Synthesis and Spectral Characteristics of 4<i>H</i>-1-Benzothiopyran-4-ones
作者:Hiroyuki Nakazumi、Teijiro Kitao
DOI:10.1246/bcsj.50.939
日期:1977.4
The physical properties of 4H-1-benzothiopyran-4-ones (thiochromones) and related compounds were characterized by means of mass, NMR, and UV spectra in order to distinguish thiochromones from 2H-1-benzothiopyran-2-ones (thiocoumarins). In the mass spectra, the fragmentation due to the retro-Diels-Alder reaction directly from the molecular ion is the most useful for differentiation. In the NMR spectra
This report focuses on the remotecontrol of anion-πcatalysis by electric fields. We have synthesized and immobilized anion-π catalysts to explore the addition reaction of malonic acid half thioesters to enolate acceptors on conductive indium tin oxide surfaces. Exposed to increasing electric fields, anion-π catalysts show an increase in activity and an inversion of selectivity. These changes originate
SYNTHESES OF<i>S</i>-PHENYL 3-OXOBUTANETHIOATES AND 2<i>H</i>-1-BENZOTHIOPYRAN-2-ONE DERIVATIVES (THIOCOUMARINS)
作者:Hiroyuki Nakazumi、Teijiro Kitao
DOI:10.1246/cl.1978.929
日期:1978.9.5
S-Phenyl 3-oxobutanethioates,precursor for preparation of thiocoumarins, were prepared from benzenethiols and diketene in the presence of triethylamine. Cyclization of these compounds with PPA gave thiocoumarin and/or isomeric thiochromone derivatives.
Selective Catalytic Transesterification, Transthiolesterification, and Protection of Carbonyl Compounds over Natural Kaolinitic Clay
作者:Datta E. Ponde、Vishnu H. Deshpande、Vivek J. Bulbule、Arumugam Sudalai、Anil S.Gajare
DOI:10.1021/jo971404l
日期:1998.2.1
Transesterification and transthiolesterification of beta-keto esters with variety of alcohols and thiols and selective protection of carbonyl functions with various protecting groups catalyzed by natural kaolinitic clay are described. The clay has been found to be an efficient catalyst in transesterifying long chain alcohols, unsaturated alcohols, and phenols to give their corresponding beta-keto esters in high yields. For the first time, transthiolesterification of beta-keto esters with a variety of thiols has been achieved under catalytic conditions. Clay also catalyzes selective transesterification of beta-keto esters by primary alcohols in the presence of secondary and tertiary alcohols giving corresponding beta-keto esters. A systematic study involving the reactivity of different nucleophiles (alcohols, amines, and thiols) toward beta-keto esters is also described. Sterically hindered carbonyl groups as well as alpha,beta-unsaturated carbonyl groups underwent protection without the deconjugation of the double bond. Chemoselective protection of aldehydes in the presence of ketones has also been achieved over natural kaolinitic clay.