Ring Closure Reactions of Substituted 4-Pentenyl-1-oxy Radicals. The Stereoselective Synthesis of Functionalized Disubstituted Tetrahydrofurans
摘要:
N-(Alkyloxy)pyridine-2( VT)-thiones 3 and benzenesulfenic acid O-esters 5 have been synthesized from substituted 4-pentenols 1 or the derived tosylates. Compounds 3 and 5 are efficient sources of free alkoxy radicals 6 which undergo synthetically useful fast ring closure reactions 6 --> 8 [k(exo) = (2 +/- 1) x 10(8) s(-1) to (6 +/- 2) x 10(9) s(-1) (T = 30 +/- 0.2 degrees C)]. Tetrahydrofurfuryl radicals 8 can be trapped with, e.g., hydrogen or chlorine atom donors to afford either trans- or cis-disubstituted tetrahydrofurans 10 or 12 depending on the substitution pattern of the 4-pentenyloxy radical. Substituted tetrahydropyrans 11 or 13 are formed in the minor 6-endo-trig cyclization. According to the data of competition kinetics, the observed stereoselectivities in free alkoxy radical cyclizations arise from steric interactions between the substituents in the transition state of the ring closure reactions. Alkyl substituents cause small differences in the measured relative rate constants of B-exo cyclizations which are reminiscent of the data obtained from the rearrangements of alkyl-substituted 5-hexenyl radicals. Likewise, a stereochemical model for oxygen radical cyclization is proposed where the pentenyloxy chain adopts a six-membered, chairlike transition state with the alkyl substituents preferentially situated in the pseudoequatorial positions leading to 2,5-trans-, 2,4-cis-, and 2,3-trans-substituted tetrahydrofurfuryl radicals 8 as the major intermediates.
Visible‐Light‐Induced
<i>ortho</i>
‐Selective Migration on Pyridyl Ring: Trifluoromethylative Pyridylation of Unactivated Alkenes
作者:Jinwon Jeon、Yu‐Tao He、Sanghoon Shin、Sungwoo Hong
DOI:10.1002/anie.201912746
日期:2020.1.2
alkenes. The overall process is initiated by the selective addition of a CF3 radical to the alkene to provide a nucleophilicalkyl radical intermediate, which enables an intramolecular endo addition exclusively to the ortho-position of the pyridinium salt. Both secondary and tertiary alkyl radicals are well-suited for addition to the C2-position of pyridinium salts to ultimately provide synthetically
Enantiopure 2,9‐Dideuterodecane – Preparation and Proof of Enantiopurity
作者:Nico Mitschke、Gülsera Eruçar、Miriam H. Fsadni、Amy R. Roberts、Majid M. Sadeghi、Bernard T. Golding、Jens Christoffers、Heinz Wilkes
DOI:10.1002/ejoc.202100360
日期:2021.7.22
Optically active (S,S)-(2,9-2H2)-n-decane was prepared in five steps from (R)-propylene oxide. Its optical purity was determined at the stage of (S)-(5-2H2)-1-hexene, being an intermediate of the synthetic approach, by NMR spectroscopy after Wacker oxidation and enantioselective α-hydroxylation. (R,R)-(2,9-2H2)-n-decane was prepared analogously.
光学活性的(小号,小号) - (2,9- 2 ħ 2) - ñ -癸烷在由(五个步骤制备- [R )-氧化丙烯。其光学纯度在 ( S )-(5- 2 H 2 )-1-己烯阶段测定,作为合成方法的中间体,在瓦克氧化和对映选择性α-羟基化后通过核磁共振光谱测定。( R , R )-(2,9- 2 H 2 )-正癸烷类似地制备。
Determining the Scope of the Organolanthanide-Catalyzed, Sequential Intramolecular Amination/Cyclization Reaction: Formation of Substituted Quinolizidines, Indolizidines, and Pyrrolizidines
作者:Gary A. Molander、Shawn K. Pack
DOI:10.1021/jo035205f
日期:2003.11.1
The scope of the lanthanide-mediated, intramolecular amination/cyclization reaction was determined for the formation of substituted quinolizidines, indolizidines, and pyrrolizidines. A methyl group was installed at diverse positions in the substrates to determine the sense and magnitude of diastereoselection. High diastereoselectivity (>20:1) was achieved for the formation of some quinolizidines and
Benzaldehyde-derived iminiumions 1 form benzoxacyclic products 2 in a photochemical reaction cascade (n=0,1). Structurally different products 3 (meta photocycloaddition) and 4 (aza Paternò–Büchi reaction) are observed depending on two key substituents (R, R1).