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a jump to content main menu main menu move to sidebar hide navigation main page contents current events random article about wikipedia contact us contribute help learn to edit community portal recent changes upload file special pages search search appearance donate create account log in personal tools donate create account log in contents move to sidebar hide top 1 ring expansions toggle ring expansions subsection 1 1 carbon insertion through migration to an exocyclic group 1 1 1 carbon insertion through opening of a bicycle 1 2 heteroatom insertion reactions 1 2 1 beckmann rearrangement 1 2 2 other n insertions 1 2 3 baeyer villiger oxidation 2 ring contractions toggle ring contractions subsection 2 1 carbenoid ring contractions 2 2 favorskii rearrangement 2 3 cation contractions 3 expansions and contractions 4 inorganic and organometallic examples 5 further reading 6 references toggle the table of contents ring expansion and contraction 3 languages čeština فارسی français edit links article talk english read edit view history tools tools move to sidebar hide actions read edit view history general what links here related changes upload file permanent link page information cite this page get shortened url switch to legacy parser print export download as pdf printable version in other projects wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia chemical phenomenon within ring systems ring expansion and ring contraction reactions expand or contract rings usually in organic chemistry the term usually refers to reactions involve making and breaking c c bonds 1 diverse pathways lead to these kinds of reactions many of these reactions are primarily of theoretical or pedagoogical interest but some are very useful the bond migration step of the pinacol type rearrangement ring expansions edit a scheme showing ring expansion by exocyclic bond migration a and ring opening of a bicyclic molecule b rings can be expanded by attack of the ring onto an outside group already appended to the ring a migration insertion opening of a bicycle to a single larger ring or coupling a ring closing with an expansion 1 these expansions can be further broken down by what type of atom they incorporate a carbon or a heteroatom into the expanded ring carbon insertion through migration to an exocyclic group edit these reactions have the general features of having an exocyclic leaving group on a carbon adjacent to the ring and an electron donating group on the ring capable of initiating a migration of an endocyclic bond a common migration introduction of carbon is a pinacol rearrangement 1 while this reaction refers specifically to a vicinal dihydroxide rearrangement there are other pinacol type rearrangements that proceed through the same general mechanism such as the tiffeneau demjanov rearrangement these semipinacol rearrangements occur under milder conditions and are thus preferable in complex syntheses 2 these reactions are useful beyond simply expanding a ring because the exocyclic group attacked may also have other functionality appended to it besides the leaving group the group to which the endocyclic bond migrates can also be selectively added to the ring based on the functionality already present for example 1 2 addition into a cyclic ketone carbon insertion through opening of a bicycle edit a generalized mechanism of the buchner ring expansion a common method for expanding a ring involves opening cyclopropane containing bicyclic intermediate the strategy can start with a simmons smith like cyclopropanation of a cyclic alkene 3 a related cyclopropane based ring expansion is the buchner ring expansion the buchner ring expansion is used to convert arenes to cycloheptatrienes the buchner ring expansion is encouraged to open to the desired product by placing electron withdrawing groups on the carbon added in order to perform the ring opening on saturated bicyclic molecules the cyclopropane must be introduced such that a neighboring group can facilitate the expansion or the ring must be opened by attackate the expansion 4 or the ring must be opened by attack from an outside group 5 ring opening as a means of ring expansion can also be applied to larger systems to give access to even larger ring syscyclization the grob fragmentation can be applied as an example of such an expansion like the pinacol type migration the grob fragmentation relies on an electron donating group to promote the bond migration and encourage the leaving group to be expelled in this case the electron donating group can be a pseudo electron donating group which is capable of eliminating and donating an electron pair into the carbon with the breaking bond working with two smaller rings can allow for elaboration of two parts of the molecule separately before working with the expanded ring the dowd beckwith ring expansion reaction is also capable of adding several carbons to a ring at a time and is a useful tool for making large rings 