Meyers modification, Ramberg-Backlund

Without doubt, the most important modification of the Ramberg-Backlund reaction is the result of the work of Meyers. In 1969, he reported that a suspension of powdered KOH in a mixture of CCU and Bu OH is a powerful chlorinating system for a variety of compounds with acidic methylene groups. ... 

In 1964, Paquette reported that although the 9,10-double bond of simple phenanthrenes can be formed using the Ramberg-Backlund reaction (NaOH in aqueous dioxane), the sterically crowded 4,5-dimethyl-phenanthrene cannot be made by this method. Staab has now shown that the highly strained proton sponge 4,5-bis(dimethylamino)phenanthrene (15) can be prepared using Meyers modification of the re-... 

In 1969, Meyers et al. at Southern Illinois University published a significant improvement that was synthetically more convenient and useful than the original Ramberg-Backlund conditions.13 The Meyers modification involves in situ halogenation of the sulfone, which, without isolation of the a-halosulfone, is converted to the alkene directly. When dibenzyl sulfone 8 was treated with KOH in the presence of a mixture of CC14 and /-BuOH as solvent, the -o efin 9 was obtained exclusively. Unfortunately, the convenience of the Meyers modification is sometimes offset by sidereactions due to polychlorination. 

Although the Meyers modification has been widely used to conveniently carry out the Ramberg-Backlund reaction, Chan and co-workers at The Chinese University of Hong Kong further modified the one-pot halogenative Ramberg-Backlund reaction in... 

Early in his academic career in 1964, Paquette carried out the Ramberg-Backlund reaction of chloro-sulfone 65 to make phenanthrene 66.44 He discovered that conformational requirements of a-sulfonyl carbanion prolonged the reaction time (5 days) in some cases. In 1986, applying the Meyers modification, Staab et al. converted sulfone 67 to phenanthrene 68.45 The two chlorine atoms on 68 were the result of overchlorination where tetrachloro-sulfone was generated in situ. 

When the sulfone has an a-halo substituent, formation of the carbanion is often accompanied by loss of the SO2 moiety via the so-called Ramberg-Backlund reaction.335 An illustration is the conversion of 1-bromo-ethyl ethyl sulfone (327) to 2-butene.336 Initial reaction with potassium hydroxide generated the sulfone carbanion (328), which displaced bromide intramolecularly to give an episulfone (329). Under the reaction conditions, 329 lost sulfur dioxide (SO2) to give the alkene. Meyers introduced a modification of this reaction in which the sulfone was converted directly to the alkene without isolating the a-halosulfone, using KOH in CCl4.337,338 Sulfuryl chloride and bromine can also be used.338... 

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