Organolithiums - Selectivity for Synthesis by Jonathan Clayden

By Jonathan Clayden

This quantity, quantity 23 within the "Tetrahedron natural Chemistry" sequence, offers organolithium chemistry from the viewpoint of a man-made natural chemist, drawing from the factitious literature to offer a unified evaluation of ways organolithiums can be utilized to make molecules. the advance of tools for the regioselective synthesis of organolithiums has changed their photo of indiscriminate excessive reactivity with considered one of controllable and refined selectivity. Organolithium chemistry has a vital position within the selective building of C-C bonds in either basic and intricate molecules, and for instance has arguably overtaken fragrant electrophilic substitution because the strongest technique for regioselective functionalisation of fragrant earrings. the dual topics of reactivity and selectivity run throughout the e-book, which reports the methods through which organolithiums could be shaped and the ways that they react. subject matters contain advances in directed metallation, reductive lithiation and organolithium cyclisation reactions, besides a dialogue of organolithium stereochemistry and the position performed by means of ligands equivalent to (-)-sparteine.

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B(OMe)3 2. H202 3. Me~ ILi 90% O~ y ~CONMe2 OSit-BuMe2 BuLi, TMEDA, THF, Et20 ( 0"- y ' C O . M e ~ - , 0 4 ~ OSit-BuMe2 ~ OMe t-BuMe2SiOE)NMe2 ~ t-BuMe2SiO Li ~ ~ " ~ "CONMe2 OSit'BuMe2 OMe O In more heavily substituted amides, the amide group is forced to lie perpendicular to the aromatic ring ~32,154- even in 169 the amide and the ring are not coplanar. ~55 Clearly this poses greater difficulties for ortholithiation, and Beak has shown that the rate of lithiation is dependent on the angle between the amide plane and the plane of the ring.

The overall synthetic result is effectively that of an ortholithiation-directing ketone or aldehyde. Me2 ~"~ 6 U ~ NMe2 BuLi > L ' "O~NMe2 ~ E+ D, E~Li ~ O~NMe2 ~ H+ ~, E 196 197 ~NMe2 R The same intermediate 196 is formed when an aryllithium attacks dimethylformamide en route to an aldehyde. H3O+ OHms/ 198 Addition of a lithiated secondary amine to an aldehyde both protects the aldehyde from attack by RLi and turns it into an ortholithiation directing group. Me / O ~ Me BuLix3, I THF,-78~ L i .

Lo7 n-BuLi ~ 234 [ ~ O ~ 237 Br2 ~ ~ 235 Li n-BuLi~[ ~ O ~ 238 Li 77% 236 Br CO2~ [ ~ O ~ 35% CO2H 239 In sulfoxides, sulfur's weak acidifying effect is enhanced, and the oxygen atom introduces a powerful coordination effect: in contrast with sulfides, sulfoxides are very powerful directors of both ortholithiation and o~-lithiation. Ortholithiation is possible with aryl sulfoxides lacking an a-proton, but since sulfoxides suffer from the disadvantage of being electrophilic at sulfur, diaryl sulfoxides must be lithiated with lithium amide bases rather than Organolithiums: Selectivityfor Synthesis 48 alkyllithiums.

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