Mass spectrometry in structural and stereochemical problems. CLXXIX. Electron impact induced rearrangements of 1-phenylheptenes. Further evidence for double bond lability
Selective formation of non-conjugated olefins by samarium(II)-mediated elimination/isomerization of allylic benzoates
作者:Sara L. Schaefer、Connor L. Roberts、Erasmus O. Volz、Monika R. Grasso、Gregory W. O’Neil
DOI:10.1016/j.tetlet.2013.08.136
日期:2013.11
Aromatic allylic benzoates can be selectively transformed to the corresponding benzoate eliminatedolefin by the action of samarium diiodide. Depending on the substrate and the elimination conditions, high selectivity for the non-conjugated alkene product can be achieved.
Replacement of hydroxyl groups in secondary and primary alcohols (1) with a fluorine atom arising from tetrafluorobote anion has been performed by the electrochemical formation of alkoxy triphenylphosphonium tetrafluoroborarates (2) from 1, followed by their thermal decomposition. The procedure is quite simple, involving : (1) constant-current electrolysis of a mixture of 1, Ph3P, and Ph3PH·BF4 in CH2Cl2 in an undivided cell; (2) refluxing a tetrahydrofuran or dioxane solution of the residue afforded by evaporation of the solvent in vacuo after the electrolysis. Cyclic secondary alcohols such as 3β-hydroxy steroids and 2-adamantanol are transformed into the corresponding fluorides in satisfactory yields when the geometry of the leaving group in 2 is suitable for the substitution or an elimination process for 2 to give an alkene is stereochemically forbidden. The fluorination of steroidal alcohols and 4-phenyl-1-cyclohexanol proceeded with complete inversion, demonstrating that a fluorine atom from the tetrafluoroborate anion attacks from the side opposite to the phosphonium moiety in 2 via an SN2 mechanism rather than as SN1 mechanism. The fluorination of acyclic secondary and primary alcohols was performed by the present method in reasonable yields, although the reaction for the latter required more forcing conditions, such as refluxing in dioxane.
A gold-catalyzed intermolecular reaction of propiolic acids with alkenes led to a [4 + 2] annulation or enyne cross metathesis. The [4 + 2] annulation proceeds with net cis-addition with respect to alkenes and provides an expedient route to α,β-unsaturated δ-lactones, for which preliminary asymmetric reactions were also demonstrated. For 1,2-disubstituted alkenes, unprecedented enyne cross metathesis
Controllable, Sequential, and Stereoselective C–H Allylic Alkylation of Alkenes
作者:Ling Qin、Mohammed Sharique、Uttam K. Tambar
DOI:10.1021/jacs.9b08801
日期:2019.10.30
new C-C bonds represents a powerful approach to generate complex molecules from simple starting materials. However, a general and controllable method for the sequential conversion of a methyl group into a fully substituted carbon center remains a challenge. We report a new method for the selective and sequential replacement of three C-H bonds at the allylicposition of propylene and other simple terminal
将 CH 键直接转化为新的 CC 键代表了一种从简单的起始材料生成复杂分子的强大方法。然而,将甲基顺序转化为完全取代的碳中心的通用且可控的方法仍然是一个挑战。我们报告了一种新方法,用于选择性和顺序替换丙烯和其他简单末端烯烃的烯丙基位置的三个 CH 键,该烯烃具有源自格氏试剂的不同碳基团。铜催化剂和富电子联芳膦配体有助于以高支链选择性形成烯丙基烷基化产物。我们还提出了在催化铜和手性膦配体存在下生成对映体富集的烯丙基烷基化产物的条件。通过这种方法,