{{Short description|Any chemical compound having one atom as the only common member of two rings}} [[Image:CSD CIF VOPHAJ.png|thumb|Structure of C<sub>17</sub>H<sub>20</sub>, which contains seven spiro atoms and eight cyclopropane rings<ref>{{cite journal |doi=10.1002/1521-3765(20010917)7:18<4021::AID-CHEM4021>3.0.CO;2-E |title=Spirocyclopropanated Bicyclopropylidenes: Straightforward Preparation, Physical Properties, and Chemical Transformations |date=2001 |last1=De Meijere |first1=Armin |last2=von Seebach |first2=Malte |last3=Zöllner |first3=Stefan |last4=Kozhushkov |first4=Sergei I. |last5=Belov |first5=Vladimir N. |last6=Boese |first6=Roland |last7=Haumann |first7=Thomas |last8=Benet-Buchholz |first8=Jordi |last9=Yufit |first9=Dmitrii S. |last10=Howard |first10=Judith A. K. |journal=Chemistry - A European Journal |volume=7 |issue=18 |pages=4021–4034 |pmid=11596945 }}</ref>]]

In [[organic chemistry]], '''spiro compounds''' are [[Organic compound|compounds]] that have at least two [[Cyclic compound|molecular rings]] sharing one common atom. Simple spiro compounds are [[bicyclic]] (having just two rings).<ref name="IUPACspiros">{{cite journal |author=Moss, G.P. |year=1999 |title=Extension and Revision of the Nomenclature for Spiro Compounds |journal=[[Pure and Applied Chemistry|Pure Appl. Chem.]] |volume=71 |issue=3 |pages=531–558 |doi=10.1351/pac199971030531 |issn=1365-3075 |s2cid=20131819 |doi-access=free}} Note, the article co-authors, the Working Party of the IUPAC (1992-1998), were P. M. Giles, Jr., E. W. Godly, K.-H. Hellwich, A. K. Ikizler, M. V. Kisakürek, A. D. McNaught, G. P. Moss, J. Nyitrai, W. H. Powell, O. Weissbach, and A. Yerin. ''Also available online at'' {{cite web |title=Extension and Revision of the Nomenclature for Spiro Compounds |url=http://www.chem.qmul.ac.uk/iupac/spiro/ |access-date=3 February 2016 |publisher=Queen Mary University of London |location=London, GBR}} ''Also available in German, with et al. indicating the same working party, at'' {{cite journal |author=Hellwich, Karl-Heinz |display-authors=etal |date=18 October 2002 |title=Erweiterung und Revision der Nomenklatur der Spiroverbindungen |journal=[[Angewandte Chemie]] |volume=114 |issue=20 |pages=4073–4089 |bibcode=2002AngCh.114.4073H |doi=10.1002/1521-3757(20021018)114:20<4073::AID-ANGE4073>3.0.CO;2-T |quote=Die Übersetzung basiert auf der "Extension and Revision of the Nomenclature for Spiro Compounds" der Commission on Nomenclature of Organic Chemistry (III.1) der Organic Chemistry Division der International Union of Pure and Applied Chemistry, veröffentlicht in Pure Appl. Chem. 1999, 71, 531–558.}}</ref>{{rp|SP-0}}<ref name=ClaydenOC12>{{cite book |author1=Clayden, Jonathan |author2=Greeves, Nick |author3=Warren, Stuart | year = 2012 | title = Organic Chemistry | edition = 2nd | pages = 319f, 432, 604, 653, 746, 803, 839, 846f | location = Oxford, UK | publisher = Oxford University Press | url = https://books.google.com/books?isbn=0199270295 | access-date = 2 February 2016 | isbn = 978-0-19-927029-3 }}</ref>{{rp|653,839}} The presence of only one common atom connecting the two rings distinguishes spiro compounds from other bicyclics.<ref name="Reusch">For all four categories, see {{cite book |author=Reusch, William |title=Virtual Text of Organic Chemistry |publisher=Michigan State University, Department of Chemistry |year=1999 |edition=Jan. 2016 |location=East Lansing, MI, USA |chapter=Saturated Hydrocarbons, Alkanes and Cycloalkanes: Cycloalkanes (Table: Examples of Isomeric C<sub>8</sub>H<sub>14</sub> Bicycloalkanes) ''or'' Nomenclature: Cycloalkanes (same Table), ''and passim'' |access-date=3 February 2016 |chapter-url=https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/intro1.htm}} The specific chapters can be found at [https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/chapt5.htm] and [https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/nomen1.htm#nom2b], respectively, same access date. For the description featuring adjacent atoms for all but the isolated category, see Clayden, op. cit.</ref><ref name=ClaydenOC12/>{{rp|653ff}} {{rp|839ff}} Spiro compounds may be fully [[carbocyclic]] (all carbon) or [[heterocyclic]] (having one or more non-carbon atom). One common type of spiro compound encountered in educational settings is a heterocyclic one— the [[acetal]] formed by reaction of a [[diol]] with a cyclic [[ketone]].

