Ramberg—Backlund reaction review

A review on the Ramberg-Backlund reaction has updated the Paquette review of 1977.45 Benzyl benzyl sulfone systems have been found to give unexpectedly high Z-stereoselectivity (up to E.Z = 1 16) in the Meyers variant of the Ramberg-Backlund (g reaction.46... 

Bi, Si, Ge, B, or metal functions and the Ramberg-Backlund reaction have been reviewed.17,18... 

The Ramberg-Backlund reaction, a novel carbon-carbon bond forming transformation, was discovered in 1940 when ethyl chloroethylsulfone 1, upon treatment with NaOH, was shown to form a mixture of cis and trans 2-butene. (Fig. 1) (7).The reaction has been used sporadically over the intervening years and has just received a comprehensive review in 2003.(2-8 )... 

It is now widely accepted that a-halo sulfones are converted into alkenes under the basic conditions of the Ramberg-Backlund reaction via intermediate thiirane 1,1-dioxides (Scheme 7). Experimental data in support of this mechanism were first put forward by Bordwell in 1951, and extensive studies carried out since that time, particularly by Bordwell and Paquette in the late 1960s and early 1970s, have substantiated this overall scheme and have provided further insight into the mechanisms of the individual steps. Very little additional work concerning the mechanism of the reaction has been published since 1975. Consequently, only a summary of the essential features is presented here, and readers are referred to the detailed reviews, written by the leaders of the key research groups themselves, for the full data which support the following broad outline. ... 

Trifluoromethylation reactions of imines, nitrones, hydrazones, iminium ions and azomethine ylides have been reviewed. Activating properties and recent synthetic applications of the arylsulfonyl group,as well as the development of the Ramberg-Backlund reaction over the last 70 years have been highlighted. 

Review articles have featured advances in the cycloisomerization of l,n-allenynes and Rn-allenenes, " reactions for synthesis of quaternary centres bearing a nitrogen substituent, " the Ramberg-Backlund reaction transforming a-halosulfones into alkenes, " and ring expansion of l,2-benzisoxazol-3-ones with a Vilsmeier reagent system, POCI3 and dimethylformamide (Scheme 75). " ... 

Methods used for opening of bicyclic oxazines by the formation of a new carbon-carbon bond to give highly substituted ring systems containing multiple stereocenters have been reviewed. A review of olefination reactions used in the synthesis of cyclophanes has been presented. This covers the Ramberg-Backlund reaction, the Wittig and related... 

Two illustrations that show the power of this reaction for the preparation of strained cycloalkenes are the contractions of 102 to the propellane 103 , an application that has been reviewed , and of 104 to the bicyclo[2.1.1]hexene 105 . The utility of the Ramberg-Backlund rearrangement in the preparation of various natural products such as steroids , terpenoids and pheromones has been demonstrated. In addition to the synthetic applications mentioned in the previous subsection, several selected examples taken from the recent literature are given in equations 66-69. These examples further demonstrate the potential of this method for alkene synthesis in general. 

An extensive review of 6 + 4-cycloaddition reactions has been published.287 The use of a precatalyst in the chromium(0)-promoted 6 + 4-cycloaddition reaction of cyclohepta-l,3,5-triene with acychc dienes ensures that only stoichiometric quantities of the metal are involved in the cycloaddition (Scheme 59).288 The first example of an aqueous 6 + 4-cycloaddition of tropone with the water-soluble diene -([l-D-glucopyranosyloxyjbuta-1,3-diene (152) yields 2-(glucopyranosyloxy)bicyclo-[4.4.1]undecanones (153) and (154) with exo selectivity (Scheme 60).289 A new benzannulation sequence is based on chromium(0)-promoted 671 + 47i-photo-cycload-dition of O/ -thicpin- l, 1 -dioxidc)tricarbonylchromium(O) in the presence of a diene followed by a Ramberg-Backlund rearrangement of the cycloadduct.290... 

Internal alkylation takes place on reaction of a-haloalkyl alkyl sulfones with bases and produces epi-sulfones as intermediaries. These intermediates are usually unstable and provide alkenes by thermal extrusion of sulfur dioxide. This reaction, known as the Ramberg-Backlund rearrangement, has been widely used in synthesis and has been thoroughly reviewed (Scheme 107, entry e).36-3. 43<.473... 

This review does not cover multiple eliminations at the same (cf.156)) or at different centres proceeding without rearrangement and which, [for e.g., the Ramberg-Backlund- 2) or the benzotriazinone-arylazide-reaction 3) (Scheme 2)], can be classified in simple stages ([l,3]-e. and [l,2]-e., or [l,4]-e., valence tautomerism, [l,l]-e., intramolecular nitrene cycloaddition, respectively). 

Li, J. J. 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). 

Intermediates in Reactions.— The utility of the Ramberg-Backlund rearrangement and the involvement of thiiran 1,1-dioxides in synthesis has been reviewed. Treatment of d,l- and meso-bis-oc-bromobenzyl sulphone with triphenylphosphine gave trans- and cis-stilbene, respectively, via a-sulphonyl carbanions which undergo cyclization at the remaining chiral centre to yield trans- and cis-2,3-diphenylthiiran 1,1-dioxides as intermediates (Scheme 3). Inversion occurred at each chiral centre. Thiiran... 

Treatment of a-halosulfones 357 bearing a -hydrogens with base gives olefins by extruding SO2 from the episulfone intermediates 359. The reaction was found by Ramberg and Backlund in 1940 and named after them, and it has been very useful for the preparation of tailor-made olefins. The reaction has been investigated in detail " and utilized widely for olefin syntheses. An excellent review on this reaction by Paquett covers the literature up to 1975, so only recent studies are dealt with in this section. The generally accepted mechanistic path is shown below. 

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