Hybridized-Functionalized Organolithium Compounds

Dilithium derivatives 102-105 were generated by reductive opening of epoxides derived from D-glucose, D-fmctose, estrone and cholestanone, respectively, and trapped with different electrophiles. In this way, 6C-substituted 6-deoxy-D-glucose, 3C-substituted D-psycose [85], 17C-substituted-17/8-estradiol and 3C-substi-tuted-3a-cholestanol [91] derivatives were prepared. 

As has been described before, one of the most important problems to be overcome in the preparation of sp -hybridized /3-functionalized organolithium compounds is their decomposition by a /3-elimination process to give olefins. Advantage of this reaction can be taken to prepare olefins starting from organomercur-ials, chlorohydrins and epoxides by performing the lithiation process at higher temperatures [92]. 

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Acyclic and cyclic sp -hybridized ketal-containing y-functionalized organolithium compounds can be generated using an arene-catalyzed Uthiation at low temperature. In the case of acyclic precursors 171 (R = H) it was necessary to lower the temperature to -90 °C in the Uthiation step under DTBB catalysis (4%) in order to avoid decomposition of intermediates 172. Final electrophilic substitution reaction of these intermediates with electrophiles occurred with retention of configuration at temperatures ranging between... 

By a DTBB-catalyzed (5%) lithiation of chlorinated unsaturated amines 191 in the presence of a carbonyl compound as electrophile, the final hydrolysis afforded 192 as a Z/E mixture of diastereomers (Scheme 66). In this process, the corresponding sp -hybridized functionalized organolithium intermediate is probably involved. 

There are several examples of a-oxygen- and nitrogen-functionalized organolithium compounds with sp and sp hybridization in acyclic and cyclic systems of general structures I-IV. These compounds show a tendency to undergo a-elim-ination processes to generate carbene intermediates. 

The number of possible structural devices increases as functionality gets further from the anionic center in functionalized organolithium compounds. So, d-func-tionalized organolithium compounds can be classified according to the hybridization of the carbon atom bonded to the lithium in alkyllithium compounds (XXI and XXII), allylic and benzylic derivatives (XXIII-XXV) and alkenyl (XXVI-XXVIII) and alkynyl systems (XXK). 

The influence of the functional group on the reactivity and the stability of functionalized organolithium compounds decreases as it gets further from the carba-nionic center, so these compounds behave in many cases as normal organolithium compounds and can be prepared through classical methodologies. They can be classified according to the hybridization of the anionic carbon as in the previous section. 

Organolithium compounds with a functional group at the / position can be represented by a great number of general structures (XI-XX) depending on the hybridization of the carbon atoms bearing both the lithium and the functional group. 

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