Chapter 37: Radical Reactions

Rather than introducing novel reactions, the material unifies aldehydes, ketones, carboxylic acids, esters, amides, and enolate intermediates through retrosynthetic analysis, teaching students to work backward from target molecules by identifying disconnections traceable to nucleophilic addition, nucleophilic acyl substitution, or enolate-mediated transformations. Classic methodologies including aldol condensations, Claisen couplings, Michael additions, and Robinson annulations are recontextualized as strategic tools within synthetic planning. A pivotal concept is umpolung or polarity reversal, wherein reagents like cyanohydrins, 1,3-dithianes, and acyl anion equivalents invert the inherent electrophilic character of carbonyl groups, enabling them to function as nucleophilic partners in carbon chain extension. The Corey-Seebach protocol exemplifies this approach. The chapter emphasizes enolate control through base selection, kinetic versus thermodynamic selectivity, and the application of chiral auxiliaries for stereochemical precision. Functional group interconversions emerge as essential tactical skills, permitting sequential transformation of carbonyl derivatives to unlock alternative reaction pathways. Students explore how multiple transformations can be telescoped into one-pot cascades or carefully orchestrated sequences that maintain selectivity while maximizing efficiency. Comprehensive case studies drawn from natural product synthesis demonstrate how these principles translate into real construction of complex, multifunctional molecules with relevance to pharmaceutical and agrochemical industries. By integrating reactivity patterns, synthetic logic, and creative problem-solving, this chapter equips students to design original syntheses from foundational principles rather than merely applying memorized reaction schemes.