Abstract
Cyclobutanone 2, a late intermediate in Wenkert’s isocomene synthesis, was prepared by a six-step sequence in 10% overall yield. Carroll rearrangement of acetoacetate 9 gave ketone 10. Peterson olefination with ethyl (trimethylsilyl)propionate followed by hydrolysis gave acid 12 as a mixture of double bond position isomers. Addition of the corresponding acid chlorides 13 to Et3N in toluene at reflux gave cyclobutanone 4. Isomerization of the double bond of 4 with hydriodic acid gave 2. Isomerization of /3-bergamotenes with hydriodic acid in benzene provided an effective route to the -bergamotenes. Tricyclic ketone 28 was prepared by oxy-Cope rearrangement of allylic alcohol 27. Oxy-Cope rearrangement of propargylie alcohol 32 gave cyclooctadienone 33. Under some reaction conditions 33 was converted to cyclooctatrienolate 35, which was protonated to give 36 and underwent electrocyclic ring opening to give 38.