Carbanionic synthons Synthon
comparison between retrosynthetic analysis , chemical synthesis ester alkylation
in 1967, e. j. corey introduced concept of synthon in retrosynthetic analysis. planning steps of complex molecule synthesis requires recognizing key synthons , identifying how can assembled desired product. in many retrosynthetic bond disconnections, bond broken heterolytically instead of homolytically, generating carbocationtic , carbanionic synthon. polar-mechanism reactions, whether nucleophilic displacements, 1,2-carbonyl additions, michael reactions, or other processes, involve fusion of nucleophilic fragment , electrophilic fragment.
there wide variety of carbanionic synthons available organic chemist construction of complex molecules. these include enolates, organometallics, acetylides, malonates, , carbanions generated in situ after addition olefins. example of carbanionic synthon ester enolate shown in fig. 1. carbon-carbon bond alpha carbonyl can disconnected enolate equivalent , carbon electrophile. in case, enolate generated direct deprotonation of substrate lithium diisopropyl amide (lda) base. electrophile methyl iodide.
since synthons idealized structures, difficult find equivalent chemical compounds in real world. many carbanion synthons, drawn, present stability issues render molecule’s existence in reality impossible. example, acyl anions not stable species, acyl anion synthon can used represent reagents such lithiated dithianes, nucleophilic , used in umpolung chemistry.
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