Nitrone reactions with cyclopropanes 3+2 dipolar cycloaddition

It should be pointed out that the alkylidenecyclopropanes are not stable due to the exo double bond and strained cyclopropane ring. The 1,3-Dipolar Cycloaddition of alkylidenecyclopropanes with nitrones was reported by Akmanova in 1982 (i.e., the reaction between A -(phenylaminooxoethylidene) aniline A -oxide and 2,2-dimethylmethylene-cyclopropane), although the 1,3-Dipolar Cycloaddition has been known since the 1960s. 

Christie and Jones first demonstrated in 2004 that appropriately substituted cyclopropanes adjacent to cobalt-alkyne complexes react with Lewis acids to yield 1,3-dipoles that are poised to participate in dipolar cycloadditions. Reaction of cyclopropane 21 with benzaldehyde and boron trifluoride provides tetrahydrofuran 22 in 83% yield. Kerr subsequently applied this strategy to the synthesis of tetrahydro-l,2-oxazines upon combination of cyclopranes like 21 with a variety of nitrones. ... 

Through the progression of the cycloaddition reaction of cyclopropane diesters with nitrones, Sapeta and Kerr thought it wise to investigate the mechanism of this [3+3] dipolar cycloaddition. 

The reaction of nitrones with vinyldiazoacetale catalysed by Rh(ll) has been shown as an efficient and diastereoselective access to multifunctionalized tricyclic heterocycles (Scheme 6). The reaction is a domino process involving dipolar cycloaddition 0 of the nitrone to the double bond followed by an intramolecular cyclopropanation, an electrocyclic ring enlargement and finally a [l,7]-oxygen migration. 

---