Acid‐Catalysed Dehydration of Tricyclic Unsaturated Alcohols

The tricyclic alcohols 3–7 , derived from the corresponding ketones 1 and 2 (Scheme 1) , by action of acids underwent dehydration with skeletal rearrangements. Dehydration of 3 and 4 with POCl 3 /pyridine (procedure A) afforded the polycyclic hydrocarbons 9, 10 , and 12, 13 , respectively. With TsOH (procedure B), on the other hand, 3 and 4 gave homo‐triquinacenes 10 and 14 respectively, as well as the polycyclic ethers 11 and 15 (Scheme 2) . Hydrocarbon 9 (or 12 ) was converted into 10 FSO 3 H to the tertiary alcohol 16 (Scheme 4) . Plausible mechanisms for these transformations are summarized in Scheme 8 . Dehydration of the secondary alcohols 5 and 7 was effected by procedure A. While treatment of alcohol 5 with POCl 3 /pyridine yielded two isomeric hydrocarbons 17 and 18 , similar dehydration of its epimeric alcohol 7 afforded hydrocarbon 21 as the sole product. The tertiary alcohol 6 was dehydrated by both procedures to yield two isomeric hydrocarbons 19 and 20 (Scheme 5) . Hydrocarbon 20 was converted into 19 by procedure B (mechanisms, Scheme 10 ). Reaction of ketone 2 with CF 3 COOH gave the addition product 22 converted into vinylsulfonyl fluorides 24 and 25 by treatment with FSO 3 H (Scheme 6). Homo ‐triquinacenes 10 and 14 reacted smoothly with 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione to give the ‘ene’‐reaction products 26 and 27 , respectively.