The common atom that connects the two (or sometimes three) rings is called the ''spiro atom''.<ref name=IUPACspiros/>{{rp|SP-0}} In carbocyclic spiro compounds like spiro[5.5]undecane, the spiro-atom is a [[quaternary carbon]], and as the ''-ane'' ending implies, these are the types of molecules to which the name ''spirane'' was first applied (though it is now used general of all spiro compounds).<ref name="ElielEtal94">{{cite book |author1=Eliel, Ernest Ludwig |url=https://books.google.com/books?id=IyfwAAAAMAAJ |title=Stereochemistry of Organic Compounds |author2=Wilen, Samuel H. |author3=Mander, Lewis N. |publisher=Wiley & Sons |year=1994 |isbn=978-0-471-01670-0 |edition=1st |location=New York, NY, USA |pages=1119–1190, esp. 1119ff, 1138ff; and ''passim'' |chapter=Chirality in Molecules Devoid of Chiral Centers (Chapter 14) |access-date=2 February 2016 |chapter-url=https://archive.org/details/stereochemistryo0000elie_a9t3/page/1138/mode/2up?q=spirane}}</ref>{{rp|1138ff}} The two rings sharing the spiro atom are most often different, although they can be identical [e.g., spiro[5.5]undecane and [[spiropentadiene]], at right].<ref name=ClaydenOC12/>{{rp|319f.846f}}

== Selected spiro compounds == <gallery widths="180px" heights="120px"> Elatol.png | Elatol, isolated from ''[[Laurencia| Laurencia dendroidea]]'' (red algae)<ref name="SmithBaxendale15">{{cite journal |author1=Smith, Laura K. |author2=Baxendale, Ian R. |name-list-style=amp | year = 2015 | title = Total Syntheses of Natural Products Containing Spirocarbocycles | journal = Org. Biomol. Chem. | volume = 13 |issue=39 | pages = 9907–9933 | doi = 10.1039/C5OB01524C |pmid=26356301 | doi-access = free }}</ref> Spironolacton.svg | [[Spironolactone]], a commercial diuretic medication Spiro-C5H4.png | [[Spiropentadiene]], which is highly strained.<ref name="SciNews91">{{cite web |date=13 July 1991 |title = Elusive bowtie pinned down |website=The Free Library |url=http://www.thefreelibrary.com/Elusive+bowtie+pinned+down.-a011134368 | access-date = 2 February 2016}}</ref> Spiroverbindung Nomenklatur.svg | '''(A)''' 1-Bromo-3-chlorospiro[4.5]decan-7-ol, and '''(B)''' '1-bromo-3-chlorospiro[3.6]decan-7-ol. </gallery>

==Carbocyclic spiro compounds== [[Bicyclic]] ring structures in [[organic chemistry]] that have two fully carbocyclic (all carbon) rings connected through a carbon atom are the usual focus of the topic of spirocycles. Simple parent spirocycles include spiropentane, spirohexane, etc. up to spiroundecane. Several exist as isomers. Lower members of the class are strained. The symmetric isomer of spiroundecane is not.

