SYNTHESIS OF PENTASUBSTITUTED PYRIDINES .4. STRUCTURAL CHARACTERIZATION OF THE ADDITION-PRODUCTS OF 1-(N,N-DIETHYLAMINE)PROP-1-YNE TO N-VINYLCARBODIIMIDE AND N-KETENIMINE

The reaction products of the addition of 1-(N,N-diethylamine)prop-1-yn e to N-vinylcarbodiimides and -ketenimines have been identified. Two p yridine regioisomers can be obtained under thermal control according t o a [4 + 2] or [2 + 2] cycloaddition mechanism. At temperatures above 100 degrees C a competing electrocyclic ring closure of the heterocumu lene is observed. The structures of the pyridines isolated are assigne d by a combination of HMBC and NOE difference spectra.