Partially hydrogenated fused

A great deal of control can nowadays be exerted over the products obtained on partial hydrogenation of fused aromatic systems. Selectivity depends on... 

Some data have been recorded for dithieno fused borepins. The resonance occurred at 8 38.9 for the ether (26 R = 0) but the corresponding partially hydrogenated species absorbed at 8 36.8, i.e. no large difference was found (73CS(4)183). 

Stelzner Method. This is a general method of applying replacement nomenclature to ring systems it differs from the Chemical Abstracts procedure in that replacement principles are applied in all cases to the name of the hydrocarbon with the same bond distribution in the rings as the heterocycle to be named. This leads to no difference for monocycles (see examples 1-3), but in the case of fused skeletons the parent hydrocarbon of a fully unsaturated heterocycle is frequently a partially hydrogenated molecule. The parent hydrocarbon name for application of either replacement method can be trivial or a name derived by fusion principles (as above). The examples 21-24 of both... 

This illustrates the correct way of naming a ketone derivative of a partially unsaturated fused heterocycle as far as determining the mode of citation of the degree of hydrogenation is concerned, the parent is structure a, not b [which could yield incorrect names such as 4,4,7,9-tetrabromo-2,3,4,5-tetrahydro- H-l-benzazepin-5-one or 4,4,7,9-tetra-bromo-2,3-dihydro-l//-l-benzazepin-5(4/f)-one] (IUPAC Rule C-315). 

The conversion of the cycloadducts (57) and (58) to isocomene proceeds accorditig to plan. Thermolysis of the former provides diene (89), which is also obtained from cycloadduct (58), presumably via a 1,3-alkyl shift which produces (57) as an intermediate. Partial hydrogenation of diene (89) affords isocomene in six steps from commercially available starting materisds. The brevity of this )i oach to such angularly-fused triquinanes is a further manifestation of the synthetic benefit arising from the complexity increase associated with the meta cycloaddition. 

The initial rate of hydrogenation of fused polycyclic aromatics increases with the number of rings present phenanthrene > naphthalene > benzene. Only one ring is generally saturated at a time. This partial hydrogenation is accomplished because... 

Polyheteroaromatic systems containing a fused pyridine ring are susceptible to partial hydrogenation, with the pyridine ring the site of attack. The following examples involve lA and 3,3 -bis(9-phenanthrenyl)-BINOL IB. ... 

Heterocyclization on alkylation of phenols with terpenoids leading to partially hydrogenated polycyclic fused furans and pyrans 00KPS198. 

Fused Systems.—Naphthalene and Derivatives. A new method of aromatization of partially hydrogenated aromatic hydrocarbons overcomes the difficulty of the competing Diels-Alder reaction of reactive arenes. The method is based on deprotonation-hydride elimination in which potassium fencholate (277) serves as the base and fenchone (278) as the hydride acceptor, catalytic amounts only of fencholate being required since it is regenerated in the aromatisation step. In this way, the conversion of 1,2-dihydronaphthalene into naphthalene and of 9,10-dihydroanthracene into anthracene proceeds almost quantitatively. 

Anhydrous zinc chloride can be made from the reaction of the metal with chlorine or hydrogen chloride. It is usually made commercially by the reaction of aqueous hydrochloric acid with scrap zinc materials or roasted ore, ie, cmde zinc oxide. The solution is purified in various ways depending upon the impurities present. For example, iron and manganese precipitate after partial neutralization with zinc oxide or other alkah and oxidation with chlorine or sodium hypochlorite. Heavy metals are removed with zinc powder. The solution is concentrated by boiling, and hydrochloric acid is added to prevent the formation of basic chlorides. Zinc chloride is usually sold as a 47.4 wt % (sp gr 1.53) solution, but is also produced in soHd form by further evaporation until, upon cooling, an almost anhydrous salt crystallizes. The soHd is sometimes sold in fused form. 

Oxadiazole (1 R = R = H) is calculated to be 8.9 kcal moU less stable than its open chain tautomer (2) (85AG(E)713>. On the other hand, 1,2,3-benzoxadiazole is about 1 kcal mol more stable than 2-diazocyclohexadienone (91JST(247)135>. The position of the equilibrium is markedly affected by substituents. The benzoxadiazole (4) is more stable than its tautomer (5) by about 1.5 kcal mol but tetrafluorobenzoxadiazole is substantially less stable than the corresponding diazocarbonyl isomer. The open-chain forms are also favoured by polar solvents and by hydrogen bonding. In the naphthalene series, the stabilization of the fused oxadiazole (6) relative to its open chain tautomer can be ascribed to partial bond fixation in the naphthalene system, which disfavours... 

The nomenclature of ring systems containing the partially or fully hydrogenated monocyclic, bicyclic, and tricyclic fused 1,2-oxazine ring skeleton are shown in Figure 1. 

A method of separation which avoids the preparation of the double fluorides consists in fusing the mixed niobic and t an tali c acids with sodium carbonate and nitrate, the product is digested with warm water and a current of carbon dioxide is passed through the solution. It is claimed that only tantalic acid is precipitated.5 This process has, however, been the subject of adverse criticism.6 Partial separation of niobium from tantalum can be effected by warming the mixed, freshly precipitated, hydrated oxides with a mixture of hydrogen peroxide and hydrochloric acid the niobium dissolves readily, while the tantalum dissolves only sparingly.7... 

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