摘要:

While 3,3-dimethylbicyclo[3.3.1]nonan-2-one (5) is stable under strongly basic conditions (t-BuO−/t-BuOH/185 °C), its isomer, 3,3-dimethylbicyclo[3.2.2]nonan-2-one (6), is slowly transformed to5. Similarly, 3,3-dimethylbicyclo-[3.2.2]non-6-en-2-one (8b) rearranges to a [3.3.1] isomer but the latter is not stable. Experiments with 3,3-dimethylbicyclo[3.3.1]non-6-en-2-one (7) revealed that it is converted to five compounds, none of which is8b. The major product, 8,8-dimethylbicyclo[4.3.0]non-1(6),-en-7-one (11) arises from β-enolate rearrangement. Enone11undergoes slow reduction tocis- andtrans-8,8-dimethylbicyclo[4.3.0]nonan-7-one, presumably by single electron transfer. Experiments with11alone showed that β-enolate rearrangement of7 → 11is unidirectional. Haller–Bauer cleavage to acidic products occurs as a minor process in the reactions of the unsaturated ketones. The structures of the products were established primarily from their1H and13C magnetic resonance spectra.

ISSN:0008-4042    

DOI:10.1139/v93-146

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Relative stabilities and features of tautomers ofN,N-dimethyl-N′-(1-nitro-9-acridinyl)-1,3-propanediamine (known as nitracrine by the World Health Organization (WHO) or as Ledakrin in Poland), which exhibits antitumour activity, and its three nitro isomers were examined by AM1 and, in some cases, by PM3 and ab initio (STO-3G) methods. The lowest energy form of three compounds was always an imino tautomer, while the energy of the amino tautomers was a few kcal mol−1higher and that of theaciforms (in the case of the 2- and 4-nitro isomers) was more than 25 kcal mol−1higher. Each tautomer can further exist in several structural forms (conformers or stereoisomers). In some of them internal hydrogen bonding interactions are feasible. The barriers to rotation of the -NHR group, as well as to inversion of the -NHR group (in amino tautomers of nitracrine and its 2-nitro isomer) and of the whole molecule (in the case of non-planar imino structures), were also evaluated, as were enthalpies of formation (total energies), entropies, free energies, dipole moments, and energies of HOMO and LUMO orbitals. Molecular electrostatic potential maps reveal that only in nitracrine are both -NO2and -NHR groups surrounded by a negative electrostatic potential, whereas in other isomers the -NHR fragment is surrounded by a positive electrostatic potential while the -NO2group remains in the region of a negative electrostatic potential. The possible influence of physicochemical features on the biological activity of the molecules is also considered.

ISSN:0008-4042    

DOI:10.1139/v93-147

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Abinitiocomputational studies have been carried out for three molecules that are commonly classed as antiaromatic: cyclobutadiene (1), 1,3-diazacyclobutadiene (7), and 1,4-dihydropyrazine (6). Their dinitro and diamino derivatives were also investigated. Stabilizing or destabilizing energetic effects were quantified by means of the isodesmic reaction procedure at the MP2/6-31G*//HF/3-21G level, and calculated molecular electrostatic potentials (HF/STO-5G//HF/3-21G) were used as a probe of electron delocalization. Our results do not show extensive delocalization in the π systems of any one of the three parent molecules. The destabilization found for1and7is attributed primarily to strain and to repulsion between the localized π electrons in the C=C and C=N bonds, respectively. However,6is significantly stabilized, presumably due to limited delocalization of the nitrogen lone pairs. NH2groups are highly stabilizing, apparently because of lone pair delocalization. NO2is neither uniformly stabilizing nor destabilizing.

ISSN:0008-4042    

DOI:10.1139/v93-148

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Eleven benzyltetrahydroisoquinoline alkaloids, with an original substitution pattern, were isolated from the stem bark ofAnibacanelillaH.B.K. (Lauraceae). Structural studies of these compounds including1H,13C, nOe difference, COSY H–H and C–H, and COLOC nuclear magnetic resonance spectroscopy led to the identification of four benzylisoquinolines, monosubstituted on ring C with an hydroxyl at C-11, (−)-norcanelilline2, (+)-canelilline3, anicanine4, and canelillinoxine5; two tetrahydroprotoberberines monosubstituted on ring D at C-9, (−)-anibacanine6and (+)-manibacanine8; two tetrahydroprotoberberines monosubstituted on ring D at C-11, (−)-pseudoanibacanine7and (+)-pseudomanibacanine9; and three protoberberines with the same substitution pattern on rings A and D with a methyl substituent at the 8α or 8β position, (−)-α-8-methylpseudoanibacanine10, (−)-β-8-methylpseudoanibacanine11, and (−)-α-8-methylanibacanine12. An examination of all isolated alkaloids suggests the existence of two enzymatic systems inA.canelilla. In the first enzymatic system, reticuline- and coclaurine-type alkaloids are involved in the bioconversion of classical proaporphine and aporphine alkaloids. In the second system, canelilline-type alkaloids are intermediate in biosynthesis of anibacanine and pseudoanibacanine protoberberine alkaloids.

