Ring compounds Hantzsch-Widman names

Hantzsch-Widman names are used for one-ring heterocyclic systems that do not have trivial names. The names are applied to monocyclic compounds containing one or more heteroatoms in three- to ten-membered rings. The names are derived by combining the appropriate prefix or prefixes for the heteroatoms with a stem denoting the size of the ring (see below). The state of hydrogenation is indicated either in the stem or by the prefixes dihydro-, tetrahydro-, etc. 

This system also can be used for simpler ring systems. Thus, phos-phabenzene was the name first used when this compound initially was synthesized in 1971 by A. Ashe." The Hantzsch-Widman name would be the less informative phosphinine. 

The names borazole, boroxole and borthiole, respectively, for the three compounds in Examples 4, 5 and 6 have been abandoned long ago as they imply five-membered rings in the Hantzsch-Widman system. The names borazin(e), boroxin and borthiin indicate six-membered rings with unsaturation and only one boron atom and one other heteroatom (although the order of the element name stems is wrong) and are also not acceptable. 

The parent isoxazolidine (1) can be named as 1,2-oxazolidine according to the extension of the Hantzsch-Widman system. However, since the corresponding heterocycle (2) with the greatest number of non-cumulative double bonds is conventionally called isoxazole, 1 is most frequently referred to as isoxazolidine, which is used in Chemical Abstracts (CA). The hydro-isoxazole or -isoxazoline nomenclature is used solely in connection with the condensed ring for instance, compound 3 may be called either octahydro-l,2-benzisoxazole (CA nomenclature) or 4,5-tetramethyleneisoxazolidine (as a derivative of the isoxazolidine), or 7-oxa-8-azabicyclol4.3.0]nonane (3 ) (Stelzner method). A bis-isoxazolidine is called tetrahydro-2//-isoxazolo[2,3-6]-isoxazole (4) (CA method), or conventionally isoxazolizidine (4 ). 

The Hantzsch-Widman system is well suited for the naming of saturated monocyclic compounds. Bridged ring systems, however, present a special challenge, and here the replacement system is preferred. An example is provided by the framework of the bicyclic hydrocarbon norbornane. Heteroatoms may in principle be substituted for any of the carbons. To illustrate, nitrogen substitution at position 7 would give rise to the name 7-azanorbomane. 

Compound (XXIV) is a clear case for the Hantzsch-Widman procedure (p. 76). The ending -ine denotes a nitrogenous six-membered ring, so the name is 1,2,4,6-tetrazine. 

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