Seven-membered rings five-atom tether

The two components of the [4 + 2] cycloaddition can be linked to react intramolecularly. The dienophile can be tethered to either a- or (3-carbon of the nitroalkene, which in turn creates bicyclic fused or bridged nitronates, depending upon the regioselectivity (Figure 16.4). To date, only cycloadditions of (3-tethered nitroalkenes are known. The reaction can be used to prepare five- and six-membered rings [58], which correspond to a three- or four-atom linker between the diene and dienophile. An attempted preparation of a seven-membered ring led to an intermolecular cycloaddition instead. 

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