Nonaromatic double-bonded

Substituted and benzo-annulated oxepins readily undergo addition of bromine across the nonaromatic double bond. Bromination of 3,6-bridged oxepins can occur in two different ways, either as a 1,2-addition164 or as formal 1,4-addition to the diene system of the corresponding benzene oxide to give products i.129 138-140 164... 

Bromine can also undergo addition to the nonaromatic double bond of dibenz[ft,/]oxe-pin.160,161 Oxygen-bridged annulenes that incorporate an oxepin structure have been shown to undergo 1,4-addition of bromine at — 78°C.159... 

In 1-benzoxepins the benzene oxide form is energetically unfavorable. Thus, the adducts 5 formed with dienophiles such as ethenetetracarbonitrile arise from the oxepin structure with the nonaromatic double bonds as diene fragment.233 The yields of these reactions arc almost quantitative. 

The use of hydrodesulfurization in the determination of the structures of unknown benzo[6]thiophenes is becoming increasingly recognized about 100 examples have now been recorded. Two sets of experimental conditions are commonly used the benzo[6]thiophene may be treated with Raney nickel alloy directly in alkaline medium (the method of Papa et al.7M), or it may be boiled in ethanol with Raney nickel of varying reactivity (commonly W-7). Even under mild conditions, nonaromatic double bonds are usually saturated, halogens are removed, and nitro groups are reduced. Raney cobalt has about one-tenth the activity of Raney nickel in the hydrodesulfurization of benzo [6]thiophenes.765... 

Under the mild conditions used, only the nonaromatic double bond was hydrogenated. 

Reaction with OH will represent an important daytime loss for 2,3-benzofuran with a lifetime 3 h for [OH] = 2.5 x 10 molecule cm . The only product quantified in both the ozonolysis and OH-initiated oxidation of 2,3-benzofuran was 2-hydroxybenzaldehyde (salicylaldehyde) (Atkinson et al., 1992a). Observed yields were 13 7% from the ozonolysis and 26 5% from the OH reaction in the presence of NO c. This product is likely obtained from attack of O3 or OH on the nonaromatic ring. Atkinson et al. (1992a) suggest that the OH reaction may proceed roughly 30% via addition to the nonaromatic double bond (leading to salicylaldehyde), and 70% via addition to the aromatic ring (products unknown). 

The participation of a single double bond of a heterocycle is found in additions of small and large rings azirines (Section 5.04.3.3) and thietes (Section 5.14.3.11) furnish examples. Azepines and nonaromatic heteronins react in this mode, especially with electron deficient dienes (Scheme 16 Section 5.16.3.8.1). 

Diene moieties, reactive in [2 + 4] additions, can be formed from benzazetines by ring opening to azaxylylenes (Section 5.09.4.2.3). 3,4-Bis(trifluoromethyl)-l,2-dithietene is in equilibrium with hexafluorobutane-2,3-dithione, which adds alkenes to form 2,3-bis-(trifluoromethyl)-l,4-dithiins (Scheme 17 Section 5.15.2.4.6). Systems with more than two conjugated double bonds can react by [6ir + 2ir] processes, which in azepines can compete with the [47t + 27t] reaction (Scheme 18 Section 5.16.3.8.1). Oxepins prefer to react as 47t components, through their oxanorcaradiene isomer, in which the 47r-system is nearly planar (Section 5.17.2.2.5). Thiepins behave similarly (Section 5.17.2.4.4). Nonaromatic heteronins also react in orbital symmetry-controlled [4 + 2] and [8 + 2] cycloadditions (Scheme 19 Section 5.20.3.2.2). 

Synthesis of the title compound is representative of a number of syntheses of nonaromatic nitrogen heterocycles via Pd(Ill-catalyzed amination of olefins. These tosylated enamines are not readily available by standard synthetic methods, and show potential for further functionalization of the heterocycle. The saturated amine can be synthesized from the title compound by hydrogenation of the double bond followed by photolytic deprotection. ... 

The nonaromatic character of oxepins makes this structure susceptible to the reduction of one or more double bonds. 10-[(2-Aminoethyl)sulfanyl]-substituted dibenz[b,/]oxepins with various substituents in position 2 smoothly react to give the 10,1 l-dihydrodibenz[b,/]oxepin system 1 on treatment with magnesium in methanol.71 202 The advantage of this method is the possibility of reducing dibenz[b,/]oxepins with various heteroatoms such as sulfur, oxygen or nitrogen in the side chain. 

