Commission on Nomenclature of Organic Chemistry (111.1) Extension and Revision of the Nomenclature for Spiro Compounds

Spiro ring systems have two or more rings linked by one common atom. Several different methods are used to name such systems. Rules A-41, A-43, B-b and B-12 (Nomenclature of Organic Chemistry, 1979) describe the basics of how to name these compounds. The alternative methods in rules A-42 and B-i 1 are abandoned. This document describes the nomenclature in greater detail and extends it to cover branched polyspiro systems and compounds where three rings have one common spiro atom. A new notation, based on the von Baeyer method of naming spiro systems where all components are monocyclic, allows both unbranched and branched polyspiro systems to be named without ambiguity. It also enables the names to be readily interpreted. PREAMBLE The nomenclature and name spirane were proposed by von Baeyer [1] for bicyclic compounds with only one atom common to both rings. When a polycyclic ring system is spiro-fused to another ring or ring system Radulescu [2] recognised that each ring system needed to be named separately and, in addition, details of the spiro-fusion must be specified. These two systems were adopted by Patterson [3] in his study of ring systems. A third method of naming spiro compounds was adopted by The Chemical Society [4], which was documented with the other two in the JUPAC rules [5]. The von Baeyer system was covered by rules A-41.1 to A-41.3, A-43.1, B-1O.1, and B-i2.i; see also C-33i.2, C-514.3, D-6.24, D-6.93 and D7.51 for further examples. Its extension to three or more monocyclic rings spiro-fused is in rule A-41 .6. The method for systems containing polycyclic components is in rules A-4i.4, A-41.7, A-43.1, B-1O.2 and B-12. 1 and the third method, which is not used in this document, is in rules A-42 and B11.1. A special method used when both polycyclic systems are identical is in rule A-41.5, B-1O.2, D-6.7i and D-6.94. See also the summary in recommendation R-2.4.3 [6]. Additional examples are given in the Radicals, Ions and Radical Ions document [7]. In this document only the von Baeyer system, the spirobi[.. ..] and spiro[. . ..] methods are documented and extended to more complex systems, for example with branched spiro systems. In most cases the methods closely follow Chemical Abstracts practice ([8], Appendix IV, ¶156). Some differences are noted below. This document replaces rules A-4i, A-43, B-iO, B-i2 and R-2.4.3. The alternative methods of rules A-42 and B-il are abandoned. SP-O Spiro A spiro compound has two (or three) rings which have only one atom in common and the two (or three) rings are not linked by a bridge. The rings may form part of other ring systems (fused ring, bridged fused ring, system named by von Baeyer nomenclature, etc.). The common atom is known as a spiro atom. Spiro-fusion has been termed spiro union. SP-1 Compounds with only monocyclic ring components SP-1.1 Monospiro hydrocarbons with two monocyclic rings are named by the prefix spiro before a von Baeyer descriptor (indicating the numbers of carbon atoms linked to the spiro atom in each ring in ascending order and separated by a full stop) placed in square brackets and then the name of the parent hydrocarbon indicating the total number of skeletal atoms, e.g. spiro[4.4]nonane. © 1999 IUPAC, Pure App!. Chem. 71, 531—558 Nomenclature for Spiro compounds 533 SP-1.2 Monospiro hydrocarbons with two monocyclic rings are numbered consecutively starting in the smaller ring at an atom next to the spiro atom, proceeding around the smaller ring back to the spiro atom and then round the second ring. Example: spiro[4.5]decane not spiro[5.4ldecane SP-1.3 Heteroatoms are indicated by replacement prefixes (rules B-4.2, B-6. 1, [5]; and rules R-1 .2.2.1 and R-9.3, [6]) and unsaturation is indicated in the usual way (rule A11.3, [5];R-3.1.1, [6]) by the endings ene, diene, etc. Examples: HN'XIJ 8-azaspiro[4.5]dec-2-ene :od: spiro[4.4]nona-2,7-diene HNX3NH 3,9-diazaspiro[5.5]undecane SP-1.4 Unbranched polyspiro hydrocarbons composed of only monocyclic rings are named using dispiro-, trispiro-, etc. indicating the total number of spiro atoms present and the name of the parent hydrocarbon corresponding to the total number of carbon atoms present. Between the prefix and hydrocarbon name there is placed the von Baeyer descriptor which indicates the number of carbon atoms linked to the spiro atom or linking spiro atoms. The numbers are cited in order starting with a terminal ring and proceeding to the other terminal ring and back to the first via the other linking