Ramberg-Backlund reaction cyclobutenes

The Ramberg-Backlund reaction is now widely utilized in organic synthesis. It has been applied in synthesizing cyclobutenes, cyclopentenes, cyclohexenes, phenanthrenes, large ring systems, dienes, enynes, polyenes, alkynes, and many natural products. 

Paquette was the first to make cyclobutenes by taking advantage of the Ramberg-Backlund reaction.30,31 Treatment of sulfone 38 with potassium r-butoxide led to cyclobutene 39 in 61% yield after distillation regardless of the configuration of the chlorine atom on the substrate (38). The ease with which cyclobutene ring formation occurred in this example was particularly noteworthy. In the same fashion, cyclobutene 42 was obtained from the Ramberg-Backlund reaction of either epimer 40 or 41.32... 

Ramberg-Backlund reactions, discussed in more detail in Chapters 1 and 2, continue to be of great significance in the synthesis of strained alkenes. Bicyclo-[2,2,l]heptenes, [4,2,2]propellanes, 1,4-tetramethylene- and 1,4-penta-methylene-Dewar-benzene, and the ethylene ketal of hydrindane-3,6-dien-l-one have been prepared, utilizing this rearrangement as the final step. 2,5-Dialkyl-sulpholans have been converted, in synthetically useful yields (20— 67%), into 1,2-dialkyl-cyclobutenes upon reaction with Bu Li in THF followed by reduction with LiAlH4. This most interesting reaction has been applied to the preparation of a wide variety of fused benzocyclobutenes. ... 

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