Contiguous double bonds

Addition to compounds with contiguous double bonds... 

The annulenes are that series of monocyclic polyolefins (C H ) containing a complete system of contiguous double bonds. While benzene (the best known member of this class of compounds) has been in evidence for some time it is only of late that interest in the higher members has become apparent. This interest has its origins in the LCAO-MO theory of re-elec-tron systems as formulated by E. Hiickel (in particular the "Hiickel rule relating aromatic stability to structure). Although the non-classical chemistry of the benzenoid hydrocarbons had previously been the subject of some conjecture, Httckel s theoretical studies provided the first satisfactory explanation of the peculiar stability of this class of compounds and, incidently, the elusiveness of cyclobutadiene. 

The vulcanization by sulphur alone is faster for ENR than for NR as isolated double bonds react more rapidly than contiguous double bonds. The presence of isolated double bonds also increases the efficiency of vulcanization as they inhibit the formation of in-chain cyclic sulphides. ... 

It is part of the general family of carotenoids, produced in nature to the tune of 100 million tons per year and responsible for the orange color of carrots and many other fruits and vegetables. Its color is due to the presence of 11 contiguous double bonds, which cause the absorption of visible light. 

Another very specific subtractive naming mode has been developed for cyclic compounds containing (if only formal) contiguous double bonds -cyclic cumulenes - whose treatment with conventional nomenclatural means would often lead to rather cumbersome combinations of ene , dehydro , and indicated H notations. 

The enol ether double bond contained within the ds-fused dioxa-bicyclo[3.2.0]heptene photoadducts can also be oxidized, in a completely diastereoselective fashion, with mCPBA. Treatment of intermediate XXII, derived in one step from a Patemo-Buchi reaction between 3,4-dimethylfuran and benzaldehyde, with mCPBA results in the formation of intermediate XXIII. Once again, consecutive photocycloaddition and oxidation reactions furnish a highly oxygenated system that possesses five contiguous stereocenters, one of which is quaternary. Intermediate XXIII is particularly interesting because its constitution and its relative stereochemical relationships bear close homology to a portion of a natural product known as asteltoxin. 

The epoxyketone 3 is a versatile precursor for a variety of tricycloundecane systems having a p,y-unsaturated carbonyl chromophore, which are not so readily accessible. The contiguous epoxy ketone functionality and the double bond present in the five-membered ring provide opportunities for further manipulation. Adduct 3 may be transformed into a variety of molecular frameworks such as linearly fused cis anti cis tricyclopentanoids, protoilludanes, and marasmanes in a stereoselective fashion after suitable chemical and photochemical manipulation.13... 

This section relates to the introduction of a double or triple bond between two contiguous carbon atoms of the backbone chain of a monosaccharide derivative. A double bond between a carbon atom of the backbone chain and an atom outside that chain, or a double or triple bond between two carbon atoms outside the backbone chain, will be treated according to the normal rules of organic nomenclature [13,14],... 

Lycorine is the most abundant alkaloid in plants of the Amaryllidaceae. Several syntheses of racemic lycorine had been reported prior to our initiation of studies directed at an asymmetric synthesis of the unnatural enantiomer 64. 2 a common theme in all of the syntheses of ( )-lycorine has been the utilization of either an intermolecular or intramolecular Diels-Alder construction of the key C-ring of the alkaloid. This six-membered ring presents a rather formidable synthetic challenge because of the four contiguous stereogenic centers, the trans 1,2-diol moiety, and the juxtaposition of the aromatic substituent and the carbon-carbon double bond. 

Alternate Conformational Representations. In some instances, the C-P formalism does not provide the most economical description, as exemplified by the six-atom ring of dihydropyran. Like cyclohexene, dihydropyran has a double bond that enforces essential coplanarity on four contiguous ring atoms. While the C-P puckering description for... 

The key problem in the preparation of 296, 297 undoubtedly is the stereoselective assembly of the chains of four to five contiguous cyclopropyl groups. The strategies of all total syntheses known so far rely on auxiliary-directed stereoselective cyclopropanations of double bonds [111a, 163,164]. The chemistry of bicyclopropylidene (1), namely its capability to be functionalized (Schemes 8, 9), dimerized (Scheme 15), and stereoselectively reduced (Scheme 53) opens up new perspectives to approach the assembly of quatercyclopropyl derivatives. 

Various degrees and kinds of unsaturation are possible. Unsaturation may be cumulative (which means that there are at least three contiguous carbon atoms joined by double bonds, C=C=C) or non-cumulative (which is another arrangement of two or more double bonds, as in -C=C-C=C-). In nomenclature, unsaturated cyclic parent hydrides have, by convention, the maximum number of non-cumulative double bonds. They are generically referred to as mancudes — derived from the acronym MANCUD, the MAximum Number of non-CUmulative Double bonds. Four classes of cyclic parent hydride are therefore recognised ... 

Cumulative double bonds are those present in a chain in which at least three contiguous carbon atoms are joined by double bonds non-cumulative double bonds comprise every other arrangement of two or more double bonds in a single structure. The generic name cumulene is given to compounds containing three or more cumulative double bonds. 

As outlined above, MeBmt contains three contiguous asymmetric carbon atoms and an (E)-trans double bond. The MeNH and OH groups are arranged in a threo configuration, whereas the OH and CH3 groups are oriented in the erythro form. 

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