Homoallyl chloroformates cyclization

Homoallyl chloroformates cyclize catalytically to a-methylene- y-butyrolactones in moderate yields at 130 C with tetrakis(triphenylphosphine)palladium(0) (equation 44).l0s This reaction only gives 1-2% of product when it is carried out intermolecularly. The presumed intermediate in the homoallyl chlorofor-mate cyclization has been isolated and kinetic measurements show that that cyclization is inhibited by an excess of triphenylphosphine. A chelated ir-alkene intermediate is proposed.1 6... 

In a diastereoselective modification of this reaction, the imidates 7 were prepared starting from primary allylic and homoallylic alcohols and the nitrile 6 following a standard procedure1 sfi. By cyclization of 7 with A -iodosuccinimide in chloroform at 20 °C, diastereomeric mixtures were obtained with one diastereomer predominating, which was easily separated. The configuration of the diastereomer was assigned on the basis of X-ray analysis. 

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