Some spirocyclic compounds occur as [[natural products]].<ref name = SmithBaxendale15/>

===Preparation=== [[File:FechtEster.svg|thumb|center|Synthesis route to Fecht's ester, illustrating a dialkylation route to a [[spiroheptane]].|320px]]

[[File:SpiroC11.svg|thumb|center|Synthesis route to spiroundecane.<ref>{{cite journal |doi=10.1021/jo01082a006 |title=Syntheses of Four Spiro Hydrocarbons |date=1960 |last1=Dixon |first1=Joseph A. |last2=Naro |first2=Paul A. |journal=The Journal of Organic Chemistry |volume=25 |issue=12 |pages=2094–2097 }}</ref>|320px]] The spirocyclic core is usually prepared by dialkylation of an activated carbon center. The dialkylating group is often a 1,3-, 1,4-, etc. dihalide.<ref>{{cite journal |doi=10.15227/orgsyn.080.0144 |title=Synthesis and &#91;3+2&#93; Cycloaddition of a 2,2-Dialkoxy-1-methylenecyclopropane: 6,6-Dimethyl-1-methylene-4,8-Dioxaspiro&#91;2.5&#93;octane and cis-5-(5,5-Dimethyl-1,3-dioxan-2-ylidene)hexahydro-1(2H)-pentalen-2-one |journal=Organic Syntheses |date=2003 |volume=80 |page=144|first1=Masaharu |last1=Nakamura |first2=Xiao Qun |last2=Wang |first3=Masahiko |last3=Isaka |first4=Shigeru |last4=Yamago |first5=Eiichi |last5=Nakamura }}</ref> In some cases the dialkylating group is a dilithio reagent, such as 1,5-dilithiopentane.<ref>{{cite journal |doi=10.15227/orgsyn.070.0204 |title=Spiroannelation Via Organobis(Cuprates): 9,9-Dimethylspiro&#91;4.5&#93;Decan-7-One |journal=Organic Syntheses |date=1992 |volume=70 |page=204| first1=Paul A. |last1=Wender |first2=Alan W. |last2=White |first3=Frank E. |last3=McDonald }}</ref> For generating spirocycles containing a cyclopropane ring, cyclopropanation with cyclic carbenoids has been demonstrated.<ref>{{cite journal |doi=10.15227/orgsyn.101.0061 |title=Preparation of a Radical Clocks Bearing Carbonyl Groups: Synthesis of N-Methoxy-N-methylspiro&#91;cyclopropane-1,9'-fluorene&#93;-2-carboxamide |date=2024 |last1=Bartolo |first1=Nicole D. |first2=Ryan N. |last2=Robson|first3=Collin H. |last3=Witt|first4=K. A. |last4=Woerpel|journal=Organic Syntheses |volume=101 |pages=61–80 |pmid=39157855 |pmc=11326668 }}</ref>

Spiro compounds are often prepared by diverse rearrangement reactions. For example, the [[Pinacol rearrangement|pinacol-pinacolone rearrangement]] is illustrated below.<ref name=ClaydenOC12/>{{rp|985}} is employed in the preparation of aspiro[4.5]decane.<ref>{{cite web|url=https://pubchem.ncbi.nlm.nih.gov/compound/291783#section=Top|title=1,1'-Bicyclopentyl-1,1'-diol|author=Pubchem|work=nih.gov|access-date=7 March 2016}}</ref>]. [[File:The synthesis of a spiro-keto compound form a symmetrical diol.png|center|The synthesis of a spiro-keto compound form a symmetrical diol]]

==Heterocyclic spiro compounds== [[Image:Ketal Synthesis V.1.svg | thumb | right | 405 px | Preparation of a spiro ketal.<ref>{{cite web|url=http://www.chemspider.com/Chemical-Structure.8739.html?rid=aa6e1001-5ee2-450c-9d26-e6b222c54f46|title=1,4-Dioxaspiro[4.5]decane|work=chemspider.com|access-date=3 February 2016}}</ref>]]

Spiro compounds are considered heterocyclic if the spiro atom or any atom in either ring are not carbon atoms. Cases with a spiro heteroatom such as boron, silicon, and nitrogen (but also other Group IVA [14] are often trivial to prepare. Many borate esters derived from glycols illustrate this case.<ref>{{cite journal |doi=10.15227/orgsyn.087.0026 |title=Synthesis of Spiroborate Esters from 1,2-Aminoalcohols, Ethylene Glycol and Triisopropyl Borate: Preparation of (S)-1-(1,3,2-Dioxaborolan-2-Yloxy)-3-Methyl-1,1-Diphenylbutan-2-Amine |journal=Organic Syntheses |date=2010 |volume=87 |page=26|author=Viatcheslav Stepanenko, Kun Huang, Margarita Ortiz-Marciales |pmid=20694191 |pmc=2915795 }}</ref> Likewise, a tetravalent neutral silicon and quaternary [[nitrogen]] atom ([[ammonium]] cation) can be the spiro center. Many such compounds have been described.<ref name=ElielEtal94/>{{rp|1139f}}

