Knorr quinoline synthesis

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Knorr quinoline synthesis
Named after Ludwig Knorr
Reaction type Ring forming reaction
Identifiers
RSC ontology ID RXNO:0000394

The Knorr quinoline synthesis is an

2-hydroxyquinoline using sulfuric acid. This reaction was first described by Ludwig Knorr (1859–1921) in 1886[1]

Knorr quinoline synthesis
Knorr quinoline synthesis

The reaction is a type of

polyphosphoric acid (PPA) but 4-hydroxyquinoline 3 when the amount of PPA is small. A reaction mechanism identified a N,O-dicationic intermediate A with excess acid capable of ring-closing and a monocationic intermediate B which fragments to aniline and (ultimately to) acetophenone
. Aniline reacts with another equivalent of benzoylacetanilide before forming the 4-hydroxyquinoline.

Staskun 1964 Knorr cyclization reaction mechanism
Staskun 1964 Knorr cyclization reaction mechanism

A 2007 study

superelectrophile) over the N,O dicationic intermediate . For preparative purposes triflic acid
is recommended:

Knorr Cyclization with triflic acid Sai 2007
Knorr Cyclization with triflic acid Sai 2007

References