Abstract
The intramolecular ene reactions of 1,6- and 1,7-enynes containing a hydrogen, methyl, or carbomethoxy substit- uent of the acetylene have been investigated. Since the acetylene is acting as the enophile, the methyl substituent retards the reaction while the carbomethoxy group significantly accelerates it. A terminal 1,6-enyne, 1, cyclizes at 210 °C while the carbomethoxy enyne 2 cyclizes at 135 °C. The cyclization of 1,7-enynes has been shown to be slow, typically requiring temperatures 100 °C higher than the corresponding 1,6-enyne. The acetylene 10 activated by both ketone and a carbomethoxy group cyclizes cleanly at 90 ° C.