摘要:

Experimental evidence is presented to support the hypothesis that, in triplyortho-substituted diphenyl ethers, conformer interconversion involves both rings. The free energy barrier, measured by p.m.r., is sensitive to substituent effects arising in the ring having only oneorthosubstituent. The exceptionally high barrier found when anorthoiodine is present is consistent with the existence of a substituent-inside intermediate occurring during conformer conversion.

ISSN:0008-4042    

DOI:10.1139/v74-487

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

The protonation of a series of methyl substituted phenols and anisoles in FSO3H has been examined. When theparaposition of the phenol is unsubstituted, protonation was found to take place exclusively at this site. A methyl group on C-4 reduces the basicity of this carbon such that protonation on C-2, C-6 or oxygen can now compete withparaprotonation. Despite claims to the contrary, in FSO3H no significant amount ofmetaprotonation was observed for any of the phenols. In FSO3H–SbF5, 2,4,6-trimethylphenol is protonated on C-3 or C-5; however, it would appear that thismetaprotonation is accompanied by a modification of the hydroxy group by either further protonation or reaction with the Lewis acid SbF5.

ISSN:0008-4042    

DOI:10.1139/v74-488

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

The protonation of a series of polymethylphenols in fluorosulfonic acid at −50° has been studied. For those phenols with no substituent at C-4, protonaton occurs exclusively at that position. Isomeric ions were obtained for all phenols with a methyl substituent at C-4. 4-Methylphenol and 2,4-dimethylphenol each gave three ions, one fromO-protonation and two from protonation at C-2 and C-4, whereas 2,4-dimethylphenol, 2,3,4-, 2,4,5-, and 3,4,5-trimethylphenol, and 2,3,4,5-tetramethylphenol gave only theC-protonated species. These studies establish that although electronic factors are important, steric factors play a predominant role in determining the relative proportions of the various species.

ISSN:0008-4042    

DOI:10.1139/v74-489

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

In a 1,2,4-trialkyl-substituted cyclohexenyl cation, two very facile degenerate rearrangements occur. One is simply a scrambling of a proton (C-3) on the allyl center with the C-4 proton. The more interesting process is one involving the specific interchange of the C-1 and -4 carbons and attached alkyl groups. Accurate rates have been measured for both these processes using specific deuterium labelling and the n.m.r. spin saturation technique, in order to probe the mechanism of the rearrangements.

ISSN:0008-4042    

DOI:10.1139/v74-490

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

2-Methoxy-5-methylbenzoquinone undergoes reaction with sodium azide in sulfuric acid to give(a) 3-hydroxy-6-methyl-1H-azepin-2,5-dione, which undergoes ring contraction with base to give 5-methyl-4-pyridone-2-carboxylic acid; (b) 4-methoxy-7-methyl-1H-azepin-2,5-dione, which reacts with phosphorus oxychloride to give methyl 2-chloro-6-methylpyridine-4-carboxylate, not 2-chloro-4-methoxy-7-methyl-5H-azepin-5-one; (c) 7-methoxy-4-methyl-1H-azepin-2,5-dione. The reactions of these compounds are discussed and the evidence for their structures is presented.

ISSN:0008-4042    

DOI:10.1139/v74-491

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

Crystals of the title compound, Me2AsC(CF3):C(CF3)AsMe2WI2(CO)3, are monoclinic,a = 15.37(2),b = 9.529(1),c = 15.967(3) Å, β = 112.03(2)°,Z = 4, space groupP21/c. The structure was determined by Patterson and Fourier syntheses and refined by full-matrix least-squares procedures to a finalRof 0.069 for 1823 observed (of a total of 2778) reflexions. The tungsten atom is seven-coordinate with a distorted capped octahedral environment, the capping group being a carbonyl (W—C, 1.94(3) Å). The capped face consists of the two remaining carbonyl groups (W—C, 1.97(4) and 2.00(4) Å) and one of the arsenic atoms from the bidentate ligand (W—As, 2.556(3) Å). The uncapped face contains the two iodine atoms (W—I, 2.848(2) and 2.856(2) Å) and the remaining arsenic atom (W—As, 2.618(3) Å), this bond length(transto CO), being significantly longer (by 0.062 Å) than the other(transto I) W—As distance.

