Preparation of quinolines from resin-bound esters using titanium reagents

Abstract

ortho-Amino homobenzylic thioacetals are prepared from ortho-nitrobenzaldehydes via homologation using an alpha-methoxy Wittig reagent. Titanium reagents are generated from the 1,3-dithianes using a low valent titanium reagent and are then used to alkylidenate resin-bound esters. An N-silylated Boc group protects the ortho-amino functionality. Traceless SPS of quinolines is completed by treating the resulting resin-bound enol ethers with TFA and then oxidizing with manganese dioxide to give 2-substituted quinolines in high purity without the need for chromatography.