The adamantane rearrangement of syn- and anti-Tricyclo[4.2.1.1.12,5] decane. Part II. Rearrangements initiated by regioselective formation of carbocations at C(3) and C(9)

The endo- and exo-alcohols 5–12 of syn-( 1 ) and anti-tricyclo4.2.1. 1^2.5]decane ( 2 ) were treated with BF₃/Et₃SiH (ionic hydrogenation) in order to study the behaviour of the corresponding regioselectively generated carbocations at C(3) ( a (syn), b (anti)) and C(9) ( c (syn), d (anti)). The anti-hydrocarbon 2 is practically the sole product obtained starting with the four 3-alcohols (via a → b from 5 and 6 (syn) and via b from 9 and 10 (anti)). The four 9-alcohols in each case yield a mixture of 2-endo, 3-endo- ( 3 ) and 2-exo,3-exo-trimethylene-8,9,10-trinorbornane (4) (via c → e from 7 and 8 (syn) and via d → f from 11 and 12 (anti)), but no hydrocarbon 2 , i.e. none of the 1,3-H shifts c → a and d → b is involved.