Other Cycloadditions Leading to Seven-Membered Rings

Other Cycloadditions Leading to Seven-Membered Rings 

Some cycloadditions can be used to simultaneously generate two rings and one is a seven-membered ring. An example of this approach is found in the work of Rigby directed at the preparation of ingenol through an impressive [6+4] cycloaddition (. 46). The reaction 

Trost employed an intramolecular [3+2] cycloaddition to form a 5,7-fused bicyclic system in quantitative yield with good diastereose-lectivity (Eq. 41) P In this reaction, a two-bond-forming cycloaddition process produces the desired one-bond closure of an acyclic precursor. 

In another example, a [3+2] cycloaddition leads to the concomitant formation of a highly substituted cycloheptane (Eq. 48)7  

Lautens recently reported superb examples of a metal-mediated cycloaddition of norbomadienes and dienes. Although this process establishes connections which deliver an eight-membered ring, the process can also be viewed and exploited as a [4+3] cycloaddition (Eq. 49). This reaction proceeds in up to 66% yield with up to 72% enantiomeric excess. 

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C. Other Cycloadditions Leading to Seven-Membered Rings... 

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