Cyclopropane deprotonation

A mechanistic interpretation for the formation of 35 is depicted in Scheme 5. Deprotonation of an allylic proton yields ylide intermediate 36. This then adds to methyl acrylate to give intermediate 37, which cyclizes to construct a cyclopropane ring together with the fission of the S-C bond to afford the final adduct 35. 

The violence of superbasic slurries towards functionalized organic molecules means that they are at their most effective with simple hydrocarbons they also tolerate ethers and fluoro substituents. LiCKOR will deprotonate allyUc, benzylic, vinylic, aromatic and cyclopropane C—H bonds with no additional assistance. From benzene, for example, it forms a mixture of mono and dimetallated compounds 617 and 618 (Scheme 241) . ( Li/K indicates metallation with a structurally ill-defined mixture of lithium and potassium.)... 

Ullmann and Buncel attempted to deprotonate A -carene-2,5-dione (4) and the benzannelated derivative 5 in the hope of generating the possibly aromatic dianions 6 and 7. However, the dianions (and the monoanions) could not be isolated. On the grounds of deuterium exchange experiments, the strain energy of benzocyclopropene (1) was estimated to at least 45.5 kcal/mol higher than that of cyclopropane. 

The stabilization of reaction intermediates RCjq and RC q to form dihydrofullerene derivatives can also be achieved by intramolecular nucleophilic substitutions (SjJ), if R contains a leaving group. As shown by Bingel [31], the generation of a carbon nucleophile by deprotonation of a-halo esters or a-halo ketones leads to a clean cyclopropanation of Cjq. 

Finally, an entirely different approach to milnacipran (2) was recently reported in the literature (Scheme 14.6). In this case, the general strategy is based on position-selective deprotonation of cyclopropane carboxamides. Thus, cyclopropane amide 27, which was easily prepared from commercially available cyclopropane carboxylic acid, underwent... 

The difference in acidity of the a-methylene groups in 2-thenyl compared to 3-thenyl derivatives is clearly shown by the reaction of the quaternary ammonium iodides (322) and (323) with sodium amide. While the former yields a cyclopropane, the latter leads to an allyl derivative (Scheme 95) showing that in the case of (323) it is not the a-methylene which is deprotonated (71JOC2236). 

Deprotonation of (alkylcyclopropylidenemethyl)cyclopropanes (alkyl = methyl, cyclopropyl) with BuLi and subsequent reactions with various electrophiles afforded the corresponding ring-substituted methylenecyclopropanes (equation 295)365. When the lithiated compounds are treated with C02, carboxylic acids are obtained, together with isomeric lactones. These can be regarded as formal 3+2 adducts of the methylenecyclopropanes with C02 (equation 295)366. 

Chiral 1,2-cycloalkanedicarboxylic acids.1 This ring system can be obtained by coupling 1,co-dihalides or -ditosylates with the dienolate of d- or /-menthyl succinate (1). The dienolate generated with lithium 2,2,6,6-tetramethylpiperidide is mainly the (E,E)-isomer, whereas deprotonation with LDA and HMPT generates mainly the (Z,Z)-isomer. Thus reaction of 1 (R = /-menthyl) with LiTMP in THF at -78° with CH2BrCl results in (S,S)-( - )-dimenthyl cyclopropane-frww-1,2-dicarboxylate (2) in 58% chemical yield and 99% de. A similar reaction of 1, R = d-menthyl, results in (R,R)-2 in 60% yield and 80% de. 

Camphor- 10-sulfonic acid, 62 (S)-2-(l-Hydroxy-1-methylethyl)-pyrrolidine, 146 a-Methylbenzylamine, 185 Quina alkaloids, 264 Cycloaddition reactions 2-Oxazolidones, chiral, 225 Cyclopropanation Diiodomethane-Diethylzinc, 276 Simmons-Smith reagent, 275 Deprotonation Lithium amides, chiral, 159... 

The addition of a-deprotonated alkyl halides to alkenes or carbonyl compounds can, because of the good leaving-group properties of halides, also lead to formation of cyclopropanes [292] or epoxides [187, 304, 306, 310], respectively. Because of the inherent instability of a-halo organometallic compounds, these intermediates should be handled carefully and on a small scale only. The ketone produced by the last reaction in Scheme 5.34 is probably formed by Oppenauer oxidation of the intermediate alcohol by the excess benzaldehyde [310],... 

Recently, Tang, Wu and co-workers have reported the synthesis of vinylcyclopro-panes using an alternative catalytic cycle for sulfur ylide-catalyzed cyclopropanation (see Scheme 10.22) [98]. Sulfonium salt 41a or 41b was deprotonated by CS2CO3 to form an ylide which then reacted with chalcones 37 to form cyclopropanes and a sulfide. The sulfonium salt was regenerated in situ through reaction... 

Scheme 10.22 Catalytic asymmetric cyclopropanation using sulfur ylides via an alkylation/deprotonation route.

Table 10.4 Catalytic asymmetric cyclopropanation with 41a using sulfide alkylation/deprotonation route (according to Scheme 10.22).

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