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iodolactonization 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 history 2 mechanism 3 scope 4 applications 5 see also 6 references toggle the table of contents iodolactonization 1 language čeština 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 reaction halolactonization reaction type ring forming reaction iodolactonization or more generally halolactonization is an organic reaction that forms a ring the lactone by the addition of an oxygen and iodine across a carbon carbon double bond it is an intramolecular variant of the halohydrin synthesis reaction the reaction was first reported by m j bougalt in 1904 and has since become one of the most effective ways to synthesize lactones 1 strengths of the reaction include the mild conditions and incorporation of the versatile iodine atom into the product iodolactonizationintroduction iodolactonization has been used in the synthesis of many natural products including those with medicinal applications such as vernolepin and vernomenin 2 two compounds used in tumor growth inhibition and vibralactone a pancreatic lipase inhibitor 3 iodolactonization has also been used by elias james corey to synthesize numerous prostaglandins 4 history edit bougalt s report of iodolactonization represented the first example of a reliable lactonization that could be used in many different systems bromolactonization was actually developed in the twenty years prior to bougalt s publication of iodolactonization 1 however bromolactonization is much less commonly used because the simple electrophilic addition of bromine to an alkene seen below can compete with the bromolactonization reaction and reduce the yield of the desired lactone 5 bromolactonization chlorolactonization methods first appeared in the 1950s 1 but are even less commonly employed than bromolactonization the use of elemental chlorine is procedurally difficult because it is a gas at room temperature and the electrophilic addition product can be rapidly produced as in bromolactonization 6 mechanism edit the reaction mechanism involves the formation of a positively charged halonium ion in a molecule that also contains a carboxylic acid or other functional group that is a precursor to it the oxygen of the carboxyl acts as a nucleophile attacking to open the halonium ring and instead form a lactone ring the reaction is usually performed under mildly basic conditions to increase the nucleophilicity of the carboxyl group iodolactonization scope edit the iodolactonization reaction includes a number of nuances that affect product formation including regioselectivity ring size preference and thermodynamic and kinetic control in terms of regioselectivity iodolactonization preferentially occurs at the most hindered carbon atom adjacent to the iodonium cation this is due to the fact that the more substituted carbon is better able to maintain a partial positive charge and is thus more electrophilic and susceptible to nucleophilic attack when multiple double bonds in a molecule are equally reactive conformational preferences dominate however when one double bond is more reactive that reactivity always dominates regardless of conformational preference 7 iodolactonizationregioselectivity both five and six membered rings could be formed in the iodolactonization shown below but the five membered ring is formed preferentially as predicted by baldwin s rules for ring closure 8 according to the rules 5 exo tet ring closures are favored while 6 endo tet ring closures are disfavored 9 the regioselectivity of each iodolactonization can be predicted and explained using baldwin s rules iodolactonization stereoselective iodolactonizations have been seen in literature and can be very useful in synthesizing large molecules such as the aforementioned vernopelin and vernomenin because the lactone can be formed while maintaining other stereocenters the ring closure can even be driven by stereocenters adjacent to the carbon carbon multiple bond as shown below 7 iodolactonization even in systems without existing stereocenters bartlett and coworkers found that stereoselectivity was achievable they were able to synthesize the cis and trans five membered lactones by adjusting reactions conditions such as temperature and reaction time the trans product was formed under thermodynamic conditions e g a long reaction time while the cis product was formed under kinetic conditions e g a relatively shorter reaction time 10 iodolactonization applications edit iodolactonization has been used in the synthesis of many biologically important products such as the tumor growth inhibitors vernolepin and vernomenin the pancreatic lipase inhibitor vibralactone and prostaglandins a lipid found in animals the following total syntheses all use iodolactonization as a key step in obtaining the desired product in 1977 samuel danishefsky and coworkers were able to synthesize the tumor growth inhibitors dl vernolepin and dl vernomenin via a multistep process in which a lactonization was employed 2 this synthesis demonstrates the use of iodolactonization to preferentially form a five membered ring over a four or six membered ring as expected from baldwin s rules danishefsky iodolactonization in 2006 zhou and coworkers synthesized another natural product vibralactone in which the key step was the formation of a lactone 3 the stereoselectivity of the iodolactonization sets a critical stereochemical configuration for the target compound iodolactonization in 1969 corey and coworkers synthesized prostaglandin e 2 using an iodolactone intermediate 4 again the stereoselectivity of the iodolactonization plays an integral role in product formation iodolactonization see also edit iodolactamization the lactam analogue halogen addition reaction references edit 1 2 3 dowle m d davies d i 1979 synthesis and synthetic utility of halolactones chemical society reviews 8 2 171 doi 10 1039 cs9790800171 1 2 danishefsky s schuda p f kitahara t etheredge s j 1977 the total synthesis of dl vernolepin and dl vernomenin journal of the american chemical society 99 18 6066 doi 10 1021 ja00460a038 1 2 zhou q snider b b 2008 synthesis of vibralactone organic letters 10 7 1401 1404 doi 10 1021 ol800118c pmc 2745174 pmid 18311992 1 2 corey e j weinshenker n m schaaf t k huber w 1969 stereo controlled synthesis of dl prostaglandins f 2α and e 2 journal of the american chemical society 91 20 5675 5677 doi 10 1021 ja01048a062 pmid 5808505 brown r s 1997 investigation of the early steps in electrophilic bromination through the study of the reaction with sterically encumbered olefins accounts of chemical research 30 3 131 137 doi 10 1021 ar960088e garratt d g ryan m d beaulieu p l 1980 additions of group 6a and 7a electrophilic reagents to dimethyl endo endo bicyclo 2 2 2 oct 5 ene 2 3 dicarboxylate competitive formation of γ and δ lactones the journal of organic chemistry 45 5 839 doi 10 1021 jo01293a016 1 2 kurth m j brown e g lewis e j mckew j c 1988 regioselectivity in the iodolactonization of 1 6 heptadien 4 carboxylic acid derivatives tetrahedron letters 29 13 1517 doi 10 1016 s0040 4039 00 80340 8 baldwin jack e 1976 rules for ring closure journal of the chemical society chemical communications 18 734 doi 10 1039 c39760000734 issn 0022 4936 hirschmann h hanson k r 1977 reflection concordant stereospecific numbering tetrahedron 33 8 891 897 doi 10 1016 0040 4020 77 80042 2 issn 0040 4020 bartlett p a myerson j 1978 stereoselective epoxidation of acyclic olefinic carboxylic acids via iodolactonization journal of the american chemical society 100 12 3950 doi 10 1021 ja00480a061 retrieved from https en wikipedia org w index php title iodolactonization oldid 1321598260 categories oxygen heterocycle forming reactions lactones hidden categories articles with short description short description is different from wikidata this page was last edited on 11 november 2025 at 14 05 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 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