General and Efficient Syntheses of C<sub>18</sub>-4,8-Sphingadienines via S<sub>N</sub>2‘-Type Homoallylic Coupling Reactions Mediated by Thioether-Stabilized Copper Reagents
The stereoselective syntheses of C(18)-4,8-sphingadienines 3 and 4 as analogues of sphingosine 1 are described. The key step in these syntheses involved a novel S(N)2'-type homoallylic coupling reaction between the corresponding thioether-stabilized allylic copper reagents and the allylic mesylate 7. The thioether-stabilized allylic copper reagents were easily prepared and retained the configuration