- HIGH-YIELD SYNTHESES OF 2,3-DISUBSTITUTED FURANS AND THIOPHENES
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The course of lithiation of furan- and thiophene-2-carboxylic acids is critically dependent on the identity of the lithium base allowing high-yielding syntheses of 2,3- and 2,5-disubstituted thiophenenes: the proposed use of a trimethylsilyl blocking group to control metallation in the furan acid provides a useful route to 2,3-disubstituted furans.
- Carpenter, Andrew J.,Chadwick, Derek J
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p. 1777 - 1780
(2007/10/02)
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- 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
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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.
- Carpenter, Andrew J.,Chadwick, Derek J.
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p. 173 - 182
(2007/10/02)
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