Phane names

Have a look at the structure (a).

(a)

calix[4]arene (trivial) pentacyclo[19.3.1.13,7.19,13.115,19]octacosa-1(25),3(28),4,6,9(27),10,12,15(26),16,18,21,23-dodecaene (von Baeyer) 1,3,5,7(1,3)-tetrabenzenacyclooctaphane (phane)

Applying von Baeyer nomenclature, we get a horrendously long and unwieldy name ‘pentacyclo[19.3.1.1^3,7.1^9,13.1^15,19]octacosa-1(25),3(28),4,6,9(27),10,12,15(26),16,18,21,23-dodecaene’. I think it’s a crime to name a beautifully symmetrical structure like (a) in such a fashion. Can’t we create a name that states the obvious: (a) is a big cycle containing four benzene rings?

I think we not just can but also should. And IUPAC provides an instrument for that in the form of phane nomenclature [1, 2]. Let’s start with cyclooctane (b):

(b)

cyclooctane

Now let us replace the atoms at positions 1, 3, 5 and 7 of cyclooctane by fat black dots thus (c):

(c)

cyclooctaphane

These fat black dots represent so-called superatoms^* that can be replaced by ring structures in an operation known as amplification [1, 2]. These ring structures are called amplificants. The name constructed in such a way is based on a “simplified skeletal name” which is basically a name of a parent hydride, e.g. cyclooctane (b), modified to contain ‘phane’, e.g. cyclooctaphane. Adding the locants for superatoms yields 1,3,5,7-tetracyclooctaphane (c). If we replace superatoms by benzene rings, we get 1,3,5,7-tetrabenzenacyclooctaphane. The recommendations [1, 2] refer to word parts such as ‘benzena’ as “amplification prefixes”, although the reader may already have guessed that they are in fact combining forms^†. If we want to specify that all benzene rings are attached at positions 1 and 3, we add these locants in parentheses following the superatom locants: 1,3,5,7(1,3)-tetrabenzenacyclooctaphane.

While replacing superatoms of (c) by furans attached at positions 2 and 5, we get 1,3,5,7(2,5)-tetrafuranacyclooctaphane (d):

(d)

calix[4]furan (trivial) 21,22,23,24-tetraoxapentacyclo[16.2.1.13,6.18,11.113,16]tetracosa-1(20),3,5,8,10,13,15,18-octaene (von Baeyer) 1,3,5,7(2,5)-tetrafuranacyclooctaphane (phane)

Phane nomenclature can be easily combined with skeletal replacement nomenclature. For instance, oxacalix[4]arene (e) is calix[4]arene (a) with four carbons replaced by oxygens. So we get the phane name for (e) by simply sticking ‘2,4,6,8-tetraoxa’ in front of the phane name for (a), thus 2,4,6,8-tetraoxa-1,3,5,7(1,3)-tetrabenzenacyclooctaphane.

(e)

oxacalix[4]arene (trivial) 2,8,14,20-tetraoxapentacyclo[19.3.1.13,7.19,13.115,19]octacosa-1(25),3(28),4,6,9(27),10,12,15(26),16,18,21,23-dodecaene (von Baeyer + replacement) 2,4,6,8-tetraoxa-1,3,5,7(1,3)-tetrabenzenacyclooctaphane (phane + replacement)

Likewise, we can derive the phane name for (f) starting from hexane (g). Here, all six carbon atoms of hexane are replaced by superatoms, thus hexahexaphane; replacing superatoms with pyridine rings results in hexapyridinahexaphane; indicating the points of attachments for pyridine rings, we get 1,6(2),2,3,4,5(2,5)-hexapyridinahexaphane. The advantage of this name over the ring assembly names is the absence of primes or superscripts.

