Highly Diastereoselective Conjugate Addition of Lithium Dialkylamides to α,β-Unsaturated Esters Having a Chiral Center at the γ-Position
摘要:
The conjugate addition of lithium amides 2 to tert-butyl 4-(OR)-substituted-2-pentenoates 1 produced a mixture of the syn-and anti-amino esters (3 and 4) in high yields. Sterically bulky OR groups, such as trityloxy and tert-butyldiphenylsilyloxy, gave the syn diastereomer 3 either exclusively or predominantly. The syn-selectivity may be explained by a modified Felkin-Anh model. The use of tert-butyldimethylsilyloxy as an OR group afforded a nearly 1:1 mixture of diastereoisomers, and the use of the smallest MeO group produced a 63:37 mixture of the syn 3 and anti isomer 4. The presence of Me group at the alpha-position (C-2 position) of the enoate enhanced the syn diastereoselectivity up to 100%; the conjugate addition to tert-butyl 4-methoxy-2-methyl-2-pentenoate (17) gave the syn-isomer 18 exclusively. This enhancement may be explained by the combination of chelation and allylic strain model 19 in which the smallest H orients inside to avoid an allylic strain. A phenyl group at the gamma-position enhanced the anti selectivity in the case of gamma-alkoxy-alpha,beta-enoates such as isopropyl 4-[(tert-butyldimethylsilyl)oxy]-4-phenyl-2-buteonoate (20), and in the case of gamma-alkyl-alpha,beta-enoates such as tert-butyl 4-phenyl-2-pentenoate (27).
Highly Diastereoselective Conjugate Addition of Lithium Dialkylamides to α,β-Unsaturated Esters Having a Chiral Center at the γ-Position
摘要:
The conjugate addition of lithium amides 2 to tert-butyl 4-(OR)-substituted-2-pentenoates 1 produced a mixture of the syn-and anti-amino esters (3 and 4) in high yields. Sterically bulky OR groups, such as trityloxy and tert-butyldiphenylsilyloxy, gave the syn diastereomer 3 either exclusively or predominantly. The syn-selectivity may be explained by a modified Felkin-Anh model. The use of tert-butyldimethylsilyloxy as an OR group afforded a nearly 1:1 mixture of diastereoisomers, and the use of the smallest MeO group produced a 63:37 mixture of the syn 3 and anti isomer 4. The presence of Me group at the alpha-position (C-2 position) of the enoate enhanced the syn diastereoselectivity up to 100%; the conjugate addition to tert-butyl 4-methoxy-2-methyl-2-pentenoate (17) gave the syn-isomer 18 exclusively. This enhancement may be explained by the combination of chelation and allylic strain model 19 in which the smallest H orients inside to avoid an allylic strain. A phenyl group at the gamma-position enhanced the anti selectivity in the case of gamma-alkoxy-alpha,beta-enoates such as isopropyl 4-[(tert-butyldimethylsilyl)oxy]-4-phenyl-2-buteonoate (20), and in the case of gamma-alkyl-alpha,beta-enoates such as tert-butyl 4-phenyl-2-pentenoate (27).
Studies on the Biodegradation of Fosfomycin: Synthesis of 13C-Labeled Intermediates, Feeding Experiments with Rhizobium huakuii PMY1, and Isolation of Labeled Amino Acids from Cell Mass by HPLC
作者:John W. McGrath、Friedrich Hammerschmidt、Hanspeter Kählig、Frank Wuggenig、Günther Lamprecht、John P. Quinn
DOI:10.1002/chem.201100725
日期:2011.11.18
fed to R. huakuii PMY1. Alanine and a mixture of valine and methionine were isolated as their N‐acetyl derivatives from the cell hydrolysate by reversed‐phase HPLC and analyzed by NMR spectroscopy. It was found that the carbon atoms of the respective carboxyl groups were highly 13C‐labeled (up to 65 %). Hydroxyacetone is therefore considered an obligatory intermediate of the biodegradation of fosfomycin
外消旋(1 R * 2 R *)-1,2-二羟基- [1- 13 C ^ 1 ]丙基膦酸和1-羟基- 〔1- 13 C ^ 1 ]丙酮的合成和馈送到R. huakuii PMY1。通过反相HPLC从细胞水解产物中分离出丙氨酸以及缬氨酸和蛋氨酸的混合物作为N乙酰基衍生物,并通过NMR光谱分析。发现各个羧基的碳原子被13 C标记高度(高达65%)。因此,羟丙酮被认为是华氏疟原虫PMY1对磷霉素进行生物降解的必不可少的中间体。
Conformationally Biased Ketones React Diastereoselectively with Allylmagnesium Halides
作者:Nicole D. Bartolo、Krystyna M. Demkiw、Jacquelyne A. Read、Elizabeth M. Valentín、Yingying Yang、Alexandra M. Dillon、Chunhua T. Hu、Michael D. Ward、K. A. Woerpel
DOI:10.1021/acs.joc.1c02844
日期:2022.3.4
The addition of the highly reactive reagent allylmagnesium halide to α-substituted acyclic chiral ketones proceeded with high stereoselectivity. The stereoselectivity cannot be analyzed by conventional stereochemical models because these reactions do not conform to the requirements of those models. Instead, the stereoselectivity arises from the approach of the nucleophile to the most accessible diastereofaces
高反应性试剂烯丙基卤化镁与α-取代的无环手性酮的加成具有高立体选择性。立体选择性无法通过常规立体化学模型进行分析,因为这些反应不符合这些模型的要求。相反,立体选择性是由于亲核试剂接近酮的最低能量构象的最容易接近的非对映面而产生的。预期具有高立体选择性,并且可以预测立体化学结果,其中构象偏向的酮具有空间上可区分的非对映面,其中只有一个面可进行亲核加成。酮的构象可以通过计算建模和在某些情况下通过 X 射线晶体学确定结构的组合来确定。
Comparative Study of the Diastereoselective Addition of Allenyl Zinc Reagents to α-Alkoxy (or Silyloxy) Aldehydes and Imines. A Straightforward Synthesis of Amino Alcohols from Imines
作者:Jean-François Poisson、Jean F. Normant
DOI:10.1021/jo005509r
日期:2000.10.1
The addition of allenylzine bromides to or-chiral imines proceeds with very high diastereoselectivity. This result is in contrast with the addition to the corresponding aldehydes, leading to poor diastereoselectivity. The anti/anti adducts are explained by Felkin-Ahn and Gaudemar-Yamamoto models of the transition state.