Other Unsaturated, Cyclic Compounds

Extension of this type of approach could provide a wide range of unsaturated compounds, illustrated by an acetylenic derivative having a Ci4 side chain in which the unsaturation occupies the central position.147 

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Boron Attached to Other Unsaturated Cyclic Compounds... 

Syntheses of 5,6- and Other Unsaturated Cyclic Compounds - A general approach to enol ethers, illustrated by conversion of nitro-alkene 37 into 38 by treatment with tetrabutylammonium hydrogen sulfate-potassium fluoride, has been described. The reaction was also found to be applicable to a wide range of acyclic sugars (see Section 4 below). 

Syntheses of 4,5- and Other Unsaturated Cyclic Compounds - Tosylhydra-zones of a-oxycarbonyl compounds are readily converted into vinyl ethers with sodium in ethylene glycol (Bamford-Stevens elimination) as illustrated by the conversion of 47 to 48. ... 

Aromatic hydrocarbons are unsaturated cyclic compounds that are resistant to addition reactions. The aromatic hydrocarbons derive their name from the distinctive odors they exhibited when discovered. Benzene is the most important aromatic compound. Because many other aromatic compounds are derived from benzene, it can be considered the parent of other aromatic compounds. Benzene molecular formula is... 

The coumarone-indene resins have been important commercial polymers produced in the sulfuric acid-catalyzed polymerization of mixed concentrates of these two compounds from coal tar naphthas. These and other unsaturated cyclics are also produced in the pyrolysis of petroleum oils for the production of manufactured gas, and the use of such petroleum-derived unsaturates is becoming of increasing significance in the production of this type of resin. 

Based on elemental composition and relative molecular mass determinations, the formula of benzene was found to be C6H6. The saturated hydrocarbon hexane has the molecular formula C6H14 and therefore it was concluded that benzene was unsaturated. Kekule in 1865 proposed the cyclic structure 4 for benzene in which the carbon atoms were joined by alternate single and double bonds. Certain reactions of benzene, such as the catalytic hydrogenation to cyclohexane, which involves the addition of six hydrogen atoms, confirmed that benzene was a ring compound and that it contained three double bonds. However, since benzene did not undergo addition reactions with HC1 and HBr, it was concluded that these double bonds were different from those in ethene and other unsaturated aliphatic compounds. 

Recent developments in the chemistry of the 1,2-unsaturated cyclic compounds, namely, the glycals and the 2-hydroxyglycals, are included in order to supplement the earlier Chapters on these topics. There follows a discussion of other cyclic and acyclic sugars which possess, at various positions in the carbon chain, alkenyl, enolic, or enamine systems. The scope has been arbitrarily restricted by the exclusion of the ends themselves [and, therefore, of reductones and compoimds related directly to L-ascorbic acid (1)], of such enones as the pyrone derivative (2), and of dienes or dienones [for example, kojic acid (3)]. Cyclohexene derivatives... 

This section deals with the reactions of amino compounds with phosgene generated from its common source or phosgene equivalents, by a direct transfer of the chlorocarbonyl group, giving carbamoyl chlorides. Reactions of imines and other unsaturated (cyclic) nitrogen compounds with phosgene will be discussed later. 

Interest has also continued in studies of the aromaticity of other unsaturated cyclic phosphorus compounds. A theoretical study of the 1,2-diphosphacyclooctatetraene system (228) has concluded that the ring system is perfectly planar when it has a global charge of —2 or +2, in contrast to the 1,2-diaza analogue which adopts a distorted, non-planar structure in the same oxidation states. However, it is thought unlikely that the phosphorus heterocycle will form planar metallocene complexes with metal ions. Theoretical and experimental studies have also been reported for the lone pair 671-aromatic anions P4 (229) and the arsenic analogue As4 . Both... 

The reaction described is of considerable general utility for the preparation of benzoyloxy derivatives of unsaturated hydrocarbons.2"8 Reactions of 2-butyl perbenzoate with various other classes of compounds in the presence of catalytic amounts of copper ions produce benzoyloxy derivatives. Thus this reaction can also be used to effect one-step oxidation of saturated hydrocarbons,9, 10 esters,6,11 dialkyl and aryl alkyl ethers,12 14 benzylic ethers,11,15 cyclic ethers,13,16 straight-chain and benzylic sulfides,12, 17-19 cyclic sulfides,11,19 amides,11 and certain organo-silicon compounds.20... 