ISSN:0008-4042    

DOI:10.1139/v93-149

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The electrochemical behavior of titanium oxysulfate, used as a redox mediator in the reduction of 4,4′-dinitrodibenzyl, is studied in a 5 N H2SO4/EtOH 50:50 medium. The role played by electrogenerated Ti3+ions in the chemical reduction of nitro groups is also defined. The results obtained allow the determination of the most suitable conditions leading to selective syntheses. Macroscale electrolyses at a constant potential in the presence of TiOSO4give 4,4′-diaminodibenzyl with a great purity and a higher yield (93%) than without mediator (75%). The homogeneous chemical reduction of 4,4′-dinitrodibenzyl by first electrogenerating the Ti3+ions, then adding the organic substrate, is particularly selective. The nature of the reduction products depends on the [Ti3+]/[dinitro derivative] ratio. The 4-amino-4′-nitrodibenzyl is synthesized in a 70% yield for a 6:1 ratio whereas the amount of diamino derivative increases and can constitute the sole reduction product for higher ratios. A comparison is made with 1,5- and 1,8-dinitronaphthalenes and 2,2′-dinitrodiphenyl. Using a 6:1 ratio, 1-amino-8-nitronaphthalene is not obtained while 45% of 1-amino-5-nitronaphthalene and 25% of 2-amino-2′-nitrodiphenyl are formed by reduction of the corresponding dinitro derivatives.

ISSN:0008-4042    

DOI:10.1139/v93-150

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

A new asterosaponin, named helianthoside (1), has been isolated from the butanolic extract of the starfishHeliasterhelianthusand its structure established on the basis of extensive spectroscopic experiments and chemical correlations. Helianthoside is the first asterosaponin with a C3′-sulphated xylopyranose. The absolute stereochemistry at C24 was determined by the Trost–Mosher method.

ISSN:0008-4042    

DOI:10.1139/v93-151

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Transannular Diels–Alder reactions of 14-membered macrocyclic trienes possessing a methyl substituent on both the diene and dienophile moiety have been investigated. Macrocyclic structures1a,1b, and1chavingcis-trans-trans(CTT),trans-cis-trans(TCT), andtrans-trans-trans(TTT) geometries could be stereoselectively constructed by coupling appropriately functionalized dienes5and dienophile4following an intramolecular displacement of an allylic halide by the anion of an appropriately located dimethyl malonate unit. The transannular Diels–Alder reaction performed on1aled to a mixture of four major tricyclic products, including34possessing the unexpectedtrans-anti-cis(TAC) stereochemistry. When heated at 300 °C, macrocycle1bunderwent an unique conversion via an ene–retroene, Diels–Alder process, producing the unexpected tricycle41(racemic form) containing five contiguous chiral centers. A rationale for the above experimental facts is presented. In contrast to the previous results, the transannular Diels–Alder reaction of macrocycle1cwas straightforward, producing a 95% isolated yield oftrans-anti-cis(TAC) tricycle34. This investigation demonstrates a general methodology for the stereocontrolled synthesis of 1,2-dimethyl A.B.C[6.6.6] tricyclic compounds, which are potential precursors to polycyclic natural products such as steroids and terpenes.

ISSN:0008-4042    

DOI:10.1139/v93-152

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The synthesis and transannular Diels–Alder reactions of 14-membered macrocyclic trienes containing a methyl-substituted diene and a methyl-substitutedcis-dienophile moiety are described. As a result of the dienophilecisgeometry the 1,7-dimethyl A.B.C.[6.6.6] tricycles obtained from the Diels–Alder reaction have a different stereochemistry at the four chiral centers than similar tricycles that were the subject of the preceding paper in this series. Thustrans-syn-cis(TSC) tricycle30was the sole product obtained from thetrans-cis-cis(TCC) macrocycle1b. In a similar fashion TCC macrocycle1dafforded onlytrans-syn-cis(TSC) tricycle31. On the contrary, the transannular Diels–Alder reaction incis-trans-cis(CTC) macrocycle1aandtrans-trans-cis(TTC) macrocycle1cled to a mixture of the same four tricyclics (30,32–34)but in different ratio. The above experimental results are rationalized by taking into consideration the interconversion of macrocyclic trienes1a,1b, and1c. Pathways for these interconversions are also proposed.

ISSN:0008-4042    

DOI:10.1139/v93-153

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Several angularly functionalized decalins, synthethized during the preparation of three keto diacetate decalins, models for clerodane diterpenoids, were tested for antifeedant activity against the spruce budworm,Choristoneurafumiferana. Definite biological activity was observed for some of these compounds. A structure–activity relationship was discussed on the basis of these results.

ISSN:0008-4042    

DOI:10.1139/v93-154

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The synthesis of new 1,2,4,3-triazaphospholes is described: a number of 5-methylthio 1,2,4,3-triazaphospholes, substituted in the 1, 2, or 4 position. The 1,5-disubstituted compound6is stable, whereas 2,5-disubstituted compounds14and16undergo an equilibrium with their tetrameric form, the cyclotetraphosphazanes [14]4and [16]4. 5-Methylthio 4-alkyl 1,2,4,3-triazaphospholes exist only in the tetrameric forms [12]4and [13]4. [12]4can be depolymerized by complexation with a Lewis acid, giving the complexed triazaphosphole12•BF3. The15N NMR spectrum of compound16, the N-silylated derivative of15, allows us to confirm the position of the trimethylsilyl group. MNDO calculations are in good agreement with experimental results, such as the reaction of 1,4-diazadienes with triazaphospholes providing new tetracoordinated phosphorus spirocompounds21–25.

ISSN:0008-4042    

DOI:10.1139/v93-155

出版商:NRC Research Press    

年代:1993

数据来源: NRC