Editing Intramolecular reaction (section)

===Molecular tethers===
Otherwise-intermolecular reactions can be made temporarily intramolecular by linking both reactants by a [[tether]] with all the advantages associated to it. Popular choices of tether contain a [[carbonate ester]], [[boronic ester]],  [[silyl ether]], or a [[silyl acetal]] link ('''silicon tethers''')<ref>{{cite book |title=Templated Organic Synthesis |editor-first=François |editor-last=Diederich |editor2-first=Peter J. |editor2-last=Stang |year=2007 |chapter=Use of the Temporary Connection in Organic Synthesis |pages=274–395 |first1=Liam R. |last1=Cox |first2=Steven V. |last2=Ley |doi=10.1002/9783527613526 |isbn=9783527296668 }}</ref><ref>{{cite journal | last1 = Bracegirdle | first1 = S. | last2 = Anderson | first2 = E. A. | year = 2010 | title =  Recent advances in the use of temporary silicon tethers in metal-mediated reactions| journal = Chem. Soc. Rev. | volume = 39 | issue = 11 | pages = 4114–4129 | doi = 10.1039/C0CS00007H | pmid = 20838677 }}</ref> which are fairly inert in many organic reactions yet can be cleaved by specific reagents.  The main hurdle for this strategy to work is selecting the proper length for the tether and making sure reactive groups have an optimal orientation with respect to each other.  An examples is a [[Pauson–Khand reaction]] of an alkene and an alkyne tethered together via a silyl ether.<ref>{{cite journal |title=The use of silicon-based tethers for the Pauson-Khand reaction |last1=Dobbs |first1=A. |last2=Miller |first2=I. |last3=Martinovic |first3=S. |journal=[[Beilstein Journal of Organic Chemistry]] |year=2007 |issue=3 |page=21 |volume=2007 |doi=10.1186/1860-5397-3-21 |pmc=1949821 |pmid=17617903 |doi-access=free }}</ref>

[[Image:Pauson-Khand Silicon Tether.png|300px|Pauson-Khand silicon tether]]

In this particular reaction, the tether angle bringing the reactive groups together is effectively reduced by placing [[isopropyl]] groups on the  silicon atom via the [[Thorpe–Ingold effect]]. No reaction takes place when these bulky groups are replaced by smaller methyl groups. Another example is a [[photochemical]] [2+2][[cycloaddition]] with two alkene groups tethered through a silicon acetal group (racemic, the other [[enantiomer]] not depicted), which is subsequently cleaved by [[TBAF]] yielding the endo-diol.

:[[Image:CycloadditionSiliconTether.png|400px|Cycloaddition silicon tether]]

Without the tether, the [[exo isomer]] forms.<ref>{{cite journal | last1 = Booker-Milburn | first1 = Kevin I. | last2 = Gulten | first2 = Sirin | last3 = Sharpe | first3 = Andrew | year = 1997| title =  Diastereoselective intramolecular photochemical [2 + 2] cycloaddition reactions of tethered l-(+)-[[valinol]] derived tetrahydrophthalimides | journal = [[Chem. Commun.]] | volume = 1997 | issue = 15 | pages = 1385–1386 | doi = 10.1039/a702386c }}</ref>