Conformational Restriction by Repulsion between Adjacent Substituents on a Cyclopropane Ring: Design and Enantioselective Synthesis of 1-Phenyl-2-(1-aminoalkyl)-N,N-diethylcyclopropanecarboxamides as Potent NMDA Receptor Antagonists
摘要:
Adjacent substituents on a cyclopropane ring mutually exert steric repulsion quite significantly, because they are fixed in eclipsed conformation to each other. Based on this structural feature of the cyclopropane ring, conformationally restricted analogs of milnacipran (1), namely 1-phenyl-2-(1-aminoalkyl)-N,N-diethylcyclopropanecarboxamides (2, 3, ent-2, and ent-3) were designed as potent NMDA receptor antagonists and were synthesized highly enantioselectively. Reaction of (R)epichlorohydrin [(R)-5] and phenylacetonitrile (6) in the presence of NaNH2 in benzene gave a chiral cyclopropane derivative that was isolated as lactone 4 with 96% ee in 67% yield, after alkaline hydrolysis of the cyano group. The nucleophilic addition reaction of Grignard reagents to aldehyde 10, which was readily prepared from 4, proceeded highly selectively from the si-face to afford addition products 11 in high yields. Although hydride reduction of the corresponding ketone 15b, prepared from 11b, with L-Selectride also proceeded highly diastereo selectively, the facial selectivity was reversed to give the re-face addition product 11b. On the other hand, reduction of 15 with DIBAL-H afforded the si-face addition product 12 in high yields. These results suggested that these nucleophilic addition reactions proceeded via either the bisected s-trans or s-cis conformation of the cyclopropylcarbonyl derivatives. From 11 and 12, the target conformationally resticted analogs, 2 and 3, were synthesized, respectively. Starting from (S)-epichlorohydrin [(S)-5], their corresponding enantiomers, ent-a and ent-3, were also synthesized. The structures of the conformationally restricted analogs detected by the X-ray crystallographic analysis suggested that their conformations can be restricted as we hypothesized. Thus, a new method for restricting the conformation of cyclopropane derivatives has been developed.
Highly stereoselective nucleophilic addition to cyclopropyl carbonyls: The facial selectivity in the cyclopropyl ketones is opposite to that in the corresponding aldehyde
作者:Shizuka Ono、Satoshi Shuto、Akira Matsuda
DOI:10.1016/0040-4039(95)02133-7
日期:1996.1
Nucleophilicaddition reaction of Grignard reagents to cyclopropylcarbaldehyde 4 proceeded highly selectively from the si-face to afford 5 in high yield. Although hydride reduction of the corresponding ketone 7 with L-Selectride® also proceeded highly diastereoselectively, the facial selectivity was reversed to give the re-face addition product 5. On the other hand, reduction of 7 with DIBAL-H afforded
The unusual 1,4-chelation-controlled nucleophilic addition to aldehydes with high stereoselectivity. A systematic study of stereoselectivity in the addition reaction of carbon nucleophiles to cis-substituted cyclopropanecarbaldehydes
The addition reaction of carbon nucleophiles to cis-substituted cyclopropanecarbaldehydes was systematically investigated. Ab initio calculations of model cyclopropanecarbaldehydes suggested that the bisected s-cis and s-trans conformers are the only two minimum energy conformers, which are stabilized due to the pi-donating stereoelectronic effect of the cyclopropane ring. The experimental results of a series of substrates, that is, cyclopropanecarbaldehydes 1-5 bearing a cis-(tert-butyldiphenyisilyloxy)methyl group, a cis-benzyloxymethyl group, a cis-(p-methoxybenzyloxy)methyl group, cis-N,N-diethylcarbamoyl and trans-phenyl groups, and cis-(tert-butyldiphenylsilyloxy)methyl and trans-phenyl groups, respectively, showed that highly anti-selective Grignard additions could be realized. It turned out that it occurred via an unusual 7-membered 1,4-chelation-controlled pathway. Highly stereoselective Grignard addition via the chelation-controlled pathway occurred even in the reaction of the usually non-chelating silyl ether-type substrate 5. The results have great importance because the 1,4-chelation-controlled stereoselective addition reactions can indeed be realized. Under non-chelation conditions, the syn-products were produced with moderate stereoselectivity, which are likely to be formed via the bisected s-cis conformation-like transition state stabilized by the characteristic orbital interaction. These reactions, especially the chelation-controlled reaction, should be useful because of their t stereoselectivity and stereochemical predictability. (C) 2004 Elsevier Ltd. All rights reserved.