Cascade carbolithiation

Krief and Barbeaux have also applied the selenium-lithium exchange methodology to some cascade carbolithiation reactions as shown in Scheme 3667. The l,l-(bis-methylseleno) derivative 128 undergoes a selenium-lithium exchange at —78 °C giving... 

Cascade carbolithiation-hydroxylation of 242 with /-BuLi and A -sulfonyloxaziridine 33 gave bicyclic allylic alcohol 243. The alcohol was isolated in 49% yield and >20 1 d.r. <2004JA3434>. 

Williams and Reeves138 developed a powerful cascade reaction process for the construction of functionalized cA-bicyclo[3.3.0]octenes. Carbolithiation of 3-methylene-1,4-cyclooctadiene 227 with 1°, 2° or 3° alkyllithium reagents leads to cyclooctadienyl anions,... 

The carbolithiation of unactivated alkenes has also proven very successful for the synthesis of complex polycyclic systems. This has typically been achieved by reaction sequences utilizing an intramolecular carbolithiation process to generate a variety of carbocycles185 and heterocycles186. To achieve the intermolecular carbolithiation reaction required to initiate a controlled cascade reaction sequence for the generation of indole ring scaffold, Kessler and coworkers44 have expanded the synthetic utility of the styrene... 

A carbolithiation cascade was used by Taylor for the synthesis of silacyclo-pentanes. Addition of -BuLi to vinyl silane 437 afforded a 2 l-diastereomeric mixture of 438 (70%), in which the /rau.s-diastereomer predominated (equation (10)) (03TL7143). Interestingly, addition of -BuLi to the alkynyl tethered vinyl silane 439 produced a 3 l-mixture containing predominantly the Z-isomer 440a in 67% yield. Addition of t- BuLi to the same substrate provided a 10 1-mixture of 440b (62%) in which the Z-isomer was also the dominant product formed (equation (11)). 

Intramolecular carbolithiation is now a common process to generate cyclic substrates, and is particularly well suited for the creation of five-membered rings via a 5-exo-trig cyclization [5, 6] (Scheme 1). Cascade reactions can be performed when starting with a diethylenic organoHthium reagent [7]. 

Begue JP, Bonnet-Delpon D, Bouvet D, Rock MH. Synthesis of hindered and functionalized I-CF3 substituted olefins via a carbolithiation-elimination-metalation cascade. J. Org. Chem. 1996 61 9111-9114. 

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