SYNTHESIS OF 11-MEMBERED ENEDIYNE KETONES BY THE INTRAMOLECULAR NICHOLAS REACTION

An efficient route to 11-membered enediyne ketones 13 and 22 was developed. This route is based on an intramolecular Nicholas reaction of 11 and 20, respectively. In the course of the preparation of the cyclization substrates 11 and 20, it was important to use the acetylenic alcohols 6 and 15 as building blocks for the construction of the cis-enediynes 8 and 17, respectively, instead of the corresponding ketones which were converted into unstable acyclic enediynes. Some transformations of enediyne ketone 22 were also studied. For example, 22 could be transformed into the 2-formyl compound 26 via the silyl enol ether 24. In addition, 24 was used for the preparation of the 2-amino ketone 29.