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Download fileCarbolithiation of o-Amino-(E)-Stilbenes: Diastereoselective Electrophile Substitution with Applications to Quinoline Synthesis
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posted on 2007-12-07, 00:00 authored by Anne-Marie L. Hogan, Donal F. O'SheaA regioselective carbolithiation of o-amino-(E)-stilbenes has been achieved with a series of alkyllithiums
when THF is employed as the reaction solvent. The use of other solvents, such as diethyl ether or
hydrocarbons, leads to a pronounced loss in regioselectivity. Moreover, high levels of diastereoselectivity
have been obtained following reaction of the lithiated intermediate in THF with different electrophiles
such as MeOD, CO2, and Bu3SnCl. It was shown that diastereoselectivity was influenced by the ortho-amino substituent and the alkyllithium utilized for carbolithiation with N-Boc substituent and t-BuLi
proving optimal. In the case of carbolithiated intermediate 3a, obtained from the reaction of N-Boc
substituted stilbene with t-BuLi, 1H and 13C NMR analysis revealed predominantly one diastereoisomer
which was stable at room temperature. Application of the carbolithiation/electrophile reaction methodology
to the synthesis of six-membered quinoline ring systems is demonstrated with substituted 3,4-dihydroquinolin-2-ones, 1,2,3,4-tetrahydroquinolines, 1,4-dihydroquinolines, and quinolines all prepared
by a common cascade route.