6 while it proceeds through an intermediate bicycle the final cyclization and ring opening take place within the same radical reaction this expansion is useful because it allows the expansion of a beta ketoester to a large cyclic ketone which can easily be elaborated using either the cyclic ketone or the exocyclic ester heteroatom insertion reactions edit some heterocycles can be made through ring expansions 7 beckmann rearrangement edit world demand for caprolactam was estimated to reach five million tons per year for 2015 it has been estimated that 90 of all caprolactam is synthesised from cyclohexanone 1 which is first converted to its oxime treatment of this oxime with acid induces the beckmann rearrangement to give caprolactam 8 the beckmann rearrangement has also been used for the introduction of nitrogen into codeine 9 other n insertions edit a minor industrial route involves the treatment of cyclohexanecarboxylic acid with nitrosylsulfuric acid the snia viscosa process this is thought to proceed via a ketene at bench scale the reaction between cyclohexanone with hydrazoic acid gives caprolactam in the schmidt reaction 10 baeyer villiger oxidation edit baeyer villiger oxidation of camphor in the baeyer villiger oxidation an o atom is introduced into a ring 11 ring contractions edit ring contraction through anionic a cationic b and carbenoid c reactive intermediates ring contractions are useful for making smaller more strained rings from larger rings the impetus for making these rings comes from the difficulty associated with making a fully elaborated small ring when such a ring could more easily be made from an elaborated larger ring from which an atom can be excised or that the original larger scaffold is more accessible 12 ring contractions proceed via anionic cationic and carbenoid intermediates 13 carbenoid ring contractions edit mechanism of the wolff rearrangement used to give a ring contracted product in the arndt eistert reaction an α diazoketone is induced to release n 2 resulting in a highly reactive sextet carbon center adjacent to the carbonyl such species convert by a wolff rearrangement to give an ester in the presence of alcohols when applied to cyclic α diazoketones ring contraction occurs 14 15 in the case of steroids this reaction has been used to convert cyclopentanone groups to cyclobutanyl derivatives 16 favorskii rearrangement edit the favorskii rearrangement is a classic anionic ring contraction 17 it proceeds through a carbanion that attacks an endocyclic carbon and expels a leaving group a halide forming a bicyclic molecule with rings smaller than the original the bicycle is then opened by nucleophilic attack on the ketone to give the contracted product 18 this reaction has been used to convert cyclohexanone to the methyl ester of cyclopentanecarboxylic acid a generalized mechanism of the favorskii rearrangement to give a ring contracted product note that anion formation has been omitted an alternative to the standard favorskii rearrangement is to perform what can be thought of as a negative pinacol rearrangement where an anionic group encourages a bond aligned with a leaving group to migrate and expel the leaving group which has been used in several syntheses 13 it should also be noted that the so called quasi favorskii rearrangement proceeds without an additional nucleophile to form the final contracted product a general pinacol type rearrangement to an unequal 5 7 ring system cation contractions edit the cationic rearrangement contraction proceeds through the loss of a leaving group and the migration of an endocyclic bond to the carbocation pinacol type rearrangements are often used for this type of contraction 19 like the expansion reaction this proceeds with an electron donating group aiding in the migration contraction reactions of one ring can be coupled with an expansion of another to give an unequal bicycle from equally sized fused ring these cationic rearrangements have found use to synthesize the cores of complex molecules 20 expansions and contractions edit the demyanov ring contraction and expansion entails diazotization of aminocyclobutanes and aminocyclopropanes loss of n 2 from the diazo cations results in secondary carbocations which tend to rearrange and then undergo hydrolysis the reaction converts aminocyclobutane into a mixture of hydroxycyclobutane and hydroxymethylcyclopropane these reactions produce an equilibrating mixture of two carbocations 21 c 4 h 7 c 3 h 5 ch 2 inorganic and organometallic examples edit ring expansion reaction of cyclopropane by formation of metallacycle of pt iv ring expansion and contraction reactions are common for transition metal complexes 22 further reading edit casadei m a calli c mandolini l february 1 1984 ring closure reactions 22 kinetics of cyclization of diethyl omega bromoalkyl malonates in the range of 4 to 21 membered rings role of ring strain journal of the american chemical society 106 4 1051 1056 bibcode 1984jachs 106 1051c doi 10 