| Abstract: | In contrast of Part II of the series, 4-alkyl-2-(difluoromethyl)-6-(trifluoromethyl)-3,5-pyridinedicarboxylates, 1 , were reacted with various strength bases to effect regio-selective reaction of electrophiles at either the benzylic carbanion of the 4-position, or at the 2-(difluoromethyl)carbanion. Weaker bases up to and including potassium butoxide or lithium bis(trimethylsilylamide) effected reaction of 1 at the 4-position to produce 2 and 3 by Stobbe-type condensations of aldehydes and ketones. In similar manner carbon disulfide, carbon dioxide, alkyl halides, silyl halides, and hexachloroethane produced the highly functionalized derivatives 4-10. In contrast, use of lithium diisopropylamide and like bases selectively effected carbanion formation at the 2-position to form, with the cited electrophiles and others, substitution products 11. The latter were further derived to the highly functional materials, 12-19. |
