Acid‐Catalysed Dehydration of Tricyclic Unsaturated Alcohols

Abstract 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 POCl3/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 FSO3H 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 POCl3/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 CF3COOH gave the addition product 22 converted into vinylsulfonyl fluorides 24 and 25 by treatment with FSO3H (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.