1021 ja00316a039 redmore d gutsche c d carbocyclic ring expansion reactions academic press ny 1968 dowd paul choi soo chang 1987 a new tributyltin hydride based rearrangement of bromomethyl beta keto esters a synthetically useful ring expansion to gamma keto esters journal of the american chemical society 109 11 3493 3494 bibcode 1987jachs 109 3493d doi 10 1021 ja00245a069 references edit 1 2 3 kantorowski e j kurth m j 2000 expansion to seven membered rings pdf tetrahedron 56 26 4317 4353 doi 10 1016 s0040 4020 00 00218 0 s2cid 34628258 archived from the original pdf on 2019 08 18 kurti l czako b 2005 strategic applications of named reactions elsevier p 350 isbn 978 0 12 429785 2 oclc 1107566236 one carbon ring expansion of cycloalkanones to conjugated cycloalkenones 2 cyclohepten 1 one organic syntheses 59 113 1979 doi 10 15227 orgsyn 059 0113 bieräugel h akkerman j m armande j c l pandit u k 1974 a specific insertion of carbenes into carbon carbon bonds tetrahedron letters 15 33 2817 2820 doi 10 1016 s0040 4039 01 91751 4 hoberg j o bozell j j september 1995 cyclopropanation and ring expansion of unsaturated sugars tetrahedron letters 36 38 6831 6834 doi 10 1016 0040 4039 95 01387 w hierold j lupton d w july 2012 synthesis of spirocyclic γ lactones by cascade beckwith dowd ring expansion cyclization organic letters 14 13 3412 3415 doi 10 1021 ol301387t pmid 22691029 mcmurry john 2008 organic chemistry 7th ed pp 945 946 isbn 978 0 495 11258 7 josef ritz hugo fuchs heinz kieczka william c moran caprolactam ullmann s encyclopedia of industrial chemistry weinheim wiley vch doi 10 1002 14356007 a05_031 pub2 isbn 978 3 527 30673 2 white j d hrnciar p stappenbeck f 1999 asymmetric total synthesis of codeine via intramolecular carbenoid insertion journal of organic chemistry 63 21 7871 7884 doi 10 1021 jo990905z eric j kantorowski mark j kurth 2000 expansion to seven membered rings tetrahedron 56 26 4317 4353 doi 10 1016 s0040 4020 00 00218 0 marchand a p kumar v s hariprakasha h k 2001 synthesis of novel cage oxaheterocycles journal of organic chemistry 66 6 2072 2077 doi 10 1021 jo001611c pmid 11300903 silva luiz f jr 2002 construction of cyclopentyl units by ring contraction reactions tetrahedron 58 45 9137 9161 doi 10 1016 s0040 4020 02 00990 0 cite journal cs1 maint multiple names authors list link 1 2 myers andrew methods for ring contraction pdf retrieved 2014 11 30 via harvard university department of chemistry and chemical biology smith michael b march jerry 2006 march s advanced organic chemistry reactions mechanisms and structure p 1599 doi 10 1002 0470084960 isbn 9780470084960 cite book cs1 maint multiple names authors list link kirmse w july 2002 100 years of the wolff rearrangement european journal of organic chemistry 2002 14 2193 doi 10 1002 1099 0690 200207 2002 14 2193 aid ejoc2193 3 0 co 2 d thomas n wheeler and j meinwald 1972 formation and photochemical wolff rearrangement of cyclic α diazo ketones d norandrost 5 en 3β ol 16 carboxylic acids organic syntheses 52 53 doi 10 15227 orgsyn 052 0053 chenier philip j 1978 the favorskii rearrangement in bridged polycyclic compounds journal of chemical education 55 5 286 291 bibcode 1978jched 55 286c doi 10 1021 ed055p286 smith michael b march jerry 2006 march s advanced organic chemistry reactions mechanisms and structure pp 1595 1596 doi 10 1002 0470084960 isbn 9780470084960 cite book cs1 maint multiple names authors list link song zhen lei fan chun an tu yong qiang 2011 semipinacol rearrangement in natural product synthesis chemical reviews 111 11 7523 7556 doi 10 1021 cr200055g pmid 21851053 büchi g hofheinz w paukstelis j v november 1969 synthesis of aromadendrene and related sesquiterpenes journal of the american chemical society 91 23 6473 6478 doi 10 1021 ja01051a051 smith michael b march jerry 2006 march s advanced organic chemistry reactions mechanisms and structure pp 1588 1592 doi 10 1002 0470084960 isbn 9780470084960 cite book cs1 maint multiple names authors list link souillart laetitia cramer nicolai 2015 catalytic c c bond activations via oxidative addition to transition metals chemical reviews 115 17 9410 9464 doi 10 1021 acs chemrev 5b00138 pmid 26044343 retrieved from https en wikipedia org w index php title ring_expansion_and_contraction oldid 1373934818 categories rearrangement reactions ring expansion reactions ring contraction reactions hidden categories articles with short description short description matches wikidata cs1 maint multiple names authors list this page was last edited on 8 september 2026 at 20 56 utc page was rendered with parsoid text is available under the creative commons attribution sharealike 4 0 license additional terms may apply by using this site you agree to the terms of use and privacy policy wikipedia is a registered trademark of the wikimedia foundation inc a non profit organization privacy policy about wikipedia disclaimers contact wikipedia legal safety contacts code of 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