It has long been known that unsaturated compounds containing a delocalized system of 71 electrons can rearrange into cyclic compounds or other n systems. Such reactions were only incidentally studied until 1930. 0. Diels and K. Alder published their first paper on diene synthesis (which was later given the name Diels-Alder reaction) in 1928. Subsequent work of K. Alder and G. Stein (1933 and 1937) proved the generality of the reaction and its high regio and stereo selectivity. This led to the interest on thermal transformations in unsaturated compounds. 

In contrast to the other large cats, the urine of the cheetah, A. jubatus, is practically odorless to the human nose. An analysis of the organic material from cheetah urine showed that diglycerides, triglycerides, and free sterols are possibly present in the urine and that it contains some of the C2-C8 fatty acids [95], while aldehydes and ketones that are prominent in tiger and leopard urine [96] are absent from cheetah urine. A recent study [97] of the chemical composition of the urine of cheetah in their natural habitat and in captivity has shown that volatile hydrocarbons, aldehydes, saturated and unsaturated cyclic and acyclic ketones, carboxylic acids and short-chain ethers are compound classes represented in minute quantities by more than one member in the urine of this animal. Traces of 2-acetylfuran, acetaldehyde diethyl acetal, ethyl acetate, dimethyl sulfone, formanilide, and larger quantities of urea and elemental sulfur were also present in the urine of this animal. Sulfur was found in all the urine samples collected from male cheetah in captivity in South Africa and from wild cheetah in Namibia. Only one organosulfur compound, dimethyl disulfide, is present in the urine at such a low concentration that it is not detectable by humans [97]. 

Much evidence has been accumulated that the ozone-olefin reaction has a predominant role in aerosol formation from alkenes, cyclic olefins, diolefins, and other unsaturated compounds. Free radicals are formed in the reaction and can react further, along with nitric oxide and nitrogen dioxide, either with the various intermediates or with the olefin itself (see the recent review by Pitts and Finlayson ). 

During the coverage period of this chapter, reviews have appeared on the following topics reactions of electrophiles with polyfluorinated alkenes, the mechanisms of intramolecular hydroacylation and hydrosilylation, Prins reaction (reviewed and redefined), synthesis of esters of /3-amino acids by Michael addition of amines and metal amides to esters of a,/3-unsaturated carboxylic acids," the 1,4-addition of benzotriazole-stabilized carbanions to Michael acceptors, control of asymmetry in Michael additions via the use of nucleophiles bearing chiral centres, a-unsaturated systems with the chirality at the y-position, and the presence of chiral ligands or other chiral mediators, syntheses of carbo- and hetero-cyclic compounds via Michael addition of enolates and activated phenols, respectively, to o ,jS-unsaturated nitriles, and transition metal catalysis of the Michael addition of 1,3-dicarbonyl compounds. ... 

In polymerizations of unsaturated compounds with Lewis acids the required reaction temperatures are below room temperature, down to -100 °C or even lower (see Example 3-16). On the other hand, cyclic monomers (see Sect. 3.2.3) frequently require higher temperatures. 

Saito et al. (32,121) developed a variety of tartaric acid derivatives, including Ci-symmetric chiral alkenes such as 76. The 1,3-dipolar cycloaddition between 76 and 77 gave primarily endo-1%. (Scheme 12.26) The diastereofacial selectivity of the reaction is excellent, as endo-1% is obtained with >98% de. Other cyclic and acyclic nitrones have been employed in reactions with 76, and in all cases, moderate to excellent endo/exo-selectivities and excellent diastereofacial selectiv-ities were obtained (32,121). Three other research groups have applied various y-hydroxylated ot,p-unsaturated carbonyl compounds in related reactions with nitrones (122-124). However, the selectivities were somewhat lower than those obtained by Saito and et al. (32,121). 

Aromatic aldehydes react very easily with tetramic acid under acidic conditions to give 3-benzylidene compounds (41). The yields are moderate, because often there are subsequent reactions. As a,/3-unsaturated carbonyl compounds, (41) react in a Michael addition with excess tetramic acid to form (67), but it can also react with other acyclic and cyclic 1,3-dicarbonyl compounds. In these reactions the aryl substituents may vary over a wide range. Thus, (67) and (68) can be cyclized with ammonium acetate to afford pharmacologically interesting compounds (70) and (71) (90TH1). The latter are dihydropyridines. Curiously, (69) does not cyclize under these conditions. (See Fig. 32.)... 

There are many other methods for carrying out 1,2 eliminations to give olefins. Several are particularly useful and widely used. Selenoxide eliminations are frequently used to install file double bond of a, /3-unsaturated carbonyl compounds. They occur by concerted, cyclic, syn processes... 

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