When dimethyl 3-benzoxepin-2,4-dicarboxylate is reacted under controlled conditions (15 min) with hydrogen it is possible to isolate dimethyl l,2-dihydro-3-benzoxepin-2,4-dicarboxylate.17 Hydrogenation of 2-nitrodibenz[, /]oxepin-10-carboxylic acid in the presence of palladium on potassium carbonate results in the reduction of the nonaromatic C C double bond and the nitro group to give 2-amino-10,l l-dihydrodibenz[i,/]oxepin-10-carboxylic acid.107... 

Foremost among the classes of the nonaromatic unsaturated systems is that of compounds in which the substituent is bonded to a carbon-carbon double bond. It is convenient to divide the data sets for carbon-carbon double bonds into five categories vinyl, vinylidene, frans-vinylene, cis-vinylene, and reactions of carbon-carbon double-bond sets. 

Perhaps the largest class of nonaromatic unsaturated systems is that of the carbon-heteroatom double bonds, including as it does the carbonyl compounds. 

Nonaromatic hydrocarbons that do not contain such a ring system. Included here are alkanes, which are fully saturated hydrocarbons alkenes, which contain one or more double bonds and alkynes, which contain one or more triple bonds. 

Reduction of dienes and polyenes has attracted much attention since it is important from both practical and theoretical aspects. In these reactions the major interest is the selective reduction of a double bond in the presence of another. In general, saturation of all the multiple double bonds of nonaromatic compounds can be carried out with any of the catalysts which are suitable for low-pressure reductions or with some reducing chemicals. 

The 4a,9b double bond in 1,2,3,4-tetrahydrodibenzothiophene 5,5-dioxide (68) and similar compounds, is essentially nonaromatic and in this respect resembles the 2,3 bond in benzo[6]thiophene 1,1-dioxide. Catalytic reduction of 68 results in the formation of l,2,3,4,4a,9b-hexahydrodibenzothiophene 5,5-dioxide (92 /o). Subsequent reduction of the sulfone with LAH yields 1,2,3,4,4a,9b-hexahydrodibenzothiophene (69) as an oil (78 /o). Oxidation of 4-keto-l,2,3,4-tetrahydrodi-benzothiophene (44a) to its sulfone with peracetic acid (63 /o) followed by... 

More precisely, Eq. (33) represents the difference between the magnetic susceptibility of a cyclic conjugated system and that of a hypothetical cyclic system with localized double bonds in which the ring current vanishes. A molecule is aromatic when A>0 and antiaromatic when A<0, and at A 0 it is nonaromatic [61JCP1996 68JA811 75MI2 83JMS( 102)377]. 

Vcyc is the contribution from nonaromatic rings containing no double bonds. 

Cyclooctatetraene (or simply cyclooctatetraene) is a bright-yellow, nonplanar, nonaromatic compound (Section 21-9A). Apparently the resonance energy of a planar structure is insufficient to overcome the unfavorable angle strain the planar structure would have with its C-C-C bond angles of 135°. Cyclooctatetraene normally assumes a tub structure with alternating single and double bonds ... 

We will take a semiempirical approach using numerous molecules, models, assumptions, and estimates rather than doing new calorimetric experiments and/or quantum chemical calculations. Indeed, we will also test what is probably the simplest assumption - that (4n + 2) n electrons found within a conjugated ring species is expected to result in enhanced stability and that this compound is called aromatic. We will consider the dihydroindene (indane) skeleton composed of a benzene ring fused to a nonaromatic five-membered ring that lacks additional double bonds, and will use this carbocyclic hydrocarbon with X = Y = Z = CH2 as a paradigm for many heterocyclic derivatives for which the possible aromaticity is of relevance to the current chapter. Similarly we use indene with -X-Y- = -CH=CH-, Z = CH2 for a variety of unsaturated heterocycles of interest here. 

Consider the dihydroindene (indane) (XIV) skeleton composed of a benzene ring fused to a nonaromatic five-membered ring that lacks additional double bonds. We may consider this carbocyclic hydrocarbon with X=Y=Z=CH2 (XV) as a paradigm for a... 

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