Nomenclature bicyclic compounds

For simplicity, the numbering of ring positions in bicyclic compounds described in this index does not correspond necessarily to systematic nomenclature. 

The nomenclature of the oxidized forms of AA is badly in need of revision. Not only is dehydroascorbic acid a long and cumbersome name, but it is also confusing in inferring that the compound is an acid. As is discussed later in this chapter, the principle structure is a bicyclic compound containing both lactone and hemiketal groups. Names such as ascorbitone or dehydroascorbitone would be better trivial representations. 

For clarity in the following discussion, structure (5.11) shows the numbering system of the 2,2,1-bicycloheptyl skeleton. This ring system nomenclature is based on the bridgehead carbon atoms. To name a bicyclic compound, one first identifies the two bridgehead carbon atoms and then counts the number of atoms in each bridge. Thus in structure... 

Current IUPAC and Chemical Abstracts nomenclature has been employed in this index with the former given preference. Substitutive nomenclature has been given preference over radicofunc-tional, additive, subtractive, conjunctive or replacement nomenclature, except where this becomes unwieldy. With many bicyclic and polycyclic compounds bearing heteroatoms, standard bicyclic or polycyclic oxa, aza, and thia replacement nomenclature has often been used. With certain functional groups, where the names are rather complex and probably not familiar to most organic chemists, such as ylides, those compounds have simply been named as sulfur, tellurium and arsonic ylides. Metal catbenes have been treated similarly. With more complex functionality and many heterocycles, the Beilstein Commander Crossfire nomenclature system has been used with certain modifications. 

As 1,4 3,6-dianhydrohexitols are bicyclic systems, the appropriate ring-index nomenclature may also be used. The numbering of the atoms in such names differs from that used in the sugar-derived names. Furthermore, the stereochemistry for each of the anomeric centers has to be separately defined. The compounds under discussion have a 2,6-dioxabicylo[3.3.0]oc-tane framework, shown in Formula 6, and incorporates hydroxyl groups on C-4 and C-8. 

The scope of this problem can be indicated by a brief consideration of the stereochemical nomenclature of hydroxy derivatives of the bicyclic terpenes. For the parent bicyclic hydrocarbon compound known in the literature at present as cam-phane, the name "bomane is recommended in this report. (Reasons for choosing "bornane are discussed later under "The Bornane Hydrocarbons .) A mono-hydroxy derivative of bornane, on the basis of IUPAC rules (41), would be named as a bornanol. Two such derivatives have the common terpene names, bomeol and isobomeol these names, on the basis of recommendations in this report would both become 2-bornanol. Obviously, this is inadequate and additional designations are necessary to distinguish between die two stereoisomers. 

Recommended systematization of the nomenclature of the bicyclic terpene hydrocarbons will now be discussed for each of the four fundamental types. The thujane, carane, and pinane groups present very few and similar nomenclature problems. Some drastic steps are indicated, however, to resolve some of the difficulties encountered in naming the bomane-group compounds. For this reason, one set of rules is formulated below for the first three groups, and the rules for naming the bornane-group bicyclics will be discussed separately. 

Furthermore, the use of special subgroup names such as fenchenes, which applies to a series of synthetic compounds to indicate their derivation from fenchyl and iso-fenchyl derivatives and reportedly (33) to distinguish them from closely related naturally occurring terpenes, obviously complicates the problem of systematizing nomenclature. Names such as cyclofenchene and /8-difenchene are two additional memory exercises. Such irregularities in nomenclature have, of course, been carried over into the nomenclature of derivatives of these bicyclic hydrocarbons. 

Structures and the recommended names of compounds belonging to the bomane group of bicyclic terpene hydrocarbons are given in Chart 14. Reasons for coining the name bornane and for the necessity of using the norbomane-type names to systematize the nomenclature of the bicyclo 2.2. [] heptane bicyclics have been presented earlier. Examination of the names in Chart 14 reveals that in the systematic bicyclo 2.2.1 ]heptane names and the recommended norbornane names the prefix numbers for substituents and double bonds and the order of names of substituents are identical. 

No official action on the names of hydrocarbon terpene radicals was taken by the Nomenclature Committee of the ACS Organic Division at its meeting in New York City, September 1954, but general recommendations were discussed. It was agreed that the earlier acceptance of the system of nomenclature for the simple acyclic, monocyclic, and bicyclic terpene hydrocarbons implied the systematization of the hydrocarbon terpene radicals derived from these compounds. Therefore this Appendix F has been added here, but it has no official status. 

These recommendations and extension of nomenclature practices to apply to points of attachment outside the ring are basic to the rules for forming the names of the bicyclic radicals. Since the enumeration of the four parent compounds larger than the ring carbon skeletons is fixed, the position number of a point of attachment on radicals derived from them is predetermined and will not always be numbered as 1. For radicals derived from the nor- structures numbered according to the bicyclo plan, preference in assigning low numbers according to accepted practice is in the order point or points of attachment, double bonds, substituents. In the nor- names the position number of a point of attachment also will not always be numbered as 1. 

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