Synthetic studies directed towards soraphen A(1alpha)
The C11-C17 segment of soraphen A1 with inverted stereochemistry at C17 as required for ring closure was prepared from the optically active dieneoate 136 in 8 steps. The C12 stereocenter was derived from the acetonide protected D-glyceraldehyde 68 , while the C17 stereocenter was introduced by 1,6-asymmetric control using coordinated triironcarbonyl moiety. The synthesis of C3-C9 segment of sohaphen A1α was investigated through two different routes. The LACDAC reaction between the optically active β-alkoxy aldehydes 163 and the activated diene 164 was found to give the dihydropyrone with cis relative stereochemistry at C2-C3 which was not the correct stereochemistry for sohaphen A1α Synthesis. The ring closure metathesis of the diene 194 produced the dihydropyrone 195 with the correct stereochemistry for soraphen Synthesis. The C2,C3 stereocenters were introduced by the addition of ( Z )-crotyltri-n -butylstannane 197 to the β-alkoxyaldehydes 163 in the presence of TiCl4 gave the desired anti,syn homoallylic alcohol 196 .
Ahmad F Eweas,
"Synthetic studies directed towards soraphen A(1alpha)"
(January 1, 2004).
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