Olefinic alkyllithiums

Mioskowski et al. examined the reductive alkylation of simple epoxides by or-ganolithiums in THF in considerable detail, and found that the best yields and stereoselectivities were obtained with secondary and tertiary alkyllithiums (Table 5.2, Entries 1-5) [42]. n-BuLi gave a mixture of olefins (Entry 6), whereas PhLi and MeLi (Entries 7 and 8) gave very poor yields. Similar transformations have been reported with the use of lithium tetraalkylcerate reagents (Entries 9 and 10) [43]. 

Addition of alkyllithium to cyclobutanones and transmetallation with VO(OEt)Cl2 is considered to give a similar alkoxide intermediates, which are converted to either the y-chloroketones 239 or the olefinic ketone 240 depending on the substituent of cyclobutanones. Deprotonation of the cationic species, formed by further oxidation of the radical intermediate, leads to 240. The oxovanadium compound also induces tandem nucleophilic addition of silyl enol ethers and oxidative ring-opening transformation to produce 6-chloro-l,3-diketones and 2-tetrahydrofurylidene ketones. (Scheme 95)... 

Most, perhaps all, of the reactions that simple alkenes undergo are also available to allenes. By virtue of their strain and of the small steric requirement of the sp-hybrid-ized carbon atom, the reactions of allenes usually take place more easily than the corresponding reactions of olefins. Because the allenes can also be chiral, they offer opportunities for control of the reaction products that are not available to simple alkenes. Finally, some reaction pathways are unique to allenes. For example, deprotonation of allenes with alkyllithium reagents to form allenyl anions is a facile process that has no counterpart in simple alkenes. These concepts will be illustrated by the discussion of cyclization reactions of allenes that follows. 

It has been found that enantio-enriched a-(homoallyloxy)alkyllithiums (84), formed from the corresponding stannanes (83) by stereoretentive transmetallation, cyclize with complete retention of configuration at the lithium-bearing -carbon to yield enantio-enriched Q ,jS-disubsfituted tetrahydrofurans (85 and 86). This is consistent with earlier theoretical calculations which suggested that the lithium might coordinate with the olefinic bond in the transition state. 

The Bamford-Stevens reaction and the Shapiro reaction share a similar mechanistic pathway. The former uses a base such as Na, NaOMe, LiH, NaH, NaNHa, heat, etc., whereas the latter employs bases such as alkyllithiums and Grignard reagents. As a result, the Bamford-Stevens reaction furnishes more-substituted olefins as the thermodynamic products, while the Shapiro reaction generally affords less-substituted olefins as the kinetic products. 

This is a catalytic-chain mechanism because the agent which adds to the olefins is regenerated in the last step.The addition reaction of the anion to the olefin is similar to the noncatalytic reaction of alkyllithium compounds with ethylene as reported by Ziegler and Gellert 37) and by Bartlett et al. 38). In this reaction (5), the less stable secondary and tertiary alkyl lithium compounds add most readily. 

The historical development of alkyllithium-initiated polymerization of olefins and diolefins for the synthesis of elastomeric materials is of interest not only because of its scientific and technological significance but also because of the insight it provides into the thinking and methodology of polymer (elastomer) researchers. 

B. Cyclization Reaction of Heteroatom-substituted Olefinic Alkyllithiums. 334... 

III. CARBOLITHIATION REACTION OF UNSATURATED ALKYLLITHIUMS A. Cyclization Reaction of Olefinic Alkyllithiums... 

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