REGIOSELECTIVITY AND STEREOSELECTIVITY OF ADDITIONS OF ORGANOMETALLICS TO ENDO- AND EXO-TRICYCLO[5.2.1.0(2,6)]DECA-4,8-DIEN-3-ONES

The regio- and stereoselectivity of the addition of selected organometallics to endo- and exo-tricyclodecadienones 12, 18 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.