Proton magnetic resonance studies of compounds with bridgehead nitrogen atoms—XIX Configurational and conformational studies with derivatives of hexahydropyrido [2,1-c][1,4]oxazin-4(3H)-ones

A series of substituted hexahydropyrido [2,1-c][1,4]oxazin-4(3H)-ones has been prepared by reaction of the sodio derivative of the appropriate piperidyl carbinol with ethyl chloroacetate. From a study of their NMR spectra the configurations of these compounds have been assigned and the conformation of the perhydro-1, 4-oxazinone moiety shown to be that with the ring oxygen atom and the angular hydrogen on the same side of the plane defined by C3? C(O)? N. The synthesis and NMR spectra of hexahydro-2H-pyrido [1,2-d][1,4]oxazepin-5(4H)-one, 1,6,11,11a-tetrahydro [1,4]-oxazino [4,3-b]isoquinolin-4(3H)-one and of hexahydropyrido [2,1-c][1,4]thiazin-4(3H)-one are also discussed. cis-6,9a-H-6-Methyl-hexahydropyrido[2,1-c][1,4]oxazin-4(3H)-one is shown to exist in a conformation containing a deformed perhydropyridine ring.     

Proton magnetic resonance studies of compounds with bridgehead nitrogen atoms—XXIV: The stereochemistry of octahydroimidazo [1,5-a] pyridine and of some N-acetyloctahydroimidazo [1,5-a] pyridines

Octahydroimidazo[1,5-a]pyridine is shown to preferentially adopt the trans-fused ring conformation in solution at room temperature. The NMR spectra of the rotational isomers of some N-acetyloctahydroimidazo[1,5-a]pyridines and N-acetyloctahydro-1H-pyrido[1,2-c]pyrimidine are described, and the stereochemistry about the N-acetyl bonds and the cis or trans nature of the ring fusion defined.     

Proton magnetic resonance studies of compounds with bridgehead nitrogen atoms—XXIII: Deformation of the piperidine ring in some bicyclic compounds possessing a bridgehead amide nitrogen atom

Some bridgehead nitrogen compounds possessing the CH(Me)-bridgehead N? C(O) system have been synthesised and their configurations assigned. The chemical shifts of the proton geminal to the methyl group provides evidence for the existence of a deformed chair conformation for the methyl substituted ring.     

Proton magnetic resonance studies of compounds with bridgehead nitrogen: XXVIII—Stereochemical studies with perhydropyrido[1,2-c] [1,6,3]dioxazocines and 2-alkylperhydropyrido[1,2-c] [1,3,6]oxdiazocines

A series of perhydropyrido[1,2-c][1,6,3]dioxazocines and 2-alkylperhydropyrido[1,2-c][1,3,6]oxdiazocines have been prepared. 6-p-Nitrophenyl-3,4-dimethylperhydropyrido[1,2-c][1,6,3]-dioxazodioxazocine is shown to adopt the cis fused ring conformation in solution with the nitrogen lone pair axial with respect to the piperidine ring. The 2-alkylperhydropyrido[1,2-c][1,3,6]oxdiazocines adopt a similar cis fused ring conformation and with increasing steric requirement of the 2-alkyl substituent the 8-membered ring increasingly favours the chair-chair conformation, rather than the chair–boat conformation favoured by the 2-methyl substituted compound.     

Compounds with bridgehead nitrogen: 45—the 1H NMR spectra and stereochemistry of some dimethylperhydro-oxazolo[3,4-a]pyridines

The positions of conformational equilibria in 1,5-, 1-6- and 1,8-dimethylperhydro-oxazolo[3,4-a]pyridines were determined by ¹H NMR spectroscopy. The cis-(H-5, H-8a)-1,6-dimethyl-perhydro-oxazolo[3,4-a]pyridine. In contrast, r-1,t-6,t-8a-1,6-dimethylperhydro-oxazolo[3,4- a]pyridine preferred the cis-fused conformation. Three of the 1,8-dimethylperhydro-oxazolo[3,4-a]pyridines adopted the trans-fused conformations (with distortion of the system in the case of the r-1,c-8,c-8a derivative) and the r-1,c-8,t-8a-1,8-dimethyl derivative adopted the cis-fused conformation.     