units. The numbers are separated by full stops and placed in square brackets. The compound is numbered in the order in which the numbers of its von Baeyer descriptor are cited. For trispiro and higher spiro systems each time a spiro atom is reached for the second time its locant is cited as a superscript number to the corresponding number of linking atoms [9]. Examples: 12 13 14 1 dispiro[4.2.4.2]tetradecane ©1 999 IUPAC, Pure App!. Chem. 71, 531—558 534 COMMISSION ON NOMENCLATURE OF ORGANIC CHEMISTRY 12 13 14 15 DK3<: trispiro[2.2.2.29.26.23lpentadecane Note: In previous rules [5,6] superscript numbers were not used but with the extension of this system to branched spiro systems (see SP1.5) where superscript numbers are essential it is clearer to use them for all polyspiro systems with three or more spiro atoms using a von Baeyer descriptor. SP-1.4.1: If there is a choice of numbers the name that gives the lower locants for spiro atoms is selected. Example: 1O43 dispiro[4. 1 .5.2]tetradecane not dispiro[5. 1 .4.2]tetradecane nor dispiro[4.2.5. 1]tetradecane nor dispiro[5.2.4. ljtetradecane (5,7 is lower than 6,8 or 5,8 or 6,9) SP-1.4.2: If there is still a choice of numbering the numbers of the von Baeyer descriptor are considered in the order of citation. The name is selected with lower numbers at the first point of difference. Example: 'IIEI< Eti>1x1A) trispiro[2.2.2.29.26.33]hexadecane not trispiro[2.2.2.29.36.23]hexadecane (2.2.2.29.26.33 is lower than 2.2.2.29.36.23) SP-1.5 Branched polyspiro hydrocarbons composed of only monocyclic rings are named using trispiro-, tetraspiro-, etc. indicating the total number of spiro atoms present and the name of the parent hydrocarbon corresponding to the total number of carbon atoms present. Between the prefix and hydrocarbon name there is placed the von Baeyer descriptor which indicates the number of carbon atoms linked to the spiro atom or linking spiro atoms. The numbers are cited in order starting with a terminal ring and proceeding to the next terminal ring and so on to the first spiro atom. The numbers are separated by full stops and placed in square brackets. The compound is numbered in the order in which its von Baeyer descriptor is cited. Each time a spiro atom is reached for the second time its locant is cited as a superscript number to the corresponding number of linking atoms [9]. trispiro[2.2.26.2.211 .23]pentadecane © 1999 IUPAC, Pure App!. Chem. 71, 531—558 Examples: Nomenclature for Spiro compounds 535 Note: Without the superscript numbers this name would be the same as the name of the second example under SP1.4 without superscript numbers. ssI._.o .7 L-1 \ H2Si \ 0 / \ ,0 O / °SiH2 H2Si-° tetraspiro[5. 1 8 1 15 1 522 16]dodecasiloxane CAS index name does not have the superscript numbers. Without superscript numbers more than one structure is possible. 17 1820____21 nonaspiro[2.O.O.O.26.O.29.05.0.O.2'3.O.216.012.04.O.219.03]henicosane 5,6,16, 17-tetraoxahexaspiro[2.O.2.O.28.2.213.07.24.O.218.23ldocosane 13, 15,28,29-tetraoxa14-silapentaspiro[5.0.57. 1.1.516.0.522.114 16]nonacosane SP-1.5.1 If there is a choice of numbering the name which gives the lowest locants for spiro atoms is selected. trispiro[2.0.24. 1.28. 13]undecane not trispiro[2.1.25.O.28.13]undecane nor trispiro[1.2.25.1.29.03]undecane (3,4,8 is lower than 3,5,8 or 3,5,9) ©1999 IUPAC, Pure App!. Chem. 71, 531—558 Examples: 536 COMMISSION ON NOMENCLATURE OF ORGANIC CHEMISTRY decaspiro[4, 1.0.1.510.28.2.1.0.2.426.223.0.2.436.233.222.120. 17.35]nonatetracontane Ref 10 name decaspiro[4.1.0(1.5.2)2.1 .0(2.4.2)0.2.4.2.2.1.1 .3]nonatetracontane SP-1.5.2 If there is still a choice of numbering the numbers of the von Baeyer descriptor are considered in the order of citation. The name is seleced with lower numbers at the first point of difference. Example: pentaspiro[2.0.24. 1.1.210.0.213. 18.23]octadecane not pentaspiro[2.0.24. 1.1 .210.0.2'3.28.l3joctadecane (2.0.24.1.1.210.0.213.18.23 is lower than 2.0.24.1.1.210.0.213.28.13) SP-1.6 Ring systems composed of three monocyclic rings with only one spiro atom (i.e. a hexavalent spiro atom) are named by placing the prefix spirobefore the von Baeyer descriptor followed by the name corresponding to the hydrocarbon with the total number of skeletal atoms present in the ring system. Heteroatoms are indicated by replacement terms (SP1.3) and non-standard valency by the lambda symbol [11] (see SP-7 for further details). The locant of the spiro atom is used as a superscript number to the corresponding number of the von Baeyer descriptor to indicate each time the spiro atom is revisited [9]. Example: