General Methods. NMR spectra were obtained on a Bruker WH-400 spectrometer in CDCl,; chemical shifts are given in ppm downfield from TMS. GLC-MS analyses were performed on Varian 1700 gas chromatograph coupled to a Varian MAT 711 mass spectrometer, column 5% SE 52 on Chromosorb G, AWDMCS, 2.5 m, lI8 in. Preparative gas chromatographic separations were run on a Aerograph A 90-P3 chromatograph, column 5% SE 30 on ...
