Enantioselective Michael Reactions of Chiral Secondary Enaminoesters with 2-Substituted Nitroethylenes. Syntheses of <i>trans,trans</i>-2,4-Disubstituted Pyrrolidine-3-carboxylates
作者:Gilbert Revial、Sethy Lim、Bernard Viossat、Pascale Lemoine、Alain Tomas、Arthur F. Duprat、Michel Pfau
DOI:10.1021/jo000206i
日期:2000.7.1
The Michael reaction of chiral 3-substituted secondary enaminoesters with 2-substituted nitroethylenes leads to (Z)-adducts, with good to excellent diastereoselectivity. The nitro group of these adducts was catalytically reduced to give, after cyclization and chiral amine elimination, pyrrolines or pyrrolidines after further reduction. In particular, the syntheses of ethyl (2R,3S,4S)-2,4-dimethylp
Stereoselective Reduction of Enantiopure β-Enamino Esters by Hydride: A Convenient Synthesis of Both Enantiopure β-Amino Esters
作者:Cristina Cimarelli、Gianni Palmieri
DOI:10.1021/jo960107y
日期:1996.1.1
The reduction of enantiopure beta-enamino esters 1 with sodium triacetoxyborohydride in acetic acid is described. This occurs with good diastereo- and enantioselectivity to yield beta-amino esters 2 and 3 (after hydrogenolysis of the N-chiral group). A model is reported for the origin of the stereoselectivity through an enol ester-diacetoxyborohydride 6, which affords the intramolecular reduction. By choosing the appropriate chiral amine, this procedure allows a straightforward preparation of both the enantiopure beta-amino esters and derivatives with known biological activity, using readily available starting materials and inexpensive reagents and conditions.
Regio- and stereoselective double alkylation of β-enamino esters with organolithium reagents followed by one-pot reduction: convenient method for the synthesis of tertiary γ-amino alcohols
stereoselective procedure for the preparation of tertiary γ-amino alcohols starting from β-enamino esters is presented. In this procedure, the double alkylation of β-enamino esters with organolithium reagents is followed by one-pot reduction with sodium borohydride in methanol/acetic acid. A hypothesis of mechanism is given, explaining the observed diastereoselectivity through molecular modeling. The configuration
提出了一种简单,高产且立体选择性的方法,该方法可从β-烯胺酯开始制备叔γ-氨基醇。在该方法中,用有机锂试剂对β-烯胺酯进行双烷基化,然后用硼氢化钠在甲醇/乙酸中一锅还原。给出了机理的假设,通过分子建模解释了观察到的非对映选择性。产物的构型通过1 H NMR光谱结合构象分析确定。
A versatile route to β-enamino esters by acylation of lithium enamines with diethyl carbonate or benzyl chloroformate
route to β-enamino esters 1, using accessible starting materials, was developed. Lithiated enamines are allowed to react with diethyl carbonate or benzyl chloroformate with the formation of the β-enamino esters 1a or 1b. The reaction is rather general from a wide array of ketimines and aldimines. Products included cyclic β-enamino esters 1aa-ac, very useful for the synthesis of natural products.