Alkyllithiums reductive lithiation

Later work examined substituent effects on kinetically controlled alkylations [68, 69] (Scheme 32). Substitution at the 5-position is well tolerated in these reactions. Reductive lithiation of a series of 4-phenylthio-l,3-dioxanes and quenching of the axial alkyllithium intermediate with dimethyl sulfate provided the flzzfz -l,3-diols in good yield, with essentially complete selectivity. 

Reductive lithiation is neatly complementary to deprotonation as a method for the synthesis of organolithiums in contrast with deprotonation, reductive formation is fastest for alkyllithiums (the more substituted the better) and slowest for aryllithiums. The order of reactivity follows logically from the relative stabilities of the intermediate radicals, whose formation is the ratedetermining step of the sequence.8... 

Catalytic DBB at much higher temperatures also allows the reductive lithiation of phenyl ethers to give alkyllithiums.5253 Functionalised benzylic organolithiums are produced from the heterocycles 3654 and 3855 and an alkyllithium is produced from 37.52... 

Beau and Sinay have developed an efficient synthesis of 2-deoxy-jS-glycosides based on anomeric phenylsulfone alkylation followed by in situ reductive lithiation with lithium naphthalenide (LN). The -C-glycoside product is established after protic quench of the intermediate axial alkyllithium (Scheme 12) [20]. 

Since different reactivity is observed for both the stoichiometric and the catalytic version of the arene-promoted lithiation, different species should be involved in the electron-transfer process from the metal to the organic substrate. It has been well-established that in the case of the stoichiometric version an arene-radical anion [lithium naph-thalenide (LiCioHg) or lithium di-ferf-butylbiphenylide (LiDTBB) for using naphthalene or 4,4 -di-ferf-butylbiphenyl (DTBB) as arenes, respectively] is responsible for the reduction of the substrate, for instance for the transformation of an alkyl halide into an alkyllithium . For the catalytic process, using naphthalene as the arene, an arene-dianion 2 has been proposed which is formed by overreduction of the corresponding radical-anion 1 (Scheme 1). Actually, the dianionic species 2 has been prepared by a completely different approach, namely by double deprotonation of 1,4-dihydronaphthalene, and its X-ray structure determined as its complex with two molecules of N,N,N N tetramethylethylenediamine (TMEDA). ... 

Finally, a reaction that clearly shows the electrophihc carbenoid-type character of a-lithiated epoxides is the reductive alkylation discovered by CrandaU and Apparu. The transformation is illustrated by the treatment of f-butyl ethylene oxide with t-butyllithium to yield ii-di-f-butylethene (equation 55). The overall reaction results in a conversion of an oxirane into an aUcene under simultaneous substitution of an a-hydrogen atom by the alkyllithium reagent ... 

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