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Paper | Regular issue | Vol 55, No. 4, 2001, pp.661-669
Published online, 1st January, 1970
DOI: 10.3987/COM-00-9141
■ Regioselective Formation of Novel Functionalized 1-Aza-9-oxafluorenes

Andreas Hilgeroth,* Kristin Brachwitz, and Ute Baumeister

*Department of Pharmacy, Institute of Pharmaceutical Chemistry, Martin-Luther-University Halle-Wittenberg, Wolfgang-Langenbeck-Str. 4, 06120 Halle, Germany

Abstract

A small series of novel 1-aza-9-oxafluorenes have been prepared by regioselective cycloaddition reaction of p-benzoquinone to the sterically unhindered side of unsymmetrically substituted N-acyl-1,4-dihydropyridines (1). The stereochemistry of the products is discussed on the basis of X-Ray crystal structure analysis of one starting structure (1a). The formation of pyridine derivatives by possible redox reaction of the adducts was not observed. Rotameric properties of the N-acyl-1,4-dihydropyridines are demonstrated by 1H and 13C NMR spectroscopy, thus stabilizing the 1,4-dihydropyridine system towards competing oxidation by the quinone.