| SYNTHESIS |
have invented an enantioselective catalyst for Diels-Alder reactions between dienes with only one oxy substituent and common aldehydes as dienophiles. Previously, dienes had to have at least two oxy substituents for the reaction to go well. And aldehydes had to be electron-deficient. The results will make hetero-Diels-Alder reactions more widely useful for making pyrans with three asymmetric carbons at once. Such pyrans offer the possibility of generating two more asymmetric carbons by reaction of the carbon-carbon double bond. For example, in the reaction shown, get 85% yield of product in 98% enantiomeric excess.
|