Furan-TBCP cycloaddition reaction

Thus, a concise and direct formal asymmetric total synthesis of platensi-mycin based on the key use of a furan-TBCP cycloaddition reaction has been described. Two sequential annulations on the oxabicyclo[3.2.1]octane core established the hydrophobic cage domain found in the natural product. 

In 1968, Tobey and Law reported on the intriguing reaction of furan, substituted furans, and cyclopentadiene with both tetrachloro- and tetrabromocyclo-propene (TBCP). The two unsaturated systems reacted smoothly to directly produce cycloheptanoid systems, the products of a formal [4-i- 3]-cycloaddition reaction. The authors proposed in their early manuscripts that the tetrahalocy-clopropenes underwent an initial thermal Diels-Alder cycloaddition to produce the cyclopropyl norbornene derivatives la and lb (Figure 2). However, these workers were unable to isolate or characterize the primary cycloadducts and instead observed a product which had spontaneously rearranged by way of a halogen atom migration to yield the bicyclo[3.2.1]octadiene nucleus 2a and 2b. 

Completion of the formal total synthesis of platensimycin enhanced our scope of furan Diels-Alder reactions with TBCP and simple substituted furans. Extension of this formal [4+3]-cycloaddition to annulated furans such as 46 would be necessary for access to the [5.4.0]undecane carbocyclic core of fron-dosin A. Although the analogous reaction between annulated furans and oxyallyl cations are known to be difficult, with simple electrophilic substitution... 

---