A novel 18-membered chiral crown ether was prepared in four steps starting from L-quebrachitol, a chiro-inositol, and its catalytic activity in the Michael addition reaction of glycine imine with several Michael acceptors was studied.
The reduction of alpha-keto esters derived from (1L)-1,2;5, 6-biscyclohexylidene-3-tert-butyldimethysilyl-chiro-inositol with Selectride(R) proceeded with high diastereoselectivity to afford the corresponding alpha-hydroxy esters. Addition of 18-Crown-6 led to dramatic changeover in diastereofacial selectivity.
AKIYAMA, TAKAHIKO;TAKECHI, NAOTO;SHIMA, HIROAKI;OZAKI, SHOICHIRO, CHEM. LETT.,(1990) N0, C. 1881-1884
Stereodivergent Synthesis of Optically Active<i>α</i>-Hydroxy Acids via Diastereoselective Reduction of<i>α</i>-Keto Esters Derived from L-Quebrachitol
Reduction of an α-keto ester derived from chiral cyclitol, readily available from l-quebrachitol, with K-Selectride proceeded via re-face attack of the ketone with high diastereoselectivity to obtain the α-hydroxy ester in 92% de. On the other hand, reduction of the α-keto ester with K-Selectride in the presence of 18-Crown-6 took place via si-face attack of the ketone to furnish the corresponding α-hydroxy ester in 92% de. Thus both enantiomers of mandelic acid were obtained in optically pure form.
Investigated are AlCl3 and NaI catalyzed chemoselective demethylation reactions of methylethers of partly protected inositol derivatives, reactions which are greatly promoted by vicinal OH group and proceed in preference to the cleavage of the cis cyclohexylidene moiety.
研究了 AlCl3 和 NaI 催化的部分保护的肌醇衍生物的甲基醚的化学选择性去甲基化反应,该反应受到邻位 OH 基团的极大促进,优先进行顺式亚环己基部分的裂解。