Particularly common spiro compounds are [[acetal|ketal (acetal)]] formed by condensation of cyclic ketones and [[diol]]s and [[dithiol]]s.<ref>{{cite journal |doi=10.15227/orgsyn.093.0210 |title=Preparation of 1,5-Dioxaspiro&#91;5.5&#93;undecan-3-one |date=2016 |last1=Craig |first1=Robert |last2=Smith |first2=R. C. |last3=Pritchett |first3=B. P. |last4=Estipona |first4=B. I. |last5=Stoltz |first5=B. M. |journal=Organic Syntheses |volume=93 |pages=210–227 |pmid=28729749 |pmc=5514842 }}</ref><ref>{{cite journal |doi=10.15227/orgsyn.071.0063 |title=Stereocontrolled Preparation of 3-Acyltetrahydrofurans from Acid-Promoted Rearrangements of Allylic Ketals: (2S,3S)-3-Acetyl-8-Carboethoxy-2,3-Dimethyl-1-Oxa-8-Azaspiro&#91;4.5&#93;Decane |journal=Organic Syntheses |date=1993 |volume=71 |page=63 }}</ref><ref>{{cite journal |doi=10.15227/orgsyn.064.0073 |title=Dichlorovinylation of an Enolate: 8-Ethynyl-8-Methyl-1,4-Dioxaspiro&#91;4.5&#93;Dec-6-Ene |journal=Organic Syntheses |date=1986 |volume=64 |page=73 }}</ref> A simple case is the acetal 1,4-dioxaspiro[4.5]decane from [[cyclohexanone]] and [[glycol]]. Cases of such ketals and dithioketals are common.

==Chirality== [[File:Spiroverbindung Chiralität.svg|thumb|Two enantiomers of a spiro diketone.]] Spiranes can be [[chirality|chiral]],<ref name = RiosCSR12>{{cite journal | author = Rios, Ramon | year = 2012 | title = Enantioselective Methodologies for the Synthesis of Spiro Compounds | journal = [[Chemical Society Reviews]] | volume = 41 | issue = 3 | pages = 1060–1074 | doi = 10.1039/C1CS15156H | pmid = 21975423 }}</ref> in various ways.<ref name=ElielEtal94/>{{rp|1138ff}} First, while nevertheless appearing to be twisted, they yet may have a chiral center making them analogous to any simple [[chiral compound]], and second, while again appearing twisted, the specific location of substituents, as with alkylidenecycloalkanes, may make a spiro compound display ''central chirality'' (rather than axial chirality resulting from the twist); third, the substituents of the rings of the spiro compound may be such that the only reason they are chiral arises solely from the twist of their rings, e.g., in the simplest bicyclic case, where two structurally identical rings are attached via their spiro atom, resulting in a twisted presentation of the two rings.<ref name=ElielEtal94/>{{rp|1138ff,1119ff}}<ref name=ClaydenOC12/>{{rp|319f.846f}} Hence, in the third case, the lack of planarity described above gives rise to what is termed [[axial chirality]] in otherwise identical isomeric pair of spiro compounds, because they differ only in the right- ''versus'' left-handed "twist" of structurally identical rings (as seen in [[allene]]s, sterically hindered [[biaryl]]s, and alkylidenecycloalkanes as well).<ref name=ElielEtal94/>{{rp|1119f}} Assignment of absolute configuration of spiro compounds has been challenging, but a number of each type have been unequivocally assigned.<ref name=ElielEtal94/>{{rp|1139ff}}

Some spiro compounds exhibit [[axial chirality]]. Spiroatoms can be the origin of [[Chirality (chemistry)|chirality]] even when they lack the required four different substituents normally observed in chirality. When two rings are identical the priority is determined by a slight modification of the [[CIP system]] assigning a higher priority to one ring extension and a lower priority to an extension in the other ring. When rings are dissimilar the regular rules apply.{{clarify|date=February 2016}}

