Regioselective Formation of Novel Functionalized 1-aza-9-Oxafluorenes

摘要

A small series of novel 1-aza-9-oxafluorenes have been prepared by regioselective cycloaddition of p-benzoquinone to the sterically unhinbered 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 obsberved.Rotameric properties of the N-acyl-1,4-dihydropyridines are demonstrated by ~1H and ~(13)C NMR spectroscopy,thus stabilizing the 1,4-dihydropyridine system towards competing oxidation by the quinone.