Manganese(III)-mediated facile synthesis of 3,4-dihydro-2(1 H)-quinolinones: selectivity of the 6- endo and 5- exo cyclization

Abstract

The 4,4-bis(ethoxycarbonyl)-3,4-dihydro-2(1 H)-quinolinones 2 were easily synthesized by the oxidative 6- endo- trig cyclization of 2-[2-( N-arylamino)-2-oxoethyl]malonates 1 with manganese(III) acetate in good to excellent yields. The same reaction of N-(2,4-dimethoxyphenyl)-substituted malonate 1t exclusively produced the 5- exo-cyclized 4,4-bis(ethoxycarbonyl)-1-azaspiro[4,5]deca-6,9-diene-2,8-dione 5t instead of the corresponding dihydroquinolinone. The regioselectivity during the cyclization could be explained by the difference in the activation energy of the transition state of the 6- endo/5- exo cyclization.