Carbolithiation regioselectivity

Unsymmetrical dienynes react regioselectively with organolithium compounds at the less substituted double bond (Scheme 2.37). Thus, addition of n-butyllithium to 2-methylhexa-l,5-dien-3-yne (107) led after hydrolysis to vinylallene 108, whereas the corresponding carbolithiation of the linear isomer 109 furnished product 110 with 55% yield [68]. 

In light of the facile 5-exo-dig carbolithiation reaction of simple acetylenic alkyllithiums, Bailey and Longstaff have studied the analogous 5-exo cyclization of a benzyne-tethered alkyllithium. Regioselectively 4-functionalized indanes 281 have been prepared... 

Negishi E, Tan Z (2005) Diastereoselective, Enantioselective, and Regioselective Carbo-alumination Reactions Catalyzed by Zirconocene Derivatives. 8 139-176 Nicolaou KC, King NP, He Y (1998) Ring-Closing Metathesis in the Synthesis of Epothilones and Polyether Natural Products. 1 73-104 Normant JF (2003) Enantioselective Carbolithiations. 5 287-310 Norton JR see Cummings SA (2005) 10 1-39... 

A regioselective carbolithiation of o-amino-( )-stilbenes has been achieved with a series of alkyllithiums when TH F was employed as reaction solvent (Figure 2.9) [60]. High levels of diastereoselectivity have been obtained following the reaction of the lithiated intermediate in TH F with different electrophiles such as MeOD, CO2, and BusSnCl. It was shown that diastereoselectivity was influenced by the orfho-amino substituent and the alkyllithium used for carbolithiation. 

Figure 2.9 A regioselective carbolithiation of o-amino- )-stilbenes [60], (Reproduced with permission.)...

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