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methylenation wikipedia 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 methods toggle methods subsection 1 1 methylene insertion into alkanes 1 2 methylene for oxo reactions 1 3 methylenation adjacent to carbonyl groups 1 4 other approaches 2 references toggle the table of contents methylenation 3 languages čeština français русский 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 wikimedia commons wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia chemical reaction which adds a ch2 group to a molecule in organic chemistry methylenation is a chemical reaction that inserts a methylene ch 2 group into a chemical compound a b a ch 2 b displaystyle ce a b longrightarrow ce a color red ce ch2 ce b in a related sense it also describes a process in which a divalent group of a starting material is removed and replaced with a terminal ch 2 group a e a ch 2 displaystyle ce a e longrightarrow ce a color red ce ch2 methylenation in this context is also known as methenylation most commonly e is an oxygen atom so that the reaction results in terminal alkenes from aldehydes and ketones or more rarely enol ethers from esters or enamines from amides methods edit methylene insertion into alkanes edit singlet methylene 1 ch 2 produced from photolysis of diazomethane under ultraviolet irradiation 1 methylenates hydrocarbons arenes and olefins undergo methylenation to give cyclopropanated products in the case of arenes the cyclopropanation product undergoes further electrocyclic ring opening to give cycloheptatriene products buchner ring expansion 2 alkenes undergo both c c methylenation and c h methylenation insertion to give a mixture of cyclopropanation and homologation products reflecting the exceptionally high reactivity of singlet methylene normally unreactive alkanes undergo methylenation to give homologation products even at 75 c 3 r h ch 2 r ch 2 h displaystyle ce r h color red ce ch2 longrightarrow ce r color red ce ch2 ce h photolysis of a solution of diazomethane in n pentane gives a mixture of hexanes and higher homologues at 75 c the product ratio is 48 35 17 mixture of n hexane 2 methylpentane and 3 methylpentane the ratio is remarkably close to the statistical product ratio of 6 4 2 50 33 17 based on the number of available c h bonds at each position that could undergo methylene insertion as a result doering and coworkers concluded methylene must be classed as the most indiscriminate reagent known in organic chemistry methylene for oxo reactions edit a common method for methylenation involves the wittig reaction using methylenetriphenylphosphorane with an aldehyde ph phenyl c 6 h 5 4 rcho ph 3 p ch 2 rch ch 2 ph 3 po displaystyle ce rcho ph3p ch2 rch ch2 ph3po a related reaction can be accomplished with tebbe s reagent which is sufficiently versatile to allow methylenation of esters 5 rco 2 r cp 2 ti cl ch 2 alme 2 rc or ch 2 cp 2 tioalme 2 cl displaystyle ce rco2r cp2ti cl ch2alme2 rc or ch2 cp2tioalme2cl other less well defined titanium reagents e g lombardo s reagent effect similar transformations 6 7 carbanions derived from methylsulfones have also been employed equivalently to the wittig reaction 8 methylenation adjacent to carbonyl groups edit ketones and esters can be methylenated at the α position to give α β unsaturated carbonyl products containing an additional terminal ch 2 group in a three step process known as the eschenmoser methylenation 9 an enolate is generated by deprotonation of the α c h bond using a hindered lithium amide linr 2 base e g lda lhmds subsequently the enolate is reacted with eschenmoser s salt me 2 n ch 2 i to give a β dimethylamino carbonyl compound mannich base the mannich base is then subjected to methylation or n oxidation to give a trimethylammonium salt or amine n oxide which is then subjected to hofmann elimination or cope elimination respectively to give the α methylene carbonyl compound if the hofmann elimination is used the process can be represented as follows rc o ch 2 r rc o ch ch 2 nme 2 r rc o ch ch 2 nme 3 r i rc o c ch 2 r displaystyle ce rc o ch2r rc o ch ch2nme2 r rc o ch ch2nme3 r i rc o c ch2 r other approaches edit ethenolysis is a method for methylenation of internal alkene as illustrated by the following example rch chr ch 2 ch 2 2 rch ch 2 displaystyle ce rch chr color red ce ch2 ch2 longrightarrow ce 2 rch color red ce ch2 in principle the addition of ch 2 across a c c double bond could be classified as a methylenation but such transformations are commonly described as cyclopropanations references edit braun w bass arnold m pilling m 1970 05 15 flash photolysis of ketene and diazomethane the production and reaction kinetics of triplet and singlet methylene the journal of chemical physics 52 10 5131 5143 bibcode 1970jchph 52 5131b doi 10 1063 1 1672751 issn 0021 9606 winberg h 1959 notes synthesis of cycloheptatriene the journal of organic chemistry 24 2 264 265 doi 10 1021 jo01084a635 issn 0022 3263 von e doering w buttery r g laughlin r g chaudhuri n 1956 indiscriminate reaction of methylene with the carbon hydrogen bond journal of the american chemical society 78 13 3224 bibcode 1956jachs 78 3224v doi 10 1021 ja01594a071 issn 0002 7863 eric j leopold 1986 selective hydroboration of a 1 3 7 triene homogeraniol organic syntheses 64 164 doi 10 15227 orgsyn 064 0164 straus daniel a morshed m monzur dudley matthew e hossain m mahmun 2006 μ chlorobis cyclopentadienyl dimethylaluminium μ methylenetitanium encyclopedia of reagents for organic synthesis doi 10 1002 047084289x rc073 pub2 isbn 0471936235 luciano lombardo 1987 methylenation of carbonyl compounds 3 methylene cis p menthane organic syntheses 65 81 doi 10 15227 orgsyn 065 0081 marsden stephen p ducept pascal c 2005 synthesis of highly substituted allenylsilanes by alkylidenation of silylketenes beilstein journal of organic chemistry 1 1 5 doi 10 1186 1860 5397 1 5 pmc 1399453 pmid 16542018 ando kaori oguchi mai kobayashi takahisa asano haruka uchida nariaki 2020 methylenation for aldehydes and ketones using 1 methylbenzimidazol 2 yl methyl sulfone the journal of organic chemistry 85 15 9936 9943 doi 10 1021 acs joc 0c01227 pmid 32608238 schreiber jakob maag hans hashimoto naoto eschenmoser albert 1971 dimethyl methylene ammonium iodide angewandte chemie international edition in english 10 5 330 331 doi 10 1002 anie 197103301 issn 0570 0833 retrieved from https en wikipedia org w index php title methylenation oldid 1367977138 category carbon carbon bond forming reactions hidden categories articles with short description short description is different from wikidata this page was last edited on 6 august 2026 at 08 39 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 conduct developers statistics cookie statement mobile view search search toggle the table of contents methylenation 3 languages add topic