(16) F. Fringuelli and A. Taticchi, J. Chem. SOC. C, 756 (1971).(17) F. Fringuelli and A. Taticchi, J. Chem. SOC. C, 1809 (1971).(18) RK Crossland and KL Service, J. Org. Chem., 35, 3195 (1970).(19) The chemical shifts given on formula 26 are taken from DK Dalling, DM Grant, and EG Paul, J. Am. Chem. Soc., 95, 3718 (1973), determined