Proton magnetic resonance studies of compounds with bridgehead nitrogen atoms—XVIII Configurational and conformational studies with derivatives of hexahydroindolizin-2(3H)-one

A series of substituted hexahydroindolizin-2(3H)-ones and some related ketones have been prepared by Dieckmann condensation of the appropriate diesters. Utilising spectral data, the configurations of these compounds have been assigned, and their conformations discussed with particular reference to the magnitude of the geminal coupling constant (J_gem) for the N? CH₂? C(O) protons. With the exception of tetrahydropyrrolizin-2(3H)-one, all the ketones in this study are shown to exist in predominantly trans-fused conformations. In the case of hexahydroindolizin-2(3H) one and hexahydro-2H-quinolizin-3 (4H)-one, the separate contributions to J_gem from the adjacent N lone pair and the carbonyl π electrons are discussed.     

Proton magnetic resonance studies of compounds with bridgehead nitrogen. 38—solvent effects in the 1H NMR spectra of nitrogen heterocyclic systems containing a 1,3-arrangement of heteroatoms

Solvent effects on the ¹H NMR parameters of perhydro-oxazolo[3,4?a]pyridine, perhydropyrido[1,2?c]?[1,3]oxazine and perhydrothiazolo[3,4?a]pyridine derivatives are described. Particularly marked are changes in the proton-proton geminal coupling constants of the NCH₂O and NCH₂S methylene protons with solvent and these are attributed to reaction field and solvation effects rather than to changes in the position of conformational equilibria.     

Proton magnetic resonance studies of compounds with bridgehead nitrogen atoms—XXVI : Configurational studies with derivatives of perhydro-oxazolo[3,4-c]oxazole and the conformational analysis of perhydro-imidazo[1,5-c]thiazole

A series of 3-monosubstituted, 3,3′-disubstituted, and 3,5-disubstitted perhydro-7a-methyloxazolo[3,4-c]oxazoles has been synthesised. Some indication of the predominant conformations of these systems and of the related perhydro-imidazo[1,5-c]thiazoles is obtainable from the magnitude of the geminal coupling constants of the methylene group protons situated between the heteroatoms.     

Proton magnetic resonance studies of compounds with bridgehead nitrogen atoms: XXXII—The 1H n.m.r. spectra and stereochemistry of 4-aryl-1,6,7,11b-tetrahydro-2H,4H-[1,3]oxazino[4,3-a]isoquinoline, 4-aryl-1,2,6,7,12,12b-hexahydro-4H-[1,3]oxazino[3′,4′:1,2]pyrido[3,4-b]indole and of related systems

cis(4-H,11b-H)-4-Aryl-1,6,7,11b-tetrahydro-2H,4H-[1,3]oxazino [4,3-a]isoquinoline and the related thiazino compound preferentially adopt in solution the O (or S) inside cis-conformation in contrast to cis(1-H,4a-H)-1-arylperhydropyrido[1,2-c][1,3]oxazine which adopts the trans fused conformation. 1-(β-Hydroxy-ethyl)-1,2,3,4-tetrahydro-β-carboline condenses with benzaldehyde to give the 1,3-oxazine derivative rather than the dimeric structure reported in the literature.     

Proton magnetic resonance studies of compounds with bridgehead nitrogen atoms. IX Configurational and conformational studies with methyl-substituted 8-phenyl-l,8-diazabicyclo[4.3.0]nonanes

The synthesis of a series of methyl-substituted 8-phenyl-1,8-diazabicyclo[4.3.0]nonanes is described. The preferred conformations of these compounds have been assigned on the basis of the 2850-2500 cm^?1 region of their infrared spectra and of the geminal coupling constant of the C-9 methylene group.     

Compounds with bridgehead nitrogen: 46—The 1H NMR spectra and stereochemistry of derivatives of 1,3,3a,4,5,6,6a,11a-octahydroindolo[3,2,1-ij][3, 1]benzoxazine

The ¹H NMR parameters of the NCH₂O protons of the reduced pyrrolo[1,2-c][1,3]oxazine moiety in rel-(3aS,6aS,11aS)-1,3,3a,4,5,6,6a,11a-octahydro-6a-methylindolo[3,2,ij][3, 1]benzoxazine and in the alkaloid rosibiline indicate a trans ring fusion for the grouping. The O-inside cis-fused moiety is present in the related rel-(3aR,6aS,11aS)-octahydro-6a-methylindolo[3,2,1-ij][3, 1]benzoxazine and in Wieland–Gumlich glycol formal.     

