Ramberg—Backlund reaction

Name Reactions, 4th ed., DOI 10.1007/978-3-642-01053-8 211, Springer-Verlag Berlin Heidelberg 2009 

Ramberg, L. Backlund, B. Arkiv. Kemi, Mineral Geol. 1940,13A, 1-50. 

Ramberg-Backlund olefin synthesis. In Name Reactions for Functional Group Transformations , Li, J. J., Corey, E. J., Eds. John WUey Sons Hoboken, NJ, 2007, pp 386-404. (Review). 

Name Reactions A Collection of Detailed Mechanisms and Synthetic Applications, DOI 10.1007/978-3-319-03979-4 226, Springer International Publishing Switzerland 2014 

Treatment of an a-halosulfone 1 with base leads to extrnsion of sulfur dioxide and formation of an alkene 2. This reaction is referred to as the Ramberg-Backlund reaction, it usnaUy yields a mixture of E- and Z-isomers of the alkene. 

An a-halosulfone 1 reacts with a base by deprotonation at the a -position to give a carbanionic species 3. An intramolecular nucleophilic substitution reaction, with the halogen substituent taking the part of the leaving group, then leads to formation of an intermediate episulfone 4 and the halide anion. This mechanism is supported by the fact that the episulfone 4 could be isolated. Subsequent extrusion of sulfur dioxide from 4 yields the alkene 2  

Named Organic Reactions, Second Edition T. Laue and A. Plagens 2005 John Wiley Sons, Ltd ISBNs 0-470-01040-1 (HB) 0-470-01041-X (PB) 

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Thiirane 1,1-dioxides extrude sulfur dioxide readily (70S393) at temperatures usually in the range 50-100 °C, although some, such as c/s-2,3-diphenylthiirane 1,1-dioxide or 2-p-nitrophenylthiirane 1,1-dioxide, lose sulfur dioxide at room temperature. The extrusion is usually stereospeciflc (Scheme 10) and a concerted, non-linear chelotropic expulsion of sulfur dioxide or a singlet diradical mechanism in which loss of sulfur dioxide occurs faster than bond rotation may be involved. The latter mechanism is likely for episulfones with substituents which can stabilize the intermediate diradical. The Ramberg-Backlund reaction (B-77MI50600) in which a-halosulfones are converted to alkenes in the presence of base, involves formation of an episulfone from which sulfur dioxide is removed either thermally or by base (Scheme 11). A similar conversion of a,a -dihalosulfones to alkenes is effected by triphenylphosphine. Thermolysis of a-thiolactone (5) results in loss of carbon monoxide rather than sulfur (Scheme 12). 

The a -halosulfone, required for the Ramberg-Backlund reaction, can for example be prepared from a sulfide by reaction with thionyl chloride (or with N-chlorosuccinimide) to give an a-chlorosulfide, followed by oxidation to the sulfone—e.g. using m-chloroperbenzoic acid. As base for the Ramberg-Backlund reaction have been used alkoxides—e.g. potassium t-butoxide in an etheral solvent, as well as aqueous alkali hydroxide. In the latter case the use of a phase-transfer catalyst may be of advantage. ... 

Cf. three-membered ring sulfones as intermediates of the Ramberg-Backlund reaction L. A. Paquette, Org. React., 25, 1 (1977). 

The formation of alkenes from thiirane dioxides may not be stereospecifically controlled in the presence of a sufficiently strong base and sufficiently acidic protons in the three-membered ring. Under such conditions (essentially those typical for the Ramberg Backlund reaction), epimerization via a carbanion intermediate produces an equilibrium mixture of thiirane dioxides19,99 and consequently a mixture of cis- and trans-alkenes. 

Since the Ramberg-Backlund reaction proceeds through the initial a-proton removal by base, followed by intramolecular nucleophilic substitution of a-carbanion 358 to form... 

In the reaction between sulfines 366 and an a-sulfonyl carbanion, a Ramberg-Backlund reaction took place via formation of the intermediate 367440. 

Block and Aslam441 reported a novel variant of the Ramberg-Backlund reaction in which a,/J-unsaturated a -bromoalkyl sulfones 368 afforded 1,3-dienes upon treatment with base. Since a -bromoalkyl sulfones 368 can be obtained readily by the initial treatment of olefins with bromomethanesulfonyl bromide under photoirradiation and subsequent treatment with triethylamine, this reaction was utilized for preparation of dienes which contain one additional carbon over that of the corresponding olefin. Starting from the cyclic olefins 369-372 the 1,3-dienes 373-376 were obtained442. 

The Ramberg-Backlund reaction has been utilized for the preparation of polyenes. 1,3-Butadienyl allyl sulfones 398 and 399 were transformed into the tri- and tetra-enes 400 and 401 by alkylcuprate addition and the Ramberg-Backlund-type S02 extrusion449. Julia and coworkers450 carried out the Michael addition of various nucleophiles such as ethanol, t-butyl acetoacetate and phenyl thioacetone to allyl dienyl sulfones 402 and then converted them to diallyl sulfones 403. The sulfones were transformed into isoprenoid, 404 by the Ramberg-Backlund reaction. 

One-pot Ramberg-Backlund reaction of sulfones 405 and 406 with KOH in CCl4-t-BuOH afforded the corresponding olefins451,452. 

Finally, an electrochemical reduction of bis-a-bromobenzyl sulfone to stilbene195 and a spectacular, so-called bis-homoconjugative, version of the Ramberg-Backlund reaction, which converts the a-chlorosulfone 100 into the bridged cyclooctatriene derivative 101 (equation 63)196-197, have also been published. 

The Michael induced Ramberg-Backlund reactions gives a mixture of ( )- and (Zy dienes via extrusion of S02 from the episulfone intermediate 57 (equation 55)47. 

Sulphonylbenzofurans 638 a-Sulphonyl carbanions 760, 766, 767, 797, 813, 951, 961 acylation of 627-636 addition to unsaturated bonds 636-642 alkylation of 627-636, 781 halogenation of 1058-1060 Michael addition of 642-649 miscellaneous reactions of 653-655 Ramberg-Backlund reaction of 649-653, 1057, 1058... 

The Ramberg-Backlund reaction can be regarded as a type of extrusion reaction (see p. 1352). 

Route a represents the classic Ramberg-Backlund reaction, the most thoroughly studied of all the routes Under the basic reaction conditions employed, the in... 

Most thiirene dioxides (and oxides) have been prepared through a modified Ramberg-Backlund reaction as the last crucial cyclization step, as illustrated in equation 40 for the benzylic series . Synthesis of thiirene dioxides requires two major modifications of the originally employed reaction first, the inorganic base has to be replaced by the less basic and less nucleophilic triethylamine - and second, the aqueous media has to be substituted by an aprotic organic solvent (e.g. methylene chloride). Under these mild reaction conditions the isolation of aryl-substituted thiirene dioxides (and oxides) is feasible . In fact, this is the most convenient way for the preparation of the aryl-disubstituted three-membered ring sulfones and sulfoxides. ... 

There have been Ramberg-Backlund-type reactions in which the leaving group is not a halide ion. For example, treatment of the polyalkylated methyl triflone 365 is known to result in a Ramberg-Backlund reaction forming the corresponding olefin. Since methyl triflone 364 can be alkylated successively regiospecifically at the two carbon atoms, Hendrickson and coworkers used this reaction for the synthesis of some tailor-made olefins. 

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