The (4+ 2) cycloaddition of ketenes and. beta.-methoxy. alpha.,. beta.-unsaturated ketones: 2-pyranones

~72%

~%

~%

~%

~%

~%

~%

~%

~%

~%

~%

~%

~75%

~%

~%

~%

~%

~%

~%

~%

~%

~%

~69%

~%

~73%

~%

~%