Compounds with bridgehead nitrogen. 42—1H NMR and stereochemistry of isomeric 6a-methylperhydroindolo[3,2,1-i,j]benzoxazines and the position of conformational equilibrium in perhydropyrrolo[1,2-c][1,3]oxazine

The ¹H NMR parameters of the NCH₂O protons in the spectrum of perhydropyrrolo[1,2-c][1,3]oxazine show its existence in solution at room temperature in the O-inside cis-fused conformation. rel-(3aS,6aS,6bR,10aS,11aS)-6a-Methylperhydroindolo[3,2,1-i,j]benzoxazine and rel-(3aS,6aS,6bS,10aR,11aS)-6a-methylperhydroindolo[3,2,1-i,j]benzoxazine are shown to adopt cis- and trans-fused conformations, respectively, for the corresponding bicyclic moiety.     

Nuclear magnetic resonance studies of 1,3-butadienes. IX—The 1H spectra of isoprene and related compounds

Full analyses of the five-spin ¹H n.m.r. spectra for the diene protons of isoprene, ethylbutadiene and β-myrcene under conditions of decoupling the sidechain α-protons are reported. The data are discussed in terms of spin–spin coupling mechanism and molecular conformation. The fully-coupled spectra of the compounds were also examined and coupling information obtained.     

Synthesis of some 4H,10H[1]benzoxepino[3,4-c]pyrazol-4-one derivatives

1H(or 2H)4H10H[1]Benzoxepino[3,4-c]pyrazol-4-ones were prepared from phenoxymethylpyrazolecarboxylic acids which in turn were synthesized from simple starting materials. Different pathways to allow the predominant formation of the N-1 or N-2 substituted derivatives are described. The isomeric 1 or 2-substituted structures were supported by ¹³C-nmr.     

Carbon-13 magnetic resonance spectra and the stereochemistry of some substituted bicyclo[2.1.1]hexanes

Using selective deuteriation and broad-band and off-resonance proton decoupling techniques, complete signal assignments are made for the ¹³C NMR spectra of a number of ketones and unsaturated esters with the bicyclo[2.1.1]hexane ring systems.     

Proton magnetic resonance studies of compounds with bridgehead nitrogen. 37–a comparison of the positions of conformational equilibria in 1-methylperhydro-oxazolo[3,4-a]pyridines and in 1-methylperhydrothiazolo [3,4-a]pyridines

cis(1-H, 8a-H)-1-Methylperhydro-oxazolo[3,4-a]pyridine and cis(1-H, 8a-H)-1-methylperhydrothiazolo[3,4-a]pyridine both adopt exclusively the trans-fused conformation in carbon tetrachloride solution at room temperature. Both parent unsubstituted systems exist under similar conditions as equilibria containing c. 67% (oxazolo compound) and 64% (thiazolo compound) of the trans-fused conformation. In marked contrast to these similar positions of conformational equilibria in both systems the trans(1-H,8a-H)-1-methylperhydrooxazolo[3,4-a]pyridine exists as c. 73% trans-fused in equilibrium with a cis-fused conformation whereas the trans(1-H, 8a-H)-1-methylperhydrothiazolo[3,4-a]pyridine exists almost exclusively in a cis-fused ring conformation. These differences in conformational equilibria are explained in terms of changes in non-bonded interactions.     

二氢吡咯并(口恶)嗪酮类化合物的EI质谱及其解析

总结和归属了(1H)-3,4-二氢吡咯[2,1-c][1,4]噁嗪-1-酮及其6个苯甲酰基衍生物和两个苯乙酰基衍生物在电子轰击电离质谱(EIMS)中的主要裂解方式和特征,指明了主要碎片离子的来源和结构。这8个芳酰基衍生物质谱图中的主要碎片峰均来自α-裂解和脱中性小分子碎片的重排裂解,由其产生的m／z 164、m／z 120和m／z 92离子是该类化合物共同的特征离子;二氢吡咯噁嗪酮苯甲酰基衍生物和苯乙酰基衍生物的基峰都为m／z 164。     

Nitrogen bridgehead compounds,Part 31 1H and 13C NMR study of tetra- and octahydro-11H-pyrido[2,1-b]quinazolin-11-ones

Conformational analysis of some tetra-and octahydro-11H-pyrido[2,1-b]quinazolin-11-ones 1-3 by ¹H and ¹³C nmr revealed that the 9-methyl-6,7,8,9-tetrahydro derivative exists mainly in the conformation containing the methyl group in a quasi-axial orientation. Of the 1,2,3,4,5,6,7,8-octahydro compounds, the 9-methyl derivative 3e contains the methyl group in a quasi-axial position, while that in the 7-methyl and the 8-methyl derivatives 3c,d is in the equatorial position, and the 6-methyl derivative 3b is a mixture of the two conformers.