Abstract
A carbanion of tert-butyl 3-(1-pyrrolidinyl)crotonate adds to nitrobenzenes to form σH-adducts, which in the presence of pivaloyl chloride and triethylamine are converted into 3-(1-pyrrolidinyl)quinolines or 3-(1-pyrrolidinyl)quinoline 1-oxides depending on the nitrobenzene structure. This is the first methodology in which a quinoline ring is constructed from a substrate bearing a pyrrolidinyl ring. Starting from optically pure enamines, the method allows synthesis of the corresponding chiral products without racemisation.
Highlights
Quinoline is a key building block in many naturally occurring and synthetically prepared compounds that have important practical applications.[1]
General methods for the synthesis of 3-(1-pyrrolidinyl)quinolines consist of transition-metal-catalyzed replacement of halogen (Fig. 2, path a),[4,7] reaction of 3-aminoquinoline with 4-chlorobutyryl chloride followed by reduction with LiAlH4,3 ring-closing metathesis in 3-diallylaminoquinolines followed by hydrogenation,[3] and alkylation of 3-aminoquinoline with 1,4-dibromobutane.[3]
In this paper we present an efficient one-pot method for the synthesis of 3-(1-pyrrolidinyl)quinoline-2-carboxylic acid esters and the corresponding quinoline 1-oxides directly from nitrobenzenes
Summary
Quinoline is a key building block in many naturally occurring and synthetically prepared compounds that have important practical applications.[1]. Less widespread are methods in which the quinoline 1-oxides are formed as a result of interaction of the nitro group with adjacent substituents in ortho-substituted nitroarenes.[9] To the best of our knowledge, the synthesis of 3-(1-pyrrolidinyl)quinoline1-oxides is still unexplored. In this paper we present an efficient one-pot method for the synthesis of 3-(1-pyrrolidinyl)quinoline-2-carboxylic acid esters and the corresponding quinoline 1-oxides directly from nitrobenzenes.
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