenolischer mehrkernverbindungen

1972

Die Ammonolyse der Essigsaureester verschiedener phenolischer Zwei- und Dreikernverbindungen, die neben Methylphenolbausteinen jeweils einen Nitrophenolbaustein enthalten, wurde untersucht. In allen Fallen wird wie bei einkernigen Nitrophenylestern die Esterbindung im Nitrophenolbaustein ammonolytisch gespalten. Wenn die Bausteine uber Methylenbrucken in ortho-Stellung zu den phenolischen Hydroxylgruppen verknupft sind, werden jedoch auch die Esterbindungen in den Methylphenolbausteinen gespalten, obwohl die Ester von Methylphenolen und Mehrkernverbindungen, die nur Methylgruppen als Substituenten tragen, unter gleichen Bedingungen durch Ammoniak nicht angegriffen werden. In ubereinstimmung…

Complex tauto- and rotamerism of 2-(R-phenyl)-1,2,3,4-tetrahydroquinazolines

2005

Detailed NMR spectral analysis of CDCl3 solutions of 2-(R-phenyl)-1,2,3,4-tetrahydroquinazolines reveals three or four tautomeric forms. Apart from 2-[(benzylideneamino)methyl]aniline, the other chain tautomeric forms are present only in minor quantities. In general, electron-donating substituents increase the contribution of all chain forms. Lowering the temperature of the CDCl3 solution of 2-(R-phenyl)-1,2,3,4-tetrahydroquinazolines decreases the content of the 2-[(benzylideneamino)methyl]aniline form. At the same time, the amount of the ring form increases. Opening of the tetrahydropyrimidine ring in 2-(R-phenyl)-1,2,3,4-tetrahydroquinazolines was found to be an endothermic process espec…

Stereoselective synthesis of glycosides and anomeric azides of glucosamine

1992

The β-azide of O-acetyl protected N-acetyl glucosamine is efficiently accessible via a phasetransfer-catalyzed reaction of the corresponding glycosyl chloride with sodium azide. The azido group revealed to be a useful anomeric protection for modifications of the protecting group pattern of the glucosamine unit. Exchange of the O-acyl groups by 4-methoxybenzylidene and 4-methoxybenzyl (Mpm) protection delivered regioselectively blocked glucosaminyl azide derivatives. In contrast, the N-phthaloyl protected glucosaminyl azide was obtained quantitatively from the corresponding glycosyl fluoride via a boron trifluoride-promoted reaction with trimethylsilyl azide. N-Phthaloyl glucosaminyl fluorid…

ChemInform Abstract: Stereoselective Synthesis of Glycosides and Anomeric Azides of Glucosamine.

2010

The β-azide of O-acetyl protected N-acetyl glucosamine is efficiently accessible via a phasetransfer-catalyzed reaction of the corresponding glycosyl chloride with sodium azide. The azido group revealed to be a useful anomeric protection for modifications of the protecting group pattern of the glucosamine unit. Exchange of the O-acyl groups by 4-methoxybenzylidene and 4-methoxybenzyl (Mpm) protection delivered regioselectively blocked glucosaminyl azide derivatives. In contrast, the N-phthaloyl protected glucosaminyl azide was obtained quantitatively from the corresponding glycosyl fluoride via a boron trifluoride-promoted reaction with trimethylsilyl azide. N-Phthaloyl glucosaminyl fluorid…

Separation of Enantiomers in a Monolayer of Racemic 3-Hexadecyl-oxy-propane-1,2-diol

1993

Monolayers of a racemic mixture and of the pure S enantiomer of 3-hexadecyloxy-propane-1,2-diol have been characterized by thermodynamic measurements at the air/water interface as well as by fluorescence microscopy. The critical temperatire T c , the limiting molecular area at high pressure and the pressure π c corresponding to the observed main phase transition, derived from the isotherms, slightly depend on chiral purity