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Zeh, J.; Hiersemann, M., Science of Synthesis: Stereoselective Synthesis, (2011) 3, 380.
Various π-acceptor functionalities can be used to stabilize a (formal) carbanion.[47] Carboxy groups are particularly useful because they generate Brønsted acidity at the α-proton, and the resulting enediolates have a high charge density as a result of the presence of the dianion of the carboxylic acids. The use of the enolate [2,3]-Wittig rearrangement is nicely illustrated in the total synthesis of (−)-C-sulfatide (122), the C-analogue of the natural product sulfatide (Scheme 37).[8] Etherification of the α-anomer of the galactoside 134 provides the glycolate ether 135, which is treated with an excess of lithium diisopropylamide to generate an enediolate. This undergoes [2,3]-Wittig rearrangement via the transition state 136 to give an α-hydroxy acid that can be directly esterified to give the enoate 137. Subsequent hydrogenation provides the building block 138, which was used in the synthesis of (−)-C-sulfatide (122).
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References
[47] | Meeee, M.; Meeeee, M.; Meee, M.; Meeeee, M.; Meeeee, M., Meeeeeeeeee Meee., (8888) 88, 88. |
[8] | Meeeee, M.; Meeeeeeeeee, M.; Meeeeee, M.; Meeeeeeee, M.; Meeeeeeee, M.; Meee, M.; Me Meeeee, M.; Meeee, M.; Meeeeeeee, M., Mee. Meee., (8888) 8, 8888. |