Regio- and stereoselectivity of additions of organometallics to - and -tricyclo[5.2.1.02,6]deca-4,8-dien-3-ones

The regio- and stereoselectivity of the addition of selected organometallics to endo - and exo -tricyclodecadienones 12 and 21 are described. RLi and R 2 CuLi add with complete 1,2- and 1,4-regioselectivity, respectively, the additions of RMgX and RMgX/CuX are only slightly less selective. Additions to 12 and 21 occur from the convex exo -face only, irrespective of the nature of both reagent and substrate. In contrast, organometallic species add from both the concave and the convex face to tricyclic ester 18 , with a selectivity that depends on the type of organometallic reagent. The observed stereoselectivities of the additions are rationalized by invoking steric control by the C 8 –C 9 ethylene bridge in 12 , by the C 10 methylene bridge in 21 and by both the C 8 –C 9 ethylene bridge and the exo -ester function at C 2 in tricyclic ester 18 .