(f)	(g)

2,2′:6′,2′′:6′′,2′′′:6′′′,2′′′′:6′′′′,2′′′′′-sexipyridine (ring assembly) 12,22:26,32:36,42:46,52:56,62-sexipyridine (ring assembly, PIN) 1,6(2),2,3,4,5(2,5)-hexapyridinahexaphane (phane) hexane

Nothing prevents us from creating phane names using non-identical amplificants. Consider UCL 1684 (h), a potent blocker of small conductance Ca²⁺-activated K⁺ (SK_Ca) channels [3]:

(h)

UCL 1684 (trivial) 17,24-diaza-1,9-diazoniaheptacyclo[23.6.2.29,16.219,22.13,7.010,15.026,31]octatriaconta-1(32),3(38),4,6,9(37),10(15),11,13,16(36),19,21,25(33),26(31),27,29,34-hexadecaene (von Baeyer + replacement) 11λ5,51λ5-6,10-diaza-3(1,3),8(1,4)-dibenzena-1,5(1,4)-diquinolinacyclodecaphane-11,51-bis(ylium) (phane + replacement)

The structure (h) can be thought of as a cyclodecane where atoms 1 and 5 are replaced by quinoline rings, atoms 3 and 8 replaced by benzene rings, and atoms 6 and 10 replaced by nitrogen atoms. The resulting phane name is 1¹λ⁵,5¹λ⁵-6,10-diaza-3(1,3),8(1,4)-dibenzena-1,5(1,4)-diquinolinacyclodecaphane-1¹,5¹-bis(ylium)^‡. It sure is long but still easier to read and interpret than von Baeyer name 17,24-diaza-1,9-diazoniaheptacyclo[23.6.2.2^9,16.2^19,22.1^3,7.0^10,15.0^26,31]octatriaconta-1(32),3(38),4,6,9(37),10(15),11,13,16(36),19,21,25(33),26(31),27,29,34-hexadecaene.

Some observations. There is no special class of compounds named “phanes”. The only thing all the structures that we can name as ‘phanes’ have in common is that they contain rings. For structures with many identical rings, phane nomenclature can give us shorter names compared to those offered by other methods.

The IUPAC recommendations say that “a phane replacement operation <...> represents an extension of the traditional skeletal replacement technique” [1]. Why can’t we name then the structure (a) simply 1,3,5,7(1,3)-tetrabenzenacyclooctane, rather than 1,3,5,7(1,3)-tetrabenzenacyclooctaphane? Knowing that the combining form ‘benzena’ is used for a replacement operation should be enough. As paradoxical it may sound, in phane nomenclature the ‘phane’ bit itself is redundant.

*	The meaning of “superatom” in phane nomenclature is completely different from that of superatom in inorganic chemistry.
†	“Amplification prefixes” are not prefixes because they contain content morphemes. For example, ‘benzena’ could be analysed as the base ‘benzen’ plus the functional morpheme ‘a’; in its turn, ‘benzen’ consists of the roots ‘benz’ and ‘en’.
‡	The descriptors 11λ5,51λ5 indicate that the nitrogen atoms at the position 1 of quinoline rings have the non-standard bonding number of five [4].

References

1. Powell, W.H. (1998) Phane nomenclature. Part I: Phane parent names (IUPAC Recommendations 1998). Pure and Applied Chemistry 70, 1513—1545.
2. Favre, H.A., Hellwinkel, D., Powell, W.H., Smith, H.A. and Tsay, S.S.-C. (2002) Phane nomenclature. Part II. Modification of the degree of hydrogenation and substitution derivatives of phane parent hydrides (IUPAC Recommendations 2002). Pure and Applied Chemistry 74, 809—834.
3. Rosa, J.C., Galanakis, D., Ganellin, C.R., Dunn, P.M. and Jenkinson, D.H. (1998) Bis-quinolinium cyclophanes: 6,10-diaza-3(1,3),8(1,4)-dibenzena-1,5(1,4)-diquinolinacyclodecaphane (UCL 1684), the first nanomolar, non-peptidic blocker of the apamin-sensitive Ca²⁺-activated K⁺ channel. Journal of Medicinal Chemistry 41, 2—5.
4. Powell, W.H. (1984) Treatment of variable valence in organic nomenclature (lambda convention) (Recommendations 1983). Pure and Applied Chemistry 56, 769—778.