The synthesis of quinolines from aniline derivatives via the Mn(III)-based oxidative cyclization of 2-(2-(arylamino)ethyl)malonates is described. The 2-(2-(arylamino)ethyl)malonates were prepared in two steps from the substituted anilines. The cyclization of nineteen arylaminoethylmalonates protected by the N-acyl and N-alkoxycarbonyl groups easily proceeded in the formal 6-endo mode regardless of the presence of halo, methyl, and methoxy groups on the aromatic ring, and the corresponding tetrahydroquinolinedicarboxylates were produced in high yields except for the 2,4-dimethoxyphenyl-substituted aminoethylmalonate which occurred by ipso-cyclization. The tetrahydroquinolinedicarboxylate could be transformed into quinoline via decarboxylation and deprotective hydrolysis. The characteristic phenomenon in the NMR spectrum of the tetrahydroquinolinedicarboxylates is also discussed. INTRODUCTIONThe cyclization reaction is an important technique for preparing useful organic molecules, 1 in which manganese(III) acetate dihydrate, Mn(OAc) 3 •2H 2 O, is one of the best reagents especially when used in the oxidative cyclization reactions. 2 It is well-known that the Mn(III)-based oxidation of 2'-hydroxychalcones and 2-hydroxybenzophenones affords aurones 3 and 9-xanthenones 4 according to the formal 5-exo and 6-endo C-O bond cyclization. Snider, 5 Citterio, 6 and Chuang 7 reported the efficient carbon-carbon bond cyclization of 3-oxo-9-aryl-6-nonenoates, 1-aryl-7-nonene-1,3-diones, and arylalkylmalonates (Scheme 1, eq. 1), which proceeded in the similar 5-exo and 6-endo modes to give the corresponding cyclization products, such as octahydrophenanthrenes, 5a tetrehydroanthracenones, 5b,c dihydroindenes, 6a tetrahydronaphthalenes, 2a,6a dihydrobenzofurans, 5d chromanes, 8 and dihydrotetraphenediones. 7a It could also be used for the N-alkyl-N-aryl-3-oxobutanamides (eq. 2) and(2-(N-alkyl-N-arylamino)-2-oxoethyl)malonates (eq. 3), producing indolinones 9,10 and dihydroquinolinones based on the reaction. 7c,11 These compounds are important as a starting material for the synthesis of substituted indoles and quinolines, which are indispensable in natural alkaloid synthesis.Although it was easy to prepare the N-arylalkanamide starting materials, reduction of lactam carbonyl group and N-alkyl deprotection of the cyclization products need at the late stage in order to synthesize the final quinolines (eq. 3) as well as indole derivatives (eq. 2). Scheme 1. Mn(III)-Based Oxidative Radical CyclizationWe then envisioned the direct preparation of (arylamino)ethylmalonates I which would undergo the Mn(III)-based cyclization to provide the dihydroquinolines II, then easily converting into the quinolines (Scheme 2). In order to realize this enterprise, we proposed the retrosynthetic scheme from inexpensive commercially-available materials (Scheme 2). The target quinolines would be obtained by the usual decarboxylation of the 2,3-dihydroquinoline-4,4-dicarboxylates II probably produced by the key oxidation of the 2-(2-(N-arylamino)ethyl)mal...