Ramberg-Backlund reaction natural products

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. 

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. 

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