Ring compounds parent hydrides

Polycyclic parent hydrides. These are classified as bridged polyalkanes (also known as von Baeyer bridged systems, from the nomenclature system developed to name them), spiro compounds, fused polycyclic systems and assemblies of identical rings. The four systems may be either carbocyclic or heterocyclic. In developing their names, the following principles are used. 

Compounds composed of rings and chains are also named using substitutive nomenclature. The ring, whether carbocyclic or heterocyclic, is always selected to be the parent hydride. 

It is also used for naming compounds formally derived from the hydrides of certain elements in groups 13-17 of the periodic table. Like carbon, these elements form chains and rings which can have many derivatives, and the system avoids the necessity for specifying the location of the hydrogen atoms of the parent hydride. 

Although 3,8-diamino-l ll/-dibenzo(c,/)-l,2-diazepine-5-oxide [67, R = NH2, and 67, R = N(CH3)2] were first prepared in 190651 52 by reduction of 2,2 -dinitro-4,4 -diaminodiphenylmethane with zinc dust and ammonium chloride and subsequent air oxidation in basic medium, the ring system has not received any attention until recent years. The dibenzo compounds (67, R = C1, Br, and I) were first prepared by the same method.53 The parent diazepine (68, R = H)54 and the dihalodiazepines (68, R = F, Cl, Br, and I)53 have been prepared by lithium aluminium hydride reduction of the appropriate 2,2 -dinitrodiphenylmethane. In the case of the reduction of 2,2 -dinitro-4,4 -diiododiphenylmethane, either 68 (R = H) or 68 (R = I) could be obtained depending upon the amount of reducing agent used. Attempts to prepare the system 68 by oxidation of 2,2 -diamino-diphenylmethanes led to inconclusive results.55... 

Derivatives of 1-methyl-3//-l,4-benzodiazepine-2,5(l/I,4/I)dione (193) were synthesized by ring closure of substituted 2-(A-chloro-acetyl-A-methylaminoJbenzamides with sodium methoxide in methanol.209 Treatment of 193 with lithium aluminum hydride led to reduction of both carbonyl groups.209 The parent tetrahydro system (194) has been prepared by reaction of the tosylate (195) with 1,2-dibromoethane followed by hydrolysis.210 The preparation of 194 by another route had previously been noted.204 Reaction of 194 with formaldehyde or benzaldehyde gave a compound formulated as 196 (R = H or C6H5).210 Hydrolysis of 196 (R = C6H5) with 0.1 N hydrochloric acid gave 194 while 196 (R = H) was not hydrolyzed at this acidity. 

It is known that the parent compound, 1,3,5-triazine, shows ring cleavage when it is treated with nucleophiles. However, 2,4-diphenyl-l, 3,5-triazine undergoes a Chichibabin-type reaction where, formally, an amide group replaces a hydride anion. This is the only reported reaction of this type where substitution occurs at a triazine ring.52 53 (See also p 753.)... 

The cyclization can be carried out with halogenated amines, and substitution products of the new ring systems can also be obtained in the conventional way, by nitration, etc. Similar compounds can be prepared directly by using arylboron dichlorides in place of boron trichloride in the procedure indicated above. The parent borazarene derivatives, with hydrogen attached to boron, can be made from the B-hydroxy compounds with lithium aluminum hydride in the presence of aluminum chloride. N-Alkyl derivatives can be made either by using N-alkyl derivatives of the aminobiphenyls as starting materials, or by N-alkylation of the unsubstituted compounds via their N-lithio derivatives. Apart from their inherent interest, compounds of this type can serve as intermediates in various syntheses. Thus benzocinnolines and 2,2 -dihydroxybiphenyls can be obtained from derivatives of 2-aminobiphenyl. ... 

As in five-membered heterocycles, ring strain in six-membered heterocycles is of little or no importance. Pyran and thiine (thiopyran), with an oxygen or sulfur atom, respectively, and pyridine, with a nitrogen atom, are the parent compounds of six-membered neutral heterocycles with one heteroatom and the maximum number of noncumulative double bonds. In contrast to pyran and thiine, pyridine exists as a cyclic conjugated system. However, by (formal) abstraction of a hydride ion, both pyran and thiine can be converted into the corresponding cyclic conjugated cations, i.e. the pyrylium and the thiinium ions (thiopyrylium ion). 

A second large family of metallabenzenes—the iridabenzenes —has been synthesized by Bleeke and co-workers. Synthesis of the parent compound, 5, is shown in Scheme 3. The first step in this reaction involves formation of a transient j/ -pentadienyl— iridium species (A), which undergoes C—H bond activation, producing iridacyclohexadiene—hydride, B. This species is then aromatized in two steps (a) removal of the metal hydride with methyl triflate (CH3O3SCF3) to produce isolable C, followed by (b) deprotonation of the saturated a-ring carbon (C5) with lithium diisopropylamide in acetone. 

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