13999-11-6Relevant articles and documents
Eda et al.
, p. 1497,1498,1499,1500 (1964)
Generation of 3- and 5-lithiothiophene-2-carboxylates via metal-halogen exchange and their addition reactions to chalcogenoxanthones
Cannon II, Michael K.,Detty, Michael R.
, p. 2647 - 2650 (2007/10/03)
Deprotonation and lithium-bromine exchange in 5- or 3-bromothiophene-2- carboxylic acids with t-BuLi form the corresponding dianion, which reacts highly regioselectively in the presence of 0.25 equiv of tetramethyl-1,2- ethylenediamine with 3,6-bis(dimethylamino) chalcogenoxanthones to give S- and Se-containing rhodamines. Quenching studies with D2O indicate that an extra equivalent of t-BuLi is not necessary in these reactions. Deprotonation is faster than metal-halogen exchange with the bromothiophene-2-carboxylic acids using t-BuLi.
Regioselective α-and β-Metallations of Thiophene Derivatives Bearing the 4,4-Dimethyloxazolin-2-yl Group. Application of the Method to Syntheses of 2,3- and 2,5-Disubstituted Thiophene Derivatives
Carpenter, Andrew J.,Chadwick, Derek J.
, p. 173 - 182 (2007/10/02)
The effects of change of solvent, metallating agent, reaction time and temperature, and of the presence or absence of agents capable of complex formation with either the lithium cation or the oxazoline moiety, on the lithiation of 4,4-dimethyl-2-(2-thienyl)oxazoline are explored.Conditions are thereby established for high-yielding syntheses of the 3- and 5-lithio-intermediates and for control of regioselectivity of metallation.The nucleophilicity of 3-lithio-intermediate is profoundly solvent dependent, and appropriate conditions for reaction of both 3- and 5-lithiated species with a wide variety of electrophiles are presented.Syntheses of a range of 2,3- and 2,5-disubstituted thiophene derivatives have thereby been achieved, utilising, in addition, a new method for the transformation of oxazolino into carboxy functionality.The balance between basicity and nucleophilicity of the 3-lithio-intermediate in its reaction with - and -acetone is shown to be sensitive to isotope effects.