ISSN:0008-4042    

DOI:10.1139/v74-492

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

2,3,4,6-Tetra-O-benzyl-α-D-glucopyranosyl bromide (1) and, in one instance, its α-D-galactoisomer (2) were condensed under conditions of the Heiferich modification of the Koenigs–Knorr reaction with the four stereoisomeric methyl 4,6-O-benzylidene-3-deoxy-3-nitrohexopyranosides having the α-D-galacto(3), β-D-galacto(4), α-D-gluco(5), and β-D-gluco(6) configurations. Six new, 1 → 2 linked, fully blocked nitro disaccharides (7–12) were isolated. The configurations of the disaccharidic linkages were established by n.m.r. spectroscopy to be α in four of the products (8, 9, 11, and12) and β in two (7and10). The steric course of the disaccharide bond formation was found to depend on the anomeric as well as the over-all configuration of the alcoholic components3–6.

ISSN:0008-4042    

DOI:10.1139/v74-493

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

Treatment of benzil monoazine with sodium methoxide gives 5-methoxy-1,2,5-triphenyl-3,4-diaza-2,4-pentadien-1-one (2), 5-benzoyl-4,5-dihydro-3,4,5-triphenylpyrazol-4-ol (3), and simple cleavage products. Compound3is hydrolyzed to 3,4,5-triphenylpyrazole and benzoic acid. It is phototropic, being reversibly converted on exposure to sunlight to a red product, which is readily autoxidized to benzil monoazine. Analogous phototropic products are formed on reaction ofp-anisil monoazine andp-tolil monoazine with sodium methoxide. Reduction of the azines to the phototropic products may occur by cleavage to α-keto imine anions followed by their dimerization; such a pathway can also account for the formation of the cleavage products. Alternatively, reduction may proceed by hydride or electron transfer; that hydride transfer need not necessarily be involved is established by the observation that treatment ofp-tolil monoazine with potassiumt-butoxide also gives the corresponding phototropic product. It is proposed that the phototropic transformations involve intramolecular hydrogen abstraction to give enolic isomers of3and its analogs in which the heterocyclic ring has been cleaved.

ISSN:0008-4042    

DOI:10.1139/v74-494

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

Proton magnetic resonance studies of 2′-deoxythymidine, its 3′ and 5′-monophosphates and the dideoxynucleoside monophosphate, 2′-deoxythymidylyl-(3′,5′)-2′-deoxythymidine are described. Assignment of the spectral bands are carried out and the derived chemical shift and coupling constant data are discussed in terms of the conformational properties of these molecules. The main conclusion reached is that 3′- and 5′-phosphorylation as well as incorporation into the dinucleoside monophosphate at either the 3′- or 5′-terminus has only slight effects on the conformation of thymidine under the experimental conditions employed.

ISSN:0008-4042    

DOI:10.1139/v74-495

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

Brief acid hydrolysis of 1,2:5,6-di-O-isopropylidene-3,4-di-O-methylsulfonyl-D-mannitol (1a), removes the isopropylidene groups giving the disulfonated hexitol,2a. Upon continued acid hydrolysis of2a, one sulfonate group is lost with formation of a sulfonated monoanhydro hexitol,5a, then the second ester group is lost to give 1,4:3,6-dianhydro-D-iditol (D-isoidide,3a). If the disulfonate,2a, is treated with base, an isomeric dianhydro hexitol, the bisoxirane4, is formed. Under similar basic conditions, the monoanhydro hexitol,5a, is stable. On acid hydrolysis, the bisoxirane,4, gives hexitols and only 20% ofD-isoidide, which indicates that4cannot be an intermediate in the conversion of2ato3a. These results indicate that, in2aat least, five-membered anhydro rings are formed preferentially in acid hydrolyses and three-membered rings in saponification.The stage and course of hydrolysis of2aare readily monitored by observing the τ 4–6 region in the n.m.r. spectra of D2O samples of the hydrolysate.

ISSN:0008-4042    

DOI:10.1139/v74-496

出版商:NRC Research Press    

年代:1974

数据来源: NRC