The 5-oxo-2,5-dihydrofuran-2-ylideneacetic
acids (2a), (3a), (9a), (10a), (11a), (12a) and (13a) have been synthesized by
a procedure which allows the unambiguous assignment of the stereochemistry about
the double bond in each isomer. The method, of general application, enables the
acids to be prepared from the corresponding t-butyl esters with acid without
isomerization about the double bond. The t-butyl esters are available from the
Wittig reaction between anhydrides and t- butoxy-carbonylmethylenetriphenylphosphorane.Where
mainly one isomer is produced in the Wittig reaction, isomerization to an
easily separable mixture of the esters can be achieved. Aspects of the isomerization
of enol-lactone esters (e.g. (2b)) are described.
5-氧代-2,5-二氢呋喃-2-亚基乙酸(2a, 3a, 9a, 10a, 11a, 12a 和 13a
(2a)、(3a)、(9a)、(10a)、(11a)、(12a)和(13a)的合成过程。
该方法可以明确地确定每种异构体中双键的立体化学结构。
双键的立体化学结构。该方法具有普遍应用性,可以
酸与相应的 t-丁基酯制备,而不会发生双键异构化。
双键的异构化。叔丁基酯可通过
t-丁基酯可通过酸酐和 t-丁氧羰基亚甲基三苯基膦之间的 Wittig 反应制得。
在 Wittig 反应中主要产生一种异构体,异构化成易于分离的酯混合物。
如果在 Wittig 反应中主要产生一种异构体,则可将其异构化为易于分离的酯混合物。烯醇-内酯的异构化
例如 (2b))的异构化。