59 不斉素子,2,5-トランス-二置換ピロリジンをもちいる不斉合成反応および天然物合成への応用

概要

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Optically active trans-2,5-bis(methoxymethyl)- and trans-2,5-bis(methoxymethoxymethyl)pyrrolidines with a C_2-axis of symmetry, were prepared as the chiral auxiliaries for asymmetric synthesis. They were transformed into the corresponding amides by conventional method in good yield. Alkylation of these amides by successive treatment with LDA and alkyl halides in THF proceeded smoothly with high chemical and excellent optical yields (over 95%ee) for a wide variety of reactant combinations. These high ee values were not affected by the change of counter cations (Li, K, Na) or of solvents (THF, Et_2O, DME). The hydrolysis of the alkylated amides could be effected without racemization by treatment with BCl_3 in CH_2Cl_2 and subsequent refluxing in 1N-HCl for the bis(methoxymethyl) compounds or by mere refluxing with 1N-HCl for the bis(methoxymethoxymethyl)compounds. The aldol condensation of the amide enolates with aldehydes also proceeded with high erythro- and enantio-selectivity (50:1〜100:1), when zirconium (Cp_2ZrCl_2) enolates were used. The amide enolates could also be acylated to chiral 2-alkyl-3-oxo amides without epimerization, and they were reduced by Zn(BH_4)_2 with high erythro-selectivity to the enantiomers of the above aldol products. Synthesis of some insect feromons was carried out to demonstrate the usefulness of the present asymmetric reactions.
天然有機化合物討論会の論文
1983-09-15