The synthesis of novel polycyclic heterocyclic ring systems via photocyclization. 10. Synthesis and structure determination of naphtho[1′,2′:4,5]thieno[3,2-a]-4,7-phenanthroline

Naphtho[1′,2′:4,5]thieno[3,2-a]-4,7-phenanthroline, a novel hexacyclic ring system has been synthesized in four steps. The ¹H and ¹³C nmr assignments have been made using two-dimensional nmr techniques. The tertiary helical structure was determined by X-ray crystallographic analysis.     

Structural isomerism of mono- and sesquiterpenoid skeletons

A generator of chemical structures (CONGEN) has been utilized to investigate two aspects of the structural isomerism of mono- and sesquiterpenoid skeletons: (1) the scope of possible isomers under various structural constraints; and (2) the scope of possible isomers based on a mechanistic model which allows interactive exploration of reactions of formation and interconversion. The possibilities, even under severe constraints, are many more than the structural types commonly encountered in natural. These results indicate the potential danger of structural assignment based in part on biogenic grounds.     

Efficient synthesis of various acycloalkenyl derivatives of pyrimidine using cross-metathesis and Pd(0) methodologies

Novel acyclonucleosides (9a-d, 10a-d, 18a,b and 19a,b) have been prepared using Pd(0) and cross-metathesis methodologies. The allylic N-alkylation under Tsuji-Trost conditions was used to introduce the nucleobase, while the Suzuki-Miyaura reaction afforded C-5 substituted uracil analogues. The cross-metathesis performed with a ruthenium catalyst was used to provide new acycloalkenyl nucleosides. The antiviral activities of all final compounds have been evaluated.     

The synthesis of novel polycyclic heterocyclic ring systems via photocyclization. 14. 14-methylbenzo[h]naphtho-[1′2′:4,5]thieno[2,3-c][1,6]naphthyridine

Benzo[h]naphtho[1′2′:4,5]thieno[2,3-c][1,6]naphthyridine, a novel polycyclic heterocyclic ring system, has been synthesized as the 14-methyl derivative 8 in four steps from known intermediates. The structure of 8 is supported by assignment of the proton and the protonated carbon atoms by 2D-nmr techniques (COSY and a carbon-hydrogen one-bond coupling experiment).     

The preparation and molecular structure oftrans-[MoCl2(PMe2Ph)4]

Summary The compoundtrans-[MoCl₂(PMe₂Ph)₄] has been prepared by the reduction of MoCl₅ (by Mg) or of [MoCl₃(PMe₂Ph)₃] (by LiBuⁿ) in the presence of PMe₂Ph in tetrahydrofuran (THF). It has _eff=2.84 B.M. and crystallises in space group P1 witha=11.591(3),b=12.931(3),c=12.703(3) Å, = 95.28(2), =105.97(2), =103.54(2)°. Refinement of the structure gave R=0.036. The Mo-Cl and Mo-P distances average 2.443(6) and 2.534(8) Å, respectively.Low-valent phosphine complexes of the Group VI metals continue to attract much attention because of their involvement in studies of the catalytic activation of dinitrogen⁽¹⁾, dihydrogen(^{2, 3}), alkenes and alkynes(⁴). As a by-product during our studies of dinitrogen(¹) and hydride(²) complexes of molybdenum and tungsten, we obtainedtrans-[MoCl_2- (PMe₂Ph)₄] as yellow, paramagnetic crystals (_eff= 2.84 B.M.). We first obtained the compound during the attempted synthesis ofcis-[Mo(N₂)₂(PMe₂Ph)₄] by reduction of MoCl₅ with Mg in the presence of PMe₂Ph (see Experimental). Upon identification of the compound we found that it could be readily synthesised by treatment of [MoCl₃(PMe₂Ph)₃]⁽⁵⁾ with LiBuⁿ in THF in the presence of PMe₂Ph (experimental).The complex was shown to have thetrans structure by x-ray analysis (Figure). Analogues oftrans-[MoCl₂(PMe₂Ph)₄] have been prepared, namely [CrCl₂(Me₂PCH₂CH₂PMe₂)₂]⁽⁶⁾,trans- [MoCl₂(PMe₃)₄]⁽⁷⁾, [WCl₂(PMe₂Ph)₄]⁽⁸⁾ and [WCl₂(PMe₃)₄]⁽⁴⁾, of which onlytrans-[MoCl₂(PMe₃)₄] has been examined by X-rays⁽⁷⁾. Its principal structural parametersi.e. d(Mo-Cl)= 2.420(6), d(Mo-P)_av=2.496(3) Å⁽⁶⁾ are close to those found here fortrans-[MoCl₂(PMe₂Ph)₄].     

Synthesis of some benzimidazole‐, benzothiazole‐ and pyridine‐derived chelating agents

Procedures are given for the preparation of new linear bidentate, tetradentate and tripodal heptadentate ligands incorporating benzimidazole, benzothiazole and pyridyl groups. The compounds were characterized by their nmr, uv and mass spectra. The crystal and molecular structure is reported for a chiral benzothiazole derived from camphoric acid.     

Rotational relaxation in the Ar—N2 system

The first (Z⁽¹⁾) and second (Z⁽²⁾) approximations to the rotational number of the Ar—N₂ system are compared for a range of temperatures. Although Z⁽¹⁾ and Z⁽²⁾ differ by a significant amount their difference remains nearly constant as a function of temperature. The effects of mass and potential parameter variations on the rotational relaxation time are also studied. When the mass of the incoming atom is decreased Z⁽²⁾ goes through a minimum while Z⁽¹⁾ steadily increases.     

A hydrogenation product derived from the diterpenoid barbatusin:A revised structure

The structure of the hydrogenation product of barbatusin, a diterpenoid from Coleus barbatus Bentham has been revised on the basis of NMR and X-ray data. A geminal coupling of unusually high magnitude has been observed and analysed.     

The NMR spectra of porphyrins—19: 13C and proton NMR spectra of metal-free porphyrins with the Type-IX substituent orientation,and of their zinc(II) complexes

The ¹³C and proton NMR spectra of six porphyrins bearing the substituent orientation characteristic of the natural “Type-IX” arrangement are reported and assigned. Significant concentration effects in the spectra of the free base porphyrins, together with the broadening of the C_α (and occasionally C_β) carbon resonances due to NH tautomerism caused a significant loss of data in these spectra. However, the spectra of the corresponding zinc(II) porphyrins (with addition of excess pyrrolidine) show that both these extraneous effects are completely removed to give well-resolved spectra with accurately reproducible chemical shifts. These spectra are assigned and an analysis of the chemical shifts allows the deduction of substituent chemical shift (SCS) parameters for the peripheral substituents at the beta and meso carbons. There is no global effect of these beta substituents, the beta carbon SCS being confined to the immediate pyrrole ring, and the meso carbon SCS to the two adjacent pyrrole rings. The SCS parameters are analyzed and it is shown how they can be used to predict the peripheral and meso carbon chemical shifts of any porphyrin bearing the substituents discussed.