The Intramolecular <i>Ramberg</i>‐<i>Bäcklund</i> Reaction: A Convenient Method for the Synthesis of Strained Bridgehead Olefins

Becker, Konrad B.; Labhart, Marco P.

doi:10.1002/hlca.19830660412

Cited by 22 publications

(1 citation statement)

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“…Following the pioneering work of Buchanan and co‐workers on the fragmentation of bicyclo[3.3.1]nonane systems,4 several groups have successfully applied this strategy for the construction of cyclooctanoids 5. The fragmentation of a bicyclo[5.1.1]nonane has been reported in an isolated example 6. Several synthetic approaches to cyclooctanoids related to the present study have been realized from a properly functionalized bicyclo[4.2.1]nonane intermediate.…”

Section: Introductionmentioning

confidence: 76%

Stereoselective Synthesis of Bicyclo[4.2.1]nonanes – a Temporary‐Bridge Approach to Cyclooctanoids

et al. 2008

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Section: Introductionmentioning

confidence: 76%

Stereoselective Synthesis of Bicyclo[4.2.1]nonanes – a Temporary‐Bridge Approach to Cyclooctanoids

et al. 2008

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Ketene Cycloadditions

1994

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The reaction of ketene with itself was described almost simultaneously in 1908 by Chick and Wilsmore in England, and by Staudinger and Klever in Germany; priority for the discovery was attributed to Wilsmore by the German group. Ketene cycloaddition was an early example of a peculiar process, one that formed carbon–carbon bonds with ease, often without the need for solvent, catalyst, or high heat. Subsequent work by others was done in the shadow of Staudinger's exhaustive and rigorous study of all phases of ketene reactivity. Three factors led to a resurgence of interest in this reaction beginning in the 1960s. Haloketenes, which had previously eluded study, were found to have high reactivity, and the halogens could easily be removed after the reaction. The increasing sophistication of powerful analytical methods, particularly nuclear magnetic resonance spectroscopy, led to discovery of the interesting stereochemical aspects of this reaction. Finally, the new theory of orbital symmetry conservation provided a conceptual framework to rationalize these puzzling “no mechanism” reactions. This chapter is a review of cycloaddition reactions of ketenes. Here, a cycloaddition is defined as a reaction of a ketene with an unsaturated organic compound to give a cyclic product by a mechanism that, in principle, involves the almost simultaneous formation of two bonds between two reactants. While there is no concern here as to whether bond formation is concerted or stepwise, no other chemical process can take place between the formation of the first and second bond. Definition here involves both structural and mechanistic factors, and it is difficult to avoid a certain amount of arbitrariness. Products, such as dehydroacetic acid, which seem to us to arise by concatenation of ketene molecules followed by cyclization are excluded. These reactions, are more properly considered to arise from a series of ionic reactions, and the prediction of the eventual product does not take advantage of the special mechanistic features commonly associated with true cycloadditions. Additions to imines to give β‐lactams are numerous and will be covered in a separate review. The literature has been searched to the end of 1988. Many reviews devoted partially or exclusively to ketene cycloadditions have been published. Specific topics that have been reviewed include haloketenes, fluoroketenes, cyanoketenes, intramolecular cycloadditions, conjugated ketenes, and β‐lactam antibiotics. Ancillary topics pertinent to ketene cycloadditions that have been reviewed include cycloreversion reactions, ketene equivalents, which provide ketene functionality with olefin‐like reactivity especially in [4 + 2] reactions, application of frontier molecular orbital theory to cycloadditions, and a critical discussion of cycloadditions with polar intermediates. Applications of cyclobutanones in synthesis have also been reviewed.

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The Ramberg‐Bäcklund Reaction

Taylor

Casy

2003

Organic Reactions

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The base‐mediated conversion of alpha‐halosulfones into region‐defined alkenes was first described by Ludwig Ramberg and Birger Backlund. This transformation has proved to be of wide synthetic value and is known as the Ramberg‐Backlund reaction (RBR). The facile nature of the RBR is surprising given the difficulties encountered when attempting to carry out nucleophilic substitution reactions on alpha‐halosulfones. In contrast to halogens adjacent to carbonyls and related electron‐withdrawing groups, polar, steric and field effects appear to combine leading to the marked deactivation of alpha‐halosulfones. The stereochemical outcome of the reaction was also unexpected: a predominance of Z‐alkenes is often observed with relatively weak bases, whereas stronger bases tend to favor E‐alkenes. The mechanism of the RBR was therefore the subject of intense interest, particularly in the 1950s and 1960s. From the synthetic viewpoint, the RBR is attractive for a number of reasons, for example, the accessibility of the precursor sulfide and sulfones; the conjunctive nature of the process; the unambiguous location of the resulting double bonds, among others. Organic sulfones are readily available, but the preparation of alpha‐halosulfones can be problematic. In view of this, perhaps the most significant synthetic advance concerning RBR has been the development of Meyer's modification, which involves in‐situ halogenation‐RBR sequence and enables sulfones to be converted directly into alkenes. This chapter discusses the mechanism of RBR, its scope and limitations, applications of the reaction in natural product synthesis, and comparison of the RBR with related procedures. Representative experimental procedures are also given.

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The Intramolecular Ramberg‐Bäcklund Reaction: A Convenient Method for the Synthesis of Strained Bridgehead Olefins

Cited by 22 publications

References 38 publications

Stereoselective Synthesis of Bicyclo[4.2.1]nonanes – a Temporary‐Bridge Approach to Cyclooctanoids

Stereoselective Synthesis of Bicyclo[4.2.1]nonanes – a Temporary‐Bridge Approach to Cyclooctanoids

Ketene Cycloadditions

The Ramberg‐Bäcklund Reaction

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