Determination of tautomeric phenotypes of β-thioxo esters and characterization of the tautomeric enethiolic constituents by means of13C NMR spectroscopy
摘要:
AbstractThe 13C NMR spectra of 28 enethiolizable β‐thioxo esters and 6 enethiolizable β‐thioxo thioloesters have been recorded in order to establish the tautomeric phenotypes of these compounds. All compounds investigated are essentially enethiolic. The carbonyl‐conjugated (Z)‐enethiol form is the exclusive or predominant tautomer of open‐chain β‐thioxo esters and thioloesters, thioacylmalonates and medium‐sized 2‐alkoxycarbonylcycloalkanethiones. The carbonyl‐conjugated (E)‐enethiol form is identifiable for open‐chain α‐unsubstituted β‐thioxo esters and thioloesters, and abundant for open‐chain α‐substituted β‐thioxo esters. Non‐conjugated enethiol forms [i.e. (Z)‐ and (E)‐isomeric β,γ‐unsaturated β‐mercapto esters] are abundant tautomeric constituents of ω‐substituted and higher 2‐alkoxycarbonylcycloalkanethiones. The chemical shifts of the carbon atoms directly involved in the tautomeric change have been rationalized in terms of substituent screening contributions. Deuterium isotope effects on the central carbon atoms of selected deuterio‐enethiolic compounds have been measured in order to depict the ester group rotamerism in CO‐conjugated (Z)‐enethiols. The abundance of the CO‐conjugated (E)‐enethiols, as well as the preferred population of the non‐conjugated (Z)‐enethiol form relative to the non‐conjugated (E)‐enethiol form, is rationalized in terms of the occurrence of a no‐bond interaction between the lone‐pair electrons of the enethiolic sulphur atom and the ‘chelating’ methylene hydrogen atoms of cis‐alkyl groups.
Visible-light-promoted aerobic metal-free aminothiocyanation of activated ketones
作者:Pan-Feng Yuan、Qing-Bao Zhang、Xiao-Ling Jin、Wen-Long Lei、Li-Zhu Wu、Qiang Liu
DOI:10.1039/c8gc02720j
日期:——
A direct, redox-neutral, highly atom-economical and metal-free aerobic method for the synthesis of multi-substituted olefins via simply coupling ammonium thiocyanate with activated ketones is described. A series of multi-substituted olefins could be easily and efficiently obtained in excellent yields by using low-toxicity and inexpensive ammonium thiocyanate as an amine and thiocyanate source, and
Irradiation of S-alkyl 3-oxobutanethioate (1) in benzene or ethanol yielded the disulfide 2. Irradiation of S-alkyl α-bromothioacetate also gave the disulfide 2. The photochemicalreaction of the 3-oxobutanethioate 1 involves the Norrish Type I reaction followed by rapid fragmentation of the radical ·CH2COSR to the thiyl radical 5.
A Chemoselective Route to β-Enamino Esters and Thioesters
作者:Dongyue Xin、Kevin Burgess
DOI:10.1021/ol5005643
日期:2014.4.18
Conditions were developed for syntheses of beta-enamino esters, thioesters, and amides. These reactions involve hydroxybenzotriazole derivatives in buffered media. Illustrative syntheses of some heterocyclic systems are given, including some related to protein protein interface mimics.