Regioselective β-metallations of 2-substituted furan and N-methylpyrrole derivatives employing the directing effect of the oxazolino group: syntheses of 2,3-disubstituted furans and N-methylpyrroles

Abstract

The effects of change of solvent and reaction time, of addition of Li⁺-chelating agent, and, in some instances, of change of temperature and metallating agent, on the metallation of 2-(2-furyl)- and 2-(N-methylpyrrol-2-yl)oxazolines by alkyl-lithium reagents are explored. Conditions are thereby established for high-yielding syntheses of lithio-intermediates and for control of regioselectivity of metallation. Syntheses of pure samples of 2-(3-hydroxyphenylmethyl-2-furyl)-, 2-(5-hydroxyphenylmethyl-2-furyl)-, 2-(3-carboxy-N-methylpyrrol-2-yl)- and 2-(5-carboxy-N-methylpyrrol-2-yl)-4,4-dimethyloxazolines, based on the results of these investigations, are reported.