Regio- and stereochemistry on the electrophilic trapping of allylic samariums generated by reductive cleavage of allylic ethers with (C5Me5)2Sm(thf)n

The C-O bond of allylic benzyl ethers was selectively cleaved with Cp-2*Sm(thf)(n) to give allylic samarium complexes in good yields. Facility of their bond fission has been found to be comparable to that of the corresponding propargylic ethers intermolecularly, but lower intramolecularly. Regio- and stereochemistry on the electrophilic trapping of the allylic complexes thus generated remarkably depended on the nature of the electrophiles. They reacted with carbonyl compounds exclusively from the most substituted terminus of the allylic moieties to yield blanched homoallylic alcohols with anti diasteroselectivity. On the other hand, trapping with silyl chlorides produced linear allylic silanes. Here, a plausible mechanism to account for the difference is proposed.