==Nomenclature and etymology == [[IUPAC nomenclature|Nomenclature]] for spiro compounds was first discussed by [[Adolf von Baeyer]] in 1900.<ref>{{Cite journal|doi=10.1002/cber.190003303187|first=Adolf |last=von Baeyer|author1-link=Adolf von Baeyer|title=Systematik und Nomenclatur Bicyclischer Kohlenwasserstoffe|volume= 33|pages= 3771–3775|year=1900|journal=Berichte der Deutschen Chemischen Gesellschaft|issue=3|url=https://zenodo.org/record/1425984 }}</ref> [[IUPAC]] provides advice on naming of spiro compounds.<ref>{{cite journal |author=Moss, G.P. |title=Extension and Revision of the Nomenclature for Spiro Compounds |journal=[[Pure and Applied Chemistry|Pure Appl. Chem.]] | volume = 71 | issue = 3 | pages = 531–558 | year = 1999 | doi = 10.1351/pac199971030531 | s2cid = 20131819 | issn = 1365-3075| doi-access = free }} The full author (Working Party) list and a link to a German translation are provided in a corresponding footnote. ''Also available online at'' {{cite web |url= http://www.chem.qmul.ac.uk/iupac/spiro/ |title= Extension and Revision of the Nomenclature for Spiro Compounds | publisher= Queen Mary University of London | location= London, GBR }}</ref>

The prefix ''spiro'' denotes two rings with a spiro junction. The main method of [[systematic nomenclature]] is to follow with square brackets containing the number of atoms in the smaller ring then the number of atoms in the larger ring, separated by a period, in each case excluding the spiroatom (the atom by which the two rings are bonded) itself. Position-numbering starts with an atom of the smaller ring adjacent to the spiroatom around the atoms of that ring, then the spiroatom itself, then around the atoms of the larger ring.<ref>{{cite web |url= https://www.acdlabs.com/iupac/nomenclature/79/r79_197.htm |title= Spiro Hydrocarbons. Rule A-41. Compounds: Method 1 }}</ref> For example, compound '''A''' in [[:File:Spiroverbindung Nomenklatur.svg|Image #4]] above ([[#Selected spiro compounds|Selected Spiro Compounds]]) is called ''1-bromo-3-chlorospiro[4.5]decan-7-ol'', and compound '''B''' is called ''1-bromo-3-chlorospiro[3.6]decan-7-ol''.

== Further reading == * {{cite book |author1=Clayden, Jonathan |author2=Greeves, Nick |author3=Warren, Stuart | year = 2012 | title = Organic Chemistry | edition = 2nd | pages = 319f, 432, 604np, 653, 746int, 803ketals, 839, 846f | location = Oxford, UK | publisher = Oxford University Press | url = https://books.google.com/books?isbn=0199270295 | access-date = 2 February 2016 | isbn = 978-0-19-927029-3 }} *{{cite book |author1=Eliel, Ernest Ludwig |title=Stereochemistry of Organic Compounds |author2=Wilen, Samuel H. |author3=Mander, Lewis N. |publisher=Wiley & Sons |year=1994 |isbn=978-0-471-01670-0 |edition=1st |location=New York, NY, USA |pages=1119–1190, esp. 1119ff, 1138ff; and ''passim'' |chapter=Chirality in Molecules Devoid of Chiral Centers (Chapter 14) |access-date=2 February 2016 |chapter-url=https://archive.org/details/stereochemistryo0000elie_a9t3/page/1138/mode/2up?q=spirane |url=https://books.google.com/books?id=IyfwAAAAMAAJ}} * Examples of spiro natural products and their synthesis: {{cite journal |author1=Smith, Laura K. |author2=Baxendale, Ian R. |name-list-style=amp | year = 2015 | title = Total Syntheses of Natural Products Containing Spirocarbocycles | journal = Org. Biomol. Chem. | volume = 13 |issue=39 | pages = 9907–9933 | doi = 10.1039/C5OB01524C |pmid=26356301 | doi-access = free }} *{{cite journal |doi=10.1021/cr0501341 |title=Spiro Compounds for Organic Optoelectronics |date=2007 |last1=Saragi |first1=Tobat P. I. |last2=Spehr |first2=Till |last3=Siebert |first3=Achim |last4=Fuhrmann-Lieker |first4=Thomas |last5=Salbeck |first5=Josef |journal=Chemical Reviews |volume=107 |issue=4 |pages=1011–1065 |pmid=17381160 |bibcode=2007ChRv..107.1011S }}

== References == {{Reflist}}

== External links == {{Navbox stereochemistry}} {{Authority control}}

[[Category:Spiro compounds|*]]