Quinolines, 2-anilino-, reaction with

An intramolecular cyclization of iV-anilino- and iV-benzyl-substituted propargyl trimethylsilyl ethers with Lewis acid catalysis provides the quinolines and isoquinolines, respectively <20040L2361>. An intramolecular aza-Diels-Alder reaction has been used as a key step in the synthesis of luotonin (Scheme 69) <20040L4913>. An analogous reaction afforded the dihydroquinoline as a single diastereomer (Equation 132) <2000TL5715>. 

Miyadera and Tachikawa168 reported that quinolizinium bromide reacted with aniline to give seven products (Scheme 2), presumably via l-anilino-4-(2-pyridyl)butadiene, with subsequent recyclization to quinolines or loss of a-picoline. Moerler and Krohnke169 were able to isolate good yields of the aminobutadienes 195 when quinolizinium salts were boiled with piperidine or morpholine. The reaction failed with 2,3,6-trimethyl- or 2,3,7-trimethyl-quinolizinium salts, presumably because of steric hindrance. 

This reaction was initially reported by Diels and Reese in 1934. It is the conjugate addition between hydroazobenzene and dimethyl acetylene-dicarboxylate. The resulting adduct can be transformed into three different heterocyclic compounds under various experimental conditions (i.e pyrazolones with acid, indoles upon heating in xylene, and quinolones with base ). For example, l,2-diphenyl-3-carbomethoxy-5-pyrazolone will be generated from the adduct in acetic acid (acidic condition), whereas dimethyl indole-2,3-dicarboxylate is produced in xylene (neutral condition) and 2-hydroxy-3-anilino-4-carbomethoxy-quinoline is yielded in pyridine (basic condition). The latter can be further converted into 2,3-dihydroquinoline upon decarboxylation and hydrolysis." This reaction has been extended to heat the 1 1 adduct in picoline. ... 

---