Melting points were determined on a Kofler block and are uncorrected. Infrared spectra were determined by use of KBr on a Unicam SP-1025 infrared spectrophotometer.'H NMR spectra were recorded on Varian EM 390, 90-MHz NMR spectrophotometer using tetramethylsilane as internal standard. Microanalyses were performed at the Chemistry Department, Faculty of Science, Cairo University, Cairo, Egypt. The calculated and experimental values agreed ...