Cyclization isocarbacyclin

Cyclization of l,b)-dihalo [or bis(tosyloxy)] alkanes with methyl methylthiomethyl sulfoxide in the presence of a base such as Bu"Li or KH gave three-, four-, five- and six-membered 1-methylsulfinyl-l-methylthiocycloalkanes that are easily converted to the corresponding ketone by acid hydrolysis. This is applicable to the formation of the key intermediate for the synthesis of isocarbacyclin, a potent prostacyclin analog. ... 

Mandai, Saito and cowoikers recently described a new synthesis of isocarbacyclin, which features a crucial one-pot, three-step transformation tandem tertiary allyl vinyl ether formation, Claisen rearrangement, and ene cyclization led from alcohol (57) directly to bicyclo[3.3.0]octane (59 Scheme 10). Clearly, due to improvements in the preparation of the allyl vinyl ether moiety, there is a trend even in the classical CHaisen rearrangement to taclde more complex structural challenges successfully. 

An intramolecular ketyl/alkyne coupling method has been employed in a synthetic approach to erigerol [91], wherein a reasonably complex tricyclic system was created in high yield (Eq. 80), and in the synthesis of isocarbacyclin (Eq. 81) [92]. Finally, the analogous >-endo cyclization process has also been applied with some success [83], creating functionalized cyclooctenols in modest yield (Eq. 82). 

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